Subject: Re: Subduction Zone Question From: Dave Nelson davenn@............... Date: Tue, 01 Jan 2008 13:59:35 +1100 Hi Jerry, happy New Year to you too Good questions you pose ... the angle of subduction does vary a bit in different locations The SW of the South Island of New Zealand is is almost vertical under the North Island , NZ it is much shallower ~ 30deg give or take a few deg (just a couple of examples) An easy way to determine how far horizontally they go before melting is to look at what is happening at the surface .... look for ranges of volcanoes ie. the Cascades in NW USA, the central North Island, NZ, volcanoes The volcanoes of the Andes in Sth America, the strings of volcanoes along the islands of Sumatera and Java in Indonesia, the volcanic island chain of the Aleutians etc etc you get the picture :) www.sydneystormcity.com/Nth_is_x.bmp <--- a quick North Is, NZ cross-section Yellowstone is a Hot Spot (correct term) as is Hawaii they are not related to subduction they are a mantle plume that ongoing reguardless of the plate motion going on above them. Look at seabed maps of the Pacific Basin and you can see many strings of islands, atolls and seamounts that indicate past and current Hot Spot activity. A more interesting study is the depth to which the descending slab goes before it melts. and one of the deepest areas for this is in the Tonga - Kermadec Trench in the South Pacific between Fiji and New Zealand. The depth to which the slab descends is directly related to the rate of plate motion in a given region. and in the T - K Trench you get quakes regularly to in excess of 600km, but horizontally maybe only a few 10's of km (20 - 100km) away from the trench. Plate motion here is ~ 7 - 8 cm/yr and decreases as you head south from the Fiji end of the zone towards the North Is of NZ. I could go into the why's of that but thats another whole lesson in itself. The faster the plate is moving, the faster the subduction, therefore the deeper the slab will descend before it melts. Another interesting effect is in this region .... the type of quakes occurring at the great depth. Picture a subducting slab 10km thick, the norm for the seafloor. and you can imagine as it starts to subduct its cold (relativey speaking) but as it subducts it starts to heat up from the outer layers towards its centre. But because of the high speed of subduction (plate motion), the core of the slab stays cold for a very long time ie. there is very high temperature differential across the slab. This results in many tremors within the slab as it internally fractures rather than events just between the surface of the slab and the surrounding rock its grinding past. Here's a project for you ..... and you can do it for any subduction zone Plot earthquakes (from the USGS/NEIC records) on a graph showing depth Vs distance from the trench line. (ie a cross-section across the subduction zone) and it easily show you 1) .. the angle of subduction, 2) the distance from the trench the subduction zone extends. Now b4 everyone screams its already been done with Alan Jones's seismic prog, why repeat it ? yes I know it has. But to actually do the exercise yourself and plot the data from the seismicity records for a given region. It gives you a ( I believe) a better insight and understanding into the processes going on :) cheers all Dave Nelson Sydney At 02:17 AM 01/01/2008, you wrote: >Hi All, >Happy New Year. >I have a question about Subduction Zones and their angle of incidence down >to the mantle. If I remember correctly, the Mariana Trench is quite steep >while others are not. >I was wondering specifically about the Pacific and Juan de Fuca plates and >their subduction angle under the Cascade Mountains. Specifically, I am >wondering how far the subduction angel goes inland before it melts into >the mantle? >The 3.8 event at the Yellowstone Park area brought the question to >mind. I know there is supposed to be a Hot Pocket under that area and >potentially explosive, but I was wondering if the subduction wedge >extended inland that far. Truthfully, I don't know how far Yellowstone is >from the coast. > >Of course, the farther inland, the deeper the wedge would be. The >Yellowstone event was shallow (6.8 km), and obviously not what I an asking >about. Nevertheless, I was wondering about that specific area >anyway. Anybody know? > >What the heck do you have to think about anyway, New Years parties? > >Regards, >Jerry > > >No virus found in this incoming message. >Checked by AVG Free Edition. >Version: 7.5.516 / Virus Database: 269.17.12/1203 - Release Date: >12/30/2007 11:27 AM __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Subduction Zone Question From: "Jerry Payton" gpayton880@....... Date: Mon, 31 Dec 2007 21:12:21 -0600 EXCELLENT answer Dave. You have the knack of explaining that I truly appreciate. I knew my question was overly simplistic and the answer complex and different for varied locals. You did a great job, thanks. Regarding your assignment, yes that is a good way to visualize the angle. I've read paragraphs and seen drawings on just that subject. Best Wishes in 2008, Jerry
EXCELLENT answer Dave. You have the knack of explaining = that I=20 truly appreciate.  I knew my question was overly simplistic and the = answer=20 complex and different for varied locals.  You did a = great=20 job, thanks.
 
Regarding your assignment, yes that is a good way to visualize the=20 angle.  I've read paragraphs and seen drawings on just that = subject.
 
Best Wishes in 2008,
Jerry
 
Subject: First STUPID Question of the New Year? From: "Jerry Payton" gpayton880@....... Date: Tue, 1 Jan 2008 15:14:55 -0600 OK, lets start out the new year with a simple question for the group showing MY ignorance and lack of training! I fully understand the theory and principle behind the Shadow Zones, but determining what MY shadow zones would be is confusing to me. Has anyone built a windows software program to calculate what the shadow zones would be given my Lat / Long coordinates? I understand the 104-140 degree zone that used, but I cannot correlate that into a spot or spots on the globe or map. Can someone please point me in the right direction to solving this, please. (If needed, my coordinates are 36.09N 094.13W.) Jerry
OK, lets start out the new year with a simple question for the = group=20 showing MY ignorance and lack of training!
 
I fully understand the theory and principle behind the Shadow = Zones,=20 but determining what MY shadow zones would be is confusing to me.  = Has=20 anyone built a windows software program to calculate what the shadow = zones would=20 be given my Lat / Long coordinates?
 
I understand the 104-140 degree zone that used, but I cannot = correlate that=20 into a spot or spots on the globe or map.  Can someone please point = me in=20 the right direction to solving this, please.
 
(If needed, my coordinates are 36.09N  094.13W.)
 
Jerry
Subject: Re: First STUPID Question of the New Year? From: tchannel1@............ Date: Tue, 1 Jan 2008 15:52:01 -0700 Happy New Year Everyone,=20 Jerry, This might help: If you have a globe, I have a 12" dia. = globe, you could compute the two different (P wave shadow zone at = 103-143 degrees) and the (S zone at 103-180 degrees,) into inches of the = surface of your globe. For a 12" globe, one degree=3D .104 inches. = 103 degrees=3D 10.712 inches. =20 Using the appropriate length of string, place one end on your home town = and using the other end of the string you could trace or otherwise mark = its length all around the globe. This line would represent the = beginning of the 103 degree shadow zone. However, I think I saw a wed site which may do this, using your = Lat/Long, and those of the earthquake. Ted ----- Original Message -----=20 From: Jerry Payton=20 To: PSN-L=20 Sent: Tuesday, January 01, 2008 2:14 PM Subject: First STUPID Question of the New Year? OK, lets start out the new year with a simple question for the group = showing MY ignorance and lack of training! I fully understand the theory and principle behind the Shadow Zones, = but determining what MY shadow zones would be is confusing to me. Has = anyone built a windows software program to calculate what the shadow = zones would be given my Lat / Long coordinates? I understand the 104-140 degree zone that used, but I cannot correlate = that into a spot or spots on the globe or map. Can someone please point = me in the right direction to solving this, please. (If needed, my coordinates are 36.09N 094.13W.) Jerry
Happy New Year = Everyone, 
 
 Jerry,   This might=20 help:   If you have a globe, I have a 12" dia. globe, you = could=20 compute the two different (P wave shadow zone at 103-143 degrees) and=20 the (S zone at 103-180 degrees,) into inches of the surface of your = globe.    For a 12" globe, one degree=3D .104 = inches.  =20 103 degrees=3D 10.712 inches. 
Using the appropriate length of string, = place one=20 end on your home town and using the other end of the string you could = trace or=20 otherwise mark its length all around the globe.  This line would = represent=20 the beginning of the 103 degree shadow zone.
However, I think I saw a wed site which = may do=20 this, using your Lat/Long, and those of the earthquake.
Ted
----- Original Message -----
From:=20 Jerry = Payton=20
To: PSN-L
Sent: Tuesday, January 01, 2008 = 2:14=20 PM
Subject: First STUPID Question = of the New=20 Year?

OK, lets start out the new year with a simple question for the = group=20 showing MY ignorance and lack of training!
 
I fully understand the theory and principle behind the = Shadow Zones,=20 but determining what MY shadow zones would be is confusing to = me.  Has=20 anyone built a windows software program to calculate what the shadow = zones=20 would be given my Lat / Long coordinates?
 
I understand the 104-140 degree zone that used, but I cannot = correlate=20 that into a spot or spots on the globe or map.  Can someone = please point=20 me in the right direction to solving this, please.
 
(If needed, my coordinates are 36.09N  094.13W.)
 
Jerry
Subject: Re: First STUPID Question of the New Year? From: tchannel1@............ Date: Tue, 1 Jan 2008 15:52:01 -0700 Happy New Year Everyone,=20 Jerry, This might help: If you have a globe, I have a 12" dia. = globe, you could compute the two different (P wave shadow zone at = 103-143 degrees) and the (S zone at 103-180 degrees,) into inches of the = surface of your globe. For a 12" globe, one degree=3D .104 inches. = 103 degrees=3D 10.712 inches. =20 Using the appropriate length of string, place one end on your home town = and using the other end of the string you could trace or otherwise mark = its length all around the globe. This line would represent the = beginning of the 103 degree shadow zone. However, I think I saw a wed site which may do this, using your = Lat/Long, and those of the earthquake. Ted ----- Original Message -----=20 From: Jerry Payton=20 To: PSN-L=20 Sent: Tuesday, January 01, 2008 2:14 PM Subject: First STUPID Question of the New Year? OK, lets start out the new year with a simple question for the group = showing MY ignorance and lack of training! I fully understand the theory and principle behind the Shadow Zones, = but determining what MY shadow zones would be is confusing to me. Has = anyone built a windows software program to calculate what the shadow = zones would be given my Lat / Long coordinates? I understand the 104-140 degree zone that used, but I cannot correlate = that into a spot or spots on the globe or map. Can someone please point = me in the right direction to solving this, please. (If needed, my coordinates are 36.09N 094.13W.) Jerry
Happy New Year = Everyone, 
 
 Jerry,   This might=20 help:   If you have a globe, I have a 12" dia. globe, you = could=20 compute the two different (P wave shadow zone at 103-143 degrees) and=20 the (S zone at 103-180 degrees,) into inches of the surface of your = globe.    For a 12" globe, one degree=3D .104 = inches.  =20 103 degrees=3D 10.712 inches. 
Using the appropriate length of string, = place one=20 end on your home town and using the other end of the string you could = trace or=20 otherwise mark its length all around the globe.  This line would = represent=20 the beginning of the 103 degree shadow zone.
However, I think I saw a wed site which = may do=20 this, using your Lat/Long, and those of the earthquake.
Ted
----- Original Message -----
From:=20 Jerry = Payton=20
To: PSN-L
Sent: Tuesday, January 01, 2008 = 2:14=20 PM
Subject: First STUPID Question = of the New=20 Year?

OK, lets start out the new year with a simple question for the = group=20 showing MY ignorance and lack of training!
 
I fully understand the theory and principle behind the = Shadow Zones,=20 but determining what MY shadow zones would be is confusing to = me.  Has=20 anyone built a windows software program to calculate what the shadow = zones=20 would be given my Lat / Long coordinates?
 
I understand the 104-140 degree zone that used, but I cannot = correlate=20 that into a spot or spots on the globe or map.  Can someone = please point=20 me in the right direction to solving this, please.
 
(If needed, my coordinates are 36.09N  094.13W.)
 
Jerry
Subject: Re: First STUPID Question of the New Year? From: "Jerry Payton" gpayton880@....... Date: Tue, 1 Jan 2008 17:33:28 -0600 That's one of my problems. I don't have a globe of any size. And, they cost soooo much for reasonably sized globes. I assume that you determine the correct length of the string and then just "scribe" a line around the globe and everything with that area is excluded, theoretically? Jerry ----- Original Message ----- From: tchannel1@............ To: psn-l@.............. Sent: Tuesday, January 01, 2008 4:52 PM Subject: Re: First STUPID Question of the New Year? Happy New Year Everyone, Jerry, This might help: If you have a globe, I have a 12" dia. globe, you could compute the two different (P wave shadow zone at 103-143 degrees) and the (S zone at 103-180 degrees,) into inches of the surface of your globe. For a 12" globe, one degree= .104 inches. 103 degrees= 10.712 inches. Using the appropriate length of string, place one end on your home town and using the other end of the string you could trace or otherwise mark its length all around the globe. This line would represent the beginning of the 103 degree shadow zone. However, I think I saw a wed site which may do this, using your Lat/Long, and those of the earthquake. Ted ----- Original Message ----- From: Jerry Payton To: PSN-L Sent: Tuesday, January 01, 2008 2:14 PM Subject: First STUPID Question of the New Year? OK, lets start out the new year with a simple question for the group showing MY ignorance and lack of training! I fully understand the theory and principle behind the Shadow Zones, but determining what MY shadow zones would be is confusing to me. Has anyone built a windows software program to calculate what the shadow zones would be given my Lat / Long coordinates? I understand the 104-140 degree zone that used, but I cannot correlate that into a spot or spots on the globe or map. Can someone please point me in the right direction to solving this, please. (If needed, my coordinates are 36.09N 094.13W.) Jerry
That's one of my problems.  I don't have a globe of any = size. =20 And, they cost soooo much for reasonably sized globes.  I assume = that you=20 determine the correct length of the string and then just "scribe" a line = around=20 the globe and everything with that area is excluded, = theoretically?
Jerry
 
 
----- Original Message -----=20
From: tchannel1@............
To: psn-l@..............
Sent: Tuesday, January 01, 2008 4:52 PM
Subject: Re: First STUPID Question of the New = Year?

Happy New Year = Everyone, 
 
 Jerry,   This might=20 help:   If you have a globe, I have a 12" dia. globe, you = could=20 compute the two different (P wave shadow zone at 103-143 degrees) and=20 the (S zone at 103-180 degrees,) into inches of the surface of your = globe.    For a 12" globe, one degree=3D .104 = inches.  =20 103 degrees=3D 10.712 inches. 
Using the appropriate length of string, = place one=20 end on your home town and using the other end of the string you could = trace or=20 otherwise mark its length all around the globe.  This line would = represent=20 the beginning of the 103 degree shadow zone.
However, I think I saw a wed site which = may do=20 this, using your Lat/Long, and those of the earthquake.
Ted
----- Original Message -----
From:=20 Jerry = Payton=20
To: PSN-L
Sent: Tuesday, January 01, 2008 = 2:14=20 PM
Subject: First STUPID Question = of the New=20 Year?

OK, lets start out the new year with a simple question for the = group=20 showing MY ignorance and lack of training!
 
I fully understand the theory and principle behind the = Shadow Zones,=20 but determining what MY shadow zones would be is confusing to = me.  Has=20 anyone built a windows software program to calculate what the shadow = zones=20 would be given my Lat / Long coordinates?
 
I understand the 104-140 degree zone that used, but I cannot = correlate=20 that into a spot or spots on the globe or map.  Can someone = please point=20 me in the right direction to solving this, please.
 
(If needed, my coordinates are 36.09N  094.13W.)
 
Jerry
Subject: How the earth moves From: tchannel1@............ Date: Fri, 4 Jan 2008 07:08:29 -0700 Happy New Year, Folks. When I receive an earthquake, the earth and my house are moved by the = event. The various phases moves the ground in different direction. This question has to do with the movement of the earth like that of a = teeter-totter. Tilt. like that measured by a level. 1. How much does the earth move? I do understand the earth would move = in many different directions, and move more, if the earthquake was = larger, and or closer. But somewhere I think I read some numbers indicating how much the earth = would be expected to move. I am asking this question, to help me understand, the approximate tilt = from an earthquake. If I hung a one meter pendulum, and a major = earthquake occurred 1000km away, the earth here, would tilt. If I were = looking at the pendulum at the moment the S wave arrived, assuming the = sensor was pointing in the correct direction, the pendulum would appear = to tilt, but unless the event was large enough I could not see it with = my eyes. If the event was large, I would be able to see it with my eyes. I saw the earth move during an earthquake 1993? I was at my kitchen = window felt or hear something, maybe the P,looked up, and maybe 4 = seconds later, I felt a wave, one up and one down. As I was looking = outside at the time I saw the wave move down the street. If I believed = my eyes. This wave was not 12", but it must have been more than 2". Anyhow I think you get the idea. 2. Completely different question: I would like to correspond with = someone who has used both AmaSeis and WinSDR. I know AmaSeis, but = would like to get some pointers on setting up WinSDR. =20 Thanks, Ted
Happy New Year, Folks.
 
When I receive an earthquake, the earth = and my=20 house are moved by the event.  The various phases moves the ground = in=20 different direction.
This question has to do with the = movement of the=20 earth like that of a teeter-totter.  Tilt. like that measured by a=20 level.
 
1.  How much does the earth = move?  I do=20 understand the earth would move in many different directions, and move = more, if=20 the earthquake was larger, and or closer.
But somewhere I think I read some = numbers=20 indicating how much the earth would be expected to move.
 
I am asking this question, to help me = understand,=20 the approximate tilt from an earthquake.   If I hung a one = meter=20 pendulum, and a major earthquake occurred 1000km away, the earth here, = would=20 tilt.  If I were looking at the pendulum at the moment the = S wave=20 arrived, assuming the sensor was pointing in the correct direction, the = pendulum=20 would appear to tilt, but unless the event was large enough I could not = see it=20 with my eyes.
If the event was large, I would be able = to see it=20 with my eyes.
 
I saw the earth move during an=20 earthquake 1993?   I was at my kitchen window felt or = hear=20 something, maybe the P,looked up, and maybe 4 seconds later, I felt a = wave, one=20 up and one down.  As I was looking outside at the time I saw the = wave move=20 down the street.   If I believed my eyes.  This wave was = not 12",=20 but it must have been more than 2".
 
Anyhow I think you get the = idea.
 
2. Completely different question:  = I would=20 like to correspond with someone who has used both AmaSeis and=20 WinSDR.   I know AmaSeis, but would like to get some pointers = on=20 setting up WinSDR. 
 
Thanks, Ted
Subject: Burning Questions From: "Jerry Payton" gpayton880@....... Date: Fri, 4 Jan 2008 09:22:45 -0600 While everyone has their "Thinking Caps" on from Ted's excellent questions, I have a couple that have been smoldering for some time: 1) Months ago I posted an event and I received an email commenting on it. He said, "It was very good, but I might try improving my P-wave." HOW does one "improve" one phase over another? It seems that the P-wave is always less stronger. 2) Much has been written about the length of a pendulum needing to be long to be effective for teleseismic detection. However, the commercial devices are quite compact and obviously have short pendulums. Can someone explain how they accomplish what they do with short pendulums? Thank you for "thinking for me." Jerry
While everyone has their "Thinking Caps" on from Ted's excellent = questions,=20 I have a couple that have been smoldering for some time:
 
1)    Months ago I posted an event and I received an = email=20 commenting on it.  He said, "It was very good, but I = might try=20 improving my P-wave."  HOW does one "improve" one phase over = another? =20 It seems that the P-wave is always less stronger.
 
2)    Much has been written about the length of a = pendulum=20 needing to be long to be effective for teleseismic detection.  = However, the=20 commercial devices are quite compact and obviously have short = pendulums. =20 Can someone explain how they accomplish what they do with short = pendulums?
 
Thank you for "thinking for me."
Jerry
 
 
Subject: Re: Burning Questions From: ChrisAtUpw@....... Date: Fri, 4 Jan 2008 11:41:22 EST In a message dated 04/01/2008, gpayton880@....... writes: While everyone has their "Thinking Caps" on from Ted's excellent questions, I have a couple that have been smoldering for some time: 1) Months ago I posted an event and I received an email commenting on it. He said, "It was very good, but I might try improving my P-wave." HOW does one "improve" one phase over another? It seems that the P-wave is always less stronger. Hi Jerry, I suggest that you ask him? Raw data files for the relevant time interval are normally submitted. It is usual to extract the digital trace and to then apply filters to it to make the waves more visible while doing your own analysis. You might set the HP and LP filters both to 1 second when searching for teleseismic P waves, for example. 2) Much has been written about the length of a pendulum needing to be long to be effective for teleseismic detection. However, the commercial devices are quite compact and obviously have short pendulums. Can someone explain how they accomplish what they do with short pendulums? They use very low noise capacitative detectors to get the very high resolution, to maybe well below 0.1 nano metre. The period may then be extended greatly by electronic feedback, or by digital feedback, or both. They may use small pendulums with a natural period of say 0.5 second or more, but these are totally controlled by the force feedback. Because direct position and not velocity is being measured, you get a fall off in the signal below resonance of only 1/f, not 1/f^2. You can extend a 'natural' 1 second system to over 1,000 seconds, but the electronics required to do this may be quite expensive. When I receive an earthquake, the earth and my house are moved by the event. The various phases move the ground in different directions. This question has to do with the movement of the earth like that of a teeter-totter. Tilt. like that measured by a level. 1. How much does the earth move? I do understand the earth would move in many different directions, and move more, if the earthquake was larger, and or closer. But somewhere I think I read some numbers indicating how much the earth would be expected to move. If you go to _http://jclahr.com/science/psn/magnitude.html_ (http://jclahr.com/science/psn/magnitude.html) you will find several graphs and tables. Remember that surface waves are often the largest in amplitude and that their amplitude is greatly effected by the local ground type. Waterlogged alluvial ground may behave very like a jelly. I am asking this question, to help me understand, the approximate tilt from an earthquake. If I hung a one meter pendulum, and a major earthquake occurred 1000km away, the earth here, would tilt. If I were looking at the pendulum at the moment the S wave arrived, assuming the sensor was pointing in the correct direction, the pendulum would appear to tilt, but unless the event was large enough I could not see it with my eyes. You need to remember the difference in response of a pendulum to both sideways motion and to direct tilts. S waves will show lateral motion, but P and Rayleigh waves may show direct tilt effects as well as motion. Regards, Chris Chapman
In a message dated 04/01/2008, gpayton880@....... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
While everyone has their "Thinking Caps" on from Ted's excellent=20 questions, I have a couple that have been smoldering for some time:
 
1)    Months ago I posted an event and I received an e= mail=20 commenting on it.  He said, "It was very good, but I might=20= try=20 improving my P-wave."  HOW does one "improve" one phase over=20 another?  It seems that the P-wave is always less=20 stronger.
Hi Jerry,
 
    I suggest that you ask him? Raw data files for=20= the=20 relevant time interval are normally submitted.
 
    It is usual to extract the digital trace and to= =20 then apply filters to it to make the waves more visible while doing your own= =20 analysis. You might set the HP and LP filters both to 1 second when searchin= g=20 for teleseismic P waves, for example.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
2)    Much has been written about the length of a pend= ulum=20 needing to be long to be effective for teleseismic detection.  Howeve= r,=20 the commercial devices are quite compact and obviously have short=20 pendulums.  Can someone explain how they accomplish what they do with= =20 short pendulums?
    They use very low noise capacitative detectors=20= to=20 get the very high resolution, to maybe well below 0.1 nano metre. The period= may=20 then be extended greatly by electronic feedback, or by digital feedback, or=20 both. They may use small pendulums with a natural period of say 0.5 second o= r=20 more, but these are totally controlled by the force feedback. Because direct= =20 position and not velocity is being measured, you get a fall off in the signa= l=20 below resonance of only 1/f, not 1/f^2. You can extend a 'natural' 1 second=20 system to over 1,000 seconds, but the electronics required to do this may be= =20 quite expensive.
 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
When I receive an earthquake, the earth a= nd my=20 house are moved by the event.  The various phases move the ground in=20 different directions. This question has= to do=20 with the movement of the earth like that of a teeter-totter.  Tilt. l= ike=20 that measured by a level.
 
1.  How much does the earth move?&nb= sp; I do=20 understand the earth would move in many different directions, and move mor= e,=20 if the earthquake was larger, and or closer. But somewhere I think I read some numbers indicating how much the= earth=20 would be expected to move.
    If you go to http://jclahr.com/scie= nce/psn/magnitude.html you=20 will find several graphs and tables. Remember that surface waves are often t= he=20 largest in amplitude and that their amplitude is greatly effected by the loc= al=20 ground type. Waterlogged alluvial ground may behave very like a jelly.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
I am asking this question, to help me und= erstand,=20 the approximate tilt from an earthquake.   If I hung a one meter= =20 pendulum, and a major earthquake occurred 1000km away, the earth here, wou= ld=20 tilt.  If I were looking at the pendulum at the moment the S wav= e=20 arrived, assuming the sensor was pointing in the correct direction, the=20 pendulum would appear to tilt, but unless the event was large enough I cou= ld=20 not see it with my eyes.
    You need to remember the difference in response= of=20 a pendulum to both sideways motion and to direct tilts. S waves will show=20 lateral motion,  but P and Rayleigh waves may show direct tilt effects=20= as=20 well as motion.
 
    Regards,
 
    Chris Chapman
Subject: Hekla volcano geophone planned From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Fri, 04 Jan 2008 17:03:55 +0000 Hi all I am going to setup a geophone close to the Hekla volcano this year (20 something km). I am going to speed up progress of setting up that geophone as I can, but at the latest the geophone is going up next summer. Hekla volcano is ready to erupt at any time. That is the reason for the speedup for that project. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: "Jerry Payton" gpayton880@....... Date: Fri, 4 Jan 2008 11:07:42 -0600 Jon, how in the world are you linking to all these geophones and back to your station?? 20 something km !!!??? Jerry ----- Original Message ----- From: Jón Frímann To: PSN-Postlist Sent: Friday, January 04, 2008 11:03 AM Subject: Hekla volcano geophone planned Hi all I am going to setup a geophone close to the Hekla volcano this year (20 something km). I am going to speed up progress of setting up that geophone as I can, but at the latest the geophone is going up next summer. Hekla volcano is ready to erupt at any time. That is the reason for the speedup for that project. Regards. -- Jón Frímann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Jon, how in the world are you linking to all these geophones = and=20  back to your station?? 20 something km !!!???
Jerry
 
 
----- Original Message -----=20
From: J=F3n = Fr=EDmann
To: PSN-Postlist
Sent: Friday, January 04, 2008 11:03 AM
Subject: Hekla volcano geophone planned

Hi all

I am going to setup a geophone close to the = Hekla=20 volcano this year (20
something km). I am going to speed up progress = of=20 setting up that
geophone as I can, but at the latest the geophone is = going up=20 next
summer.

Hekla volcano is ready to erupt at any time. That = is the=20 reason for the
speedup for that project.

Regards.
-- =
J=F3n=20 Fr=EDmann
http://www.jonfr.com
http://earthquakes.jonfr.comhttp://www.net303.net
http://www.mobile-coverage.com/<= /A>

__________________________________________________________
=
Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@............... with=20
the body of the message (first line only): unsubscribe
See http://www.seismicnet.co= m/maillist.html=20 for more information.
Subject: Re: Hekla volcano geophone planned From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Fri, 04 Jan 2008 17:10:47 +0000 Hi The geophone is going to be located at a house that is ~20 km away from Hekla volcano. But the connection from there to my main computer I am going to use the internet. Regards.=20 --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: "Jerry Payton" gpayton880@....... Date: Fri, 4 Jan 2008 11:17:19 -0600 Hmmmm That's interesting, Jon. I'd like to know more how you accomplish that without a different IP address for each geophone that you use. You might contact me directly gpayton880@....... with an explanation and/or drawing when you have time. Regards, Jerry ----- Original Message ----- From: Jón Frímann To: psn-l@.............. Sent: Friday, January 04, 2008 11:10 AM Subject: Re: Hekla volcano geophone planned Hi The geophone is going to be located at a house that is ~20 km away from Hekla volcano. But the connection from there to my main computer I am going to use the internet. Regards. -- Jón Frímann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Hmmmm  That's interesting, Jon.  I'd like to know more = how you=20 accomplish that without a different IP address for each geophone that = you=20 use.  You might contact me directly  gpayton880@.......  with an=20 explanation and/or drawing when you have time.
Regards,
Jerry
 
 
----- Original Message -----=20
From: J=F3n = Fr=EDmann
Sent: Friday, January 04, 2008 11:10 AM
Subject: Re: Hekla volcano geophone planned

Hi

The geophone is going to be located at a house = that is=20 ~20 km away from
Hekla volcano. But the connection from there to my = main=20 computer I am
going to use the internet.

Regards.
-- =
J=F3n=20 Fr=EDmann
http://www.jonfr.com
http://earthquakes.jonfr.comhttp://www.net303.net
http://www.mobile-coverage.com/<= /A>

__________________________________________________________
=
Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@............... with=20
the body of the message (first line only): unsubscribe
See http://www.seismicnet.co= m/maillist.html=20 for more information.
Subject: RE: Hekla volcano geophone planned From: "Timothy Carpenter" geodynamics@....... Date: Fri, 4 Jan 2008 13:24:03 -0500 Jon & Jerry, I too would be interested in how you are setting up your internet connection(s) =96 so let=92s keep the discussion on-list. -Tim- Timothy Carpenter =20 From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Jerry Payton Sent: Friday, January 04, 2008 12:17 PM To: psn-l@.............. Subject: Re: Hekla volcano geophone planned =20 Hmmmm That's interesting, Jon. I'd like to know more how you = accomplish that without a different IP address for each geophone that you use. You might contact me directly gpayton880@....... with an explanation = and/or drawing when you have time. Regards, Jerry =20 =20 ----- Original Message -----=20 From: J=F3n Fr=EDmann =20 To: psn-l@................. Sent: Friday, January 04, 2008 11:10 AM Subject: Re: Hekla volcano geophone planned =20 Hi The geophone is going to be located at a house that is ~20 km away from Hekla volcano. But the connection from there to my main computer I am going to use the internet. Regards.=20 --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)

Jon & Jerry,

I too would be interested in how you are setting up your internet connection(s) – so let’s keep the discussion = on-list.

-Tim-

Timothy Carpenter

 

From:= psn-l-request@.............. [mailto:psn-l-request@............... On = Behalf Of Jerry Payton
Sent: Friday, January 04, 2008 12:17 PM
To: psn-l@..............
Subject: Re: Hekla volcano geophone planned

 

Hmmmm  That's interesting, Jon.  I'd like = to know more how you accomplish that without a different IP address for each = geophone that you use.  You might contact me directly  gpayton880@.......  with an explanation and/or drawing when you have time.

Regards,

Jerry

 

 

----- Original Message -----

Sent:<= /b> Friday, = January 04, 2008 11:10 AM

Subject: Re: Hekla = volcano geophone planned

 

Hi

The geophone is going to be located at a house that is ~20 km away = from
Hekla volcano. But the connection from there to my main computer I = am
going to use the internet.

Regards.
--
J=F3n Fr=EDmann
http://www.jonfr.com
http://earthquakes.jonfr.com http://www.net303.net
http://www.mobile-coverage.com/<= /a>

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@............... with
the body of the message (first line only): unsubscribe
See http://www.seismicnet.co= m/maillist.html for more information.

Subject: RE: Hekla volcano geophone planned From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Fri, 04 Jan 2008 18:45:23 +0000 Hi I have a pc with each geophone. The internet is used to send me the data back to my main computer. It looks like this, Main PC (hvt station) --- Internet --- Hekla geophone+pc I try to use the internet connection that already there, rather then have to buy one on my own. I have used this type of setup already. The Mosfellsb=E6r station is connecteted in this way already. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Fri, 04 Jan 2008 20:28:53 +0000 Hi, to answer the question below, more than 1 data source per ip address, here's 2 approaches (many more no doubt are possible): tcp/ip sockets. Using these, each ip address can be split into 65536 channels, or sockets, 0 to 65535. Some of these are already allocated, like 25 for mail and 80 for web browsing. Anything above 1000 should be available but check or be alert to something no longer working and try another socket number. These are also what those nasty hacker creatures use for sneaking into unprotected pcs. You could have 1 socket per sensor. Under this regime you would need to have a server program running in the pc for each socket. It "listens" for incoming connections. When a connection request is made, it starts serving up the stream of data for that particular sensor. But rather than have 1 sensor on a single socket it is more sensible to have many sensors on a single socket using a data protocol. This is how I have designed my system. It sends out a continuous stream (50 samples per second) of "(Lehman reading) (geophone reading) (time stamp)". My graphing program makes a connection to the "data server" and plots the values from the 2 sensors as they arrive. See http://www.iasmith.com. As you'll see, my above-ground system is badly affected by wind. I recently achieved a big increase in sensitivity and was rewarded by the now increased significance of the wind :-( . I need to dig down and make a below-ground system. Segway to the next topic... Cheers Ian Jerry Payton wrote: > Hmmmm That's interesting, Jon. I'd like to know more how you > accomplish that without a different IP address for each geophone that > you use. You might contact me directly gpayton880@....... > with an explanation and/or drawing when > you have time. > Regards, > Jerry > > > ----- Original Message ----- > *From:* Jón Frímann > *To:* psn-l@.............. > *Sent:* Friday, January 04, 2008 11:10 AM > *Subject:* Re: Hekla volcano geophone planned > > Hi > > The geophone is going to be located at a house that is ~20 km away from > Hekla volcano. But the connection from there to my main computer I am > going to use the internet. > > Regards. > -- > Jón Frímann > http://www.jonfr.com > http://earthquakes.jonfr.com > http://www.net303.net > http://www.mobile-coverage.com/ > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. > with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: "Jerry Payton" gpayton880@....... Date: Fri, 4 Jan 2008 15:48:56 -0600 Thank you Ian, Jon and Tim, All good answers. When I heard something new to me, my mind says, "Hmmm. Wonder how that works or how that is hooked up." I appreciate each input. Jerry ----- Original Message ----- From: ian To: psn-l@.............. Sent: Friday, January 04, 2008 2:28 PM Subject: Re: Hekla volcano geophone planned Hi, to answer the question below, more than 1 data source per ip address, here's 2 approaches (many more no doubt are possible): tcp/ip sockets. Using these, each ip address can be split into 65536 channels, or sockets, 0 to 65535. Some of these are already allocated, like 25 for mail and 80 for web browsing. Anything above 1000 should be available but check or be alert to something no longer working and try another socket number. These are also what those nasty hacker creatures use for sneaking into unprotected pcs. You could have 1 socket per sensor. Under this regime you would need to have a server program running in the pc for each socket. It "listens" for incoming connections. When a connection request is made, it starts serving up the stream of data for that particular sensor. But rather than have 1 sensor on a single socket it is more sensible to have many sensors on a single socket using a data protocol. This is how I have designed my system. It sends out a continuous stream (50 samples per second) of "(Lehman reading) (geophone reading) (time stamp)". My graphing program makes a connection to the "data server" and plots the values from the 2 sensors as they arrive. See http://www.iasmith.com. As you'll see, my above-ground system is badly affected by wind. I recently achieved a big increase in sensitivity and was rewarded by the now increased significance of the wind :-( . I need to dig down and make a below-ground system. Segway to the next topic... Cheers Ian Jerry Payton wrote: > Hmmmm That's interesting, Jon. I'd like to know more how you > accomplish that without a different IP address for each geophone that > you use. You might contact me directly gpayton880@....... > with an explanation and/or drawing when > you have time. > Regards, > Jerry > > > ----- Original Message ----- > *From:* Jón Frímann > *To:* psn-l@.............. > *Sent:* Friday, January 04, 2008 11:10 AM > *Subject:* Re: Hekla volcano geophone planned > > Hi > > The geophone is going to be located at a house that is ~20 km away from > Hekla volcano. But the connection from there to my main computer I am > going to use the internet. > > Regards. > -- > Jón Frímann > http://www.jonfr.com > http://earthquakes.jonfr.com > http://www.net303.net > http://www.mobile-coverage.com/ > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. > with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Thank you Ian, Jon and Tim,
 
All good answers.  When I heard something new to me, my mind = says,=20 "Hmmm. Wonder how that works or how that is hooked up."  I = appreciate each=20 input.
Jerry
 
 
----- Original Message -----=20
From: ian
Sent: Friday, January 04, 2008 2:28 PM
Subject: Re: Hekla volcano geophone planned

Hi,

to answer the question below, more than 1 data = source=20 per ip address,
here's 2 approaches (many more no doubt are=20 possible):

tcp/ip sockets.  Using these, each ip address can = be=20 split into 65536
channels, or sockets, 0 to 65535.  Some of = these are=20 already allocated,
like 25 for mail and 80 for web browsing.  = Anything=20 above 1000 should be
available but check or be alert to something no = longer=20 working and try
another socket number.  These are also what = those nasty=20 hacker creatures
use for sneaking into unprotected pcs.

You = could=20 have 1 socket per sensor.  Under this regime you would need to =
have a=20 server program running in the pc for each socket.  It "listens" =
for=20 incoming connections.  When a connection request is made, it starts =
serving up the stream of data for that particular sensor.

But = rather=20 than have 1 sensor on a single socket it is more sensible to
have = many=20 sensors on a single socket using a data protocol.  This is how =
I have=20 designed my system.  It sends out a continuous stream (50 samples =
per=20 second) of "(Lehman reading) (geophone reading) (time stamp)".  My=20
graphing program makes a connection to the "data server" and plots = the=20
values from the 2 sensors as they arrive.  See http://www.iasmith.com.

As = you'll see,=20 my above-ground system is badly affected by wind.  I
recently = achieved=20 a big increase in sensitivity and was rewarded by the
now increased=20 significance of the wind  :-( .  I need to dig down and =
make a=20 below-ground system.  Segway to the next=20 topic...

Cheers

Ian



Jerry Payton = wrote:
>=20 Hmmmm  That's interesting, Jon.  I'd like to know more how you =
> accomplish that without a different IP address for each = geophone that=20
> you use.  You might contact me directly  gpayton880@.......
> = <mailto:gpayton880@.......> = ; with an=20 explanation and/or drawing when
> you have time.
> = Regards,
>=20 Jerry
> 
> 
> ----- Original Message = -----
>=20 *From:* J=F3n Fr=EDmann <mailto:jonfr@.........>
> = *To:* psn-l@.............. <mailto:psn-l@..............><= BR>>=20 *Sent:* Friday, January 04, 2008 11:10 AM
> *Subject:* Re: Hekla = volcano=20 geophone planned
>
> Hi
>
> The geophone is = going to be=20 located at a house that is ~20 km away from
> Hekla volcano. But = the=20 connection from there to my main computer I am
> going to use the=20 internet.
>
> Regards.
> --
> J=F3n = Fr=EDmann
> http://www.jonfr.com
> http://earthquakes.jonfr.com> http://www.net303.net
> http://www.mobile-coverage.com/<= /A>
>
>=20 __________________________________________________________
>
>= ;=20 Public Seismic Network Mailing List (PSN-L)
>
> To leave = this list=20 email PSN-L-REQUEST@............... =20
> <mailto:PSN-L-REQUEST@SEISMIC= NET.COM>=20 with
> the body of the message (first line only): = unsubscribe
> See=20 http://www.seismicnet.co= m/maillist.html=20 for more information.

--

<http://www.festivalpreviews.com<= /A>>
__________________________________________________________
=
Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@............... with=20
the body of the message (first line only): unsubscribe
See http://www.seismicnet.co= m/maillist.html=20 for more information.
Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Sat, 5 Jan 2008 00:20:26 EST In a message dated 04/01/2008, gpayton880@....... writes: But rather than have 1 sensor on a single socket it is more sensible to have many sensors on a single socket using a data protocol. This is how I have designed my system. It sends out a continuous stream (50 samples per second) of "(Lehman reading) (geophone reading) (time stamp)". My graphing program makes a connection to the "data server" and plots the values from the 2 sensors as they arrive. See _http://www.iasmith.com_ (http://www.iasmith.com/) . Hi Ian, The limitation tends to be the total data throughput speed reqired. 50 SPS is quite fast. The ADC sample rate can also impose limitations. This starts to become serious when you have, say several three off three channel sensors on the same ADC. Regards, Chris Chapman
In a message dated 04/01/2008, gpayton880@....... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>But=20 rather than have 1 sensor on a single socket it is more sensible to
ha= ve=20 many sensors on a single socket using a data protocol.  This is how <= BR>I=20 have designed my system.  It sends out a continuous stream (50 sample= s=20
per second) of "(Lehman reading) (geophone reading) (time stamp)".&nbs= p;=20 My
graphing program makes a connection to the "data server" and plots=20= the=20
values from the 2 sensors as they arrive.  See http://www.iasmith.com.
Hi Ian,
 
    The limitation tends to be the total data=20 throughput speed reqired. 50 SPS is quite fast. The ADC sample rate can= =20 also impose limitations. This starts to become serious when you have, say=20 several three off three channel sensors on the same ADC.
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sat, 05 Jan 2008 09:35:41 +0000 Hi, actually, I don't think I'm near any limits. The A/D I use can handle 20K samples/sec. I only have 2 instruments (though I sample each on 3 A/D channels to get the resolution up to 22 bits), so that's only 6 x 50, or 300 samples/sec. So I could connect up all of the A/D's 16 input channels and still not stress it. The data server does burn up 80% of the PC's CPU but it's only an old 800 MHz machine and wouldn't cost much to replace with one twice the speed. Data across the network connection is only 32 characters x 50 or 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth (being generous). All of the above though, implies that you are happy to write your own code. Buying building blocks off the shelf can be very attractive. For multiple instruments you could buy several PSN A/D boards. To overcome the potential problem of connecting up multiple RS232 cables, you could use a network terminal server (such as http://www.perle.com/products/IOLAN-STS-Terminal-Server.shtml?rack ). These aggregate up to 4/8/16/24 rs232 connections on to one network connection. They usually come with software for the pc which creates multiple virtual COM ports, so your A/D boards would look like they are plugged into an array of COM ports on the PC. Isn't technology wonderful! Cheers Ian ChrisAtUpw@....... wrote: > In a message dated 04/01/2008, gpayton880@....... writes: > > But rather than have 1 sensor on a single socket it is more > sensible to > have many sensors on a single socket using a data protocol. This > is how > I have designed my system. It sends out a continuous stream (50 > samples > per second) of "(Lehman reading) (geophone reading) (time > stamp)". My > graphing program makes a connection to the "data server" and plots > the > values from the 2 sensors as they arrive. See > http://www.iasmith.com . > > Hi Ian, > > The limitation tends to be the total data throughput > speed reqired. 50 SPS is quite fast. The ADC sample rate can also > impose limitations. This starts to become serious when you have, say > several three off three channel sensors on the same ADC. > > Regards, > > Chris Chapman -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 05 Jan 2008 11:28:55 +0000 Hi All of my remote sensors are going to be connected over the internet. I have ~6mb ADSL connection, so it should be able to handle it. The data flow isn't a lot, about ~100mb pr day on each station. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Large earthquake near cost of Canada From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 05 Jan 2008 11:32:14 +0000 Hi all There appears to have been a large earthquake near the cost of Canada this morning (GMT time). I am unsure what the size is, but usgs is reporting M6.5 Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: ian ian@........... Date: Sat, 05 Jan 2008 11:44:53 +0000 Hi, yes thanks, I can see it. It's a bit windy here, so my trace is not pristine... Cheers Ian http://www.iasmith.com http://www.festivalpreviews.com Jón Frímann wrote: > Hi all > > There appears to have been a large earthquake near the cost of Canada > this morning (GMT time). I am unsure what the size is, but usgs is > reporting M6.5 > > Regards. > -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 05 Jan 2008 12:15:43 +0000 Hi At 11:44 GMT there was a second large earthquake near the east cost of Canada, USGS early size gives it M6.5. This is quite unusual for this area to have two earthquakes with this short period. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re[2]: Hekla volcano geophone planned From: Angel sismos@.............. Date: Sat, 5 Jan 2008 13:57:23 +0000 Hello Jon, Timothy and all, I would like this thread on the list also. Angel Friday, January 4, 2008, 6:24:03 PM, you wrote: > Jon & Jerry, > I too would be interested in how you are setting up your internet > connection(s) – so let’s keep the discussion on-list. > -Tim- > Timothy Carpenter > > From: psn-l-request@.............. > [mailto:psn-l-request@............... On Behalf Of Jerry Payton > Sent: Friday, January 04, 2008 12:17 PM > To: psn-l@.............. > Subject: Re: Hekla volcano geophone planned > > Hmmmm That's interesting, Jon. I'd like to know more how you > accomplish that without a different IP address for each geophone > that you use. You might contact me directly gpayton880@....... > with an explanation and/or drawing when you have time. > Regards, > Jerry > > > ----- Original Message ----- > From: Jón Frímann > To: psn-l@.............. > Sent: Friday, January 04, 2008 11:10 AM > Subject: Re: Hekla volcano geophone planned > > Hi > The geophone is going to be located at a house that is ~20 km away from > Hekla volcano. But the connection from there to my main computer I am > going to use the internet. > Regards. -- Best regards, Angel __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Burning Questions From: Brett Nordgren Brett3mr@............. Date: Sat, 05 Jan 2008 10:12:06 -0500 Jerry, re: 2) Almost all modern commercial sensors use some form of an astatic leaf-spring suspension. See fig. 10 of http://jclahr.com/science/psn/wielandt/node15.html With careful design and very careful adjustment, even quite a small pendulum (2") can be made to have a long free period. However, such a setup is very prone to drift from temperature and other changes and is only useful when it is combined with feedback such as Chris describes, to broaden its frequency response curve and stabilize its tendency to 'wander'. In such an instrument the real benefit of the long free period is to make it easier for the feedback to accurately control its motion. Long free period = low restoring force = less feedback force needed to control the pendulum. Brett At 09:22 AM 1/4/2008 -0600, you wrote: >While everyone has their "Thinking Caps" on from Ted's excellent >questions, I have a couple that have been smoldering for some time: > >1) Months ago I posted an event and I received an email commenting on >it. He said, "It was very good, but I might try improving my >P-wave." HOW does one "improve" one phase over another? It seems that >the P-wave is always less stronger. > >2) Much has been written about the length of a pendulum needing to be >long to be effective for teleseismic detection. However, the commercial >devices are quite compact and obviously have short pendulums. Can someone >explain how they accomplish what they do with short pendulums? > >Thank you for "thinking for me." >Jerry My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re[2]: Hekla volcano geophone planned From: Angel sismos@.............. Date: Sat, 5 Jan 2008 15:39:15 +0000 Hello Ian, I have not read each messages of this thread careful but I will. All of the software needed to link a large distributed seismic system is free and freely available. Anyone who has one of Larry's 16 bit 8 channel boards with GPS (wwv) timing and a full time internet connection can share data and PSN can a global or regional system auto locating system. Angel Saturday, January 5, 2008, 9:35:41 AM, you wrote: > Hi, > actually, I don't think I'm near any limits. The A/D I use can handle > 20K samples/sec. I only have 2 instruments (though I sample each on 3 > A/D channels to get the resolution up to 22 bits), so that's only 6 x > 50, or 300 samples/sec. So I could connect up all of the A/D's 16 input > channels and still not stress it. > The data server does burn up 80% of the PC's CPU but it's only an old > 800 MHz machine and wouldn't cost much to replace with one twice the > speed. Data across the network connection is only 32 characters x 50 or > 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth > (being generous). > All of the above though, implies that you are happy to write your own > code. Buying building blocks off the shelf can be very attractive. For > multiple instruments you could buy several PSN A/D boards. To overcome > the potential problem of connecting up multiple RS232 cables, you could > use a network terminal server (such as > http://www.perle.com/products/IOLAN-STS-Terminal-Server.shtml?rack ). > These aggregate up to 4/8/16/24 rs232 connections on to one network > connection. They usually come with software for the pc which creates > multiple virtual COM ports, so your A/D boards would look like they are > plugged into an array of COM ports on the PC. > Isn't technology wonderful! > Cheers > Ian > ChrisAtUpw@....... wrote: >> In a message dated 04/01/2008, gpayton880@....... writes: >> But rather than have 1 sensor on a single socket it is more >> sensible to >> have many sensors on a single socket using a data protocol. This >> is how >> I have designed my system. It sends out a continuous stream (50 >> samples >> per second) of "(Lehman reading) (geophone reading) (time >> stamp)". My >> graphing program makes a connection to the "data server" and plots >> the >> values from the 2 sensors as they arrive. See >> http://www.iasmith.com . >> Hi Ian, >> >> The limitation tends to be the total data throughput >> speed reqired. 50 SPS is quite fast. The ADC sample rate can also >> impose limitations. This starts to become serious when you have, say >> several three off three channel sensors on the same ADC. >> >> Regards, >> >> Chris Chapman -- Best regards, Angel __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sat, 05 Jan 2008 15:57:40 +0000 Hi, yes, you're right, all free. I was really addressing the earlier (possibly hypothetical) question of how to connect many sensors to 1 network connection. The engineer in me probably made my response a bit enthusiastic and suitable for connecting dozens of sensors. Back to (free) reality! Cheers Ian http://www.iasmith.com/ http://www.festivalpreviews.com Angel wrote: > Hello Ian, > > I have not read each messages of this thread careful but I will. All of the software needed to link a large distributed seismic system is free and freely available. > > Anyone who has one of Larry's 16 bit 8 channel boards with GPS (wwv) timing and a full time internet connection can share data and PSN can a global or regional system auto locating system. > > Angel > > > > Saturday, January 5, 2008, 9:35:41 AM, you wrote: > > >> Hi, >> > > >> actually, I don't think I'm near any limits. The A/D I use can handle >> 20K samples/sec. I only have 2 instruments (though I sample each on 3 >> A/D channels to get the resolution up to 22 bits), so that's only 6 x >> 50, or 300 samples/sec. So I could connect up all of the A/D's 16 input >> channels and still not stress it. >> > > >> The data server does burn up 80% of the PC's CPU but it's only an old >> 800 MHz machine and wouldn't cost much to replace with one twice the >> speed. Data across the network connection is only 32 characters x 50 or >> 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth >> (being generous). >> > > >> All of the above though, implies that you are happy to write your own >> code. Buying building blocks off the shelf can be very attractive. For >> multiple instruments you could buy several PSN A/D boards. To overcome >> the potential problem of connecting up multiple RS232 cables, you could >> use a network terminal server (such as >> http://www.perle.com/products/IOLAN-STS-Terminal-Server.shtml?rack ). >> These aggregate up to 4/8/16/24 rs232 connections on to one network >> connection. They usually come with software for the pc which creates >> multiple virtual COM ports, so your A/D boards would look like they are >> plugged into an array of COM ports on the PC. >> > > >> Isn't technology wonderful! >> > > >> Cheers >> > > >> Ian >> > > >> ChrisAtUpw@....... wrote: >> >>> In a message dated 04/01/2008, gpayton880@....... writes: >>> > > >>> But rather than have 1 sensor on a single socket it is more >>> sensible to >>> have many sensors on a single socket using a data protocol. This >>> is how >>> I have designed my system. It sends out a continuous stream (50 >>> samples >>> per second) of "(Lehman reading) (geophone reading) (time >>> stamp)". My >>> graphing program makes a connection to the "data server" and plots >>> the >>> values from the 2 sensors as they arrive. See >>> http://www.iasmith.com . >>> > > >>> Hi Ian, >>> >>> The limitation tends to be the total data throughput >>> speed reqired. 50 SPS is quite fast. The ADC sample rate can also >>> impose limitations. This starts to become serious when you have, say >>> several three off three channel sensors on the same ADC. >>> >>> Regards, >>> >>> Chris Chapman >>> > > > > > -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re[2]: Hekla volcano geophone planned From: Angel sismos@.............. Date: Sat, 5 Jan 2008 16:13:08 +0000 Hello Ian, Just to get an idea, how many PSN-ADC-SERIAL Version II with GPS timing and full time internet connection are there out there. I have one. Angel Saturday, January 5, 2008, 3:57:40 PM, you wrote: > Hi, > yes, you're right, all free. I was really addressing the earlier > (possibly hypothetical) question of how to connect many sensors to 1 > network connection. The engineer in me probably made my response a bit > enthusiastic and suitable for connecting dozens of sensors. > Back to (free) reality! > Cheers > Ian > http://www.iasmith.com/ > http://www.festivalpreviews.com > Angel wrote: >> Hello Ian, >> I have not read each messages of this thread careful but I will. All of the software needed to link a large distributed seismic system is free and freely available. >> Anyone who has one of Larry's 16 bit 8 channel boards with GPS (wwv) timing and a full time internet connection can share data and PSN can a global or regional system auto locating system. >> Angel >> Saturday, January 5, 2008, 9:35:41 AM, you wrote: >> >>> Hi, >>> >> >>> actually, I don't think I'm near any limits. The A/D I use can handle >>> 20K samples/sec. I only have 2 instruments (though I sample each on 3 >>> A/D channels to get the resolution up to 22 bits), so that's only 6 x >>> 50, or 300 samples/sec. So I could connect up all of the A/D's 16 input >>> channels and still not stress it. >>> >> >>> The data server does burn up 80% of the PC's CPU but it's only an old >>> 800 MHz machine and wouldn't cost much to replace with one twice the >>> speed. Data across the network connection is only 32 characters x 50 or >>> 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth >>> (being generous). >>> >> >>> All of the above though, implies that you are happy to write your own >>> code. Buying building blocks off the shelf can be very attractive. For >>> multiple instruments you could buy several PSN A/D boards. To overcome >>> the potential problem of connecting up multiple RS232 cables, you could >>> use a network terminal server (such as >>> http://www.perle.com/products/IOLAN-STS-Terminal-Server.shtml?rack ). >>> These aggregate up to 4/8/16/24 rs232 connections on to one network >>> connection. They usually come with software for the pc which creates >>> multiple virtual COM ports, so your A/D boards would look like they are >>> plugged into an array of COM ports on the PC. >>> >> >>> Isn't technology wonderful! >>> >> >>> Cheers >>> >> >>> Ian >>> >> >>> ChrisAtUpw@....... wrote: >>> >>>> In a message dated 04/01/2008, gpayton880@....... writes: >>>> >> >>>> But rather than have 1 sensor on a single socket it is more >>>> sensible to >>>> have many sensors on a single socket using a data protocol. This >>>> is how >>>> I have designed my system. It sends out a continuous stream (50 >>>> samples >>>> per second) of "(Lehman reading) (geophone reading) (time >>>> stamp)". My >>>> graphing program makes a connection to the "data server" and plots >>>> the >>>> values from the 2 sensors as they arrive. See >>>> http://www.iasmith.com . >>>> >> >>>> Hi Ian, >>>> >>>> The limitation tends to be the total data throughput >>>> speed reqired. 50 SPS is quite fast. The ADC sample rate can also >>>> impose limitations. This starts to become serious when you have, say >>>> several three off three channel sensors on the same ADC. >>>> >>>> Regards, >>>> >>>> Chris Chapman >>>> >> -- Best regards, Angel __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sat, 05 Jan 2008 16:24:56 +0000 Hi, I don't know. I don't have one. Presumably an approximation can be got from http://www.sydneystormcity.com/people.htm Cheers Ian Angel wrote: > Hello Ian, > > Just to get an idea, how many PSN-ADC-SERIAL Version II with GPS timing and full time internet connection are there out there. > > I have one. > > Angel > > Saturday, January 5, 2008, 3:57:40 PM, you wrote: > > >> Hi, >> > > >> yes, you're right, all free. I was really addressing the earlier >> (possibly hypothetical) question of how to connect many sensors to 1 >> network connection. The engineer in me probably made my response a bit >> enthusiastic and suitable for connecting dozens of sensors. >> > > >> Back to (free) reality! >> > > >> Cheers >> > > >> Ian >> http://www.iasmith.com/ >> http://www.festivalpreviews.com >> > > >> Angel wrote: >> >>> Hello Ian, >>> > > >>> I have not read each messages of this thread careful but I will. All of the software needed to link a large distributed seismic system is free and freely available. >>> > > >>> Anyone who has one of Larry's 16 bit 8 channel boards with GPS (wwv) timing and a full time internet connection can share data and PSN can a global or regional system auto locating system. >>> > > >>> Angel >>> > > > > >>> Saturday, January 5, 2008, 9:35:41 AM, you wrote: >>> > > >>> >>> >>>> Hi, >>>> >>>> > > >>> >>> >>>> actually, I don't think I'm near any limits. The A/D I use can handle >>>> 20K samples/sec. I only have 2 instruments (though I sample each on 3 >>>> A/D channels to get the resolution up to 22 bits), so that's only 6 x >>>> 50, or 300 samples/sec. So I could connect up all of the A/D's 16 input >>>> channels and still not stress it. >>>> >>>> > > >>> >>> >>>> The data server does burn up 80% of the PC's CPU but it's only an old >>>> 800 MHz machine and wouldn't cost much to replace with one twice the >>>> speed. Data across the network connection is only 32 characters x 50 or >>>> 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth >>>> (being generous). >>>> >>>> > > >>> >>> >>>> All of the above though, implies that you are happy to write your own >>>> code. Buying building blocks off the shelf can be very attractive. For >>>> multiple instruments you could buy several PSN A/D boards. To overcome >>>> the potential problem of connecting up multiple RS232 cables, you could >>>> use a network terminal server (such as >>>> http://www.perle.com/products/IOLAN-STS-Terminal-Server.shtml?rack ). >>>> These aggregate up to 4/8/16/24 rs232 connections on to one network >>>> connection. They usually come with software for the pc which creates >>>> multiple virtual COM ports, so your A/D boards would look like they are >>>> plugged into an array of COM ports on the PC. >>>> >>>> > > >>> >>> >>>> Isn't technology wonderful! >>>> >>>> > > >>> >>> >>>> Cheers >>>> >>>> > > >>> >>> >>>> Ian >>>> >>>> > > >>> >>> >>>> ChrisAtUpw@....... wrote: >>>> >>>> >>>>> In a message dated 04/01/2008, gpayton880@....... writes: >>>>> >>>>> > > >>> >>> >>>>> But rather than have 1 sensor on a single socket it is more >>>>> sensible to >>>>> have many sensors on a single socket using a data protocol. This >>>>> is how >>>>> I have designed my system. It sends out a continuous stream (50 >>>>> samples >>>>> per second) of "(Lehman reading) (geophone reading) (time >>>>> stamp)". My >>>>> graphing program makes a connection to the "data server" and plots >>>>> the >>>>> values from the 2 sensors as they arrive. See >>>>> http://www.iasmith.com . >>>>> >>>>> > > >>> >>> >>>>> Hi Ian, >>>>> >>>>> The limitation tends to be the total data throughput >>>>> speed reqired. 50 SPS is quite fast. The ADC sample rate can also >>>>> impose limitations. This starts to become serious when you have, say >>>>> several three off three channel sensors on the same ADC. >>>>> >>>>> Regards, >>>>> >>>>> Chris Chapman >>>>> >>>>> > > > > > >>> >>> > > > > > -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: "Thomas Dick" dickthomas01@............. Date: Sat, 5 Jan 2008 10:39:25 -0600 Are you familiar with UltraVNC Viewer. It allows me to access the earthquake recording computer anywhere I can find wifi? Some business computer articles give it a high security rating. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sat, 05 Jan 2008 16:54:20 +0000 Hi, yes, I use it to look directly at my seismometer pc which is in the workshop. It works very well. Ian Thomas Dick wrote: > Are you familiar with UltraVNC Viewer. It allows me to access the > earthquake recording computer anywhere I can find wifi? Some business > computer articles give it a high security rating. > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Sat, 5 Jan 2008 14:41:40 EST In a message dated 05/01/2008, ian@........... writes: Hi, actually, I don't think I'm near any limits. The A/D I use can handle 20K samples/sec. Hi Ian, What ADC are you using? 20 K SPS is 50 micro sec / sample. My ADC takes 20 muS/S. How does it's accuracy depend on it's sample rate? Does it have an onboard processor chip to take and average multiple samples? What data rate does the ADC board to computer link support? I only have 2 instruments (though I sample each on 3 A/D channels to get the resolution up to 22 bits), so that's only 6 x 50, or 300 samples/sec. You need to average four samples to get 1 additional bit of accuracy, 16 samples to get two bits extra, etc. So I could connect up all of the A/D's 16 input channels and still not stress it. This is likely to be ~40 bytes total with the overheads at 50 SPS, say 16 K bits/ sec. If you are using a 24 bit ADC, it is likely double this. Then it largely depends on whether you are sending datapackets, or individual bytes. If you are sending asynchronous bytes, you have to wait for the signal to be transmitted, the receiving server to respond and the ACK to be received. Transmission delays can be significant. I am 12 km from the phone terminal, so the delay would be well over 80 micro sec per byte. Coupled to a a 56 K modem, I certainly could not transmit this much data. The data server does burn up 80% of the PC's CPU but it's only an old 800 MHz machine and wouldn't cost much to replace with one twice the speed. Data across the network connection is only 32 characters x 50 or 1600 bytes/sec. Less than a 500th of the 100 Mb/s network bandwidth (being generous). So, do you know what minimum speed you can actually get for asynchronous transmissions? The broadband data rates quoted by the service providers are usually maximums in the best possible conditions, not the average and certinly not guaranteed. They may not allow for transmission delays. Reality may be only a small fraction of the specs advertised! A recent BB survey in the UK suggested a far lower preformance, nearer to that of the 56 K modems. Regards, Chris Chapman
In a message dated 05/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>Hi,
actually, I don't think I'm near any limits.  The A/D= I use=20 can handle 20K samples/sec. 
Hi Ian,
 
    What ADC are you using? 20 K SPS is 50 micro se= c /=20 sample. My ADC takes 20 muS/S.
    How does it's accuracy depend on it's sample=20 rate?
    Does it have an onboard processor chip to take=20= and=20 average multiple samples?
    What data rate does the ADC board to computer l= ink=20 support?
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I only=20 have 2 instruments (though I sample each on 3 A/D channels to get the=20 resolution up to 22 bits), so that's only 6 x 50, or 300 samples/sec. = ;=20
    You need to average four samples to get 1=20 additional bit of accuracy, 16 samples to get two bits extra, etc.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>So I=20 could connect up all of the A/D's 16 input channels and still not stress=20 it.
    This is likely to be ~40 bytes total with the=20 overheads at 50 SPS, say 16 K bits/ sec. If you are using a 24 bit ADC, it i= s=20 likely double this. Then it largely depends on whether you are sending=20 datapackets, or individual bytes.
    If you are sending asynchronous bytes, you have= to=20 wait for the signal to be transmitted, the receiving server to respond and t= he=20 ACK to be received. Transmission delays can be significant. 
    I am 12 km from the phone terminal, so the dela= y=20 would be well over 80 micro sec per byte. Coupled to a a 56 K modem, I certa= inly=20 could not transmit this much data.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>The data=20 server does burn up 80% of the PC's CPU but it's only an old 800 MHz machi= ne=20 and wouldn't cost much to replace with one twice the speed.  Data acr= oss=20 the network connection is only 32 characters x 50 or 1600 bytes/sec. = =20 Less than a 500th of the 100 Mb/s network bandwidth
(being=20 generous).
    So, do you know what minimum speed you=20 can actually get for asynchronous transmissions? The broadband data rat= es=20 quoted by the service providers are usually maximums in the best possible=20 conditions, not the average and certinly not guaranteed. They may not a= llow=20 for transmission delays. Reality may be only a small fraction of the specs=20 advertised! A recent BB survey in the UK suggested a far lower preformance,=20 nearer to that of the 56 K modems.
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sat, 05 Jan 2008 22:08:22 +0000 Hi, I was waiting nervously for your reply and an array of astute questions; here they are! :-) I'll try to answer as best as possible. My A/D is a National Instruments AT-MIO-16XE-50 which plugs directly into the motherboard, so no communication issues. The data sheet is at http://www.ni.com/pdf/products/us/2mhw254-255e.pdf and the manual is at http://www.ni.com/pdf/manuals/370507a.pdf From the manual, sampling rate is only a consideration when switching gain between channels (which I am, see later), otherwise full tilt is fine. The board does have a micro with which it can perform various tricks. Higher bit systems give both higher resolution and higher dynamic range. I think the main concern for seismometry, amongst cash limited amateurs, is the dynamic range to try to avoid saturation when a strong signal comes in. So, with my 16 bit A/D, I feed the signal into 3 separate channels and sample each of them at 3 different gains, +/-0.1V, +/-1.0V and +/-10V. The software then chooses the reading with the greatest gain which hasn't saturated. So that gives it an "effective" bit rating of 20V/3.05e-6V or just over 22 bits for dynamic range but still 16 bits for resolution. As said above, changing gain between channels does have settling issues. To eliminate this effect, I should increase the intra-channel sampling time. However, this would increase the skew between the 3 samples, which would introduce another source of noise. I should really measure/calculate these competing effects and find the optimum point. For this application, though, I am content. I used to use a 12 bit system, so my present system is much better even with these features. I'm squirting the data across my own intranet to the graphing computer, so am getting most of the available 100 Mb/s bandwidth with minimal latency. For those using the internet, there shouldn't be a problem provided the data are timestamped at source. It then doesn't matter how long the data takes to arrive or whether the times between samples varies, the data can be properly reassembled using the individual timestamps. Things though are more limited with 56K modems. I'd be interested to hear how there is a 12 Km "gap" in your system. Cheers Ian http://www.iasmith.com/ http://www.festivalpreviews.com/ ChrisAtUpw@....... wrote: > In a message dated 05/01/2008, ian@........... writes: > > Hi, > actually, I don't think I'm near any limits. The A/D I use can > handle 20K samples/sec. > > Hi Ian, > > What ADC are you using? 20 K SPS is 50 micro sec / sample. My ADC > takes 20 muS/S. > How does it's accuracy depend on it's sample rate? > Does it have an onboard processor chip to take and average > multiple samples? > What data rate does the ADC board to computer link support? > > I only have 2 instruments (though I sample each on 3 A/D channels > to get the resolution up to 22 bits), so that's only 6 x 50, or > 300 samples/sec. > > You need to average four samples to get 1 additional bit of > accuracy, 16 samples to get two bits extra, etc. > > So I could connect up all of the A/D's 16 input channels and still > not stress it. > > This is likely to be ~40 bytes total with the overheads at 50 SPS, > say 16 K bits/ sec. If you are using a 24 bit ADC, it is likely double > this. Then it largely depends on whether you are sending datapackets, > or individual bytes. > If you are sending asynchronous bytes, you have to wait for the > signal to be transmitted, the receiving server to respond and the ACK > to be received. Transmission delays can be significant. > I am 12 km from the phone terminal, so the delay would be well > over 80 micro sec per byte. Coupled to a a 56 K modem, I certainly > could not transmit this much data. > > The data server does burn up 80% of the PC's CPU but it's only an > old 800 MHz machine and wouldn't cost much to replace with one > twice the speed. Data across the network connection is only 32 > characters x 50 or 1600 bytes/sec. Less than a 500th of the 100 > Mb/s network bandwidth > (being generous). > > So, do you know what minimum speed you can actually get for > asynchronous transmissions? The broadband data rates quoted by the > service providers are usually maximums in the best possible > conditions, not the average and certinly not guaranteed. They may not > allow for transmission delays. Reality may be only a small fraction of > the specs advertised! A recent BB survey in the UK suggested a far > lower preformance, nearer to that of the 56 K modems. > > Regards, > > Chris Chapman -- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Wrong clock From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sun, 06 Jan 2008 01:04:33 +0000 Hi all I did noticet that station that has the id jcc1 has a wrong clock in place. But according to the event file list, this is the date that it is using. 12/05/08 11:01 UTC 12/05/08 03:01 Local Time This is a massive time error. I hope that the owner can fix this before the next big quake near west coast of Canada. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sun, 06 Jan 2008 01:15:31 +0000 Hi all I do belive that West coast of Canada is at risk of getting a new big earthquake, possible around mag 6.5, but there is at least 12% chance of mag 7.0 or bigger earthquake in the area close to the two mag 6.5 earthquakes that did happen yesterday. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Sat, 5 Jan 2008 21:20:06 EST In a message dated 05/01/2008, ian@........... writes: I'm squirting the data across my own intranet to the graphing computer, so am getting most of the available 100 Mb/s bandwidth with minimal latency. Hi Ian, Communication links usually have fixed baud rates. What are you using? For those using the internet, there shouldn't be a problem provided the data are timestamped at source. It then doesn't matter how long the data takes to arrive or whether the times between samples varies, the data can be properly reassembled using the individual rimestamps. ? If you are sending asynchronous data, you send a byte maybe ~11 cycles long overall, which has start and stop bits. You usually send the signal, the receiver processes it and sends an ACK signal back. Then you send the next byte. If you try simply sending at a fixed baud rate, you inevitably get dropouts. You have to complete the process with the time stamp data to be able to reassemble it. Your bus also has a fixed interrupt repeat rate, when the CPU checks what tasks are currently waiting. Only a few interrupts in a multitasking system redirect the CPU instantly. Things though are more limited with 56K modems. I'd be interested to hear how there is a 12 Km "gap" in your system. Dead simple. This is the distance between my modem and the digital receiver in the phone exchange. 56 K modems rarely work at this rate. I limit mine to 38 K, sometimes less. This avoids my computer having to request a lot of data repeats, which can waste a lot of time. I note that the ADC board uses the computer supply lines. These can be quite noisy. What noise do you generally see with the input line to earth? How many times has your system had to use a restricted amplification range channel? These are only common if you get local quakes. I have yet to receive an out of range quake signal with my 16 bit +/-1/2 lsb system. Regards, Chris Chapman
In a message dated 05/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I'm=20 squirting the data across my own intranet to the graphing computer, so am=20 getting most of the available 100 Mb/s bandwidth with minimal=20 latency.
Hi Ian,
 
    Communication links usually have fixed baud rat= es.=20 What are you using?
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>For=20 those using the internet, there shouldn't be a problem provided the data a= re=20 timestamped at source.  It then doesn't matter how long the data take= s to=20 arrive or whether the times between samples varies, the data can be proper= ly=20 reassembled using the individual rimestamps.
    ? If you are sending asynchronous data, you sen= d a=20 byte maybe ~11 cycles long overall, which has start and stop bits. You usual= ly=20 send the signal, the receiver processes it and sends an ACK signal back. The= n=20 you send the next byte. If you try simply sending at a fixed baud=20 rate, you inevitably get dropouts. You have to complete the process wit= h=20 the time stamp data to be able to reassemble it. Your bus also has a fixed=20 interrupt repeat rate, when the CPU checks what tasks are currently=20 waiting. Only a few interrupts in a multitasking system redirect the CP= U=20 instantly.
 
    Things though are more limited with 56K=20 modems.  I'd be interested to hear how there is a 12 Km "gap" in your=20 system.
 
    Dead simple. This is the distance between my mo= dem=20 and the digital receiver in the phone exchange.
 
    56 K modems rarely work at this rate. I lim= it=20 mine to 38 K, sometimes less. This avoids my computer having to request a lo= t of=20 data repeats, which can waste a lot of time.
 
    I note that the ADC board uses the computer sup= ply=20 lines. These can be quite noisy. What noise do you generally see with the in= put=20 line to earth?
 
    How many times has your system had to use a=20 restricted amplification range channel? These are only common if you ge= t=20 local quakes. I have yet to receive an out of range quake signal with my 16=20= bit=20 +/-1/2 lsb system.
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Sun, 06 Jan 2008 13:03:04 +0000 Hi, I've just had a refresher look at the software. The A/D board has it's own crystal controlled timing to trigger the sampling and to control the time between channel samples. There is also a 4000 sample FIFO buffer to store the readings, so the timing of the samples is absolutely rock solid and unaffected by activities on the pc. Where I deserve a wrist smack is the timestamps. These are applied as each sample group (the 3 samples for each of the 2 instruments) are read from the FIFO buffer and therefore are affected by activities on the pc. I'll add this to my todo list to use the A/D's internal timing for timestamps. For communication it's just standard 100 mbit tcp/ip. Totally transparent to the user and given that the data is all timestamped (sort of!) not something to worry about. I'll need to measure the noise to answer the noise question. Looking back I can see that there are a few traces (not many) which flipped between channel gains +/-0.1V and +/-1.0V. So the feature is giving me more gain to look into the weaker signals without being clobbered with saturation on the stronger traces - both the high and low pass filters apply a 20db gain to compensate for the attenuation of the filters. I asked about your 12 Km gap as I was wondering if there was a way to plug it with equipment running at broadband rates. I'm in one of the BT(our telco) "black spots", condemned to never have broadband and I eventually had to put together our own community wireless broadband (http://www.gmccbroadband.org/ ). This partly involves filling "gaps" across the countryside. Our biggest gap is only 5 Km so the stuff we use might not help. We use Tranzeo 5Ghz point-to-point access points, these require line of sight between the two locations. They might cover 12 Km but I'm not sure. Equipment is about Ł450 and you'll need to pay someone to install it on the roof. The other method is to rent a "private circuit" or EPS line from BT - a private wire between two premises sharing the same exchange - over which you can connect a pair of sdsl modems. These may not work over the distance, again I'm not sure. Costs about Ł45/month. Maybe that's what you are already doing. Cheers Ian http://www.iasmith.com http://www.festivalpreviews.com ChrisAtUpw@....... wrote: > In a message dated 05/01/2008, ian@........... writes: > > I'm squirting the data across my own intranet to the graphing > computer, so am getting most of the available 100 Mb/s bandwidth > with minimal latency. > > Hi Ian, > > Communication links usually have fixed baud rates. What are you using? > > For those using the internet, there shouldn't be a problem > provided the data are timestamped at source. It then doesn't > matter how long the data takes to arrive or whether the times > between samples varies, the data can be properly reassembled using > the individual rimestamps. > > ? If you are sending asynchronous data, you send a byte maybe ~11 > cycles long overall, which has start and stop bits. You usually send > the signal, the receiver processes it and sends an ACK signal back. > Then you send the next byte. If you try simply sending at a fixed baud > rate, you inevitably get dropouts. You have to complete the process > with the time stamp data to be able to reassemble it. Your bus also > has a fixed interrupt repeat rate, when the CPU checks what tasks are > currently waiting. Only a few interrupts in a multitasking system > redirect the CPU instantly. > > Things though are more limited with 56K modems. I'd be interested > to hear how there is a 12 Km "gap" in your system. > > Dead simple. This is the distance between my modem and the digital > receiver in the phone exchange. > > 56 K modems rarely work at this rate. I limit mine to 38 K, > sometimes less. This avoids my computer having to request a lot of > data repeats, which can waste a lot of time. > > I note that the ADC board uses the computer supply lines. These > can be quite noisy. What noise do you generally see with the input > line to earth? > > How many times has your system had to use a restricted > amplification range channel? These are only common if you get local > quakes. I have yet to receive an out of range quake signal with my 16 > bit +/-1/2 lsb system. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: "Geoff" gmvoeth@........... Date: Sun, 6 Jan 2008 16:34:47 -0700 Isnt that area a subduction zone ? You get the biggest EQs at subduction Zones. You might get one like thay had off sumatra one day. ----- Original Message ----- From: "Jón Frímann" To: Sent: Saturday, January 05, 2008 6:15 PM Subject: Re: Large earthquake near cost of Canada Hi all I do belive that West coast of Canada is at risk of getting a new big earthquake, possible around mag 6.5, but there is at least 12% chance of mag 7.0 or bigger earthquake in the area close to the two mag 6.5 earthquakes that did happen yesterday. Regards. -- Jón Frímann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: Bob Hancock carpediem1@......... Date: Sun, 06 Jan 2008 16:54:21 -0700 Geoff - The Queen Charlotte fault is a transform fault; however, there are sections both north and south that have different names and are either transform or subduction. The mechanics of these two major recent events indicate a strike slip movement. Bob Hancock On 1/6/08 4:34 PM, "Geoff" wrote: > Isnt that area a subduction zone ? > You get the biggest EQs at subduction Zones. >=20 > You might get one like thay had off sumatra one day. >=20 > ----- Original Message ----- > From: "J=F3n Fr=EDmann" > To: > Sent: Saturday, January 05, 2008 6:15 PM > Subject: Re: Large earthquake near cost of Canada >=20 >=20 > Hi all >=20 > I do belive that West coast of Canada is at risk of getting a new big > earthquake, possible around mag 6.5, but there is at least 12% chance of > mag 7.0 or bigger earthquake in the area close to the two mag 6.5 > earthquakes that did happen yesterday. >=20 > Regards. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Sun, 6 Jan 2008 19:15:48 EST In a message dated 06/01/2008, ian@........... writes: Looking back I can see that there are a few traces (not many) which=20 flipped between channel gains +/-0.1V and +/-1.0V. So the feature is=20 giving me more gain to look into the weaker signals without being=20 clobbered with saturation on the stronger traces - both the high and low=20 pass filters apply a 20db gain to compensate for the attenuation of the =20 filters. Hi Ian, =20 I would expect that all your out of range signals will be due to the=20 surface waves?=20 I asked about your 12 Km gap as I was wondering if there was a way to=20 plug it with equipment running at broadband rates. I'm in one of the=20 BT(our telco) "black spots", condemned to never have broadband and I =20 eventually had to put together our own community wireless broadband =20 (http://www.gmccbroadband.org/ ). This partly involves filling "gaps"=20 across the countryside. Our biggest gap is only 5 Km so the stuff we=20 use might not help.=20 The delay that I quoted was due to the speed of light over the distance= ,=20 but the phase velocity in the wires will be lower. I have not measured it.=20 I only require four or five channels, not eight. =20 One standard fix is to send the data as packets, so greatly reducing th= e=20 number of delays..=20 We use Tranzeo 5Ghz point-to-point access points, these require line of=20 sight between the two locations. They might cover 12 Km but I'm not sure.=20= =20 Equipment is about =A3450 and you'll need to pay someone to install it on th= e roof. This is quite expensive. Even if I did install an aerial on my roof,=20 there is still a hill in the way. Nor does it solve the problem of the two= way=20 signal delays. =20 // At the RF level, the system also reduces latency and improves=20 throughput by allowing the user to adjust the RF ACK time, changing the amo= unt of=20 time the system will wait for an RF ACK to be returned. Radio waves take a=20 finite amount of time to reach a destination, namely the speed of light. Ev= ery=20 packet sent via an RF link needs to be acknowledged, in order to ensure that the packet was=20 received intact. // The other method is to rent a "private circuit" or EPS line from BT - a=20 private wire between two premises sharing the same exchange - over which y= ou can=20 connect a pair of sdsl modems. These may not work over the distance, agai= n=20 I'm not sure. Costs about =A345/month. Maybe that's=20 what you are already doing. I have not tried to explore this recently. When I last enquired, BT were no= t=20 prepared to lay an additional 12 km of phone line. And they didn't have a=20 spare line on their local cable. There is a relationship between the distan= ce=20 to the phone exchange and the maximum speed. There was also a maximum=20 distance. From memory this was about 5 km when I enquired. =20 Regards, =20 Chris Chapman =20
In a message dated 06/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Looking=20 back I can see that there are a few traces (not many) which
flipped=20 between channel gains +/-0.1V and +/-1.0V.  So the feature is
giv= ing=20 me more gain to look into the weaker signals without being
clobbered w= ith=20 saturation on the stronger traces - both the high and low
pass filters= =20 apply a 20db gain to compensate for the attenuation of the=20
filters.
Hi Ian,
 
    I would expect that all your out of range signa= ls=20 will be due to the surface waves? 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I asked=20 about your 12 Km gap as I was wondering if there was a way to
plug it=20= with=20 equipment running at broadband rates.  I'm in one of the
BT(our=20 telco)  "black spots", condemned to never have broadband and I=20
eventually had to put together our own community wireless broadband=20
(http://www.gmccbroadband.org/ ).  This partly involves filling=20 "gaps"
across the countryside.  Our biggest gap is only 5 Km so t= he=20 stuff we
use might not help.
    The delay that I quoted was due to the spe= ed=20 of light over the distance, but the phase velocity in the wires will be lowe= r. I=20 have not measured it.
    I only require four or five channels, not=20 eight.
 
    One standard fix is to send the data=20 as packets, so greatly reducing the number of delays..
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>We use=20 Tranzeo 5Ghz point-to-point access points, these require line of sight bet= ween=20 the two locations.  They might cover 12 Km but I'm not sure. =20 Equipment is about =A3450 and you'll need to pay someone to install it on=20= the=20 roof.
    This is quite expensive. Even if I did install=20= an=20 aerial on my roof, there is still a hill in the way. Nor does it  solve= the=20 problem of the two way signal delays.
 
//    At the RF level, the system also reduces late= ncy=20 and improves throughput by allowing the user to adjust the RF ACK time, chan= ging=20 the amount of time the system will wait for an RF ACK to be returned. Radio=20 waves take a finite amount of time to reach a destination, namely the speed=20= of=20 light. Every packet sent via an
RF link needs to be acknowledged, in orde= r to=20 ensure that the packet was received intact.
//
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>The=20 other method is to rent a "private circuit" or EPS line from BT - a privat= e=20 wire between two premises sharing the same exchange -  over which you= can=20 connect a pair of sdsl modems.  These may not work over the distance,= =20 again I'm not sure.  Costs about =A345/month.  Maybe that's
= what=20 you are already doing.
    I have not tried to explore this recently. When= I=20 last enquired, BT were not prepared to lay an additional 12 km of phone line= ..=20 And they didn't have a spare line on their local cable. There is a relations= hip=20 between the distance to the phone exchange and the maximum speed. There= was=20 also a maximum distance. From memory this was about 5 km when I=20 enquired.
 
    Regards,
 
    Chris Chapman
Subject: Re: Large earthquake near cost of Canada From: John Lahr johnjan@........ Date: Sun, 06 Jan 2008 16:58:21 -0800 The two M6.5 earthquakes of 1/5/2008 on the Queen=20 Charlotte Islands Fault were well recorded by=20 AS-1 stations all across the US. I've posted=20 some information from Robert Butler, along with two seismograms. http://jclahr.com/science/psn/as1/queen08/index.html They were both predominately strike-slip events. Cheers, John At 03:54 PM 1/6/2008, you wrote: >Geoff - > >The Queen Charlotte fault is a transform fault; however, there are sections >both north and south that have different names and are either transform or >subduction. The mechanics of these two major recent events indicate a >strike slip movement. > >Bob Hancock > > >On 1/6/08 4:34 PM, "Geoff" wrote: > > > Isnt that area a subduction zone ? > > You get the biggest EQs at subduction Zones. > > > > You might get one like thay had off sumatra one day. > > > > ----- Original Message ----- > > From: "J=F3n Fr=EDmann" > > To: > > Sent: Saturday, January 05, 2008 6:15 PM > > Subject: Re: Large earthquake near cost of Canada > > > > > > Hi all > > > > I do belive that West coast of Canada is at risk of getting a new big > > earthquake, possible around mag 6.5, but there is at least 12% chance of > > mag 7.0 or bigger earthquake in the area close to the two mag 6.5 > > earthquakes that did happen yesterday. > > > > Regards. > > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with >the body of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: "Thomas Dick" dickthomas01@............. Date: Sun, 6 Jan 2008 19:17:43 -0600 Wouldn't P be expected to be larger for this magnitude of a quake and the nearness to the epicenter? ----- Original Message ----- From: "John Lahr" To: Sent: Sunday, January 06, 2008 6:58 PM Subject: Re: Large earthquake near cost of Canada The two M6.5 earthquakes of 1/5/2008 on the Queen Charlotte Islands Fault were well recorded by AS-1 stations all across the US. I've posted some information from Robert Butler, along with two seismograms. http://jclahr.com/science/psn/as1/queen08/index.html __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: John Lahr johnjan@........ Date: Sun, 06 Jan 2008 18:20:01 -0800 Not really. At my station the P-wave amplitude was about 1.5 micrometers zero to peak. Based on this, I computed an mb of 7.0, using AmaSeis' built-in magnitude calculations: I added an image showing the calculation window to this page: http://jclahr.com/science/psn/as1/queen08/index.html (You may have to refresh your browser to see the new image at the bottom.) Given all of the factors that can influence the magnitude calculation, such as the approximate station calibration that we use for the AS-1 and the event radiation pattern (the USGS mb is computed from an average of for stations at many azimuths and distances), coming within 0.5 units is not too bad. The computed USGS mb was 6.2, so my amplitude was, if anything, a bit too large. The USGS preferred magnitude of 6.5 is an Mw. John At 05:17 PM 1/6/2008, Thomas Dick wrote: >Wouldn't P be expected to be larger for this magnitude of a quake >and the nearness to the epicenter? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: "Thomas Dick" dickthomas01@............. Date: Sun, 6 Jan 2008 21:45:31 -0600 > Not really. At my station the P-wave amplitude was about 1.5 micrometers > zero to peak. Based on this, I computed an mb of 7.0, using AmaSeis' > built-in magnitude calculations: > > I added an image showing the calculation window to this page: > http://jclahr.com/science/psn/as1/queen08/index.html > (You may have to refresh your browser to see the new image at the bottom.) > Thanks for taking the time for me. I didn't know. Because of the shallowness of the focus and the closeness of your recording site, I "expected" P and S to have a more similar amplitude.....I am not taking about my recordings....it did surprise me that the Lehmans at my location seemed to be noisey in the P to PcS arrival time frame. And since I am taking up your time, another question, does the AS-1 show any directional sensitivity....maybe as the result of improper setup? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: John Lahr johnjan@........ Date: Sun, 06 Jan 2008 21:10:49 -0800 This image: http://jclahr.com/science/psn/as1/as1_dim.jpg shows the construction of the AS-1. As long as the center of mass of the boom is at the same vertical elevation as the boom knife edge there will be no horizontal cross-axis sensitivity. The boom is prevented from rocking back and forth by the width of the knife edge. Also, rocking motion would not generate nearly as large a voltage, as it would not have the optimum orientation of 90 degrees for the cross product of the velocity vector with magnetic field vector. A knife edge is NOT the best type of hinge. You can find a lot of discussion of better hinge designs in the PSN E-mail archives. John At 07:45 PM 1/6/2008, Thomas Dick wrote: ..... does the AS-1 show any directional sensitivity....maybe as the result of improper setup? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: ChrisAtUpw@....... Date: Mon, 7 Jan 2008 17:30:44 EST In a message dated 07/01/2008, johnjan@........ writes: This image: _http://jclahr.com/science/psn/as1/as1_dim.jpg_ (http://jclahr.com/science/psn/as1/as1_dim.jpg) shows the construction of the AS-1. As long as the center of mass of the boom is at the same vertical elevation as the boom knife edge there will be no horizontal cross-axis sensitivity. Hi Dick, One setup instruction seems to be missing from the current AS1 manual. When you have added load washers to the vertical bolt to level the arm for your particular spring / mass combination, you should then dismount the arm and hang it ~vertically (without the spring) by a strip of adhesive tape from the knife edge / hinge line. You then compare this to a vertical thread on a nut / a plumb line. You adjust the arm to hang vertically by moving the position of the mass balance washers held between the two clamp nuts. This offsets the mass of the red Alnico U magnet on the lower side of the arm. If you don't do this, the C of G will not be level with the hinge and you can get an appreciable sensitivity to horizontal Love waves. As far as I am aware, there is NO comparable method for setting up an EQ1 properly. Regards, Chris Chapman
In a message dated 07/01/2008, johnjan@........ writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>This=20 image:  http://jclahr.com/s= cience/psn/as1/as1_dim.jpg=20 shows the construction of the AS-1.  As long as the center of mass of= the=20 boom is at the same vertical elevation as the boom knife edge
there wi= ll=20 be no horizontal cross-axis sensitivity.
Hi Dick,
 
    One setup instruction seems to be missing=20= from=20 the current AS1 manual.
    
    When you have added load washers to the vertica= l=20 bolt to level the arm for your particular spring / mass combination, you sho= uld=20 then dismount the arm and hang it ~vertically (without the spring) by a= =20 strip of adhesive tape from the knife edge / hinge line. You then compare th= is=20 to a vertical thread on a nut / a plumb line. You adjust the arm to han= g=20 vertically by moving the position of the mass balance=20 washers held between the two clamp nuts. This offsets the mass of=20= the=20 red Alnico U magnet on the lower side of the arm. 
 
    If you don't do this, the C of G will not be le= vel=20 with the hinge and you can get an appreciable sensitivity to horizontal Love= =20 waves.
 
    As far as I am aware, there is NO comparable me= thod=20 for setting up an EQ1 properly.
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Mon, 7 Jan 2008 19:15:07 EST In a message dated 06/01/2008, ian@........... writes: I asked about your 12 Km gap as I was wondering if there was a way to plug it with equipment running at broadband rates. I'm in one of the BT "black spots", condemned to never have broadband and I eventually had to put together our own community wireless broadband (http://www.gmccbroadband.org/ ). This partly involves filling "gaps" across the countryside. Our biggest gap is only 5 Km so the stuff we use might not help. Hi Ian, I rang BT today about Broadband. They offer 5 Meg at about 1 mile, 2 Meg at 3 miles and only 256 K much over that. The maximum length of a phone line is 14 miles. However, the UK is supposed to be fully rewired by 2010. ADSL are offering 5x the normal dial up rate, with signal compression and packeting, but I would like to see it in operation in a rural situation first. My experience is that I can only get about 38 K reliably at 12 km. I suspect that the current coverage outside towns with a phone exchange is very patchy. Your blog on the above website doesn't seem to work. Regards, Chris Chapman
In a message dated 06/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I asked=20 about your 12 Km gap as I was wondering if there was a way to plug it with= =20 equipment running at broadband rates.  I'm in one of the BT "black=20 spots", condemned to never have broadband and I eventually had to put toge= ther=20 our own community wireless broadband
(http://www.gmccbroadband.org/=20 ).  This partly involves filling "gaps" across the countryside. = Our=20 biggest gap is only 5 Km so the stuff we use might not help.=20
Hi Ian,
 
    I rang BT today about Broadband. They offer 5 M= eg=20 at about 1 mile, 2 Meg at 3 miles and only 256 K much over that. The maximum= =20 length of a phone line is 14 miles. However, the UK is supposed to be fully=20 rewired by 2010. ADSL are offering 5x the normal dial up rate, with signal=20 compression and packeting, but I would like to see it in operation in a rura= l=20 situation first.
 
    My experience is that I can only get about 38 K= =20 reliably at 12 km. I suspect that the current coverage outside towns with a=20 phone exchange is very patchy.
 
    Your blog on the above website doesn't seem to=20 work.
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: "Thomas Dick" dickthomas01@............. Date: Mon, 7 Jan 2008 18:51:38 -0600 Would something like the amateur communication system using computers here in the U.S. be fast enough for you? And is it available to you? This is quite a bit of automation associated with that setup now (within the software).. I rang BT today about Broadband. They offer 5 Meg at about 1 mile, 2 Meg at 3 miles and only 256 K much over that. The maximum length of a phone line is 14 miles. However, the UK is supposed to be fully rewired by 2010. ADSL are offering 5x the normal dial up rate, with signal compression and packeting, but I would like to see it in operation in a rural situation first. My experience is that I can only get about 38 K reliably at 12 km. I suspect that the current coverage outside towns with a phone exchange is very patchy. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: "Thomas Dick" dickthomas01@............. Date: Mon, 7 Jan 2008 19:28:31 -0600 One setup instruction seems to be missing from the current AS1 manual. When you have added load washers to the vertical bolt to level the arm for your particular spring / mass combination, you should then dismount the arm and hang it ~vertically (without the spring) by a strip of adhesive tape from the knife edge / hinge line. You then compare this to a vertical thread on a nut / a plumb line. You adjust the arm to hang vertically by moving the position of the mass balance washers held between the two clamp nuts. This offsets the mass of the red Alnico U magnet on the lower side of the arm. If you don't do this, the C of G will not be level with the hinge and you can get an appreciable sensitivity to horizontal Love waves. As far as I am aware, there is NO comparable method for setting up an EQ1 properly. Hi Chris, hope you are doing OK with the New Year. The above seems hard... at least, to understand why. I didn't have to add any washers.I have been disappointed with my AS-1. It was the first instrument I had commerically built. The Lehmans are doing fine; sometimes a little noisier than I'd like. The performance of the AS-1 seems to vary---- I got better results from my 4.5 Hz geophone than on the AS-1 from yesterday's 1.4 mg on the New Madrid fault and yet the AS-1 did OK on the Greek quake. During the 2nd Queen Charlotte quake, the AS-1 showed little P while more LQ & LR than I expected. That is what precipitated my queries to John. I expected P to be higher in amplitude in Oregon -- even on the 1.4 mg on the New Madrid, the P was larger than the S . His comment about using something other than a razor blade edge didn't fall on deft ears...been wondering about that. Got a new billfold for Xmas...now have to find some money to put into it...JoAnn has reduced my allowance! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Large earthquake near cost of Canada From: John Lahr johnjan@........ Date: Mon, 07 Jan 2008 18:54:41 -0800 Hi Thomas, How does your AS-1 record compare with those posted here: http://www.iris.edu/amaseis/schools/ What is the closest station to you that has a record showing? When the AS-1 isn't working well the problem is often due to slight contact between the magnet and the coil, or between the damping washer and the oil container. Be sure to check these areas. The system will appear to work, as it will respond to your presence around the sensor, but it's will not record earthquakes well if there is any friction at these points. John At 05:28 PM 1/7/2008, you wrote: > One setup instruction seems to be missing from the current AS1 manual. > > When you have added load washers to the vertical bolt to level > the arm for your particular spring / mass combination, you should > then dismount the arm and hang it ~vertically (without the spring) > by a strip of adhesive tape from the knife edge / hinge line. You > then compare this to a vertical thread on a nut / a plumb line. You > adjust the arm to hang vertically by moving the position of the > mass balance washers held between the two clamp nuts. This offsets > the mass of the red Alnico U magnet on the lower side of the arm. > > If you don't do this, the C of G will not be level with the > hinge and you can get an appreciable sensitivity to horizontal Love waves. > > As far as I am aware, there is NO comparable method for setting > up an EQ1 properly. > > Hi Chris, hope you are doing OK with the New Year. The above seems > hard... at least, to understand why. I didn't have to add any > washers.I have been disappointed with my AS-1. It was the first > instrument I had commerically built. The Lehmans are doing fine; > sometimes a little noisier than I'd like. The performance of the > AS-1 seems to vary---- I got better results from my 4.5 Hz geophone > than on the AS-1 from yesterday's 1.4 mg on the New Madrid fault > and yet the AS-1 did OK on the Greek quake. During the 2nd Queen > Charlotte quake, the AS-1 showed little P while more LQ & LR than I > expected. That is what precipitated my queries to John. I expected > P to be higher in amplitude in Oregon -- even on the 1.4 mg on the > New Madrid, the P was larger than the S . His comment about using > something other than a razor blade edge didn't fall on deft > ears...been wondering about that. Got a new billfold for Xmas...now > have to find some money to put into it...JoAnn has reduced my > allowance! __________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with the body >of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Mon, 7 Jan 2008 22:47:10 EST In a message dated 08/01/2008, dickthomas01@............. writes: Would something like the amateur communication system using computers here in the U.S. be fast enough for you? And is it available to you? This is quite a bit of automation associated with that setup now (within the software).. Hi Tom, Thanks for the thought. The basic problem is that my phone is about 12 km from the BT phone station. Even at the speed of light, the signal delay would be about 40 micro seconds each way, so a transmit + ACK would be >80 micro seconds assuming that the rest of the system were infinitely fast. This delay severely limits the communication speeds when you are sending single bytes. That way around it is to use a system which sends a large information packet. However, I can just about cope at the moment. Regards, Chris Chapman
In a message dated 08/01/2008, dickthomas01@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Would=20 something like the amateur communication system using computers here in th= e=20 U.S. be fast enough for you? And is it available to you? This is quite a b= it=20 of automation associated with that setup now (within the=20 software)..
Hi Tom,
 
    Thanks for the thought. The basic problem is th= at=20 my phone is about 12 km from the BT phone station. Even at the speed of ligh= t,=20 the signal delay would be about 40 micro seconds each way, so a transmit + A= CK=20 would be >80 micro seconds assuming that the rest of the system were= =20 infinitely fast. This delay severely limits the communication speeds when yo= u=20 are sending single bytes.
    That way around it is to use a system which sen= ds a=20 large information packet. However, I can just about cope at the moment.= =20
 
    Regards,
 
    Chris Chapman
Subject: Re: Hekla volcano geophone planned From: "Thomas Dick" dickthomas01@............. Date: Mon, 7 Jan 2008 22:46:49 -0600 Thanks for the thought. The basic problem is that my phone is about 12 km from the BT phone station. Even at the speed of light, the signal delay would be about 40 micro seconds each way, so a transmit + ACK would be >80 micro seconds assuming that the rest of the system were infinitely fast. This delay severely limits the communication speeds when you are sending single bytes. That way around it is to use a system which sends a large information packet. However, I can just about cope at the moment. Hey, when we get to heaven we will have all the speed and bandwideth we want ...... I wonder if there will be any earthquakes?? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Thu, 10 Jan 2008 19:38:04 +0000 Hi, [earthquakish] I'm still not sure why you need deterministic communications. Isn't the data time stamped at source? If so, you don't need a deterministic link. I assume I've missed something. [non-earthquakish] I look forward to 2010 when I can give up my volunteer broadband service. I suspect, though, that those without service in the countryside now, won't get the new system either... The blog is only available to our subscribers as it is located on our intranet. We should make this clear on the web page. Yesterday's entry was about the 7 hour power cut caused by the storm that screamed across Scotland... Cheers Ian ChrisAtUpw@....... wrote: > In a message dated 06/01/2008, ian@........... writes: > > I asked about your 12 Km gap as I was wondering if there was a way > to plug it with equipment running at broadband rates. I'm in one > of the BT "black spots", condemned to never have broadband and I > eventually had to put together our own community wireless broadband > (http://www.gmccbroadband.org/ ). This partly involves filling > "gaps" across the countryside. Our biggest gap is only 5 Km so > the stuff we use might not help. > > Hi Ian, > > I rang BT today about Broadband. They offer 5 Meg at about 1 mile, > 2 Meg at 3 miles and only 256 K much over that. The maximum length of > a phone line is 14 miles. However, the UK is supposed to be fully > rewired by 2010. ADSL are offering 5x the normal dial up rate, with > signal compression and packeting, but I would like to see it in > operation in a rural situation first. > > My experience is that I can only get about 38 K reliably at 12 km. > I suspect that the current coverage outside towns with a phone > exchange is very patchy. > > Your blog on the above website doesn't seem to work. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Thu, 10 Jan 2008 15:32:52 EST In a message dated 10/01/2008, ian@........... writes: [earthquakish] I'm still not sure why you need deterministic communications. Isn't the data time stamped at source? If so, you don't need a deterministic link. I assume I've missed something. Hi Ian, How are you defining 'deterministic communications' in this particular instance, please? The data is sent as individual bytes in a handshake process. If you don't receive all the bytes in a sequence correctly / all of them, how are you going to reconstitute / display / use that record? Regards, Chris Chapman
In a message dated 10/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>[earthquakish]
I'm still not sure why you need deterministic=20 communications.  Isn't the
data time stamped at source?  If=20= so,=20 you don't need a deterministic
link.  I assume I've missed=20 something.
Hi Ian,
 
    How are you defining 'deterministic communicati= ons'=20 in this particular instance, please?
 
    The data is sent as individual bytes in a=20 handshake process. If you don't receive all the bytes in a sequence correctl= y /=20 all of them, how are you going to reconstitute /  display / use that=20 record? 
 
    Regards,
 
    Chris Chapman
 
Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Fri, 11 Jan 2008 12:02:01 +0000 I note that the ADC board uses the computer supply lines. These can be quite noisy. What noise do you generally see with the input line to earth? > > Chris Chapman I just did a very crude noise test: I unplugged the output of the filter (which is the input to the A/D in the PC) and shorted it. So, with a 1 metre cable attached I got mostly +/- 1 LSB and sometimes +/- 2 LSBs. I think that's pretty good, considering. Cheers Ian __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Hekla volcano geophone planned From: ChrisAtUpw@....... Date: Fri, 11 Jan 2008 09:34:58 EST In a message dated 11/01/2008, ian@........... writes: I note that the ADC board uses the computer supply lines. These can be quite noisy. What noise do you generally see with the input line to earth? I just did a very crude noise test: I unplugged the output of the filter (which is the input to the A/D in the PC) and shorted it. So, with a 1 metre cable attached I got mostly +/- 1 LSB and sometimes +/- 2 LSBs. I think that's pretty good, considering. Hi Ian, This sounds about average to me. It would be a lot better if you could take 16 samples and average them to give maybe +/-1/2 lsb. Cutting your dynamic range by x4 is better avoided. Regards, Chris Chapman
In a message dated 11/01/2008, ian@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2> =20   I note that the ADC board uses the computer supply lines. These can= be=20 quite noisy. What noise do you generally see with the input line to=20 earth?

I just did a very crude noise test: I unplugged the output o= f=20 the filter (which is the input to the A/D in the PC) and shorted it. = So,=20 with a 1 metre cable attached I got mostly +/- 1 LSB and sometimes +/- 2=20 LSBs.  I think that's pretty good,=20 considering.
Hi Ian,
 
    This sounds about average to me. It would be a=20= lot=20 better if you could take 16 samples and average them to give maybe +/-1/2 ls= b.=20 Cutting your dynamic range by x4 is better avoided.
 
    Regards,
 
    Chris Chapman
Subject: Icelandic earthquake numbers for 2007 From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 12 Jan 2008 23:10:03 +0000 Hi all I am in school from Monday to Friday, so delays might happen on me sending in new earthquakes. IMO has released new earthquake numbers for the year 2007. But in 2007 IMO did record 15102 earthquakes. For earthquake numbers from 1991 to 2007 from IMO, check this web page. http://hraun.vedur.is/ja/viku/2007/vika_52/arlegur_qu.html Does anyone have an program that counts psn files and makes a text file output? I would really like to have such program, so I can get an idea how many earthquakes I am recording pr year. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Nice local 2.1 From: Pete Rowe ptrowe@......... Date: Sun, 13 Jan 2008 10:32:34 -0800 (PST) My storm related noise has finally subsided. There is crisp 2.1 at 12:27 UTC this morning on my website. Pete ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Metal Suppliers From: ChrisAtUpw@....... Date: Sun, 13 Jan 2008 17:07:59 EST Hi Gerry, You might find some cost savings on a range of metals at _http://www.onlinemetals.com_ (http://www.onlinemetals.com) Regards, Chris Chapman
Hi Gerry,
 
    You might find some cost savings on a rang= e of=20 metals at http://www.onlinemetals.com
 
    Regards,
 
    Chris Chapman
 Subject: Re: Metal Suppliers From: "Jerry Payton" gpayton880@....... Date: Sun, 13 Jan 2008 16:16:28 -0600 Thanks Chris, but I didn't ask about metal suppliers. You must have run across an older email. Jerry ----- Original Message ----- From: ChrisAtUpw@....... To: gpayton880@....... ; psn-l@.............. Sent: Sunday, January 13, 2008 4:07 PM Subject: Re: Metal Suppliers Hi Gerry, You might find some cost savings on a range of metals at http://www.onlinemetals.com Regards, Chris Chapman
Thanks Chris, but I didn't = ask about=20 metal suppliers.  You must have run across an older = email.
Jerry
 
 
----- Original Message -----=20
From: ChrisAtUpw@.......=20
To: gpayton880@....... ; psn-l@..............
Sent: Sunday, January 13, 2008 4:07 PM
Subject: Re: Metal Suppliers

Hi Gerry,
 
    You might find some cost savings on a = range of=20 metals at http://www.onlinemetals.com
 
    Regards,
 
    Chris Chapman
 Subject: Unable To Verify This Quake ? From: "Geoff" gmvoeth@........... Date: Mon, 14 Jan 2008 02:01:27 -0700 Regional Event to GVA Pn = 11:13:45.2 2008JAN13 UTC Pg = 11:14:06.0 2008JAN13 UTC Sb = 11:15:14.8 2008JAN13 UTC Sg = 11:15:26.0 2008JAN13 UTC Estimated Origin Time 11:12:13 2008JAN13 UTC Delta about 6.0 Deg or 414 Statute Miles from GVA Magnatude estimated at around 4.0 from past experience at receiving such signals in the past. Can anyone concurr with this data because I do not see it reported anywhere and am not going to report it if no one else but ME has seen it too. I believe my arrival times to be good. Anyone Know ?? Regards; geoff GVA __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Unable To Verify This Quake ? From: AHrubetz@....... Date: Mon, 14 Jan 2008 11:56:54 EST I recorded this event which was prominent on both my vertical and short period horizontal. There was only one deflection which I presumed was the P wave?? I am away from home so cannot give you the exact time of the event now, but remember the event well because I kept checking the USGS web site to see if it was posted. Al Hrubetz Dallas, Texas **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
I recorded this event which was prominent on both my vertical a= nd=20 short period horizontal.  There was only one deflection which I=20 presumed was the P wave??  I am away from home so cannot give you the e= xact=20 time of the event now, but remember the event well because I kept=20 checking the USGS web site to see if it was posted.
Al Hrubetz
Dallas, Texas



Start the year off right. Easy wa= ys to stay in shape in the new year.
Subject: Re: Unable To Verify This Quake ? From: "Geoff" gmvoeth@........... Date: Mon, 14 Jan 2008 10:13:57 -0700 Howdy Al; You are not giving me enough information. This quake if it was real was big enough to be seen throughout this region and possibly into texas but not sure. If no one but me got it then someone may be feeding me false vibrations through the ground like a neighbor or ??? Low Rider with a fancy vibration player attached to his hydraulics ??? I would not put it past the human specie to play such games. Just a thought. Regards; geoff GVA ----- Original Message ----- From: To: Sent: Monday, January 14, 2008 9:56 AM Subject: Re: Unable To Verify This Quake ? >I recorded this event which was prominent on both my vertical and short > period horizontal. There was only one deflection which I presumed was the P > wave?? I am away from home so cannot give you the exact time of the event now, > but remember the event well because I kept checking the USGS web site to see > if it was posted. > Al Hrubetz > Dallas, Texas > > > > **************Start the year off right. Easy ways to stay in shape. > http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Metal Suppliers From: "Jack Ivey" ivey@.......... Date: Mon, 14 Jan 2008 13:47:18 -0500 More unsolicited advice: Also look at www.discountsteel.com - they have e.g. 5052 Aluminum plate 1/4" x 12" x 12" $19.04 =20 Jack =20 ________________________________ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Jerry Payton Sent: Sunday, January 13, 2008 5:16 PM To: psn-l@.............. Subject: Re: Metal Suppliers =20 Thanks Chris, but I didn't ask about metal suppliers. You must have run across an older email. Jerry =20 =20 ----- Original Message -----=20 From: ChrisAtUpw@.......... To: gpayton880@....... ; psn-l@................. Sent: Sunday, January 13, 2008 4:07 PM Subject: Re: Metal Suppliers =20 Hi Gerry, =20 You might find some cost savings on a range of metals at http://www.onlinemetals.com =20 Regards, =20 Chris Chapman

More unsolicited advice: Also look = at www.discountsteel.com – = they have e.g. 5052 Aluminum plate 1/4” x 12” x 12” = $19.04

 

Jack

 

From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Jerry Payton
Sent: Sunday, January 13, = 2008 5:16 PM
To: psn-l@..............
Subject: Re: Metal = Suppliers

 

Thanks Chris, but I didn't ask = about metal suppliers.  You must have run across an older = email.

Jerry

 

=

 

=

----- Original Message ----- =

Sent: Sunday, January 13, 2008 4:07 = PM

Subject: Re: Metal Suppliers

 

=

Hi = Gerry,

 

=

    You might find some cost savings on a range of metals at http://www.onlinemetals.com

 

=

    Regards,

 

=

    Chris = Chapman

Subject: Re: Nice local 2.1 From: "Thomas Dick" dickthomas01@............. Date: Mon, 14 Jan 2008 13:32:48 -0600 I forgot -- Pete are your inj Arkansas ----- Original Message ----- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Nice local 2.1 From: Pete Rowe ptrowe@......... Date: Mon, 14 Jan 2008 11:38:49 -0800 (PST) Hi Thomas I'm in the east foothills of San Jose, CA. The nice thing about living in this location is that I never run out of nice local earthquakes. We had another little one at 15:16Z this morning. regards, Pete --- Thomas Dick wrote: > I forgot -- Pete are your inj Arkansas > ----- Original Message ----- > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email > PSN-L-REQUEST@.............. with > the body of the message (first line only): > unsubscribe > See http://www.seismicnet.com/maillist.html for more > information. > ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Nice local 2.1 From: "Thomas Dick" dickthomas01@............. Date: Mon, 14 Jan 2008 14:00:10 -0600 OK...there was 2.1 in Conring AR as well about that time.... __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: what is the email adr From: "Thomas Dick" dickthomas01@............. Date: Tue, 15 Jan 2008 10:09:36 -0600 what is the address for putting new files on PSN network...lost computer = that did it automatically?
what is the address for putting new = files on PSN=20 network...lost computer that did it = automatically?
Subject: WinSDR From: tchannel1@............ Date: Thu, 17 Jan 2008 06:32:35 -0700 I would like some help getting started using WinSDR. I don't wish to = bother the group, but if someone would like to email back and forth, I = have a bunch of basic questions. =20 Thanks, Ted
I would like some help getting started = using=20 WinSDR.   I don't wish to bother the group, but if someone = would like=20 to email back and forth, I have a bunch of basic = questions.   =20
 
Thanks, Ted
Subject: Shadow Zone map From: "Randy" rpratt@............. Date: Fri, 18 Jan 2008 21:59:07 -0600 Hi All, I think it was Jerry that asked about determining a shadow zone acouple = weeks back. I have found the link I remembered seeing that could be of = value. Try http://gc.kls2.com/ in the middle of the page for ranges. = You can paste in 6000nm,8000nm@........... to see a zone between 6000 = and 8000nm from my approx location as an example. Randy
Hi All,
 
I think it was Jerry that asked about = determining a=20 shadow zone acouple weeks back.  I have found the link I remembered = seeing=20 that could be of value.  Try http://gc.kls2.com/  in the middle = of the=20 page for ranges.  You can paste in 6000nm,8000nm@........... to see = a zone=20 between 6000 and 8000nm from my approx location as an = example.
 
Randy

 Subject: Re: Shadow Zone map From: "Jerry Payton" gpayton880@....... Date: Fri, 18 Jan 2008 22:06:47 -0600 Yes, it was me. And, I substituted my coordinates for a display. Thank you, Randy. Regard, Jerry ----- Original Message ----- From: Randy To: psn-l@.............. Sent: Friday, January 18, 2008 9:59 PM Subject: Shadow Zone map Hi All, I think it was Jerry that asked about determining a shadow zone acouple weeks back. I have found the link I remembered seeing that could be of value. Try http://gc.kls2.com/ in the middle of the page for ranges. You can paste in 6000nm,8000nm@........... to see a zone between 6000 and 8000nm from my approx location as an example. Randy
Yes, it was me.  And, I substituted my coordinates for a=20 display.  Thank you, Randy.
Regard,
Jerry
 
 
----- Original Message -----=20
From: Randy
Sent: Friday, January 18, 2008 9:59 PM
Subject: Shadow Zone map

Hi All,
 
I think it was Jerry that asked about = determining a=20 shadow zone acouple weeks back.  I have found the link I remembered = seeing=20 that could be of value.  Try http://gc.kls2.com/  in the middle = of the=20 page for ranges.  You can paste in 6000nm,8000nm@........... to see = a zone=20 between 6000 and 8000nm from my approx location as an = example.
 
Randy

 Subject: Shadow zone From: "Randy" rpratt@............. Date: Fri, 18 Jan 2008 22:52:24 -0600 I see you can also combine options. For instance I used a quake from = Yukon in first option along with shadow none in second option to get = both plotted. Example: mhe-67.93N 136.28W uses nearest airport in = place of coordinates to me about 3 miles and the quake coordinates. = Then second box is=20 6240nm,8520nm@.............. for the shadow zone. Randy
I see you can also combine = options.  For=20 instance I used a quake from Yukon in first option along with shadow = none in=20 second option to get both plotted.  Example:  mhe-67.93N = 136.28W =20 uses nearest airport in place of coordinates to me about 3 miles and the = quake=20 coordinates.  Then second box is
6240nm,8520nm@.............. = for the=20 shadow zone.
 
Randy

 Subject: Re: Shadow Zone map From: John Lahr johnjan@........ Date: Fri, 18 Jan 2008 21:50:21 -0800 Although it would make little difference to the display at the scale of the world map, the distances in nautical miles would more accurately be: 104 degrees * 111.2 km/degree = 11,565 km converts to 6244 nm 140 degrees * 111.2 km/degree = 15,568 km converts to 8406 nm I used this site for converting from km to nm: http://www.csgnetwork.com/nsmilekmconverter.html Cheers, John At 07:59 PM 1/18/2008, you wrote: >Hi All, > >I think it was Jerry that asked about determining a shadow zone >acouple weeks back. I have found the link I remembered seeing that >could be of value. Try http://gc.kls2.com/ in >the middle of the page for ranges. You can paste in >6000nm,8000nm@........... to see a zone between 6000 and 8000nm from >my approx location as an example. > >Randy __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Shadow Zone map From: "Jerry Payton" gpayton880@....... Date: Sat, 19 Jan 2008 07:40:21 -0600 "I used this site for converting from km to nm: http://www.csgnetwork.com/nsmilekmconverter.html" This one is quite good too: http://joshmadison.com/software/convert/ Jerry
"I used this site for converting from km to nm:  http://www.csgn= etwork.com/nsmilekmconverter.html"
This one is quite good too:  http://joshmadison.com/= software/convert/
 
Jerry
Subject: optical mouse sensor From: Randall Peters PETERS_RD@.......... Date: Sat, 19 Jan 2008 09:41:05 -0500 My colleague, John Lee, and I have developed a package that may be interesting to amateur seismologists. A paper has been posted at http://physics.mercer.edu/hpage/mouse-sensor.pdf As noted in this article, John will make available free to anybody who sends him an email request for a password--the LabView executable to operate the mouse. The resolution, at about 50 microns, is too small for direct application to seismology; however the method might be useful for calibrating instruments. Also, anybody wanting to monitor the earth (stable pendulum as a plumb-bob) should be able to use this technique to watch for changes greater than 50 microradians. The typical diurnal thermoelastic variation is about one-third that value, but over the course of weeks to months I predict there will be observable changes that are not being routinely measured in nearly the 'global' sense they ought to be. To allow easier use of the sensor I removed some materal from the bottom of my mouse using sandpaper. By this means the gap-space over which the unit can operate is approximately doubled. Without doing so, one has to be more careful with alignment and stability of the pendulum. With my present capability (as wide as 3 mm) it is very easy to work with this instrument. Additionally, I have an idea that some of you may want to consider. Any truly outstanding vertical seismograph requires force-feedback. The traditional approach is one that uses force balance. The same 'strong' force that keeps the instrument from even moving substantially (much less 'goiing to the rails' because of temperature/pressure changes) is also used to provide the required near-critical damping. For more than a year I have demonstrated with my modified Sprengnether, that a 'soft' force feedback has advantages over the traditional approach. The feedback I have used with my Sprengnether derives from a long time constant integrated output from the capacitive sensor (large dynamic range area-varying, fully-differential unit). Based on my experience with this instrument, I propose the following: Since the sensor used for force feedback can have terrible sensitivity compared to the sensor used for detecting earthquakes--build a `centering' (feedback) package that uses the mouse sensor. The requirement for DAC output for the coil of the actuator can be managed (it appears) with a 'dirt cheap' homebuilt piece of electronics (an example at http://www.allaboutcircuits.com/vol_4/chpt_13/3.html ) Without a parallel port, your USB computer would need a printer cable (< $20) to operate this R/2R DAC. Randall Subject: Re: optical mouse sensor From: Brett Nordgren Brett3mr@............. Date: Sat, 19 Jan 2008 11:06:46 -0500 Dr. Peters, Could you elaborate a bit on your comment that one sensor used for force feedback can have low sensitivity compared with another one used for detecting earthquakes? It's not clear to me why that is. Thanks for your help, Brett Nordgren At 09:41 AM 1/19/2008 -0500, you wrote: >My colleague, John Lee, and I have developed a package that may be >interesting to amateur seismologists. > Additionally, I have an idea that some of you may want to >consider. > Any truly outstanding vertical seismograph requires force-feedback. >The traditional approach is one that uses force balance. >Since the sensor used for force feedback can have terrible >sensitivity compared to the sensor used for detecting earthquakes--build >a `centering' (feedback) package that uses the mouse sensor. My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Shadow Zone map From: John Lahr johnjan@........ Date: Sat, 19 Jan 2008 08:48:41 -0800 At 05:40 AM 1/19/2008, you wrote: >"I used this site for converting from km to >nm: >http://www.csgnetwork.com/nsmilekmconverter.html" >This one is quite good >too: >http://joshmadison.com/software/convert/ > >Jerry It probably makes more sense to use the definition of nautical mile to convert directly from degrees to nautical miles. http://en.wikipedia.org/wiki/Nautical_mile: A nautical mile "corresponds approximately to one minute of latitude along any meridian. " Since there are 60 minutes per degree, 104*60 = 6240 nm 140*60 = 8400 nm Cheers, John __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: optical mouse sensor From: ChrisAtUpw@....... Date: Sat, 19 Jan 2008 23:10:59 EST In a message dated 19/01/2008, PETERS_RD@.......... writes: A paper has been posted at _http://physics.mercer.edu/hpage/mouse-sensor.pdf_ (http://physics.mercer.edu/hpage/mouse-sensor.pdf) Hi Randall, The AD698 LVDT chip is not suitable for use with seismometers. Apart from being hideously expensive, it is also quite noisy. You can't get the very high resolution required. Single channel 16 bit Sigma Delta ADC chips start from about $5, not $25. The Linear ones seem to work fine. Regards, Chris
In a message dated 19/01/2008, PETERS_RD@.......... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>A paper=20 has been posted at http://physics.m= ercer.edu/hpage/mouse-sensor.pdf
Hi Randall,
 
    The AD698 LVDT chip is not suitable for use wit= h=20 seismometers. Apart from being hideously expensive, it is also quite noisy.=20= You=20 can't get the very high resolution required.
 
    Single channel 16 bit Sigma Delta ADC chips sta= rt=20 from about $5, not $25. The Linear ones seem to work fine.
 
    Regards,
 
    Chris
Subject: RE: optical mouse sensor From: "Fikke, Audun" Audun.Fikke@......... Date: Sun, 20 Jan 2008 08:08:31 +0100 I wonder if the high end models for gaming and design purposes will make = a difference.=20 They utilize a lazer and some has a resolution of 9000dpi. Just wondering Audun=20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Randall Peters Sent: l=F8rdag 19 januar 2008 15:41=20 To: psn-l@.............. Subject: optical mouse sensor My colleague, John Lee, and I have developed a package that may be = interesting to amateur seismologists. A paper has been posted at = http://physics.mercer.edu/hpage/mouse-sensor.pdf As noted in this article, John will make available free to anybody = who sends him an email request for a password--the LabView executable to = operate the mouse. The resolution, at about 50 microns, is too small for direct = application to seismology; however the method might be useful for = calibrating instruments. Also, anybody wanting to monitor the earth = (stable pendulum as a plumb-bob) should be able to use this technique to = watch for changes greater than 50 microradians. The typical diurnal = thermoelastic variation is about one-third that value, but over the = course of weeks to months I predict there will be observable changes = that are not being routinely measured in nearly the 'global' sense they = ought to be. To allow easier use of the sensor I removed some materal from the = bottom of my mouse using sandpaper. By this means the gap-space over = which the unit can operate is approximately doubled. Without doing so, = one has to be more careful with alignment and stability of the pendulum. = With my present capability (as wide as 3 mm) it is very easy to work = with this instrument. Additionally, I have an idea that some of you may want to = consider. Any truly outstanding vertical seismograph requires force-feedback. The traditional approach is one that uses force balance. The same = 'strong' force that keeps the instrument from even moving substantially = (much less 'goiing to the rails' because of temperature/pressure changes) is also used to provide the required near-critical damping. For more than a year I have demonstrated with my modified Sprengnether, = that a 'soft' force feedback has advantages over the traditional = approach. The feedback I have used with my Sprengnether derives from a = long time constant integrated output from the capacitive sensor (large = dynamic range area-varying, fully-differential unit). Based on my = experience with this instrument, I propose the following: Since the sensor used for force feedback can have terrible = sensitivity compared to the sensor used for detecting earthquakes--build = a `centering' (feedback) package that uses the mouse sensor. The = requirement for DAC output for the coil of the actuator can be managed = (it appears) with a 'dirt cheap' homebuilt piece of electronics (an = example at http://www.allaboutcircuits.com/vol_4/chpt_13/3.html ) Without a parallel port, your USB computer would need a printer = cable (< $20) to operate this R/2R DAC. Randall __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: AD698 chip From: Randall Peters PETERS_RD@.......... Date: Sun, 20 Jan 2008 07:39:39 -0500 Chris, Have you actually built an instrument with the AD698 chip and determined that it is unsuitable for seismometers? I remember you telling me this some time ago; but it turns out that Denny Goodwin (mentioned in the paper that John and I just wrote) put together a circuit for me, also some time ago. Only in the last month did I try his breadboarded unit. He had been unsuccessful with it due to a solder bridge that I found only after looking at the board carefully with magnification. You will remember that for much of the two decades I have been using my fully differential capacitive sensors for internal friction research--that the work-horse for that work was the NE5521 chip that is no longer manufactured (following the fire at the plant in France). Well, I have done a direct comparison of the AD698 with the Ne5521 and do not find a great enough performance difference to agree with your claim! In fact, with the prototype new vertical that I recently built (the details of which I will soon share with list-serve readers), it picked up the Charlotte Is earthquake with this chip, even though the instrument was sitting on a lab bench here in the physics building. So I don't think you can make a defensible claim that the chip is unsuitable for seismometers. Insofar as expense is concerned, the webpage I recently viewed at Analog Devices indicates a price of about $25 (straight from the companry) for the version that I would use (in large quantities). I haven't enquired about single chip prices, although I know from Larry Cochrane that if bought from some of the 'distributors' it is indeed hideously expensive. They love to mark-up units, evidently in this case by a huge amount. The price I mention for ADC's in our paper ($25) is not for ADC chips that require peripheral components and labor to make operational, but rather the ones 'ready to go' from the distributor (like the 10-bit unit from Dataq). Randall Subject: mouse with 9000 dpi From: Randall Peters PETERS_RD@.......... Date: Sun, 20 Jan 2008 09:27:46 -0500 Audun, I believe the now fairly old Compaq optical mouse that was used for our paper has only 800 dpi. Thus, the 9000 dpi of a laser mouse should yield at least an order of magnitude improvement in the resolution. Since it would be relatively easy to operate with a pendulum at least 2 m long (enclosed, of course to prevent the influence of air drafts), such a mouse should permit one to observe angular displacement changes at the level of about 2 micro radians. I think this would be well worth pursuing, especially for purpose of studying long term changes in the 'figure' of the Earth. ( Even at 20 micro-radians the daily thermoelastic variation should be close to observable with the right kind of filtering. ) I have spent a good part of my career looking at motions with periods greater than 1000 s, a field deserving of much more study. For example, the VolksMeter data from both Redwood City and also here in Macon show an unmistakeable terdiurnal tide (8-h periodicity) that has never before been observed with a simple pendulum. I believe that an "army of amateurs" looking at diurnal variations of a simple pendulum monitored by a mouse just might uncover some unknown secrets of our planet. The terdiurnal tide is best known in relationship to the atmosphere. Randall Subject: seismometer misconceptions From: Randall Peters PETERS_RD@.......... Date: Sun, 20 Jan 2008 09:57:03 -0500 From a number of comments and questions that have appeared on the list serve over the last month or so, it appears that some of you might benefit (if I were to write it) from something booklet-like titled, "The Physics of a Seismometer" ?? The appropriate level of mathematics (language of physics) is something I haven't yet decided. There are important issues that could be addressed, independent of the math (unless proof is required for unbelievers), such as the following: Seismometer misconceptions There is a great deal of misunderstanding when it comes to the physics of seismometers. The biggest single contributor to confusion involves 'period' of the instrument. Only for a simple (ideal) pendulum (horizontal seismometer) or a simple (idealized) vertical spring holding a mass (vertical seismometer)--does the inherent (mechanical) sensitivity of the device depend quadratically on the natural period of oscillation; i.e., proportional to T squared. This is the natural period T of harmonic motion if the unit were not dampened to prevent oscillation, as is done with virtually all instruments other than some I find (evidently as a 'heretic'), quite useful. The sensitivity to the ground's acceleration (ONLY thiing that any seismometer responds to) is only 'half' the story. The instrument's sensitivity to its own structural changes is also proportional to T-squared. Because the instrument is under considerable stress by attempting to statically support at equilibrium the inertial mass required for it to function--the structural changes can not be ignored for any truly useful instrument. In particular, creep never ceases, and even miniscule varaiations in temperature can have a large effect. Trying to eliminate the structural influence as compared to the acceleration influence is the GREAT challenge of any instrument design. The tradeoff that is part of the design must weigh mechanical benefit versus electronics benefit. Keep in mind that linear electronics by iteself (WITHOUT force feedback) can never influence the instrument in a quadratic manner (as implied by the very word LINEAR). In other words reducing the corner freqeuency of the passive electronics (devoid of an actuator to provide feedback) can NEVER be as influential as lowering the natural frequency (lengthening the period) of the mechanical oscillator itself. Because electronics establishes a lower threshold of detectability (due to 1/f noise from the amplifiers and also white (frequency independent) noise due to ADC bit resolution) there is a vastly greater benefit from mechanical improvement than there is from electronics improvement. That shouldn't come as a great surprise. After all, you could have perfect electronics, but if the mass doesn't move under the influence of ground acceleration, then the seismometer will not respond. At low levels that is exactly what can prevent earthquake detection. It has nothing to do with the motion being below the threshold established by the noise of the electronics; it has everything to do with the system being 'latched' in a metastability that derives from internal friction that operates at the mesoscale. When seismologists talk about nonlinearity of the mechanical system (which is religiously avoided), what they are discussing is elastic anharmonicity (nonlinearity)--undesirable distortions at large levels of motion. Also very important but unknown until recently, are the influences of damping anharmonicity that derives from internal friction (changes in the defect structure of the spring) and which operates at the other extreme; i.e., at low levels. For information about damping anharmonicity, consult the article titled "anharmonic oscillator" that I wrote for the 10th Ed. of the McGraw Hill Encyclopedia of Science and Technology Practical seismometers are rarely configured with an appearance even remotely similar to the simple harmonic oscillators of idealized type mentioned above (pendulum or mass/spring). Their performance is governed by properties due to their "compound" nature. Many of the commercial instruments employ "force-balance", in which the inertial mass is constrained (by means of an actuator that is part of a force-feedback network) to execute very little motion in response to earth acceleration. Instead of monitoring the motion of the inertial mass relative to the case, what is monitored is the error signal of the electronics required to keep the mass from moving. In the case of force-balance this is indeed a large force, since it is used to not only keep the mean position of the mass from changing; but it is even great enough to prevent oscillation. In other words, the feedback is tailored to provide the desired near critical damping. With the forcing function of the actuator being large enough to provide this damping, it is also true that the feedback can be designed (in a manner analogous to PID controller design) to yield an instrument that behaves (by reason of the feedback) as though it were a simple oscillator with a much longer natural period. Keep in mind that the period lengthening results only from the feedback force supplied by the actuator. Electronics without feedback can never accomplish the same thing! Note also that it is the strong feedback force that results in a quadratic improvement in the idealized sensitivity--because the "effective mechanical natural period" has been increased. One might then think that force-feedback is the answer to every problem; but it is not! The additional complexity and cost are only part of the matter. There must be a small amount of inertial mass motion for the electronics to be able to generate an error signal. This is not always possible. The damping anharmonicity that I mentioned 'wars against' the force-balance concept. An alternative approach which has merit and which I alone appear to have used, is the following--instead of (i) a 'hard' feedback force (commercial standard) that is able to greatly alter the properties of the equivalent mechanical oscillator, use (ii) a 'soft' feedback force that keeps the system from migrating out the range of acceptable motion, but which allows the instrument to 'seek its own best equilibrium' while 'skating over the metastabilities of its real as opposed to idealized harmonic potential'. Randall Subject: Re: seismometer misconceptions From: "Daryl P. Dacko" mycrump@........ Date: Sun, 20 Jan 2008 11:37:24 -0500 Randall, I've been following your arguments about seismometer design for quite some time. I need a few answers to help my understanding. First, what's your definition of "mesoscale." Second, if you use "soft" damping, how do you separate the signal from the noise (overshoot and metainstabilitys that are allowed by the soft damping.) Third, when you talked before about using totally undamped systems, again, how do you separate signal from the undamped response ? Thanks for all the thought provoking ideas, Daryl > >From a number of comments and questions that have appeared on the list serve over the last month or so, > it appears that some of you might benefit (if I were to write it) from something booklet-like titled, > "The Physics of a Seismometer" ?? > The appropriate level of mathematics (language of physics) is something I haven't yet decided. > There are important issues that could be addressed, independent of the math (unless proof is required for > unbelievers), such as the following: > > Seismometer misconceptions > > There is a great deal of misunderstanding when it comes to the physics of seismometers. The biggest > single contributor to confusion involves 'period' of the instrument. Only for a simple (ideal) pendulum > (horizontal seismometer) or a simple (idealized) vertical spring holding a mass (vertical > seismometer)--does the inherent (mechanical) sensitivity of the device depend quadratically on the > natural period of oscillation; i.e., proportional to T squared. This is the natural period T of harmonic > motion if the unit were not dampened to prevent oscillation, as is done with virtually all instruments > other than some I find (evidently as a 'heretic'), quite useful. > The sensitivity to the ground's acceleration (ONLY thiing that any seismometer responds to) is only > 'half' the story. The instrument's sensitivity to its own structural changes is also proportional to > T-squared. Because the instrument is under considerable stress by attempting to statically support at > equilibrium the inertial mass required for it to function--the structural changes can not be ignored for > any truly useful instrument. In particular, creep never ceases, and even miniscule varaiations in > temperature can have a large effect. Trying to eliminate the structural influence as compared to the > acceleration influence is the GREAT challenge of any instrument design. > The tradeoff that is part of the design must weigh mechanical benefit versus electronics benefit. > Keep in mind that linear electronics by iteself (WITHOUT force feedback) can never influence the > instrument in a quadratic manner (as implied by the very word LINEAR). In other words reducing the > corner freqeuency of the passive electronics (devoid of an actuator to provide feedback) can NEVER be as > influential as lowering the natural frequency (lengthening the period) of the mechanical oscillator > itself. Because electronics establishes a lower threshold of detectability (due to 1/f noise from the > amplifiers and also white (frequency independent) noise due to ADC bit resolution) there is a vastly > greater benefit from mechanical improvement than there is from electronics improvement. That shouldn't > come as a great surprise. After all, you could have perfect electronics, but if the mass doesn't move > under the influence of ground acceleration, then the seismometer will not respond. At low levels that is > exactly what can prevent earthquake detection. It has nothing to do with the motion being below the > threshold established by the noise of the electronics; it has everything to do with the system being > 'latched' in a metastability that derives from internal friction that operates at the mesoscale. When > seismologists talk about nonlinearity of the mechanical system (which is religiously avoided), what they > are discussing is elastic anharmonicity (nonlinearity)--undesirable distortions at large levels of > motion. Also very important but unknown until recently, are the influences of damping anharmonicity that > derives from internal friction (changes in the defect structure of the spring) and which operates at the > other extreme; i.e., at low levels. For information about damping anharmonicity, consult the article > titled "anharmonic oscillator" that I wrote for the 10th Ed. of the McGraw Hill Encyclopedia of Science > and Technology > Practical seismometers are rarely configured with an appearance even remotely similar to the simple > harmonic oscillators of idealized type mentioned above (pendulum or mass/spring). Their performance is > governed by properties due to their "compound" nature. Many of the commercial instruments employ > "force-balance", in which the inertial mass is constrained (by means of an actuator that is part of a > force-feedback network) to execute very little motion in response to earth acceleration. Instead of > monitoring the motion of the inertial mass relative to the case, what is monitored is the error signal of > the electronics required to keep the mass from moving. In the case of force-balance this is indeed a > large force, since it is used to not only keep the mean position of the mass from changing; but it is > even great enough to prevent oscillation. In other words, the feedback is tailored to provide the > desired near critical damping. With the forcing function of the actuator being large enough to provide > this damping, it is also true that the feedback can be designed (in a manner analogous to PID controller > design) to yield an instrument that behaves (by reason of the feedback) as though it were a simple > oscillator with a much longer natural period. Keep in mind that the period lengthening results only from > the feedback force supplied by the actuator. Electronics without feedback can never accomplish the same > thing! Note also that it is the strong feedback force that results in a quadratic improvement in the > idealized sensitivity--because the "effective mechanical natural period" has been increased. > One might then think that force-feedback is the answer to every problem; but it is not! The > additional complexity and cost are only part of the matter. There must be a small amount of inertial > mass motion for the electronics to be able to generate an error signal. This is not always possible. > The damping anharmonicity that I mentioned 'wars against' the force-balance concept. An alternative > approach which has merit and which I alone appear to have used, is the following--instead of (i) a 'hard' > feedback force (commercial standard) that is able to greatly alter the properties of the equivalent > mechanical oscillator, use (ii) a 'soft' feedback force that keeps the system from migrating out the > range of acceptable motion, but which allows the instrument to 'seek its own best equilibrium' while > 'skating over the metastabilities of its real as opposed to idealized harmonic potential'. > > Randall > > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Shadow Zone From: "Randy" rpratt@............. Date: Sun, 20 Jan 2008 16:10:34 -0600 The 1 NM per minute of latitude conversion is where I started as that is = what we used when I was flying. I see the shadow zone has a range of = definitions from 102 to 105 as beginning and 140 to 142 as ending = depending on the reference. Is there a most accepted range or is it = somewhat dependent on location? Is it a sharp cutoff or a gradual = reduction over a few degrees? Randy
The 1 NM per minute of latitude = conversion is where=20 I started as that is what we used when I was flying.  I see the = shadow zone=20 has a range of definitions from 102 to 105 as beginning and 140 to 142 = as ending=20 depending on the reference.  Is there a most accepted range or is = it=20 somewhat dependent on location?  Is it a sharp cutoff or a gradual=20 reduction over a few degrees?
 
Randy
Subject: Re: optical mouse sensor From: Charles R Patton charles.r.patton@........ Date: Sun, 20 Jan 2008 18:30:29 -0800 Dr. Peters, I’d like to comment on one point in your pendulum paper where you mention, “In general there is a tendency for the mean position of the displayed waveform to migrate in spite of the absence of actual physical migration.” You surmise a Windows problem. I don’t believe it’s in Windows. Windows can’t tell what mouse is on the end of the plug – just that it’s a mouse, not if it’s made of encoder disks or optical sensor. These sensors would require different algorithms to process raw data. A while back I started looking at the optical mouse as a optical encoder for use as a (ham) antenna position indicator. I abandoned the project when it became clear that the mouse itself does not put out a consistent, repeatable stream of pulses. I attribute this to the method of sensing that essentially does a center-of-light or center-of-darkness (the microscopic shadows cast from edge lighting of surface roughness) then estimates their change in position on the optical cell fields. The problem is that this is fuzzy involving coarse resolution a/d’s (that are very likely noisy, also) for each cell. So the simple test I did was just to run the mouse back and forth along a straight edge to stops. I would see the endpoints drift as this was repeated. I tried to develop a grating like pattern to turn the estimation into a fixed grating on the cells, figuring maybe I could get around the granularity, but didn’t finish the project. Nonetheless, sometimes the sensor will sit there and jitter or drift, even when it is standing still, which again I attribute to poor sensor algorithms in the mouse itself. Some optical mice use early versions of the HP sensor that can be re-jumpered to put out quadrature pulses instead of the mouse communication bytes. I didn’t do this experiment, but your pendulum would be perfect for it – just re-jumper one of those units for quadrature, and verify that the total is zero at the end of a swing down run. I’m sure you’ll find that it won’t be. Regards, Charles R. Patton __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: AD698 chip From: ChrisAtUpw@....... Date: Sun, 20 Jan 2008 22:45:19 EST In a message dated 20/01/2008, PETERS_RD@.......... writes: Chris, Have you actually built an instrument with the AD698 chip and determined that it is unsuitable for seismometers? I remember you telling me this some time ago; but it turns out that Denny Goodwin put together a circuit for me, also some time ago. Only in the last month did I try his breadboarded unit. He had been unsuccessful with it due to a solder bridge that I found only after looking at the board carefully with magnification. Hi Randall, If you read up the specifications, you will find that the output of the AD698 is PULSED ! The pulse length is modified to give the temperature compensation. I don't know what the ??designers?? at AD thought that they were doing. DigiKey list the AD698 DIP version at $70.88. The AD598 does not have this problem, but the DIP version still costs $52.53 for 1 off. The SOIC versions are about half this in small quantities, when stocked. You will remember that for much of the two decades I have been using my fully differential capacitive sensors for internal friction research--that the work-horse for that work was the NE5521 chip that is no longer manufactured. Well, I have done a direct comparison of the AD698 with the NE5521 and do not find a great enough performance difference to agree with your claim! In fact, with the prototype new vertical that I recently built (the details of which I will soon share with list-serve readers), it picked up the Charlotte Is earthquake with this chip, even though the instrument was sitting on a lab bench here in the physics building. So I don't think you can make a defensible claim that the chip is unsuitable for seismometers. The correction is temperature dependant, so there will likely be one temperature at which the correction is zero, presumably at one end of the range. If you digitise the output directly, you will get an uncompensated signal and occasional glitches due to the variable zero output periods. To get the compensated output you need to provide a low pass filter to integrate the signal. This may slow up the response if you want to get low noise. Trying to use a chip with a stepped level output in a low noise application seems to be 'simply buying trouble'. I am quite happy to avoid using it, particulaly when I can make up a good detector for a small fraction of the cost. _http://www.keckec.com/seismo/_ (http://www.keckec.com/seismo/) Insofar as expense is concerned, the webpage I recently viewed at Analog Devices indicates a price of about $25 (straight from the companry) for the version that I would use (in large quantities). I haven't enquired about single chip prices, although I know from Larry Cochrane that if bought from some of the 'distributors' it is indeed hideously expensive. They love to mark-up units, evidently in this case by a huge amount. You might cross check those prices again? The ''low'' AD website price I saw quoted was for the PLCC version in 1,000 off quantities. The 15 off price for the DIP version is $60. Regards, Chris
In a message dated 20/01/2008, PETERS_RD@.......... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>Chris,
      Have you actually built an instrum= ent=20 with the AD698 chip and determined that it is unsuitable for=20 seismometers?
I remember you telling me this some time ago; but it turn= s=20 out that Denny Goodwin put together a circuit for me, also some time=20 ago.  Only in the last month did I try his breadboarded unit. &n= bsp;=20 He had been unsuccessful with it due to a solder bridge that I found only=20 after looking at the board carefully with magnification.
Hi Randall,
 
    If you read up the specifications, you will fin= d=20 that the output of the AD698 is PULSED ! The pulse length is modified t= o=20 give the temperature compensation. I don't know what the ??designers?? at AD= =20 thought that they were doing. DigiKey list the AD698 DIP version at $70.88.=20= The=20 AD598 does not have this problem, but the DIP version still costs $52.53 for= 1=20 off. The SOIC versions are about half this in small quantities, when stocked= ..=20
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>       You will remember that for m= uch of=20 the two decades I have been using my fully differential
capacitive sens= ors=20 for internal friction research--that the work-horse for that work was the=20 NE5521 chip that is no longer manufactured. Well, I have done a direct=20 comparison of the AD698 with the NE5521 and do not find a great enough=20 performance difference to agree with your claim!  In fact, with the=20 prototype new vertical that I recently built (the details of which I will=20= soon=20 share with list-serve readers), it picked up the Charlotte Is earthquake w= ith=20 this chip, even though the instrument was sitting on a lab bench here in t= he=20 physics building. So I don't think you can make a defensible claim th= at=20 the chip is unsuitable for seismometers. 
    The correction is temperature dependant, so the= re=20 will likely be one temperature at which the correction is zero, presumably a= t=20 one end of the range.
    If you digitise the output directly, you will g= et=20 an uncompensated signal and occasional glitches due to the variable zero=20 output periods. To get the compensated output you need to provide a low= =20 pass filter to integrate the signal. This may slow up the response if you wa= nt=20 to get low noise.
    Trying to use a chip with a stepped level=20 output in a low noise application seems to be 'simply buying=20 trouble'. I am quite happy to avoid using it, particulaly when I can ma= ke=20 up a good detector for a small fraction of the cost. http://www.keckec.com/seismo/ <= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Insofar=20 as expense is concerned, the webpage I recently viewed at Analog Devices=20 indicates a price of about $25 (straight from the companry) for the versio= n=20 that I would use (in large quantities).  I haven't enquired about sin= gle=20 chip prices, although I know from Larry Cochrane that if bought from some=20= of=20 the 'distributors' it is indeed hideously expensive. They love to mark-up=20 units, evidently in this case by a huge amount.
    You might cross check those prices again? The=20 ''low'' AD website price I saw quoted was for the PLCC version in 1,000 off=20 quantities. The 15 off price for the DIP version is $60.
    
    Regards,
 
    Chris
Subject: Re: Shadow Zone From: ChrisAtUpw@....... Date: Sun, 20 Jan 2008 23:02:39 EST In a message dated 20/01/2008, rpratt@............. writes: I see the shadow zone has a range of definitions from 102 to 105 as beginning and 140 to 142 as ending depending on the reference. Is there a most accepted range or is it somewhat dependent on location? Is it a sharp cutoff or a gradual reduction over a few degrees? Hi Randy, The shadow zone is due to the large dense core of the Earth 'shadowing' the signal transmission. The core refracts P waves, but it will not transmit S waves directly. You also get some variation due to the depth of the quake. The cut off is gradual. Regards, Chris Chapman
In a message dated 20/01/2008, rpratt@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I see the shadow zone has a range of definitions fro= m 102 to=20 105 as beginning and 140 to 142 as ending depending on the reference. = ; Is=20 there a most accepted range or is it somewhat dependent on location? = Is=20 it a sharp cutoff or a gradual reduction over a few=20 degrees?
Hi Randy,
 
    The shadow zone is due to the large dense core=20= of=20 the Earth 'shadowing' the signal transmission. The core refracts P waves, bu= t it=20 will not transmit S waves directly. You also get some variation due to the d= epth=20 of the quake. The cut off is gradual.
 
    Regards,
 
    Chris Chapman
Subject: Re: Shadow Zone- Inner Core too From: "Jim ODonnell" geophysics@.......... Date: Mon, 21 Jan 2008 05:56:43 GMT Randy- Until Chris mentioned it I had forgotten about Inge Lehmann, who = I once met at UCBerkeley when she was visiting Prof Perry Byerly. See http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_l= ehmann.html Jim O'Donnell = Geological/Geophysical Consultant GEOTECHNICAL APPLICATIONS 702.293.5664 geophysics@.......... 702.281.9081 cell jimo17@........ -- "Randy" wrote: The 1 NM per minute of latitude conversion is where I started as that is= what we used when I was flying. I see the shadow zone has a range of d= efinitions from 102 to 105 as beginning and 140 to 142 as ending dependi= ng on the reference. Is there a most accepted range or is it somewhat d= ependent on location? Is it a sharp cutoff or a gradual reduction over = a few degrees? Randy

Randy- Until Chris mentioned it I had forgotten about Inge Lehm= ann, who I once met at UCBerkeley when she was visiting Prof Perry Byerl= y.

See http://www.amnh.org/education/resources/rfl/w= eb/essaybooks/earth/p_lehmann.html




         &nb= sp;        Jim O'Donnell  &= nbsp;  
        Geo= logical/Geophysical Consultant
      &n= bsp;    GEOTECHNICAL APPLICATIONS
702.293.5664 &n= bsp;  geophysics@..........
702.281.9081 cell   j= imo17@........

-- "Randy" <rpratt@.............> wrote:
=

The 1 NM per minute of latitude convers= ion is where I started as that is what we used when I was flying.  = I see the shadow zone has a range of definitions from 102 to 105 as begi= nning and 140 to 142 as ending depending on the reference.  Is ther= e a most accepted range or is it somewhat dependent on location?  I= s it a sharp cutoff or a gradual reduction over a few degrees?
 
Randy
Subject: Specs for Lehman type sensor From: jonfr@......... Date: Mon, 21 Jan 2008 13:32:24 -0500 (EST) Hi all I am looking for specs for Lehman type sensor. As I can build a lehman type sensor in my school with an help. However, the specs I already aren't good, so I need better onces. If someone has them ready. If no one has them, I need to write them up my self. I need the size and length in cm. I also need a suggestion for the material needed for the mass, I was thinking about using led. But I don't know how good idea that is. For the base of the sensor I was thinking about using aluminum. Please send this to my main email address, jonfr [at] jonfr.com Thanks in advance. Regards. Jón Frímann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Specs for Lehman type sensor From: ChrisAtUpw@....... Date: Mon, 21 Jan 2008 20:42:55 EST In a message dated 21/01/2008 18:32:46 GMT Standard Time, jonfr@......... writes: I am looking for specs for Lehman type sensor. As I can build a Lehman type sensor in my school with help. However, the specs I already aren't good, so I need better ones. If someone has them ready. If no one has them, I need to write them up my self. I need the size and length in cm. I also need a suggestion for the material needed for the mass, I was thinking about using led. But I don't know how good idea that is. For the base of the sensor I was thinking about using aluminum. Please send this to my main email address, jonfr [at] jonfr.com Hi Jon, I use 3" x 1" U channel Al with 1/8" thick Al corner plates for the frame. The arm is about 24" long overall. You want a natural pendulum length of at least 1.5 seconds, 22". If you make it shorter, you may have problems getting a final 20 second period. Have a look our school seismometer at _http://www.bgs.ac.uk/education/school_seismology/seismometer.html_ (http://www.bgs.ac.uk/education/school_seismology/seismometer.html) and _http://jclahr.com/science/psn/chapman/lehman/index.html_ (http://jclahr.com/science/psn/chapman/lehman/index.html) This latter design was modified using a rigid top tube and tungsten carbide rod suspensions, from the SS balls and plates. It is probably easier to use brass for the mass. I make the arm out of 15 mm SS water pipe, but you can also use Al tube. They seem to work well. Regards, Chris Chapman
In a message dated 21/01/2008 18:32:46 GMT Standard Time, jonfr@........ om=20 writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I am=20 looking for specs for Lehman type sensor. As I can build a Lehman type sen= sor=20 in my school with help.

However, the specs I already aren't good, s= o I=20 need better ones. If someone has them ready. If no one has them, I need to= =20 write them up my self.

I need the size and length in cm. I also nee= d a=20 suggestion for the material needed for the mass, I was thinking about usin= g=20 led. But I don't know how good idea that is. For the base of the sensor I=20= was=20 thinking about using aluminum.

Please send this to my main email=20 address, jonfr [at] jonfr.com
Hi Jon,
 
    I use 3" x 1" U channel Al with 1/8" thick Al=20 corner plates for the frame. The arm is about 24" long overall.
    You want a natural pendulum length of at least=20= 1.5=20 seconds, 22". If you make it shorter, you may have problems getting a f= inal=20 20 second period. Have a look our school seismometer at h= ttp://www.bgs.ac.uk/education/school_seismology/seismometer.html an= d=20 http://jcla= hr.com/science/psn/chapman/lehman/index.html This=20 latter design was modified using a rigid top tube and tungsten carbide=20= rod=20 suspensions, from the SS balls and plates. 
    It is probably easier to use brass for the mass= .. I=20 make the arm out of 15 mm SS water pipe, but you can also use Al tube.
    They seem to work well.
 
    Regards,
 
    Chris Chapman
Subject: RE: Specs for Lehman type sensor From: "Steve Hammond" shammon1@............. Date: Mon, 21 Jan 2008 21:43:13 -0800 Hi Jon, Here is a good place to start. http://pw2.netcom.com/~shammon1/equip.htm And here are some photos you = can look at of a Lehman I built to help get you going. http://pw2.netcom.com/~shammon1/AptosStn.htm. And yes, you can use led. Scroll to the bottom of the page in the last URL and you will see the = specs. Regards, Steve Hammond, PSN Aptos, California. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of jonfr@......... Sent: Monday, January 21, 2008 10:32 AM To: psn-l@.............. Subject: Specs for Lehman type sensor Hi all I am looking for specs for Lehman type sensor. As I can build a lehman = type sensor in my school with an help. However, the specs I already aren't good, so I need better onces. If = someone has them ready. If no one has them, I need to write them up my self. I need the size and length in cm. I also need a suggestion for the = material needed for the mass, I was thinking about using led. But I don't know = how good idea that is. For the base of the sensor I was thinking about using aluminum. Please send this to my main email address, jonfr [at] jonfr.com Thanks in advance. Regards. J=F3n Fr=EDmann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Specs for Lehman type sensor From: jonfr@......... Date: Tue, 22 Jan 2008 14:12:10 -0500 (EST) Hi I am looking for a more advanced design. But this is a old design. I am also wondering what size I should use. I was thinking about 60 cm in length for the arm. 60 cm high and with 20 kg mass in order to get 20 sec period. Please let me know this is good or not. Regards. Jón Frímann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: QUESTION about Slip Faults From: "Jerry Payton" gpayton880@....... Date: Sun, 27 Jan 2008 11:25:45 -0600 Since it is rather slow now, let me throw out a question that I have never had satisfactorily answered to me; directly or reading. Differentiating between a Left Lateral or Right Lateral Slip Fault's movement, the USGS Visual Glossary states: "If you were to stand on the fault and look along its length, this is a type of strike-slip fault where the left block moves toward you and the right block moves away" IF I were to turn around looking the opposite direction the description would change. It is all relative to the direction you are facing. If I assumed that I was always looking North, the answer would work. BUT, not all faults run generally North-South. So, when describing a Right or Left Lateral Slip Fault, how does one know what is being described to them? There must be some "standard" or "point of view" that explains this. Or, does it matter, as long as you realize it IS a slip fault. I have spent some time on archaeological digs near the Dead Sea in Israel. The Dead Sea Rift transverses through there and is described as moving southward on the Israel side and northward on the Jordan side. If I were able to straddle the fault and face North, I could call it a Right Lateral, but the reverse is true if I faced South. Signed: Confused, but not Lost, Jerry
Since it is rather slow now, let me throw out a question that I = have never=20 had satisfactorily answered to me; directly or reading.
 
Differentiating between a Left Lateral or Right Lateral Slip = Fault's=20 movement, the USGS Visual Glossary states: "If you were to stand on the = fault=20 and look along its length, this is a type of strike-slip fault where the = left=20 block moves toward you and the right block moves away"
 
IF I were to turn around looking the opposite direction the = description=20 would change.  It is all relative to the direction you are = facing.  If=20 I assumed that I was always looking North, the answer would work.  = BUT, not=20 all faults run generally North-South.  So, when describing a Right = or Left=20 Lateral Slip Fault, how does one know what is being described to = them? =20 There must be some "standard" or "point of view" that explains = this.  Or,=20 does it matter, as long as you realize it IS a slip fault.
 
I have spent some time on archaeological digs near the Dead = Sea in=20 Israel. The Dead Sea Rift transverses through there and is = described as=20 moving southward on the Israel side and northward on the Jordan = side.  If I=20 were able to straddle the fault and face North, I could call it a Right = Lateral,=20 but the reverse is true if I faced South. 
 
Signed: Confused, but not Lost,
Jerry
 
 
Subject: Re: QUESTION about Slip Faults From: "Jim ODonnell" geophysics@.......... Date: Sun, 27 Jan 2008 17:46:47 GMT Jerry- You do not straddle the fault but stand on 1 side and see the oth= er side go Left or Right; Left lateral fault & Right lateral fault. You= step on the other side and the directions are reversed, so Left is alwa= ys Left, etc, regardless of the strike direction of the fault. = See http://www.abag.ca.gov/bayarea/eqmaps/fixit/ch2/sld003.htm We are talking about Strike slip faults which are mostly horizontal move= ment like the San Andreas fault. Actually, faults usually have both comp= onents Horizontal & Vertical movement. Normal Faults have mostly vertical movement, so you can be on the Up sid= e or Down side. More damage seems to occur on the Down side. Jerry- Can you write me off line so I can hear more about your archeolog= y digs....Jim Jim O'Donnell = Geological/Geophysical Consultant GEOTECHNICAL APPLICATIONS 702.293.5664 geophysics@.......... 702.281.9081 cell jimo17@........ -- "Jerry Payton" wrote: Since it is rather slow now, let me throw out a question that I have nev= er had satisfactorily answered to me; directly or reading. Differentiati= ng between a Left Lateral or Right Lateral Slip Fault's movement, the US= GS Visual Glossary states: "If you were to stand on the fault and look a= long its length, this is a type of strike-slip fault where the left bloc= k moves toward you and the right block moves away" IF I were to turn aro= und looking the opposite direction the description would change. It is = all relative to the direction you are facing. If I assumed that I was a= lways looking North, the answer would work. BUT, not all faults run gen= erally North-South. So, when describing a Right or Left Lateral Slip Fa= ult, how does one know what is being described to them? There must be s= ome "standard" or "point of view" that explains this. Or, does it matte= r, as long as you realize it IS a slip fault. I have spent some time on = archaeological digs near the Dead Sea in Israel. The Dead Sea Rift trans= verses through there and is described as moving southward on the Israel = side and northward on the Jordan side. If I were able to straddle the f= ault and face North, I could call it a Right Lateral, but the reverse is= true if I faced South. Signed: Confused, but not Lost,Jerry

Jerry- You do not straddle the fault but stand on 1 side and se= e the other side go Left or Right; Left lateral fault & Right latera= l fault.  You step on the other side and the directions are reverse= d, so Left is always Left, etc, regardless of the strike direction = of the fault.
See http://www.abag.ca.gov/bayarea/eqmaps/fixit/ch2/sld= 003.htm

We are talking about Strike slip faults which are mostly horizontal m= ovement like the San Andreas fault. Actually, faults usually have b= oth components Horizontal & Vertical movement.
Normal Faults= have mostly vertical movement, so you can be on the Up side or Down sid= e.  More damage seems to occur on the Down side.

Jerry- Can = you write me off line so I can hear more about your archeology digs....J= im

          &n= bsp;       Jim O'Donnell   =   
        Geologic= al/Geophysical Consultant
       &= nbsp;   GEOTECHNICAL APPLICATIONS
702.293.5664  &= nbsp; geophysics@..........
702.281.9081 cell   jimo17= @........

-- "Jerry Payton" <gpayton880@.......> wrote:
=

Since it is rather slow now, let me throw out a question that I hav= e never had satisfactorily answered to me; directly or reading.
 
Differentiating between a Left Lateral or Right Lateral Slip F= ault's movement, the USGS Visual Glossary states: "If you were to stand = on the fault and look along its length, this is a type of strike-slip fa= ult where the left block moves toward you and the right block moves away= "
 
IF I were to turn around looking the opposite direction the descrip= tion would change.  It is all relative to the direction you are fac= ing.  If I assumed that I was always looking North, the answer woul= d work.  BUT, not all faults run generally North-South.  So, w= hen describing a Right or Left Lateral Slip Fault, how does one know wha= t is being described to them?  There must be some "standard" or "po= int of view" that explains this.  Or, does it matter, as long as yo= u realize it IS a slip fault.
 
I have spent some time on archaeological digs near the Dead Se= a in Israel. The Dead Sea Rift transverses through there and is des= cribed as moving southward on the Israel side and northward on the Jorda= n side.  If I were able to straddle the fault and face North, I cou= ld call it a Right Lateral, but the reverse is true if I faced South.&nb= sp;
 
Signed: Confused, but not Lost,
Jerry
 
 
Subject: Re: QUESTION about Slip Faults From: "Jerry Payton" gpayton880@....... Date: Sun, 27 Jan 2008 12:01:00 -0600 Jerry- You do not straddle the fault but stand on 1 side and see the other side go Left or Right; Left lateral fault & Right lateral fault. I think we are saying the same thing. I was quoting the USGS site: http://earthquake.usgs.gov/learning/glossary.php?term=left-lateral My confusion is HOW to accurately communicate to someone else about a particular fault. If I said it was "right-lateral", how would the other person visualize what I was saying? Describing a Normal Fault, one would give the Strike, Dip and etc. The person then could visualize the whole thing. Maybe, I am just over emphasizing a point? (My email is gpayton@....... if you want to talk about the digs.........) Jerry
Jerry- You do not straddle the fault but stand on 1 side and see = the other=20 side go Left or Right; Left lateral fault & Right lateral = fault. =20
 
I think we are saying the same thing.  I was quoting = the USGS=20 site:  http://earthquake.usgs.gov/learning/glossary.php?term=3Dleft-lateral=
 
My confusion is HOW to accurately = communicate to=20 someone else about a particular fault.  If I said it was = "right-lateral",=20 how would the other person visualize what I was saying?  Describing = a=20 Normal Fault, one would give the Strike, Dip and etc.  The person = then=20 could visualize the whole thing.  Maybe, I am just over emphasizing = a=20 point?
 
(My email is gpayton@....... = if you=20 want to talk about the digs.........)
 
Jerry
Subject: Re: QUESTION about Slip Faults From: Stephen & Kathy skmort@............ Date: Sun, 27 Jan 2008 11:27:46 -0800 It doesn't matter which scenario you pick, (watching the opposite block from east, or west, or straddling the fault facing north, or south), the relative motion to the body will always be the same. The opposite block will move left, or the block on the left side will move toward you. Changing the way you face doesn't matter. A very simple test. Get two pieces of paper lay them side by side. draw arrows for the direction you want them to move relative to each other. Stand on one, face the other and move it in the direction of its arrow,, then stand on the other paper, face the original and move it in the direction of its arrow. Notice, they both moved the same relative to your body,, left for a left lateral fault. Now straddle, put one paper in front of each foot. Notice the left paper arrow is pointing toward you,, go to the opposite side of the paper and face the opposite direction,, the arrow on the left paper, (the other paper) is still pointing toward you. This is literally what I had to do to get it through my simple mind. Stephen PSN Station #55 Jerry Payton wrote: > Jerry- You do not straddle the fault but stand on 1 side and see the > other side go Left or Right; Left lateral fault & Right lateral fault. > > *I think we are saying the same thing. I was quoting the USGS site: > http://earthquake.usgs.gov/learning/glossary.php?term=left-lateral* > ** > *My confusion is* *HOW to accurately communicate to someone else about > a particular fault. If I said it was "right-lateral", how would the > other person visualize what I was saying? Describing a Normal Fault, > one would give the Strike, Dip and etc. The person then could > visualize the whole thing. Maybe, I am just over emphasizing a point?* > > (My email is gpayton@....... if you want to > talk about the digs.........) > > *Jerry* It doesn't matter which scenario you pick, (watching the opposite block from east, or west, or straddling the fault facing north, or south), the relative motion to the body will always be the same.=A0 The opposite block will move left, or the block on= the left side will move toward you.=A0 Changing the way you face doesn't matter.=A0 A very simple test.=A0 Get two pieces of paper lay them side b= y side.=A0 draw arrows for the direction you want them to move relative to each other.=A0 Stand on one, face the other and move it in the direction of its arrow,, then stand on the other paper, face the original and move it in the direction of its arrow.=A0 Notice, they both moved the same relative to your body,,=A0=A0 left for a left lateral fault.=A0 Now straddle, put one paper in front of each foot.=A0 Notice the left paper arrow is pointing toward you,,=A0 go to the opposite side of the paper and face the opposite direction,,=A0 the arrow on the left paper, (the other paper) is still pointing toward you.=A0=A0 This is literally what I= had to do to get it through my simple mind.
=A0 Stephen
=A0 PSN Station #55

Jerry Payton wrote:
Jerry- You do not straddle the fault but stand on 1 side and see the other side go Left or Right; Left lateral fault & Right lateral fault.=A0
=A0
I think we are saying the same thing.=A0 I was quoting the= USGS site:=A0 http://earthquake.usgs.gov/learning/glossary.php?term=3Dleft-latera= l
=A0
My confusion is HOW to accurately communicate to someone else about a particular fault.=A0 If I said it was= "right-lateral", how would the other person visualize what I was saying?=A0 Describing a Normal Fault, one would give the Strike, Dip and etc.=A0 The person then could visualize the whole thing.=A0 Maybe, I am just over emphasizing a point?
=A0
=A0
Jerry
Subject: Re: QUESTION about Slip Faults From: "Jerry Payton" gpayton880@....... Date: Sun, 27 Jan 2008 13:35:41 -0600 Thanks a million! Now, I think I understand. It is the relative movement of the "opposite" block that determines the description. Soooo simple. Regards, Jerry ----- Original Message ----- From: Stephen & Kathy To: psn-l@.............. Sent: Sunday, January 27, 2008 1:27 PM Subject: Re: QUESTION about Slip Faults It doesn't matter which scenario you pick, (watching the opposite block from east, or west, or straddling the fault facing north, or south), the relative motion to the body will always be the same. The opposite block will move left, or the block on the left side will move toward you. Changing the way you face doesn't matter. A very simple test. Get two pieces of paper lay them side by side. draw arrows for the direction you want them to move relative to each other. Stand on one, face the other and move it in the direction of its arrow,, then stand on the other paper, face the original and move it in the direction of its arrow. Notice, they both moved the same relative to your body,, left for a left lateral fault. Now straddle, put one paper in front of each foot. Notice the left paper arrow is pointing toward you,, go to the opposite side of the paper and face the opposite direction,, the arrow on the left paper, (the other paper) is still pointing toward you. This is literally what I had to do to get it through my simple mind. Stephen PSN Station #55 Jerry Payton wrote: Jerry- You do not straddle the fault but stand on 1 side and see the other side go Left or Right; Left lateral fault & Right lateral fault. I think we are saying the same thing. I was quoting the USGS site: http://earthquake.usgs.gov/learning/glossary.php?term=left-lateral My confusion is HOW to accurately communicate to someone else about a particular fault. If I said it was "right-lateral", how would the other person visualize what I was saying? Describing a Normal Fault, one would give the Strike, Dip and etc. The person then could visualize the whole thing. Maybe, I am just over emphasizing a point? (My email is gpayton@....... if you want to talk about the digs.........) Jerry
Thanks a million!  Now, I think I understand.  It is the = relative=20 movement of the "opposite" block that determines the description.  = Soooo=20 simple.
Regards,
Jerry
 
 
----- Original Message -----=20
Sent: Sunday, January 27, 2008 1:27 PM
Subject: Re: QUESTION about Slip Faults

It doesn't matter which scenario you = pick,=20 (watching the opposite block from east, or west, or straddling the fault = facing=20 north, or south), the relative motion to the body will always be the = same. =20 The opposite block will move left, or the block on the left side will = move=20 toward you.  Changing the way you face doesn't matter.  A very = simple=20 test.  Get two pieces of paper lay them side by side.  draw = arrows for=20 the direction you want them to move relative to each other.  Stand = on one,=20 face the other and move it in the direction of its arrow,, then stand on = the=20 other paper, face the original and move it in the direction of its = arrow. =20 Notice, they both moved the same relative to your body,,   = left for a=20 left lateral fault.  Now straddle, put one paper in front of each=20 foot.  Notice the left paper arrow is pointing toward you,,  = go to the=20 opposite side of the paper and face the opposite direction,,  the = arrow on=20 the left paper, (the other paper) is still pointing toward = you.   This=20 is literally what I had to do to get it through my simple = mind.
 =20 Stephen
  PSN Station #55

Jerry Payton = wrote:=20
Jerry- You do not straddle the fault but stand on 1 side and see = the=20 other side go Left or Right; Left lateral fault & Right lateral=20 fault. 
 
I think we are saying the same thing.  I was quoting = the=20 USGS site:  http://earthquake.usgs.gov/learning/glossary.php?term=3Dleft-lateral=
 
My confusion is HOW to accurately = communicate to=20 someone else about a particular fault.  If I said it was = "right-lateral",=20 how would the other person visualize what I was saying?  = Describing a=20 Normal Fault, one would give the Strike, Dip and etc.  The person = then=20 could visualize the whole thing.  Maybe, I am just over = emphasizing a=20 point?
 
(My email is gpayton@....... if you=20 want to talk about the digs.........)
 
Jerry
Subject: Re: QUESTION about Slip Faults From: Stephen & Kathy skmort@............ Date: Sun, 27 Jan 2008 12:11:14 -0800 At least that is the way I understand it. It doesn't matter if the block on the other side doesn't move and the one you are standing on moves right, it is still a left lateral fault. Corrections to my understanding are of course always welcome. Stephen Station #55 Jerry Payton wrote: > Thanks a million! Now, I think I understand. It is the relative > movement of the "opposite" block that determines the description. > Soooo simple. > Regards, > Jerry > > > ----- Original Message ----- > *From:* Stephen & Kathy > *To:* psn-l@.............. > *Sent:* Sunday, January 27, 2008 1:27 PM > *Subject:* Re: QUESTION about Slip Faults > > It doesn't matter which scenario you pick, (watching the opposite > block from east, or west, or straddling the fault facing north, or > south), the relative motion to the body will always be the same. The > opposite block will move left, or the block on the left side will move > toward you. Changing the way you face doesn't matter. A very simple > test. Get two pieces of paper lay them side by side. draw arrows for > the direction you want them to move relative to each other. Stand on > one, face the other and move it in the direction of its arrow,, then > stand on the other paper, face the original and move it in the > direction of its arrow. Notice, they both moved the same relative to > your body,, left for a left lateral fault. Now straddle, put one > paper in front of each foot. Notice the left paper arrow is pointing > toward you,, go to the opposite side of the paper and face the > opposite direction,, the arrow on the left paper, (the other paper) > is still pointing toward you. This is literally what I had to do to > get it through my simple mind. > Stephen > PSN Station #55 > > Jerry Payton wrote: >> Jerry- You do not straddle the fault but stand on 1 side and see the >> other side go Left or Right; Left lateral fault & Right lateral fault. >> >> *I think we are saying the same thing. I was quoting the USGS site: >> http://earthquake.usgs.gov/learning/glossary.php?term=left-lateral* >> ** >> *My confusion is* *HOW to accurately communicate to someone else >> about a particular fault. If I said it was "right-lateral", how >> would the other person visualize what I was saying? Describing a >> Normal Fault, one would give the Strike, Dip and etc. The person >> then could visualize the whole thing. Maybe, I am just over >> emphasizing a point?* >> >> (My email is gpayton@....... if you want to >> talk about the digs.........) >> >> *Jerry* At least that is the way I understand it.=A0 It doesn't matter if the block on the other side doesn't move and the one you are standing on moves right, it is still a left lateral fault.=A0=A0 Corrections to my understanding are of course always welcome.
=A0 Stephen
=A0 Station #55

Jerry Payton wrote:
Thanks a million!=A0 Now, I think I understand.=A0 It is the relative movement of the "opposite" block that determines the description.=A0 Soooo simple.
Regards,
Jerry
=A0
=A0
----- Original Message -----
Sent: Sunday, January 27, 2008 1:27 PM
Subject: Re: QUESTION about Slip Faults

It doesn't matter which scenario you pick, (watching the opposite block from east, or west, or straddling the fault facing north, or south), the relative motion to the body will always be the same.=A0 The opposite block will move left, or the block on= the left side will move toward you.=A0 Changing the way you face doesn't matter.=A0 A very simple test.=A0 Get two pieces of paper lay them side b= y side.=A0 draw arrows for the direction you want them to move relative to each other.=A0 Stand on one, face the other and move it in the direction of its arrow,, then stand on the other paper, face the original and move it in the direction of its arrow.=A0 Notice, they both moved the same relative to your body,,=A0=A0 left for a left lateral fault.=A0 Now straddle, put one paper in front of each foot.=A0 Notice the left paper arrow is pointing toward you,,=A0 go to the opposite side of the paper and face the opposite direction,,=A0 the arrow on the left paper, (the other paper) is still pointing toward you.=A0=A0 This is literally what I= had to do to get it through my simple mind.
=A0 Stephen
=A0 PSN Station #55

Jerry Payton wrote:
Jerry- You do not straddle the fault but stand on 1 side and see the other side go Left or Right; Left lateral fault & Right lateral fault.=A0
=A0
I think we are saying the same thing.=A0 I was quoting the USGS site:=A0 http://earthquake.usgs.gov/learning/glossary.php?term=3Dleft-latera= l
=A0
My confusion is HOW to accurately communicate to someone else about a particular fault.=A0 If I said it was= "right-lateral", how would the other person visualize what I was saying?=A0 Describing a Normal Fault, one would give the Strike, Dip and etc.=A0 The person then could visualize the whole thing.=A0 Maybe, I am just over emphasizing a point?
=A0
=A0
Jerry
Subject: Re: QUESTION about Slip Faults From: "Thomas Dick" dickthomas01@............. Date: Sun, 27 Jan 2008 14:29:19 -0600 will the "p" wave created by movement along a strike-slip fault be = distinct from other types?
will the "p" wave created by movement = along a=20 strike-slip fault be distinct from other = types?
Subject: Re: QUESTION about Slip Faults From: "Jerry Payton" gpayton880@....... Date: Sun, 27 Jan 2008 17:59:06 -0600 Thomas, I suspect that the body and surface waves are NOT different from any other EQ's; since, it is still basically a release of elastic tension. I would think that regardless if it were a upward, downward, sideward's movement. Te amount of stored energy would be the same depending upon the rock enviroment and intensity of the quake. That's my 2 cents. I'm sure that there are people here more qualified than me to answer that. Jerry ----- Original Message ----- From: Thomas Dick To: psn-l@.............. Sent: Sunday, January 27, 2008 2:29 PM Subject: Re: QUESTION about Slip Faults will the "p" wave created by movement along a strike-slip fault be distinct from other types?
Thomas, I suspect that the body and surface waves are NOT = different=20 from any other EQ's; since, it is still basically a release of elastic=20 tension.  I would think that regardless if it were a upward, = downward,=20 sideward's movement.  Te amount of stored energy would be the = same=20 depending upon the rock enviroment and intensity of the quake.  = That's my 2=20 cents.
 
I'm sure that there are people here more qualified than me to = answer=20 that.
 
Jerry 
 
 
----- Original Message -----=20
Sent: Sunday, January 27, 2008 2:29 PM
Subject: Re: QUESTION about Slip Faults

will the "p" wave created by movement = along a=20 strike-slip fault be distinct from other = types?
Subject: Re: QUESTION about Slip Faults From: John Lahr johnjan@........ Date: Sun, 27 Jan 2008 19:12:50 -0800 Hi Thomas, The sense (polarity) of motion of the phases recorded at a seismic station can be used, when combined with many other stations, to determine the focal mechanism of the earthquake. Here's a web site where an explanation is attempted. http://quake.usgs.gov/recenteqs/beachball.html Cheers, John At 12:29 PM 1/27/2008, Thomas Dick wrote: >will the "p" wave created by movement along a strike-slip fault be >distinct from other types? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: QUESTION about Slip Faults From: "Thomas Dick" dickthomas01@............. Date: Mon, 28 Jan 2008 08:57:05 -0600 > > The sense (polarity) of motion of the phases recorded at a seismic station > can be used, I thought that sometimes the strike-slip as being like dragging a bow acrossed a violin string as the sides of the fault "bounce" along while the reverse and normal faulting are more like to being like breaking a limb off a tree. I thought I had seen some "stepping" of P on some of the earthquakes off the west coast...my imagination? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Interesting article From: Pete Rowe ptrowe@......... Date: Tue, 29 Jan 2008 08:30:22 -0800 (PST) There is still so much to learn... http://www.sciencedaily.com/releases/2008/01/080124145022.htm Pete ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Interesting article From: "Jerry Payton" gpayton880@....... Date: Tue, 29 Jan 2008 11:05:06 -0600 Yes, Pete, that is an interesting theory. I wonder what is the "electrical" component of an earthquake that is measured by a seismograph? I thought all the seismic waves were physical movements. Comments out there?? Jerry ----- Original Message ----- From: Pete Rowe To: psn-l Sent: Tuesday, January 29, 2008 10:30 AM Subject: Interesting article There is still so much to learn... http://www.sciencedaily.com/releases/2008/01/080124145022.htm Pete ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Yes, Pete, that is an interesting theory.  I wonder what is = the=20 "electrical" component of an earthquake that is measured by a = seismograph? =20 I thought all the seismic waves were physical movements.  Comments = out=20 there??
Jerry
 
 
----- Original Message -----=20
From: Pete Rowe =
To: psn-l
Sent: Tuesday, January 29, 2008 10:30 AM
Subject: Interesting article

There is still so much to learn...

ht= tp://www.sciencedaily.com/releases/2008/01/080124145022.htm

Pete


     =20 _________________________________________________________________________= ___________
Never=20 miss a thing.  Make Yahoo your home page.
http://www.yahoo.com/r/hs
_____= _____________________________________________________

Public=20 Seismic Network Mailing List (PSN-L)

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Subject: Re: Interesting article From: ChrisAtUpw@....... Date: Tue, 29 Jan 2008 20:59:18 EST In a message dated 29/01/2008, gpayton880@....... writes: Yes, Pete, that is an interesting theory. I wonder what is the "electrical" component of an earthquake that is measured by a seismograph? I thought all the seismic waves were physical movements. Comments out there? Hi Jerry, Note that the depths concerned are from 400 to 1800 miles - deeper than most earthquake sources. The para-magnetic properties of the iron compounds vary. You are unlikely to see electrical effects at the surface due to this, although there may be other surface electrical / magnetic effects. Seismometers do not measure changes in potential or magnetic fields, only physical movements. Regards, Chris Chapman
In a message dated 29/01/2008, gpayton880@....... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Yes,=20 Pete, that is an interesting theory.  I wonder what is the "electrica= l"=20 component of an earthquake that is measured by a seismograph?  I thou= ght=20 all the seismic waves were physical movements.  Comments out=20 there?
Hi Jerry,
 
    Note that the depths concerned are from 400 to=20= 1800=20 miles - deeper than most earthquake sources. The para-magnetic properti= es=20 of the iron compounds vary. You are unlikely to see electrical effects at th= e=20 surface due to this, although there may be other surface electrical / magnet= ic=20 effects. Seismometers do not measure changes in potential or magnetic fields= ,=20 only physical movements.
 
    Regards,
 
    Chris Chapman
Subject: Re: Interesting article From: "Geoff" gmvoeth@........... Date: Wed, 30 Jan 2008 03:25:28 -0700 All it says is that they modled in a lab a phenomena that seems to be real and the seismic modle should be re-calculated or reprogrammed to include this phenomena When there exists an intense velocity change it is like turning into a mirror and will reflect or refract waves more intensely in that region just outside the liquid outer core sort of like an increase in the index of refraction or so I understand. They do not say to me HOW this electrical phenomena actually causes the effect only that it is associated with it. Regards; geoff ----- Original Message ----- From: To: Sent: Tuesday, January 29, 2008 6:59 PM Subject: Re: Interesting article > > In a message dated 29/01/2008, gpayton880@....... writes: > > Yes, Pete, that is an interesting theory. I wonder what is the "electrical" > component of an earthquake that is measured by a seismograph? I thought > all the seismic waves were physical movements. Comments out there? > > > Hi Jerry, > > Note that the depths concerned are from 400 to 1800 miles - deeper than > most earthquake sources. The para-magnetic properties of the iron compounds > vary. You are unlikely to see electrical effects at the surface due to this, > although there may be other surface electrical / magnetic effects. > Seismometers do not measure changes in potential or magnetic fields, only physical > movements. > > Regards, > > Chris Chapman > > > > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Comparison of available seismometers From: "K.-Benoit Evans" kevans@............ Date: Wed, 30 Jan 2008 21:52:22 -0500 I am interested in acquiring a simple seismometer package for amateur=20 use that is sensitive enough to detect teleseismic events. I would like=20= to acquire a ready-to-use instrument rather than build something from=20 scratch or from a kit. My main question is which seismometer to buy. I=20= have come across the following instruments on the Web: AS-1 Amateur Seismologist (Jeff Batten) $550 ??? http://www.amateurseismologist.com Vertical School Seismometer Ward=92s Natural Science $500 http://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602 EQ-1 Next Generation Science $600 http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1 Volksmeter II RLL Instruments (Zoltech) $995 single channel, $1495=20= dual channel (patented Symmetric Differential Capacitor (SDC) array sensor) http://www.rllinstruments.com In spite of the price difference, the Volksmeter seems interesting. As=20= far as I an tell, it is based on recent technology that is different=20 form the other three, which seem to be of the traditional Lehman type. Does anyone have any opinions or advice to give a rank beginner who has=20= not been in a science classroom or lab in over 40 years? Regards, Beno=EEt Evans Qu=E9bec, Canada= I am interested in acquiring a simple seismometer package for amateur use that is sensitive enough to detect teleseismic events. I would like to acquire a ready-to-use instrument rather than build something from scratch or from a kit. My main question is which seismometer to buy. I have come across the following instruments on the Web: AS-1 Amateur Seismologist (Jeff Batten) $550 ??? http://www.amateurseismologist.com Vertical School Seismometer Ward=92s Natural Science $500 http://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602 EQ-1 Next Generation Science $600 http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1 Volksmeter II RLL Instruments (Zoltech) $995 single channel, $1495 dual channel (patented Symmetric Differential Capacitor (SDC) array sensor) http://www.rllinstruments.com In spite of the price difference, the Volksmeter seems interesting. As far as I an tell, it is based on recent technology that is different form the other three, which seem to be of the traditional Lehman type. Does anyone have any opinions or advice to give a rank beginner who has not been in a science classroom or lab in over 40 years? Regards, Beno=EEt Evans Qu=E9bec, Canada= Subject: Re: Your message to the psn-l mailing list From: "K.-Benoit Evans" kevans@............ Date: Wed, 30 Jan 2008 22:45:06 -0500 One minute after receiving the following message, I received another =20 one saying my message had been bounced as spam. Can you get this =20 message to the list? Your spam filter is too strong. I have been =20 sending e-mail regularly for 20 years and this is the first message of =20= mine that has ever been bounced in this way. On 30 Jan 2008, at 21:52, postmaster@.............. wrote: > The attached message has been sent to the psn-l mail list. > > From: "K.-Benoit Evans" > Date: 30 January 2008 21:52:22 EST > To: PSN-L@.............. > Subject: Comparison of available seismometers > Reply-To: psn-l@.............. > > > I am interested in acquiring a simple seismometer package for amateur =20= > use that is sensitive enough to detect teleseismic events. I would =20 > like to acquire a ready-to-use instrument rather than build something =20= > from scratch or from a kit. My main question is which seismometer to =20= > buy. I have come across the following instruments on the Web: > > AS-1 Amateur Seismologist (Jeff Batten) $550 ??? > http://www.amateurseismologist.com > > Vertical School Seismometer Ward=92s Natural Science $500 > http://www.wardsci.com/=20 > Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602 > > EQ-1 Next Generation Science $600 > http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1 > > Volksmeter II RLL Instruments (Zoltech) $995 single channel, =20 > $1495 dual channel > (patented Symmetric Differential Capacitor (SDC) array sensor) > http://www.rllinstruments.com > > In spite of the price difference, the Volksmeter seems interesting. As = =20 > far as I an tell, it is based on recent technology that is different =20= > form the other three, which seem to be of the traditional Lehman type. > > Does anyone have any opinions or advice to give a rank beginner who =20= > has not been in a science classroom or lab in over 40 years? > > > Regards, > > Beno=EEt Evans > Qu=E9bec, Canada > > Regards, Beno=EEt Evans One minute after receiving the following message, I received another one saying my message had been bounced as spam. Can you get this message to the list? Your spam filter is too strong. I have been sending e-mail regularly for 20 years and this is the first message of mine that has ever been bounced in this way. On 30 Jan 2008, at 21:52, postmaster@.............. wrote: The attached message has been sent to the psn-l mail list. = Helvetica0000,0000,0000 From: = Helvetica"K.-Benoit= Evans" < 0000,0000,0000Date: 30 January 2008 21:52:22 EST 0000,0000,0000To: PSN-L@.............. 0000,0000,0000Subject: Comparison of available seismometers 0000,0000,0000Reply-To: psn-l@.............. I am interested in acquiring a simple seismometer package for amateur use that is sensitive enough to detect teleseismic events. I would like to acquire a ready-to-use instrument rather than build something from scratch or from a kit. My main question is which seismometer to buy. I have come across the following instruments on the Web: AS-1 Amateur Seismologist (Jeff Batten) $550 ??? http://www.amateurseismologist.com Vertical School Seismometer Ward=92s Natural Science $500 http://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602 EQ-1 Next Generation Science $600 http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1 Volksmeter II RLL Instruments (Zoltech) $995 single channel, $1495 dual channel (patented Symmetric Differential Capacitor (SDC) array sensor) http://www.rllinstruments.com In spite of the price difference, the Volksmeter seems interesting. As far as I an tell, it is based on recent technology that is different form the other three, which seem to be of the traditional Lehman type. Does anyone have any opinions or advice to give a rank beginner who has not been in a science classroom or lab in over 40 years? Regards, Beno=EEt Evans Qu=E9bec, Canada Regards, Beno=EEt Evans Subject: Re: Comparison of available seismometers From: "Les LaZar" llazar@.................. Date: Wed, 30 Jan 2008 23:01:28 -0800 Hello Benoit, I am the project engineer for the VolksMeter. I would be happy to = answer any questions you have on the VolksMeter. Regards, Les LaZar RLL Instruments / a division of Zoltech Corporation ----- Original Message -----=20 From: K.-Benoit Evans=20 To: PSN-L@................. Sent: Wednesday, January 30, 2008 6:52 PM Subject: Comparison of available seismometers I am interested in acquiring a simple seismometer package for amateur = use that is sensitive enough to detect teleseismic events. I would like = to acquire a ready-to-use instrument rather than build something from = scratch or from a kit. My main question is which seismometer to buy. I = have come across the following instruments on the Web: AS-1 Amateur Seismologist (Jeff Batten) $550 ??? http://www.amateurseismologist.com Vertical School Seismometer Ward=92s Natural Science $500 = http://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602 EQ-1 Next Generation Science $600 http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1 Volksmeter II RLL Instruments (Zoltech) $995 single channel, $1495 = dual channel (patented Symmetric Differential Capacitor (SDC) array sensor) http://www.rllinstruments.com In spite of the price difference, the Volksmeter seems interesting. As = far as I an tell, it is based on recent technology that is different = form the other three, which seem to be of the traditional Lehman type. Does anyone have any opinions or advice to give a rank beginner who = has not been in a science classroom or lab in over 40 years? Regards, Beno=EEt Evans Qu=E9bec, Canada
Hello Benoit,
 
I am the project engineer for the = VolksMeter. =20 I would be happy to answer any questions you have on the=20 VolksMeter.
 
Regards,
 
Les LaZar
RLL Instruments / a division of Zoltech = Corporation
----- Original Message -----
From:=20 K.-Benoit=20 Evans
Sent: Wednesday, January 30, = 2008 6:52=20 PM
Subject: Comparison of = available=20 seismometers

I am interested in acquiring a simple seismometer = package for=20 amateur use that is sensitive enough to detect teleseismic events. I = would=20 like to acquire a ready-to-use instrument rather than build something = from=20 scratch or from a kit. My main question is which seismometer to buy. I = have=20 come across the following instruments on the Web:

AS-1 Amateur=20 Seismologist (Jeff Batten) $550=20 ???
http://www.amateurseismologist.com

Vertical School = Seismometer=20 Ward=92s Natural Science=20 = $500
http://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG= 0018602

EQ-1=20 Next Generation Science=20 = $600
http://www.nexgensci.com/store/pc/viewPrd.asp?idproduct=3D1
Volksmeter=20 II RLL Instruments (Zoltech) $995 single channel, $1495 dual=20 channel
(patented Symmetric Differential Capacitor (SDC) array=20 sensor)
http://www.rllinstruments.com

In spite of the price=20 difference, the Volksmeter seems interesting. As far as I an tell, it = is based=20 on recent technology that is different form the other three, which = seem to be=20 of the traditional Lehman type.

Does anyone have any opinions = or advice=20 to give a rank beginner who has not been in a science classroom or lab = in over=20 40 years?


Regards,

Beno=EEt Evans
Qu=E9bec, = Canada Subject: Re: Comparison of available seismometers From: Brett Nordgren Brett3mr@............. Date: Thu, 31 Jan 2008 11:06:00 -0500 Les, Yes, I do have one question. I may just have missed it, but it wasn't clear to me from the literature, exactly what the frequency response of the VolksMeter was. Is it flat to velocity between two frequencies and what are its sensitivity and corner frequencies? Also how fast does the velocity response fall as you approach zero? If it's easier to express these in terms of displacement or acceleration response, that's fine, too. Poles and zeros would be OK also. Thanks for your help, Brett At 11:01 PM 1/30/2008 -0800, you wrote: >Hello Benoit, > >I am the project engineer for the VolksMeter. I would be happy to answer >any questions you have on the VolksMeter. > >Regards, > >Les LaZar You can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Comparison of available seismometers From: "Les LaZar" llazar@.................. Date: Thu, 31 Jan 2008 13:40:28 -0800 Hi Brett, I believe that the VolksMeter User's Manual, Appendix A - Theory Of Operation, addresses the frequency response issue. The User's Manual is available on-line at our website, www.rllinstruments.com Section 7 (which starts on page 7 of the appendix document) is relevant to your question: http://www.rllinstruments.com/PDF_Files/VM%20II%20UM%20-%20App%201.pdf In short, the frequency response is flat from DC to the natural frequency of the pendulum (~0.9 sec) and then falls off exponentially (linearly on a log scale) at higher frequencies. The practical high frequency limit is 40Hz, which is set by the maximum sampling rate of 80 samples per second (of the electronics). Further, there is a drop off in usable sensor resolution at higher sample rates, so 16 bits is the highest resolution that is usable at 80 sps due to sensor/electronics noise issues. Resolution of 20-24 bits is practical at sample rates in the 20 to 10 sps range (10Hz - 5Hz maximum frequency). For lower frequencies, digital filtering (signal averaging) that is available in the software package can reduce noise still further. The VolksMeter sensor responds to acceleration and/or tilt. Velocity information is derived from the raw data through signal processing (integration in this case) which is part of the included WinSDR/WinQuake software package. I hope this answers your questions. If not, please let me know. Regards, Les LaZar RLL Instruments / a division of Zoltech Corporation ----- Original Message ----- From: "Brett Nordgren" To: Sent: Thursday, January 31, 2008 8:06 AM Subject: Re: Comparison of available seismometers > Les, > > Yes, I do have one question. I may just have missed it, but it wasn't > clear to me from the literature, exactly what the frequency response of > the VolksMeter was. Is it flat to velocity between two frequencies and > what are its sensitivity and corner frequencies? Also how fast does the > velocity response fall as you approach zero? > > If it's easier to express these in terms of displacement or acceleration > response, that's fine, too. Poles and zeros would be OK also. > > Thanks for your help, > > Brett > > At 11:01 PM 1/30/2008 -0800, you wrote: >>Hello Benoit, >> >>I am the project engineer for the VolksMeter. I would be happy to answer >>any questions you have on the VolksMeter. >> >>Regards, >> >>Les LaZar > > > You can always use my mail form at: http://bnordgren.org/contactB.html > using your Web browser. > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Comparison of available seismometers From: Brett Nordgren Brett3mr@............. Date: Thu, 31 Jan 2008 18:44:21 -0500 Les, Many thanks. I hadn't looked at the manual, only the spec. page. It sounds like that should have what I'm looking for. Brett At 01:40 PM 1/31/2008 -0800, you wrote: >Hi Brett, > >I believe that the VolksMeter User's Manual, Appendix A - Theory Of >Operation, addresses the frequency response issue. The User's Manual is >available on-line at our website, www.rllinstruments.com Section 7 (which >starts on page 7 of the appendix document) is relevant to your question: >http://www.rllinstruments.com/PDF_Files/VM%20II%20UM%20-%20App%201.pdf > >I hope this answers your questions. If not, please let me know. > >Regards, > >Les LaZar >RLL Instruments / a division of Zoltech Corporation __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Comparison of available seismometers From: "Connie and Jim Lehman" lehmancj@........... Date: Fri, 1 Feb 2008 09:11:38 -0500 Brett--It is always encouraging to see someone gaining an interest in amateur seismology. My suggestion is TO BUILD something for your first system--(there is a half dozen designs out there) and later on you can move to a "black box" that does the work for you. Any seismic system is an electro/mechanical device that you can tune into--understand its workings & improve performance as you go along. There is a satisfaction in a working system where you are part of the nuts & bolts. Best wishes, Jim ----- Original Message ----- From: "Brett Nordgren" To: Sent: Thursday, January 31, 2008 6:44 PM Subject: Re: Comparison of available seismometers > Les, > > Many thanks. I hadn't looked at the manual, only the spec. page. It > sounds like that should have what I'm looking for. > > Brett > > At 01:40 PM 1/31/2008 -0800, you wrote: > >Hi Brett, > > > >I believe that the VolksMeter User's Manual, Appendix A - Theory Of > >Operation, addresses the frequency response issue. The User's Manual is > >available on-line at our website, www.rllinstruments.com Section 7 (which > >starts on page 7 of the appendix document) is relevant to your question: > >http://www.rllinstruments.com/PDF_Files/VM%20II%20UM%20-%20App%201.pdf > > > > > >I hope this answers your questions. If not, please let me know. > > > >Regards, > > > >Les LaZar > >RLL Instruments / a division of Zoltech Corporation > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Design or build? (was Comparison of available seismometers) From: Brett Nordgren Brett3mr@............. Date: Sat, 02 Feb 2008 10:06:09 -0500 Jim, Your suggestion is greatly appreciated. It is perhaps a whole lot more appropriate than you might first have thought, and I hope that I may be forgiven if I use List bandwidth for some random babbling. I have struggled for years deciding whether I wanted to spend my available time working on designing and analyzing (I had done my first primitive feedback seismo. design back in the 60's) or whether I wanted to really build something and become a 'wiggle watcher'. Before my neighbor, Bob Barns, died last spring, I satisfied the latter need by working with his setup. Now I'm facing the question of whether to start diverting time from analysis and design (always more to be done) to construction. With the enormous amount of data available online, watching wiggles does sometimes seem like reinventing the wheel, however, creating and running a station would be an excellent experience for our grandkids who live nearby, and that's now tipping my thinking in favor of taking your suggestion to start building something. As a retired instrument designer, I tend to fall into the old pattern. You spent as much time as was available designing and analyzing on paper. Then you turned your design over to someone to build a prototype. When the protype was done, you tested it, and if your design and analysis had been done well it would work pretty much as expected and could promptly be sent on to Production. Though it's many years since I was doing that, I still find that the creating of good designs is very satisfying to me. And then, I enjoy trying to put the results of my work into a form that can be shared, hopefully to help out folks who are wanting to build and understand their own feedback instruments. Guess I'd better get to work before the grandkids grow up and are out of here. Best regards, Brett At 09:11 AM 2/1/2008 -0500, you wrote: >Brett--It is always encouraging to see someone gaining an interest in >amateur seismology. My suggestion is TO BUILD something for your first >system--(there is a half dozen designs out there) and later on you can move >to a "black box" that does the work for you. Any seismic system is an >electro/mechanical device that you can tune into--understand its workings & >improve performance as you go along. There is a satisfaction in a working >system where you are part of the nuts & bolts. > Best wishes, Jim __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Comparison of available seismometers From: Brett Nordgren Brett3mr@............. Date: Sat, 02 Feb 2008 12:23:01 -0500 Benoit, I think I may have replied to a message from Jim Lehman that he had meant=20 for you. However, I can offer a couple of comments on your question. The first=20 three designs are verticals, more like the LaCoste design than the=20 Lehman. It's not clear what their sensitivity and frequency responses are,= =20 but they look like they would be flat to velocity over a moderate frequency= =20 range. How wide a range would depend on how much damping they are getting= =20 with their oil dampers. The Volksmeter is a horizontal device, narrow-band to velocity centered at= =20 1Hz and with an acceleration response flat from DC to 1Hz. Whether a vertical or horizontal device is 'better' can be debated, but=20 they each have their own advantages and disadvantages. Brett At 09:52 PM 1/30/2008 -0500, you wrote: >I am interested in acquiring a simple seismometer package for amateur use= =20 >that is sensitive enough to detect teleseismic events. I would like to=20 >acquire a ready-to-use instrument rather than build something from scratch= =20 >or from a kit. My main question is which seismometer to buy. I have come=20 >across the following instruments on the Web: > >AS-1 Amateur Seismologist (Jeff Batten) $550 ??? >http://www.amateurseismologist.com > >Vertical School Seismometer Ward=92s Natural Science $500 >h= ttp://www.wardsci.com/Product.asp_Q_cmss_E_seismometer_A_pn_E_IG0018602=20 > > >EQ-1 Next Generation Science $600 >http://www.nex= gensci.com/store/pc/viewPrd.asp?idproduct=3D1=20 > > >Volksmeter II RLL Instruments (Zoltech) $995 single channel, $1495=20 >dual channel >(patented Symmetric Differential Capacitor (SDC) array sensor) >http://www.rllinstruments.com > >In spite of the price difference, the Volksmeter seems interesting. As far= =20 >as I an tell, it is based on recent technology that is different form the= =20 >other three, which seem to be of the traditional Lehman type. > >Does anyone have any opinions or advice to give a rank beginner who has=20 >not been in a science classroom or lab in over 40 years? > > >Regards, > >Beno=EEt Evans >Qu=E9bec, Canada > > > > > My e-mail address above should be working, but if not >you can always use my mail form at: http://bnordgren.org/contactB.html > using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Digest from 02/02/2008 00:00:01 From: Randall Peters PETERS_RD@.......... Date: Sun, 03 Feb 2008 10:49:46 -0500 Brett, When you refer to the VolksMeter's response being flat from D.C. to 1 Hz, you are correct; however, to say that the velocity response is narrow-band is not. The difference between acceleration response (position sensor such as the VolksMeter0 and velocity response (most seismometers) is summed up by the upper right pair of graphs shown on John Lahr's page at http://jclahr.com/science/psn/response/plots.jpg These illustrate (for perfect electronics if it existed) the difference between an 'acceleration' detector (VolksMeter) and a 'jerk' detector (conventional instruments that use a Faraday-law--magnet coil- detector) in terms of their response to earth's motion. The only thing that causes any seismometer to respond is acceleration (or tilt as a special case therof), and so the conventional instrument is measuring the derivative of the acceleration, which engineers call the 'jerk'. For 'perfect' electronics, the acceleration response is superior for sensing lower frequencies of earth motion, whereas the jerk response is superior for higer frequencies. The limit of detectability, within the differing constraints of their architecture, is the noise introduced by the electronics. My statement about 'superiority' assumes equally effective electronics for the cases. Randall Subject: Re: Digest from 02/02/2008 00:00:01 From: Brett Nordgren Brett3mr@............. Date: Sun, 03 Feb 2008 13:20:48 -0500 Randall, I think I might have done better if I had made it clearer that the instrument response is distinct from the transducer response. I completely agree that to create the highest performance instrument you have to use a good displacement transducer, as the VolksMeter does. At 10:49 AM 2/3/2008 -0500, you wrote: >Brett, > When you refer to the VolksMeter's response being flat from D.C. to > 1 Hz, you >are correct; however, to say that the velocity response is narrow-band is not. >The difference between acceleration response (position sensor such as the >VolksMeter0 and velocity response (most seismometers) is summed up by the >upper >right pair of graphs shown on John Lahr's page at >http://jclahr.com/science/psn/response/plots.jpg However, the overall instrument response to sinusoidal ground motion described by displacement, shown as the blue line in figure P2 of the User's Manual, rises from DC at 40db per decade, and levels out at unity at about 0.9Hz. That implies that the instrument response, if the ground motion were instead described by its velocity, would rise from DC at 20db per decade to a maximum at 0.9Hz at which point it begins to fall at 20db per decade. I had understood that in commercial instruments, that was usually described as a narrow-band velocity response. I would contend that the same instrument can be characterized by stating either its response to displacement (flat above 0.9Hz) or to velocity (peaking at 0.9Hz), or for that matter to ground acceleration (flat below 0.9Hz). Different curves, same device. > These illustrate (for perfect electronics if it existed) the difference >between an 'acceleration' detector (VolksMeter) and a 'jerk' detector >(conventional instruments that use a Faraday-law--magnet coil- detector) >in terms >of their response to earth's motion. The only thing that causes any >seismometer >to respond is acceleration (or tilt as a special case therof), and so the >conventional instrument is measuring the derivative of the acceleration, which >engineers call the 'jerk'. Yes. I was first introduced to the technical use of the term when I was 15 by my engineer father. It was, as I recall, in connection with my early attempts at driving. > For 'perfect' electronics, the acceleration response is superior for > sensing >lower frequencies of earth motion, whereas the jerk response is superior >for higer >frequencies. The limit of detectability, within the differing constraints of >their architecture, is the noise introduced by the electronics. My statement >about 'superiority' assumes equally effective electronics for the cases. > Randall Brett My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Volksmeter (was Digest...) From: Brett Nordgren Brett3mr@............. Date: Mon, 04 Feb 2008 14:18:41 -0500 Randall, In order to clear my thinking, I put together an Excel spreadsheet which describes an experiment with the VolksMeter in which it is placed on a horizontal shaker table, oscillating with constant amplitude of 0.01mm, swept over a frequency range of 0.002Hz to 10Hz. The pendulum parameters and sensitivity numbers were obtained from the VM User Manual and its response was plotted in several ways. The zipped file is at http://bnordgren.org/seismo/VolksMeter.zip (Note that upper/lower case counts on my server). This unzips to 'VolksMeter.xls' which has a worksheet with the calculations and three charts to display the results. Please let me know if/where I may have gotten my sums wrong, Many thanks, Brett Nordgren At 10:49 AM 2/3/2008 -0500, you wrote: >Brett, > When you refer to the VolksMeter's response being flat from D.C. to > 1 Hz, you >are correct; however, to say that the velocity response is narrow-band is not. >The difference between acceleration response (position sensor such as the >VolksMeter0 and velocity response (most seismometers) is summed up by the >upper >right pair of graphs shown on John Lahr's page at >http://jclahr.com/science/psn/response/plots.jpg > These illustrate (for perfect electronics if it existed) the difference >between an 'acceleration' detector (VolksMeter) and a 'jerk' detector >(conventional instruments that use a Faraday-law--magnet coil- detector) >in terms >of their response to earth's motion. The only thing that causes any >seismometer >to respond is acceleration (or tilt as a special case therof), and so the >conventional instrument is measuring the derivative of the acceleration, which >engineers call the 'jerk'. > For 'perfect' electronics, the acceleration response is superior for > sensing >lower frequencies of earth motion, whereas the jerk response is superior >for higer >frequencies. The limit of detectability, within the differing constraints of >their architecture, is the noise introduced by the electronics. My statement >about 'superiority' assumes equally effective electronics for the cases. > Randall My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: transfer functions From: Randall Peters PETERS_RD@.......... Date: Mon, 04 Feb 2008 17:37:12 -0500 Brett, I see nothing wrong with the Excel sheets that you've generated--at least in terms of the relative shapes of the transfer functions expressed in terms of either (i) ground acceleration, or (ii) velocity, or (iii) displacement (the system state variables). It is critically important to understand, however, that these three transfer curves are not all equally important. Acceleration is what results in velocity, which in turn results in displacement. The only way to treat the dynamics is by means of Newton's 2nd law, which is in terms of acceleration. Moreover, the only state variable responsible for moving the inertial mass relative to the case of a seismometer is ACCELERATION. Even in the case of tilt, the response is due to acceleration. In this special case of tilt, it is the case moving relative to the essentially stationary pendulum that gives rise to a response. And the amount of response is determined by the component of the earth's field (little g = 9.8 m/s^2) that is perpendicular to the pendulum. Where the tilt is different from the usual acceleration response is that it has no frequency response associated with it. Now about your analysis approach (which is conventional): it is a steady state analysis, assuming harmonic excitation. The only excitation mechanism is (as I've tried to emphatically point out) -- ground acceleration. The velocity is obtained from this acceleration by means of integration, and in turn the displacement is obtained by integrating the velocity. ONLY if the harmonic excitation persists for a long enough interval of time to be reasonably monochromatic--is it possible to obtain an approximation for the aforementioned integrals by simply dividing a given expression by the angular frequency. I can give you a good example of where this does not work. With the VolksMeter I routinely see near-discontinuous displacements (due to tilt). Sometimes they are a step and sometimes they are a pulse (bistability). They generally happen at levels close to that of the noise (whether ground or electronic). If one takes the derivative of such a signal (what one would see with the conventional detectors), they are almost never observable--even though they are clearly visible in the raw data. This is for two reasons: (i) the derivative only yields two spikes that look much like noise, and (ii) the derivative is fundamentally a 'noise-producing' operation. What has confused so many people derives from the nature of the detectors employed. For example, the Faraday law detector (magnet/coil) that has been used for many years, does not really measure the velocity of the ground. The output that it generates is proportional to the velocity of the inertial mass relative to the case of the seismometer. Since the mass movement is proportional to the acceleration of the earth, the common detector is thus really responding to the derivative of ground acceleration (the jerk). If one wants to really see an output that is a proper representation of ground velocity, then take a look at the VolksMeter's integrated signal. The world is hung up on steady state, linear system analysis--not recognizing that it has limitations. One can't simply operate with a convenient but aritificial transfer function (such as 'velocity' or 'displacment') and get the right answer all the time by means of the simple transformations involving the angular frequency. The proper treatment iinvolves actually doing the integrals! Even the pole/zero description that is routinely mentioned is one that at its foundation embraces the transient consequences of changes that are too short-lived for the steady state assumptions to be valid. Just because the instrument is near-critically damped does not mean that there are no transient features! Randall Subject: more on transfer functions From: Randall Peters PETERS_RD@.......... Date: Wed, 06 Feb 2008 16:11:33 -0500 Brett, Probably the most important thing about the differences among the transfer functions for the different state variables is their differing functional dependence of SNR. The multiplication by angular frequency, when working with the derivative ('velocity sensor')--causes the power spectral density in that case to approach the electronics noise level more rapidly at low frequencies than is true for the position sensor case. In other words the signal goes below noise more rapidly for the velocity sensor than for the position sensor, as the frequency decreases. A sensor that is 'flat to velocity' is not immune to this limitation; since acceleration, being fundamental (and not velocity) is what regulates the frequency dependence of the signal to noise ratio. A way to understand the importance of the electronic noise in this matter is as follows. Nobody should question the fact that the only thing that allows any sensor to function is the transfer of power to it. In the case of a seismometer, the specific power (power divided by the magnitude of the inertial mass) is given by the product of velocity and acceleration. Students of physics should remember the expression for mechanical power as the dot product of force and velocity. In terms of acceleration, the specific power is given by the square of the peak acceleration divided by the angular frequency--having units of meters squared per second cubed. When the spectral density of the power is graphed Log-Log (or dB-Log), the logarithmic linear 'compression' in frequency of the FFT values (which are equispaced for a linear scale) causes the reciprocal omega term to disappear. In other words, for a position sensor, the mechanical specific power, in a spectral density sense, is constant for frequencies below the corner frequency. Those familiar with Jon Berger's well known paper on earth noise will remember that the ordinate of his power spectral density (PSD) graphs is specified in terms of meters squared per second cubed per one-seventh decade (expressed in dB). (Note: his graphs do not specifically mention the bin-width of one-seventh decade; this must be understood from written descriptions in the paper.) His units are consistent with what I have just indicated, but the common (erroneous) meters squared per second to the fourth per Hz are not! In fact, these common units cannot be a proper power spectral density statement, because they are dimensionally unacceptable. Whereas the PSD is flat below the corner when calculated with data from a position sensor, the same is not true in the case of a velocity sensor. In the velocity case, the power is given by omega times the square of the peak value of the velocity. The PSD is in turn (because of the compression mentioned in the usual Log-Log representation) given by omega squared times the square of the peak velocity. Thus, as omega (two pi times the frequency) decreases below the corner value, the PSD expression decreases with the square of the frequency--falling off 20 dB per decade. Just from the electronics noise alone, we see that with the velocity sensor--as frequency decreases--a point is reached where the mechanical PSD falls below the power spectral density of electronics noise. Thereafter, unless some noise reduction scheme is employed the signal responsible for mechanical motion below those frequencies--cannot be seen with the velocity sensor. They can, however, still be seen with the position sensor. Randall Subject: Re: more on transfer functions From: Brett Nordgren Brett3mr@............. Date: Thu, 07 Feb 2008 21:31:41 -0500 Randall, Thanks for the excellent discussion. You answered a number of questions that had been bugging me regarding PSD. And I would also highly recomment your VolksMeter manual http://rllinstruments.com/UM_index.htm Appendix I, for a more extensive discussion of noise. Just for the record, I have always believed that you could get better performance by using a position transducer as the detector. The main justification for velocity sensing is that it is likely to be quite a bit easier to implement, and if your goal is to successfully view earthquakes, a velocity sensor can do a fine job. However when you start wanting to push the envelope in terms of sensitivity, frequency span, etc. I agree with your point that you are going to have to start seriously considering position sensing. There is a related issue, concerning the use of feedback to shape the instrument response. If the signal to noise you are describing is ground motion signal to instrument noise, one of the precepts of feedback theory is that feedback can never improve or degrade signal to noise ratio. Any time you reduce a signal in a particular frequency band by means of feedback, you also reduce the instrument noise in that band in the identical proportion. Similarly you can not improve signal to noise by using feedback. Only in the case where the signal and noise energy are predominately in different frequency bands, can you can make use of feedback to, in some degree, reject one and enhance the other. (which can sometimes be quite useful) I realize that doesn't particularly relate to your point, but it's useful to bear in mind when considering feedback designs. Brett At 04:11 PM 2/6/2008 -0500, you wrote: >Brett, > Probably the most important thing about the differences among the > transfer >functions for the different state variables is their differing >functional dependence of SNR. The multiplication by angular frequency, when >working >with the derivative ('velocity sensor')--causes >the power spectral density in that case to approach the electronics noise >level >more >rapidly at low frequencies than is true for the >position sensor case. In other words the signal goes below noise more >rapidly for >the >velocity sensor than for the position sensor, as >the frequency decreases. A sensor that is 'flat to velocity' is not immune to >this >limitation; since acceleration, being fundamental (and not velocity) is what >regulates >the frequency dependence of the signal to noise ratio. > A way to understand the importance of the electronic noise in this > matter is >as >follows. Nobody should question the fact >that the only thing that allows any sensor to function is the transfer of >power to > >it. In the case of a seismometer, the specific power >(power divided by the magnitude of the inertial mass) is given by the >product of >velocity and acceleration. Students of physics should >remember the expression for mechanical power as the dot product of force and >velocity. In terms of acceleration, the specific power is given by the >square of >the >peak acceleration divided by the angular frequency--having units of meters >squared >per >second cubed. When the spectral density of the power is graphed Log-Log (or >dB-Log), >the logarithmic linear 'compression' in frequency of the FFT values (which are >equispaced for a linear scale) causes the reciprocal omega term to >disappear. In >other words, for a position sensor, the mechanical specific power, in a >spectral >density sense, is constant for frequencies below the corner frequency. Those >familiar >with Jon Berger's well known paper on earth noise will remember that the >ordinate >of >his power spectral density (PSD) graphs is specified in terms of meters >squared >per >second cubed per one-seventh decade (expressed in dB). (Note: his graphs >do not >specifically mention the bin-width of one-seventh decade; this must be >understood >from >written descriptions in the paper.) His units are consistent with what I have >just >indicated, but the common (erroneous) meters squared per second to the >fourth per >Hz >are not! In fact, these common units cannot be a proper power spectral >density >statement, because they are dimensionally unacceptable. > Whereas the PSD is flat below the corner when calculated with data > from a >position sensor, the same is not true in the case of a velocity >sensor. In the >velocity case, the power is given by omega times the square of the peak >value of >the >velocity. The PSD is in turn (because of the compression mentioned in the >usual >Log-Log representation) given by omega squared times the square of the peak >velocity. >Thus, as omega (two pi times the frequency) decreases below the corner >value, the >PSD >expression decreases with the square of the frequency--falling off 20 dB per >decade. > Just from the electronics noise alone, we see that with the velocity >sensor--as >frequency decreases--a point is reached where the mechanical PSD falls >below the >power >spectral density of electronics noise. Thereafter, unless some noise >reduction >scheme >is employed the signal responsible for mechanical motion below those >frequencies--cannot be seen with the velocity sensor. They can, however, >still be > >seen with the position sensor. > >Randall > > > you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Digest from 02/07/2008 00:00:25 From: Randall Peters PETERS_RD@.......... Date: Fri, 08 Feb 2008 08:55:25 -0500 Thanks, Brett. Clearly you're both willing and able to look at the physics facts involving seismometers. What's appalling to me is how much false information exists on the matter. Considering the widespread deployment and importance of seismometers, one would naturally believe that the performance issues would have been properly treated by theory many years ago. Fact is, they have not been, insofar as I can tell. The power spectral density is the means to understand not just performance, but also what's happening in the earth--whether earthquakes or whatever. (Actually, the cumulative spectral power, obtained from the PSD--permits us to more easily observe the evolutionary changes.) Other than myself, equipment manufacturers seem to be the only ones who ever look at the PSD; and they limit their plots to benchmarking (to tout their wares)--and what gets graphed is dimensionally incorrect, even though they've got the right numbers on their plots (by accident, it appears). On this matter I have been trying for some time now to bring long overdue corrections to the professional seismology community. They remain `quiet' and seemingly unwilling to debate the issues. I've tried to follow the path of diplomacy, but it seems to have failed. Consequently, my next choice has been to 'speak to the issues plainly'; which is not without controversy. In the famous words of the astronomer Fritz Zwicki, there is a resulting tendency for antagonists to view one another as 'spherical bastards' ".... bastards, when looked at from any side". On 'everything2.com' we find the comment: Zwicky was well-known for his colorful metaphors, but what makes people the angriest is that, regarding the existence of dark matter, he seems to have been right. We in physics (not just astronomy) strive diligently to discover 'what is right'; and I believe that what I've been telling people is correct. It is alien to my profession to try and 'kill with silence'. Issues get debated--sometimes with the appearance that a 'knock-down drag out fight' is about to happen. But after the 'truth' has been hammered out, such combatants have not in my experience become great enemies; they are not given to either (i) gloating over success, nor (ii) simmering in a 'pitty-party' for having been wrong. I must admit that I don't understand how the geoscience profession appears from my perspective to be so different. About your statement concerning feedback. It's been the better part of a decade that I've been trying to tell folks that feedback (of the force balance type) is not the 'cure-all' that everybody wants to believe. Its most important deficiencies derive from the fact that mother nature is never linear. Thank God that many of our linear approximations are at times quite adequate. But in the case of force-balance at low frequencies, my position has been (and remains) the following. Internal friction of the seismometer structure 'wars against' the very premise around which the instruments are designed. The system is characterized, not by a harmonic potential (basis for linear theory) but rather by 'fine structure' in the potential well. These exist at the mesoscale--place where I've been doing research for nearly two decades. This fine structure is a form of nonlinearity that is much more important to seismometer performance (at low frequencies and low levels) than the nonlinearity that seismometer designers talk about; i.e., at large amplitude. Nature has two forms of anharmonicity--`elastic' that is important at large levels with springs that don't `work right', and `damping' (due to deffect structures) at low levels. If my article dealing with these forms of anharmonicity, published in the 10th Ed. of the McGraw Hill Encyclopedia of Science and Technology should be a valid indicator; then I'm the only person to have researched the 'damping' type that regulates seismometer performance. As an engineer you will appreciate something that is needed for the improvement of force balance instruments. Friction-limited systems have to be dithered to overcome the adversities of the friction. In the modern terminology of physics, we describe this in terms of 'stochastic resonance'. Fact is, nobody understands friction from 'first principles'. All we know derives from empericism. The level of our universal ignorance needs to decrease, if we are to make really small seismometers work well (which they do not). I maintain that the SNR limitations of MEMS-type instruments derives from the mesoanelastic complexity (internal friction) that is not understood. Among other things, I believe this complexity is responsible for a totally worthless calculation that is routinely used by professional seismologists; i.e., calculate the Brownian motion of the seismic mass as though the mechanical noise could be assumed to derive from a system with only two square terms iin the Hamiltonian (equipartition theorem, associated wtih fluctuation-dissipation). Randall psn-l-digest-request@.............. wrote: > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 1 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Re: more on transfer functions > From: Brett Nordgren > Date: Thu, 07 Feb 2008 21:31:41 -0500 > > Randall, > > Thanks for the excellent discussion. You answered a number of questions > that had been bugging me regarding PSD. And I would also highly recomment > your VolksMeter manual http://rllinstruments.com/UM_index.htm Appendix > I, for a more extensive discussion of noise. > > Just for the record, I have always believed that you could get better > performance by using a position transducer as the detector. The main > justification for velocity sensing is that it is likely to be quite a bit > easier to implement, and if your goal is to successfully view earthquakes, > a velocity sensor can do a fine job. However when you start wanting to > push the envelope in terms of sensitivity, frequency span, etc. I agree > with your point that you are going to have to start seriously considering > position sensing. > > There is a related issue, concerning the use of feedback to shape the > instrument response. If the signal to noise you are describing is ground > motion signal to instrument noise, one of the precepts of feedback theory > is that feedback can never improve or degrade signal to noise ratio. Any > time you reduce a signal in a particular frequency band by means of > feedback, you also reduce the instrument noise in that band in the > identical proportion. Similarly you can not improve signal to noise by > using feedback. Only in the case where the signal and noise energy are > predominately in different frequency bands, can you can make use of > feedback to, in some degree, reject one and enhance the other. (which can > sometimes be quite useful) > > I realize that doesn't particularly relate to your point, but it's useful > to bear in mind when considering feedback designs. > > Brett > > At 04:11 PM 2/6/2008 -0500, you wrote: > >Brett, > > Probably the most important thing about the differences among the > > transfer > >functions for the different state variables is their differing > >functional dependence of SNR. The multiplication by angular frequency, when > >working > >with the derivative ('velocity sensor')--causes > >the power spectral density in that case to approach the electronics noise > >level > >more > >rapidly at low frequencies than is true for the > >position sensor case. In other words the signal goes below noise more > >rapidly for > >the > >velocity sensor than for the position sensor, as > >the frequency decreases. A sensor that is 'flat to velocity' is not immune to > >this > >limitation; since acceleration, being fundamental (and not velocity) is what > >regulates > >the frequency dependence of the signal to noise ratio. > > A way to understand the importance of the electronic noise in this > > matter is > >as > >follows. Nobody should question the fact > >that the only thing that allows any sensor to function is the transfer of > >power to > > > >it. In the case of a seismometer, the specific power > >(power divided by the magnitude of the inertial mass) is given by the > >product of > >velocity and acceleration. Students of physics should > >remember the expression for mechanical power as the dot product of force and > >velocity. In terms of acceleration, the specific power is given by the > >square of > >the > >peak acceleration divided by the angular frequency--having units of meters > >squared > >per > >second cubed. When the spectral density of the power is graphed Log-Log (or > >dB-Log), > >the logarithmic linear 'compression' in frequency of the FFT values (which are > >equispaced for a linear scale) causes the reciprocal omega term to > >disappear. In > >other words, for a position sensor, the mechanical specific power, in a > >spectral > >density sense, is constant for frequencies below the corner frequency. Those > >familiar > >with Jon Berger's well known paper on earth noise will remember that the > >ordinate > >of > >his power spectral density (PSD) graphs is specified in terms of meters > >squared > >per > >second cubed per one-seventh decade (expressed in dB). (Note: his graphs > >do not > >specifically mention the bin-width of one-seventh decade; this must be > >understood > >from > >written descriptions in the paper.) His units are consistent with what I have > >just > >indicated, but the common (erroneous) meters squared per second to the > >fourth per > >Hz > >are not! In fact, these common units cannot be a proper power spectral > >density > >statement, because they are dimensionally unacceptable. > > Whereas the PSD is flat below the corner when calculated with data > > from a > >position sensor, the same is not true in the case of a velocity > >sensor. In the > >velocity case, the power is given by omega times the square of the peak > >value of > >the > >velocity. The PSD is in turn (because of the compression mentioned in the > >usual > >Log-Log representation) given by omega squared times the square of the peak > >velocity. > >Thus, as omega (two pi times the frequency) decreases below the corner > >value, the > >PSD > >expression decreases with the square of the frequency--falling off 20 dB per > >decade. > > Just from the electronics noise alone, we see that with the velocity > >sensor--as > >frequency decreases--a point is reached where the mechanical PSD falls > >below the > >power > >spectral density of electronics noise. Thereafter, unless some noise > >reduction > >scheme > >is employed the signal responsible for mechanical motion below those > >frequencies--cannot be seen with the velocity sensor. They can, however, > >still be > > > >seen with the position sensor. > > > >Randall > > > > > > > > you can always use my mail form at: http://bnordgren.org/contactB.html > using your Web browser. > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-DIGEST-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. Subject: Re: Hekla volcano geophone planned From: ian ian@........... Date: Fri, 08 Feb 2008 14:23:47 +0000 Hi, today's mid-Atlantic quake saturated my high gain channel (+/-0.1V), so a lot of the data comes from the mid-gain channel (+/-1.0V) The trace is a bit noisy with the strong winds here causing the trees to bend and twist. Cheers Ian http://www.iasmith.com ChrisAtUpw@....... wrote: > In a message dated 06/01/2008, ian@........... writes: > > Looking back I can see that there are a few traces (not many) which > flipped between channel gains +/-0.1V and +/-1.0V. So the feature is > giving me more gain to look into the weaker signals without being > clobbered with saturation on the stronger traces - both the high > and low > pass filters apply a 20db gain to compensate for the attenuation > of the > filters. > > Hi Ian, > > I would expect that all your out of range signals will be due to > the surface waves? > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: More on transfer functions From: Brett Nordgren Brett3mr@............. Date: Fri, 08 Feb 2008 12:11:09 -0500 Randall, Since you and I both seem to think in terms of paragraphs and chapters rather than sentences, I'll take the liberty of only quoting the things that I am replying to, so that folks' in-boxes don't get overloaded. Hope that's OK. At 08:55 AM 2/8/2008 -0500, you wrote: >Thanks, Brett. > About your statement concerning feedback. It's been the better part of a >decade that I've been trying to tell folks that feedback (of the force balance >type) is not the 'cure-all' that everybody wants to believe. I have a paper in the works that is directed at some aspects of that issue, but I need to fix up a few errors, before I let it out. I believe that feedback can accomplish a lot (perhaps more than you do), but there are many things that it doesn't do, and that's one thing I was planning to illustrate. >Its most important >deficiencies derive from the fact that mother nature is never >linear. Thank God >that many of our linear approximations are at times quite adequate. But >in the >case of force-balance at low frequencies, my position has been (and >remains) the >following. Internal friction of the seismometer structure 'wars against' >the very >premise around which the instruments are designed. The system is >characterized, >not by a harmonic potential (basis for linear theory) but rather by 'fine >structure' in the potential well. In particular, would it be sufficient to treat these issues by defining the without-feedback device as if it had a damping coefficient which is nonlinear to velocity and perhaps even time-varying? i.e. can you write the equations in a quasi-linear form, simply identifying the terms which don't behave? Then you might be able to apply the usual linear feedback equations and hopefully (for me) demonstrate that the 'bad' terms become insignificant in the result. Or is there some better approach which can allow us to properly incorporate the effects which you describe into an analysis of the actual device characteristics we would obtain with feedback, for instruments of the size of interest to this group? I'm uncomfortable with taking the approach that because there exist some fairly small (I think) nonlinear effects, then no quantitative analysis can be valid at all. Although it's somewhat beyond my experience, I believe that feedback designers today routinely deal with highly nonlinear, time-varying, and stochastic system variables and still are able to obtain quite useful results. If they couldn't there would be a lot fewer airplanes out there and our cars wouldn't handle as well. Brett >These exist at the mesoscale--place where I've >been doing research for nearly two decades. This fine structure is a form of >nonlinearity that is much more important to seismometer performance (at low >frequencies and low levels) than the nonlinearity that seismometer >designers talk >about; i.e., at large amplitude. Nature has two forms of >anharmonicity--`elastic' >that is important at large levels with springs that don't `work right', and >`damping' (due to deffect structures) at low levels. If my article >dealing with >these forms of anharmonicity, published in the 10th Ed. of the McGraw Hill >Encyclopedia of Science and Technology should be a valid indicator; then >I'm the >only person to have researched the 'damping' type that regulates seismometer >performance. > Randall __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: fine structure nonlinearity vs dithering From: "Charles R. Patton" charles.r.patton@........ Date: Fri, 08 Feb 2008 11:50:54 -0800 Randall, One brief thought -- I''m familiar with dithering to solve frictional problems. So why not dither the force feedback at the A/D sample rate? The friction non-linearity would generate harmonics of the dither frequency, but these would also be rejected by the synchronous sampling of the A/D (they would show up as a DC offset -- i.e., it would appear as if the seismometer had a tilt that was not there in reality.) The question is, "Does the "fine structure nonlinearity" show up as random stiction/rachetting?" I.e., if one was to dither the force feedback, would the result be a lifting of the noise spectrum floor and result in overwhelming broadband noise? As an aside, Brett asked you to start a direct email of this discussion off the PSN list. I would hope this doesn't happen. I can't learn from a discussion I don't have contact with. :-) Regards, Charles R. Patton Randall Peters wrote: > As an engineer you will appreciate something that is needed for the improvement > of force balance instruments. Friction-limited systems have to be dithered to > overcome the adversities of the friction. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: dithering From: Randall Peters PETERS_RD@.......... Date: Fri, 08 Feb 2008 17:00:28 -0500 Charles, I had started to correspond with Brett as he indicated. Copied below is what I sent to him. About your question--I would need to give some serious thought to your idea before commenting. As engineers, you and Brett probably have more experience with some of these issues than myself. At any rate, as noted below--I don't think dithering of force-balance velocity sensing instruments is the way to go. What is needed at low frequencies is a whole different approach that I mention. Incidently, I have proven its viability (soft-feedback with a long time constant integrator) with my modified Sprengnether (LaCoste vertical). Randall Brett, I'm not saying that the feedback systems are not good. The STS-1 ( 'crown jewel') is a marvel of technology when it comes to earthquake detection most anywhere. What I am trying to communicate is the very thing you alluded to in one of your points--as frequency goes toward zero (where the community wants to operate for studying 'earth hum'), the ability to see important motions with a velocity sensor also goes toward zero. The sad part is that the seismo-pro's don't seem to undertand how this can be so. I am not at all opposed to feedback; what I'm opposed to is the insistence that the only way to do it is by forcing the system into a 'flat-to-velocity' response by means of force balance. For a long time now I've been advocating what is the obvious solution to the low frequency conundrum; i.e., a soft-force feedback (not force balance) that keeps the system from 'going to the rails' as the period is lengthened to give the kind of mechanical sensitivity that is needed for good teleseismic response using a displacement sensor. Without feedback in the case of a vertical seismometer, the sensitivity can never be great enough to yield outstanding performance--because of the effects of (i) buoyancy change due to atmospheric pressure variations, and (ii) spring constant change with temperature because of the thermal coefficient of the modulus. Without some type of compensation, the latter is a killer when one tries to obtain a natural period of 20 s. I didn't intend to suggest that force balance is not a great technological achievement (since clearly it is). It is not, however, the cure-all for every sensing regime that many folks seem to believe. About state of the art--one has to be careful what is meant by the term. There are those who believe we must somehow continue with force-balance improvement in order to study the long-period features of the earth. This is not the case, and I think that force balance has gone as far as it can toward low frequencies. The VolksMeter, at about one-tenth of the price of the force balance instruments will outperform the very best of them when it comes to measurements with periods longer than a few thousand seconds. On the other hand, as compared to their telesismic sensitivity, the VolksMeter is severely limited. Bottom line--there is not (and probably never will be) a single instrument that can cover the whole spectrum of interest to seismologists. Randall Subject: Re: fine structure nonlinearity vs dithering From: Brett Nordgren Brett3mr@............. Date: Fri, 08 Feb 2008 19:16:47 -0500 Charles, I'm very glad to hear that you're interested in following the discussion. My only concern had been that we were taking up bandwidth on stuff that might not have been of interest to all that many folks. I'll happilly continue posting my comments, though will also be happy to take this elsewhere if there's a sense that we should. In reply to your comments, I don't yet understand how the nonlinearity acts and how it should mathematically be treated. In a flat to velocity design, if it acts at all like regular linear spring-mass damping, it would be completely overwhelmed by the feedback. The amount of linear velocity damping of a spring-mass has virtually no effect on the response of a flat-to velocity feedback instrument. The way spring-mass damping acts in feedback designs with other responses (flat to acceleration?) might well be different. Regards, Brett FYI, below is what I'd written to Randall, He may want to post his reply. >Randall, > >I assume that you don't believe that feedback is worthless in the >implemtation of seismic sensors, but you obviously feel that there are >some deficiencies in the presently available feedback instruments. The >first question that comes to mind, is what effects would you expect to see >in the performance of those instruments which would relate to the effects >you describe? Can one come up with some experimental design to highlight >the areas in which they fall short? > >I'm reluctant at this point to throw the baby out with the bath water and >accept that linear analysis is of no value in feedback seismometer design, >but I am quite willing to accept that there are areas that have not been >adequately explored in both theory and experiment. For one thing, I need >to understand to what degree you feel the anomalous behavior you describe >extends to designs which aren't attempting to push the state of the >art. Just when would these effects begin to be felt as you tried to >extend performance? > >Regards, >Brett At 11:50 AM 2/8/2008 -0800, you wrote: >Randall, >One brief thought -- I''m familiar with dithering to solve frictional >problems. So why not dither the force feedback at the A/D sample rate? >The friction non-linearity would generate harmonics of the dither >frequency, but these would also be rejected by the synchronous sampling of >the A/D (they would show up as a DC offset -- i.e., it would appear as if >the seismometer had a tilt that was not there in reality.) The question >is, "Does the "fine structure nonlinearity" show up as random >stiction/rachetting?" I.e., if one was to dither the force feedback, >would the result be a lifting of the noise spectrum floor and result in >overwhelming broadband noise? > >As an aside, Brett asked you to start a direct email of this discussion >off the PSN list. I would hope this doesn't happen. I can't learn from a >discussion I don't have contact with. :-) >Regards, >Charles R. Patton __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: fine structure nonlinearity vs dithering From: ChrisAtUpw@....... Date: Fri, 8 Feb 2008 23:29:24 EST In a message dated 09/02/2008, Brett3mr@............. writes: Charles, I'm very glad to hear that you're interested in following the discussion. My only concern had been that we were taking up bandwidth on stuff that might not have been of interest to all that many folks. In reply to your comments, I don't yet understand how the nonlinearity acts and how it should mathematically be treated. Hi Brett, I would be quite happy to 'go public' if no one else objects? I'm uncomfortable with taking the approach that because there exist some fairly small (I think) nonlinear effects, then no quantitative analysis can be valid at all. Although it's somewhat beyond my experience, I believe that feedback designers today routinely deal with highly nonlinear, time-varying, and stochastic system variables and still are able to obtain quite useful results. If they couldn't there would be a lot fewer airplanes out there and our cars wouldn't handle as well. Read through the papers on Randall's Website? Your car analogy misses the point. We are concerned mostly with microscopic as opposed to macroscopic variations. The mechanical properties of springs have a 'fine structure' of discontinuous steps, a bit like ferro magnetic domains. This gives small 'step function' variations and limits the ultimate performance of seismometers, clocks, MEMS devices, etc. The macroscopic properties are also not quiite linear and are time dependant. Hooke's Law is only an approximation. How would you suggest incorporating step functions which are random in time, sense and amplitude into the calculations / properties of a feedback loop? The stochastic processes you mentioned? Regards, Chris Chapman
In a message dated 09/02/2008, Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>Charles,
I'm very glad to hear that you're interested in follo= wing=20 the discussion.  My only concern had been that we were taking up=20 bandwidth on stuff that might not have been of interest to all that many=20 folks. In reply to your comments, I don't yet understand how the=20 nonlinearity acts and how it should mathematically be=20 treated. 
Hi Brett,
 
    I would be quite happy to 'go public' if no one= =20 else objects?  
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I'm=20 uncomfortable with taking the approach that because there exist some fairl= y=20 small (I think) nonlinear effects, then no quantitative analysis can be va= lid=20 at all.  Although it's somewhat beyond
my experience, I believe t= hat=20 feedback designers today routinely deal with highly nonlinear, time-varyin= g,=20 and stochastic system variables and still are able to obtain quite useful=20 results.   If they couldn't there would be a lot fewer airplanes= out=20 there and our cars wouldn't handle as well.
    Read through the papers on Randall's Website?
    
    Your car analogy misses the point. We are conce= rned=20 mostly with microscopic as opposed to macroscopic variations.
 
    The mechanical properties of springs have a 'fi= ne=20 structure' of discontinuous steps, a bit like ferro magnetic domains. This g= ives=20 small 'step function' variations and limits the ultimate performance of=20 seismometers, clocks, MEMS devices, etc. The macroscopic propertie= s=20 are also not quiite linear and are time dependant. Hooke's Law is only an=20 approximation.
    
    How would you suggest incorporating step functi= ons=20 which are random in time, sense and amplitude into the calculations / proper= ties=20 of a feedback loop? The stochastic processes you mentioned?
 
    Regards,
 
    Chris Chapman
    
Subject: Re: fine structure nonlinearity vs dithering From: Charles R Patton charles.r.patton@........ Date: Fri, 08 Feb 2008 22:01:59 -0800 Hi Chris, My thought experiment goes something like this. If one dithers the instrument at the A/D sample frequency (let that be Fc) , then effectively one has created a mixer where the molecular slip/stiction ends up as sidebands of Fc. That spectrum would trend to zero at zero frequency, much as a sigma-delta A/D does. So if the resulting A/D spectrum is lo-pass filtered, the low frequency response spectrum is improved as the filter is cutting off the stiction generated noise sidebands surrounding Fc. I would surmise that Brett could model this as a switching (or sampling) mixer with co-injected random noise with a noise spectrum matching the known molecular stiction spectrum numbers Randall could supply from his observations. Brett, I would argue that you can’t have linear force feedback in the face of stiction-like elements. At the amplitude level of the stiction, the feedback will reflect the discontinuities. I.e., if the force feedback by definition is linear, then it has to linearly follow the discontinuities. The way we blur this is to generally ignore the small imperfections and assume macro properties where all the discontinuities blur into smooth motion (or set the frequency response bandwidth less than the frequency of the noise spectrum of the stiction.) But the discussion here is exactly whether we can legitimately do this if what we’re interested in is the very small movements of seismic activity that may be comparable in scale, or perhaps smaller than the molecular effects causing the slip/stick phenomenon. Which also brings me in round-robin fashion to the reason for dithering – it can supply that “blurring” (both in frequency and motion) function for the force-feedback to work with. Now for the sanity check, – comments, please. Regards, Charles R. Patton ChrisAtUpw@....... wrote: > In a message dated 09/02/2008, Brett3mr@............. writes: > > Charles, > I'm very glad to hear that you're interested in following the > discussion. My only concern had been that we were taking up > bandwidth on stuff that might not have been of interest to all that > many folks. In reply to your comments, I don't yet understand how > the nonlinearity acts and how it should mathematically be treated. > > Hi Brett, > > I would be quite happy to 'go public' if no one else objects? > > I'm uncomfortable with taking the approach that because there exist > some fairly small (I think) nonlinear effects, then no quantitative > analysis can be valid at all. Although it's somewhat beyond > my experience, I believe that feedback designers today routinely > deal with highly nonlinear, time-varying, and stochastic system > variables and still are able to obtain quite useful results. If > they couldn't there would be a lot fewer airplanes out there and our > cars wouldn't handle as well. > > Read through the papers on Randall's Website? > > Your car analogy misses the point. We are concerned mostly with > microscopic as opposed to macroscopic variations. > > The mechanical properties of springs have a 'fine structure' of > discontinuous steps, a bit like ferro magnetic domains. This gives small > 'step function' variations and limits the ultimate performance of > seismometers, clocks, MEMS devices, etc. The macroscopic properties are > also not quiite linear and are time dependant. Hooke's Law is only an > approximation. > > How would you suggest incorporating step functions which are random > in time, sense and amplitude into the calculations / properties of a > feedback loop? The stochastic processes you mentioned? > > Regards, > > Chris Chapman > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Dampng anharmonicity and Seismometry From: Randall Peters PETERS_RD@.......... Date: Sat, 09 Feb 2008 08:44:28 -0500 Too all: For reason of its length and other properties, I previously resisted supplying to the listserve the comments which follow. It appears now appropriate to mention them. Damping Anharmonicity and Seismometry The fine structure of the otherwise smooth (Hooke’s law) potential invalidates the linear (viscous) damping model used to describe simple harmonic oscillation. There are few mechanical systems that even come close to being in agreement with it. This is the case even at substantial amplitudes of oscillation, if the frequency is low—which means that nonlinear processes dominate the damping of seismic instruments in the regime where many now with frustrations want to go to study the earth. An important feature involves ‘self-similarity’, the hallmark of fractal (complex, chaotic) systems. Thus there are properties of even the (huge) earth itself that are similar to what is found in a (small) seismometer. In some respects it is conceptually easier to envision what goes on inside the earth. Our planet is like a multiply-cracked hard-boiled egg. The influence of the tidal forces of sun and moon are vitally significant to its dynamics. One way to think about this is as follows. Roll the hard boiled egg between your hands; as the shell fragments undergo rapid snap, crackle, pops (ala subduction of plates in the earth), the.egg must itself oscillate after each event. A ‘local ping’ of the egg will cause oscillations that persist longer than the oscillations caused by the ‘tidal’ rolling. In similar manner, a large earthquake is followed by long lived eigenmode oscillations. For example, the earth rang like a bell for weeks after the great Andeman-Sumatra earthquake. To believe that it does not also ‘ring’ due to rapid relaxation after a snap, crackle, or pop is to ignore the physics. Those of us trained in solid state physics know that the earth must oscillate all the time (due to its temperature) over the full range of admissible states; i.e., the so-called ‘density of states’. It was Einstein’s analysis of the heat capacity of solids along these lines that constituted one part of the modern physics revolution of the last century. So what is the primary difference between the two oscillation cases just mentioned. First of all, as was noted, the large amplitude motions in which the system ‘skates’ over the fine structure ‘bumps’ is more ‘monochromatic’ (longer lived). Just because the coherence time of the lower level ones is much shorter doesn’t mean they are non-existent. It means they are harder to observe. With my cumulative spectral power (CSP) analysis they are much easier to study. As compared to the power spectral density (PSD) approach, it is much better suited to the manner in which the eye/brain is able to assess information. The CSP allows fine structure of frequency domain type to be readily seen without having to resort to the more complicated ‘waterfall’ methods of conventional spectral type. There’s another conceptual analogy that I have used. Imagine yourself on a gravel road having fine structure (not smooth, but with washboard features that always develop over time). As long as you move at the right speed (not too fast, not too slow) the motion at these large levels allows one to ‘negotiate’ the road. If in a shallow depression, one can travel back and forth (first forward, then in reverse) ‘skating’ over the ‘fine structure’. If however, you get too slow near the bottom, you will get hung up in one of the localized minima. This is precisely what happens with a force-balance seismometer when trying to observe low energy earth motions. The force-balance instrument is without equal for looking at earthquakes all over the world, but in my opinion it will never yield insights into the physics I’ve been recently researching. For example, the VolksMeter allows me to look at diurnal and seasonal changes of importance. Most recently I’ve discovered that there is energy exchange between the eigenmodes and the microseisms. Nobody to my knowledge has previously postulated this. I have also with this pendulum seen in Larry Cochrane’s data the terdiurnal tide having a period of 8 hours. The 12-h and 24-h components are easily seen with a variety of instruments like strain gauges; but the terdiurnal component was previously seen almost solely in meteorological (upper atomosphere) measurements using radar. In the case of mechanical oscillators, the potential well in general has features having some similarity to the various analogies that I’ve mentioned. The details of the fine structure have not been worked out; since internal friction is not understood from first principles. I have postulated that individual ‘grain boundary’ regions (ala Chris Chapman’s comment concerning the analogy with magnetic domains) become altered when strain energies exceed certain thresholds. If that 'quantum' postulate could be proven, it would probably result in a Nobel prize; however, the challenge of reproducibility in experiments is Herculean (and nobody other than myself is to my knowledge yet trying to prove the matter). The problem requires extreme patience, because the frequencies required for study are so low. Thus the lifetime of the investigator comes into play. Concerning the friction ‘force’— Linear damping in the equation of motion causes the friction force to be sinusoidal and shifted in phase by 90 degrees from the sinusoidal displacement (proportional to velocity). It also requires that the quality factor Q as a function of natural frequency f be of the form Q proportional to f. Seismometers DO NOT conform to this! Gunar Strekeisen was apparently the first person to observe this nonconformity, while he was a grad-student working with a LaCoste spring. What he observed was Q proportional to f-squared. This quadratic dependence is the hallmark of hysteretic damping (that engineers have known about for a long time, but for which physicists are almost universally ignorant). What I have shown through experimentation is that the friction force is not sinusoidal. It is more nearly an attenuating square wave! Its amplitude falls off as the amplitude of the displacement decreases, thus giving rise to an exponential decay. Just because the decay is exponential, does not mean the damping is linear!! Only the fundamental of the Fourier component of this square wave friction is important in establishing the Q. Thus the nonlinear damping masquerades as linear even though it is far from being so! Among other of its features, there is no damping redshift; i.e., the natural frequency does not decrease as the amount of damping increases. Randall Subject: Cumulative Spectral Power example From: Randall Peters PETERS_RD@.......... Date: Sat, 09 Feb 2008 10:34:21 -0500 In my previous submission I alluded to how the CSP allows one to readily observe time dependent changes in the spectral content of the earth's motions. Of course earthquakes are among the most important of those, but it is incredible how little attention is given to the details of their spectral nature. There is great to-do about the arrival times of P, S and surface waves; but it's as though folks only want to know (i) how big, (ii) how deep, and (iii) where did it happen. There is SO MUCH more to be gleaned from the records, if the calculations were simply done. On my webpage that was just generated at http://physics.mercer.edu/hpage/evolve.html I show one example of the wealth of information that is available to us and which is not yet being mined! Why there has not been at least some attention given to more routine PSD calculations is mind boggling. To those of you who would want to similarly calculate PSD/CSP curves from data recorded with your own seismometer--by means of the LabView algorithm that Dr. Lee produced (used to generate the figure in the above reference)--John has indicated his willingness to provide the program free of charge to anyone who would simply send him an email. I don't know to what extent that code can be simply packaged in a zip form for email attachment; it was in my case transferred to my computer with a flash drive. Randall Subject: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Sat, 09 Feb 2008 11:24:17 -0500 Hi all, I think I must have a haunted system. I have been running a SG seismometer for about seven years. The mechanical design is very similar to the one described on the PSN web site, and I am Using Larry's electronics board. Over nearly the entire time I have been running this system I have had repeated episodes of extreme noise or some sort of spurious signal. When It occurs, the problem persists with little change for anywhere from a few days to several months, and then seems to fade away over the course of several days. The problem reoccurred a couple of weeks ago. It was apparently precipitated by the disturbance I caused by adjusting the leveling screw to recenter the pendulum (something I do frequently, with no problem). Before making the adjustment, I was getting about +/- 30 counts of signal excursion from the low frequency channel. Immediately after, I got around +/- 350 counts, rendering the system essentially worthless. I have put a lot of effort into trying to figure out what is going on, to no avail. In one of the previous episodes, I disconnected the power to the oscillator that drives the antenna plate, and opened the loop for the feedback damping. There was no significant change in the output, which led me at the time to conclude that there must either be something wrong with the electronics board, or some sort of electrical/magnetic pick-up. Despite a lot of diddling around, I couldn't determine a cause, and eventually, the system settled down without my having done anything specific to fixing it. And, neither theory fits well with this current episode, which started when I mechanically disurbed the sensor a little by adjusting the leveling. So, do I have a poltergeist detector when I thought I had a seismometer? I threw together a web page that shows the onset of the problem, as well as short time intervals before and after the problem started this time. If anyone cares to take a look at it and offer their thoughts (or condolences), I'd like to hear them. http://home.twcny.rr.com/lwconklin/Seismograph_Noise_Problem.html Larry Conklin Liverpool, NY lconklin@............ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Seismograph noise problem From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 09 Feb 2008 16:35:44 +0000 Hi Do you have a volcano near by ? Because an volcano can be an source of great noise that can last for months, even years. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: unsubscribe From: "John Vidale" john.vidale@......... Date: Sat, 9 Feb 2008 09:05:37 -0800 unsubscribe unsubscribe
Subject: Re: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Sat, 09 Feb 2008 13:19:08 -0500 Hi Jon, Well the nearest volcano to me is probably in your native Iceland, or possibly Mt. Ranier in Washington state. In either case, several thousand miles away. So, I think I can rule that out as a cause. Larry Jón Frímann wrote: > Hi > > Do you have a volcano near by ? Because an volcano can be an source of > great noise that can last for months, even years. > > Regards. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Dampng anharmonicity and Seismometry From: Brett Nordgren Brett3mr@............. Date: Sat, 09 Feb 2008 13:51:25 -0500 Randall, I'd like to use an adaptation of your analogy to try to make a very non-rigorous argument, though I believe an accurate one, as to how a specific type of force-balance instrument deals with potholes in your road. I am here making the assumption that your analogy can be applied to the spring force in a vertical device. I will also assume that the pothole forces are very small compared with the spring force and just represent small variations from linearity. I realize that your example probably applies to much lower frequencies and much smaller motions than the regime I am describing and it's not surprising that you can discover some 'interesting' issues down there. It is probably true that there is a practical limit as to how much low frequency sensitivity you can build into a vertical (i.e. a device which depends on a spring). I gather that most verticals give up once you get beyond a hundred seconds or so. For the specific case of a force balance vertical designed to be flat to velocity, the feedback in the flat portion of the instrument response is dominated by feedback via the derivative branch. I will assume that here we are using ideal components, and that the spring is the only non linear element. We are monitoring the position of the test mass, greatly amplifying that measurement and differentiating it to achieve a large signal proportional to the velocity of the mass. That signal we are then sending to a forcing coil which pushes on the mass so as to oppose its motion. To begin with we are moving smoothly down the road and everything is more or less in balance. Now we hit one of the potholes and the mass motion suddenly slows very slightly. As a result, the derivitave feedback branch quickly responds by reducing its resistance to the motion, allowing the spring-mass to more easily rise out of the pothole. Then when the velocity suddenly begins to rise as we come back onto the flat road, the feedback quickly increases the resisting force to help keep the velocity constant. The feedback effectively makes the pothole appear shallower than it realy is. Quantitatively, the apparent 'depth' of the pothole is reduced by the strength of the feedback (loop gain). In a good design that should be over 100 and possibly much greater. The pothole appears to be only 1% or less as 'deep' as it was without feedback. I should mention that the above discussion will also apply to any other small damping forces, linear or non linear. Brett At 08:44 AM 2/9/2008 -0500, you wrote: > There's another conceptual analogy that I have used. Imagine yourself > on a gravel road >having fine structure (not smooth, but with washboard features that always >develop over >time). As long as you move at the right speed (not too fast, not too >slow) the motion at >these large levels allows one to 'negotiate' the road. If in a shallow >depression, one >can travel back and forth (first forward, then in reverse) 'skating' over >the 'fine >structure'. If however, you get too slow near the bottom, you will get >hung up in one of >the localized minima. This is precisely what happens with a force-balance >seismometer >when trying to observe low energy earth motions. > Randall __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: fine structure nonlinearity vs dithering From: Brett Nordgren Brett3mr@............. Date: Sat, 09 Feb 2008 14:04:05 -0500 At 11:29 PM 2/8/2008 -0500, you wrote: > > >Hi Brett, > > I would be quite happy to 'go public' if no one else objects? >I'm uncomfortable with taking the approach that because there exist some >fairly small (I think) nonlinear effects, then no quantitative analysis >can be valid at all. Although it's somewhat beyond >my experience, I believe that feedback designers today routinely deal with >highly nonlinear, time-varying, and stochastic system variables and still >are able to obtain quite useful results. If they couldn't there would be >a lot fewer airplanes out there and our cars wouldn't handle as well. > Read through the papers on Randall's Website? > > Your car analogy misses the point. We are concerned mostly with > microscopic as opposed to macroscopic variations. > > The mechanical properties of springs have a 'fine structure' of > discontinuous steps, a bit like ferro magnetic domains. This gives small > 'step function' variations and limits the ultimate performance of > seismometers, clocks, MEMS devices, etc. The macroscopic properties are > also not quiite linear and are time dependant. Hooke's Law is only an > approximation. Certainly for the tiny MEMS stuff the world looks a lot different, and the effects may be an important consideration in a successful design. Otherwise, I'm not yet sure I see why I should get out my microscope to look for the fine structure effects when there are plenty of other error terms which I think are quite a lot larger. For example, in the STM-8 vertical the spring has a temperature sensitivity which amounts to about 200,000 nm / deg C. > > How would you suggest incorporating step functions which are random > in time, sense and amplitude into the calculations / properties of a > feedback loop? The stochastic processes you mentioned? > I'm no nonlinear guru, but there are approaches out there that should be able to deal with it. The easiest, is to prove that the effects are small enough to not affect the results and treat the system as linear. Deep down that's what I really think is the situation, though am certainly not in a position to prove it. It could be that the effects show up as some form of noise in the system, which is straight forward to analyze. Many feedback systems today are digital, in which all the signals are quantized, so dealing with that sort of issue, in general, hasn't posed any insurmountable problems to the design community. In fact they are doing things with digital feedback that could never have been considered otherwise, like making airplanes appear to be well behaved which without the feedback are inherently unstable and impossible to fly. You could, on paper, start by treating the system as linear, then inject a signal of random step functions at the appropriate point in the feedback loop to simulate the situation and look at the effect at the output. That would probably be how I would first approach the analysis. Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: feedback limitations due to damping anharmonicity From: Randall Peters PETERS_RD@.......... Date: Sat, 09 Feb 2008 14:35:10 -0500 Brett, I don't see an obvioius 'showstopper' with what you've mentioned, but then I certainly don't understand all the nuances. Let me give you one of the thoughts that I posed on this matter the better part of a decade ago. The following is copied from one of my webpages: 3.3 Gedanken to illustrate that limitations exist Lest one believe that force-balance feedback is infinitely superior to conventional seismometry, consider the following logic. Why even bother with the leaf-spring that is commonly used to support the test mass in these instruments? Why not just add a feedback network to a solid state mass balance instrument that works with resistive strain gauges? Place a big test mass on the pan of the modified mass balance (mmb), add a magnetic transducer of some type to provide a significant lifting force on the mass, and ``voila''-with proper feedback adjustment we suddenly can see earthquakes with the simplest of instruments. Hopefully everyone will quickly recognize the folly of this reasoning and know that such a modified mass measuring instrument is not capable of functioning as a bonafide seismometer. But why? The answer to this question lies in the following observation. System adaptability is no better than the integrity of the ``spring'' used in generation of the error signal. As noted earlier, any error signal requires the measurement of strain. In the case of the hypothetical modified mmb, the ``spring'', in the absence of feedback, has an exceedingly large k. In the case of the W/S leaf-spring seismometer, the leaf has a considerably larger k than that of the conventional seismometer. Can electronics soften even the hardest springs? The answer is obviously no! What are the limitations to softening? I submit to the reader that there are a host of unanswered questions in the matter. It is easy to see that electronics limitations (addressed earlier) pose an ultimate upper limit on the size of k. But anelasticity of the support is probably even more important than the electronics-and the problems borne of it are mostly unstudied. This is true in spite of the fact that practictioners understand that an instrument must be allowed to settle for some time after initial loading, before it becomes dependable. This settling is necessary to minimize the effects of anelasticity, through a type of work-hardening. There is a factor in all this that is unavoidable and of much greater influence than I ever expected until some experiments that I did in the last year--concerned with creep. The results will be reported in the Chapter 1 that I wrote titled "Building on old foundations with new technologies", of Nova's "Science Education in the 21st Century"--due out this quarter. There is apparently no level below which creep isn't significant and it's influence depends on which way the temperature was moving at the time the system is observed (total temperature swings of only about 5 C over 24 h.) I found significant, peculiar disruptions due to creep at energy levels of the pendulum at only 10^(-12) J. Bottom line--engineering the feedback network to compensate for the multiplicity of anomalous possibilities appears to me to be a staggering proposition. My own opinion is that it is best to let the seismometer 'find its own best equilbirium', rather than forcing it into the 'one preferred by the chosen point of the feedback circuitry'. Why mess with mother nature's preference? Randall Subject: Re: Seismograph noise problem From: ChrisAtUpw@....... Date: Sat, 9 Feb 2008 17:22:38 EST In a message dated 09/02/2008, lconklin@............ writes: I have put a lot of effort into trying to figure out what is going on, to no avail. In one of the previous episodes, I disconnected the power to the oscillator that drives the antenna plate, and opened the loop for the feedback damping. There was no significant change in the output, which led me at the time to conclude that there must either be something wrong with the electronics board, or some sort of electrical/magnetic pick-up. Despite a lot of diddling around, I couldn't determine a cause, and eventually, the system settled down without my having done anything specific to fixing it. And, neither theory fits well with this current episode, which started when I mechanically disurbed the sensor a little by adjusting the leveling. I threw together a web page that shows the onset of the problem, as well as short time intervals before and after the problem started this time. If anyone cares to take a look at it and offer their thoughts (or condolences), I'd like to hear them. Hi Larry, The problem seems to be with the first opamp or it's circuit. Clean the input connectors with fine wire wool and coat them with vaseline. If the resistors are NOT metal film, check them for damage / the correct resistance, maybe replace the input circuit ones with metal film resistors. This could simply be a faulty resistor. Visually inspect the solder joints with a magnifying glass for any which appear faulty. You can get a solder fault called crevice corrosion, when corrosion creeps in between the copper board and the solder joints. Remove one solder blob on say a resistor and then scratch the tinned area with a knife. If you have crevice corrosion, the solder will peel off leaving a dark brown oxide film on the copper strip. It could also be that the opamp is faulty. Does it unplug, or is it soldered in? Can you replace it easily? You can buy a spray can of freezing fluid. You monitor the signal output and then spray freeze the components in turn. If one is faulty, you are likely to see a large change in the output signal. If the board gets damp while in use, you can brush coat it with single pack polyurethane varnish for protection. Regards, Chris Chapman
In a message dated 09/02/2008, lconklin@............ writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I have=20 put a lot of effort into trying to figure out what is going on, to no=20 avail.  In one of the previous episodes, I disconnected the power to=20= the=20 oscillator that drives the antenna plate, and opened the loop for the feed= back=20 damping.  There was no significant change in the output, which led me= at=20 the time to conclude that there must either be something wrong with the=20 electronics board, or some sort of electrical/magnetic pick-up.  = ;=20 Despite a lot of  diddling around, I couldn't determine a cause, and=20 eventually, the system settled down without my having done anything specif= ic=20 to fixing it.  And,
neither theory fits well with this current=20 episode, which started when I mechanically disurbed the sensor a little by= =20 adjusting the leveling.

  I threw together a web page that sho= ws=20 the onset of the problem, as well as short time intervals  before and= =20 after the problem started this time.  If anyone cares to take a look=20= at=20 it and offer their thoughts (or condolences), I'd like to hear=20 them.
Hi Larry,
 
    The problem seems to be with the first opamp or= =20 it's circuit.
 
    Clean the input connectors with fine wire wool=20= and=20 coat them with vaseline.
    If the resistors are NOT metal film, check them= for=20 damage / the correct resistance, maybe replace the input circuit ones with m= etal=20 film resistors. This could simply be a faulty resistor.
    Visually inspect the solder joints with a=20 magnifying glass for any which appear faulty.
    You can get a solder fault called crevice=20 corrosion, when corrosion creeps in between the copper board and the so= lder=20 joints. Remove one solder blob on say a resistor and then scratch the tinned= =20 area with a knife. If you have crevice corrosion, the solder will peel off=20 leaving a dark brown oxide film on the copper strip.
    It could also be that the opamp is faulty.= =20 Does it unplug, or is it soldered in? Can you replace it easily?
 
    You can buy a spray can of freezing fluid. You=20 monitor the signal output and then spray freeze the components in turn. If o= ne=20 is faulty, you are likely to see a large change in the output signal.
    If the board gets damp while in use, you can br= ush=20 coat it with single pack polyurethane varnish for protection.
 
    Regards,
 
    Chris Chapman
Subject: Re: fine structure nonlinearity vs dithering From: ChrisAtUpw@....... Date: Sat, 9 Feb 2008 22:11:01 EST In a message dated 09/02/2008 19:03:59 GMT Standard Time, Brett3mr@............. writes: Otherwise, I'm not yet sure I see why I should get out my microscope to look for the fine structure effects when there are plenty of other error terms which I think are quite a lot larger. For example, in the STM-8 vertical the spring has a temperature sensitivity which amounts to about 200,000 nm / deg C. Hi Brett, I am not saying thet there are not other effects which can and do limit the sensitivity / stability. You could replace the steel spring by a NiSpanC one? The extreme sensitivity to temperature suggests that this would be highly desirable and probably beyond the stability that you could achieve with a thermostat. > How would you suggest incorporating step functions which are random > in time, sense and amplitude into the calculations / properties of a > feedback loop? The stochastic processes you mentioned? I'm no nonlinear guru, but there are approaches out there that should be able to deal with it. The easiest, is to prove that the effects are small enough to not affect the results and treat the system as linear. Deep down that's what I really think is the situation, though am certainly not in a position to prove it. It could be that the effects show up as some form of noise in the system, which is straight forward to analyze. The effects are not insignificant and involve a shift in the mean level. Many feedback systems today are digital, in which all the signals are quantized, so dealing with that sort of issue, in general, hasn't posed any insurmountable problems to the design community. In fact they are doing things with digital feedback that could never have been considered otherwise, like making airplanes appear to be well behaved which without the feedback are inherently unstable and impossible to fly. Sure, but the digitisation steps are then small compared to the background noise signals / control signals. If the steps are large, you may well not be able to stabilise the system, or you are left with the output switching between two levels. You could, on paper, start by treating the system as linear, then inject a signal of random step functions at the appropriate point in the feedback loop to simulate the situation and look at the effect at the output. That would probably be how I would first approach the analysis. Noise generally has a zero average level. These are steps in the zero level. One of the costs of making long period seismometers is in reducing / controlling the inherent noise in the spring. Regards, Chris Chapman
In a message dated 09/02/2008 19:03:59 GMT Standard Time,=20 Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>Otherwise, I'm not yet sure I see why I should get out my microsc= ope to=20 look for the fine structure effects when there are plenty of other error t= erms=20 which I think are quite a lot larger.  For example, in the STM-8 vert= ical=20 the spring has a temperature sensitivity which amounts to about 200,000 nm= /=20 deg C.
Hi Brett,
 
    I am not saying thet there are not other effect= s=20 which can and do limit the sensitivity / stability. You could replace the st= eel=20 spring by a NiSpanC one? The extreme sensitivity to temperature suggests=20 that this would be highly desirable and probably beyond the stability t= hat=20 you could achieve with a thermostat.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>>     How would you suggest incorporating step=20 functions which are random
> in time, sense and amplitude into the=20 calculations / properties of a
> feedback loop? The stochastic=20 processes you mentioned?

I'm no nonlinear guru, but there are=20 approaches out there that should be able to deal with it.  The easies= t,=20 is to prove that the effects are small enough to not affect the results an= d=20 treat the system as linear.  Deep down that's what I really think is=20= the=20 situation, though am certainly not in a position to prove it.  It cou= ld=20 be that the effects show up as some form of noise in the system, which is=20 straight forward to analyze.
    The effects are not insignificant and involve a= =20 shift in the mean level.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Many=20 feedback systems today are digital, in which all the signals are quantized= , so=20 dealing with that sort of issue, in general, hasn't posed any insurmountab= le=20 problems to the design community.  In fact they are doing things with= =20 digital feedback that could never have been considered
otherwise, like= =20 making airplanes appear to be well behaved which without the feedback are=20 inherently unstable and impossible to fly.
    Sure, but the digitisation steps are=20 then small compared to the background noise signals / control signals.=20= If=20 the steps are large, you may well not be able to stabilise the system, or yo= u=20 are left with the output switching between two levels.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>You=20 could, on paper, start by treating the system as linear, then inject a sig= nal=20 of random step functions at the appropriate point in the feedback loop to=20 simulate the situation and look at the effect at the output. That would=20 probably be how I would first approach the analysis.
    Noise generally has a zero average level. These= are=20 steps in the zero level. One of the costs of making long period seismometers= is=20 in reducing / controlling the inherent noise in the spring.
 
    Regards,
 
    Chris Chapman
Subject: Re: Dampng anharmonicity and Seismometry From: ChrisAtUpw@....... Date: Sat, 9 Feb 2008 22:21:57 EST In a message dated 09/02/2008, Brett3mr@............. writes: I will also assume that the pothole forces are very small compared with the spring force and just represent small variations from linearity. Hi Brett, This is the trouble. They are NOT small compared to the restoring force. To get a really long period, the gradient of the spring force with position is nearly flat, but you are still offsetting the full mass Mg. Consequently the deflection produced by a small step change in the spring properties can produce a large mass movement. Note that noise is assumed to have a mean level of zero. The effects we have to cope with are discreet steps in the zero level. Regards, Chris Chapman
In a message dated 09/02/2008, Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>  I=20 will also assume that the pothole forces are very small compared with the=20 spring force and just represent small variations from=20 linearity.
Hi Brett,
 
    This is the trouble. They are NOT small compare= d to=20 the restoring force.
    To get a really long period, the gradient of th= e=20 spring force with position is nearly flat, but you are still offsetting the=20= full=20 mass Mg.
    Consequently the deflection produced by a small= =20 step change in the spring properties can produce a large mass=20 movement. 
    Note that noise is assumed to have a mean level= of=20 zero. The effects we have to cope with are discreet steps in the zero=20 level.
 
    Regards,
 
    Chris Chapman
Subject: Re: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Sat, 09 Feb 2008 23:32:22 -0500 Hi Chris, Thanks for your suggestions. I haven't yet made any serious attempt to work the current manifestation of this problem, mostly for lack of new ideas for something new to try. But a couple of years ago when the same sort of thing happened, I did replace the input op amp and didn't see any obvious change. My theory at the time was that since I can see problems in both outputs, whatever is causing it must be upstream of where the two channels diverge, and that doesn't leave much. The chip is soldered to the board, so all of those connections got a workover as a byproduct of the change. And, after changing the chip, I did a thorough cleaning of the board to get rid of stray solder flux. The other possibility would be in the power supply. I pretty much ruled that out by measuring the power at right at the op-amp pins on all of the chips individually. Thought a decoupling cap might be getting flakey. But everything looked flat to within +/- 10 mv, which is the resolution limit of my inexpensive DVM. Don't know what sort of resistors are used in the board, other than they certainly aren't cheap composition resistors. I'll take a closer look at them, and maybe I should resolder the joints in the input stage. But, the board looks to be very well made, and I'd be pretty surprised if there was a bad joint. It looks like it was professionally built, probably with a wave soldering machine. I have also tried the freeze spray idea. It seemed like I could spray the board pretty much anywhere and the output would jump all over the place. So, I wasn't able to draw any useful conclusions from the experiment. If the problem really is something in the circuit board, I can't account for the fact that things were running ok right up to the exact moment that I disturbed it, as you can see from the data record. I suppose it is possible that the large signal excursion caused by walking up to the sensor and making the adjustment aggravated some latent problem, but I have a hard time persuading myself that it's likely. I have recorded a quakes that drove the thing to saturation and never have seen any similar consequence. I don't have to touch the board, the case or the cables to do a leveling adjustment, just tweak the screw with a screwdriver. I guess my most convincing theory at the moment is that there is a poltergeist living in my basement. Larry ChrisAtUpw@....... wrote: > In a message dated 09/02/2008, lconklin@............ writes: > > I have put a lot of effort into trying to figure out what is going > on, to no avail. In one of the previous episodes, I disconnected > the power to the oscillator that drives the antenna plate, and > opened the loop for the feedback damping. There was no significant > change in the output, which led me at the time to conclude that > there must either be something wrong with the electronics board, or > some sort of electrical/magnetic pick-up. Despite a lot of > diddling around, I couldn't determine a cause, and eventually, the > system settled down without my having done anything specific to > fixing it. And, > neither theory fits well with this current episode, which started > when I mechanically disurbed the sensor a little by adjusting the > leveling. > > I threw together a web page that shows the onset of the problem, > as well as short time intervals before and after the problem > started this time. If anyone cares to take a look at it and offer > their thoughts (or condolences), I'd like to hear them. > > Hi Larry, > > The problem seems to be with the first opamp or it's circuit. > > Clean the input connectors with fine wire wool and coat them with > vaseline. > If the resistors are NOT metal film, check them for damage / the > correct resistance, maybe replace the input circuit ones with metal film > resistors. This could simply be a faulty resistor. > Visually inspect the solder joints with a magnifying glass for any > which appear faulty. > You can get a solder fault called crevice corrosion, when corrosion > creeps in between the copper board and the solder joints. Remove one > solder blob on say a resistor and then scratch the tinned area with a > knife. If you have crevice corrosion, the solder will peel off leaving a > dark brown oxide film on the copper strip. > It could also be that the opamp is faulty. Does it unplug, or is it > soldered in? Can you replace it easily? > > You can buy a spray can of freezing fluid. You monitor the signal > output and then spray freeze the components in turn. If one is faulty, > you are likely to see a large change in the output signal. > If the board gets damp while in use, you can brush coat it with > single pack polyurethane varnish for protection. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Seismograph noise problem From: Roger Sparks rsparks@.......... Date: Sat, 09 Feb 2008 22:20:31 -0800 Hi Larry, Sorry that you are having the noise problem after adjusting your seismometer. I had a similar problem for a while that was caused by poor contact to the solid surface. In my case, I was going through a rug to a concrete surface. For a while, one leg did not properly contact the hard surface. The microsiems caused a rocking that displayed as noise. I did not know I had a problem until an FFT of the noisy signal showed a higher frequency spectra that was not present in the older traces. The fix was simply to beef up my penetrations through the rug. Are you using a three leg mount? Are the contacts to the hard surface made with points? Do you have a locking nut or other mechanism to fix the adjusting screws after adjustment? Do you have any loose parts that could "rock" due to the microsiems? Do you "set" your seismometer after adjustment by putting extra pressure to help reset the contact points? Good luck on the repairs, Roger > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 3 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Seismograph noise problem > From: Larry Conklin > Date: Sat, 09 Feb 2008 11:24:17 -0500 > > Hi all, > > I think I must have a haunted system. I have been running a SG > seismometer for about seven years. The mechanical design is very > similar to the one described on the PSN web site, and I am Using Larry's > electronics board. Over nearly the entire time I have been running this > system I have had repeated episodes of extreme noise or some sort of > spurious signal. When It occurs, the problem persists with little > change for anywhere from a few days to several months, and then seems to > fade away over the course of several days. The problem reoccurred a > couple of weeks ago. It was apparently precipitated by the disturbance > I caused by adjusting the leveling screw to recenter the pendulum > (something I do frequently, with no problem). Before making the > adjustment, I was getting about +/- 30 counts of signal excursion from > the low frequency channel. Immediately after, I got around +/- 350 > counts, rendering the system essentially worthless. > > I have put a lot of effort into trying to figure out what is going on, > to no avail. In one of the previous episodes, I disconnected the power > to the oscillator that drives the antenna plate, and opened the loop for > the feedback damping. There was no significant change in the output, > which led me at the time to conclude that there must either be something > wrong with the electronics board, > or some sort of electrical/magnetic pick-up. Despite a lot of diddling > around, I couldn't determine a cause, and eventually, the system settled > down without my having done anything specific to fixing it. And, > neither theory fits well with this current episode, which started when I > mechanically disurbed the sensor a little by adjusting the leveling. > > So, do I have a poltergeist detector when I thought I had a seismometer? > I threw together a web page that shows the onset of the problem, as > well as short time intervals before and after the problem started this > time. If anyone cares to take a look at it and offer their thoughts (or > condolences), I'd like to hear them. > > http://home.twcny.rr.com/lwconklin/Seismograph_Noise_Problem.html > > Larry Conklin > Liverpool, NY > lconklin@............ > > > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: nature of the mesoscopic nonlinearity From: Randall Peters PETERS_RD@.......... Date: Sun, 10 Feb 2008 09:14:18 -0500 Brett, I've been able now to give enough thought to your comments about "potholes" to provide the following response. Chris 'hit the nail on the head' with his statement "... to cope with discrete steps in the zero level". In other words, if the term is at all appropriate, it is not your 'average' pothole as found in northern climate highways where temperatures are at times routinely below freezing. The 'potholes of seismic type' are 'diffusive' in terms of both temperature and stress. There is a paper of mine at http://arxiv.org/html/physics/0307016 titled "Harmonic oscillator potential to describe internal dissipation". As discussed there, the potential function is not fixed. As the seismometer mass moves back and forth, the equilibrium position, to which it would go if motion were suppressed, shifts back and forth. This is the basis for hysteresis--reason the term 'hysteretic damping' is appropriate. The problem with this hysteresis is that the mesoanelastic steps associated with it are not themselves fixed. My study of creep mentioned earlier is proof positive of that fact. What happens is the strain energy that accumulates at polycrystalline grain boundaries causes a rearrangement of the atoms (redistribution of the defect structures) when various thresholds are exceeded. Such is the nature of work-hardening. In primary creep (exponential variation), the material is trying to arrest the changes brought about by the external forcing. 'Success' in so doing results in a conversion to secondary (linear variation) creep. If the temperature were zero--end of story. But temperature serves to undo the hardening and so a 'balance' results between hardening and softening. If the stress levels become large enough, the defect structural reorganizations become much bigger, resulting in cracks and eventual fatigue failure. Truly, what I'm discussing is one of the most important and yet still mysterious of scientific phenomena. Its complexity has so far prohibited understanding of the processes from first principles. Perhaps another analogy is of some related value--that of a non-Newtonian liquid. Maybe you've seen the Mythbusters episode in which they filled a 'small swimming pool' with such a liquid (huge amount of corn starch with water). One of the team was able to easily 'walk on water' across the surface of this mix as long as he moved quickly. But if he tried to do so slowly, he sank all the way to his neck. The more natural example of the same phenomenon is that of quicksand. Still another fascinating example of such complexity is ordinary sea sand mixed with ocean water. If the sand is too dry, it is hard to walk on. Same if the sand is too wet. Get the amount of water just right and you can drive tanks on it! What we're dealing with are the yet-unknown properties of granular materials, which is an advancing frontier of science and engineering. One of my favorite examples is a can of nuts. If you briskly shake a can of mixed nuts the larger ones will migrate toward the upper surface, in seeming defiance of the influence of gravity--because of their interaction with smaller nuts responsible for 'symmetry breaking'. Randall Subject: Re: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Sun, 10 Feb 2008 10:39:43 -0500 Hi Roger, I it very interesting that you have had a similar problem, and I appreciate your suggestions. I my case, the sensor in in the basement, sitting on a concrete floor. Several years ago I epoxied three small aluminum plates to the floor for the settling screws to sit on. My concern at the time was that turning the leveling screw against the concrete was grinding into the floor, leaving concrete dust under the screw. One of the probable flaws in my construction is that the leveling screw is very small (#4) and more than likely not really firm enough. But, when I'm not being "haunted" the thing performs pretty well. Seems like problems stemming from the mechanical design shouldn't be episodic the way I have having them. I am using a 3 point mount, and the other two feet (base of the triangle) are sturdier. One thing that your comments encourage me to revisit is the way the cover over the sensor is made. It is made of 1/4/inch particle board and a little heavy on the heavy side. I is just sitting on the base frame of the sensor, held down by it's own weight. There are soft plastic feet attached where the contact is made to the frame. I don't normally make a point of pressing everything down to reseat things after i adjust it. Never occurred to me to do that. One thing I did try since this last episode started was to put a little piece of tape under each foot, to introduce a little "sqisshyness" to prevent the kind of "micro-rocking" that you apparently had. I didn't see any obvious difference. Guess I'm going to have to embark on a real science project. Larry Roger Sparks wrote: > > Hi Larry, > > Sorry that you are having the noise problem after adjusting your > seismometer. > > I had a similar problem for a while that was caused by poor contact to > the solid surface. In my case, I was going through a rug to a concrete > surface. For a while, one leg did not properly contact the hard > surface. The microsiems caused a rocking that displayed as noise. > > I did not know I had a problem until an FFT of the noisy signal showed a > higher frequency spectra that was not present in the older traces. The > fix was simply to beef up my penetrations through the rug. > > Are you using a three leg mount? Are the contacts to the hard surface > made with points? Do you have a locking nut or other mechanism to fix > the adjusting screws after adjustment? Do you have any loose parts that > could "rock" due to the microsiems? Do you "set" your seismometer after > adjustment by putting extra pressure to help reset the contact points? > > Good luck on the repairs, > > Roger > > >> >> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. >> | Message 3 | >> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' >> Subject: Seismograph noise problem >> From: Larry Conklin >> Date: Sat, 09 Feb 2008 11:24:17 -0500 >> >> Hi all, >> >> I think I must have a haunted system. I have been running a SG >> seismometer for about seven years. The mechanical design is very >> similar to the one described on the PSN web site, and I am Using >> Larry's electronics board. Over nearly the entire time I have been >> running this system I have had repeated episodes of extreme noise or >> some sort of spurious signal. When It occurs, the problem persists >> with little change for anywhere from a few days to several months, and >> then seems to fade away over the course of several days. The problem >> reoccurred a couple of weeks ago. It was apparently precipitated by >> the disturbance I caused by adjusting the leveling screw to recenter >> the pendulum (something I do frequently, with no problem). Before >> making the adjustment, I was getting about +/- 30 counts of signal >> excursion from the low frequency channel. Immediately after, I got >> around +/- 350 counts, rendering the system essentially worthless. >> >> I have put a lot of effort into trying to figure out what is going on, >> to no avail. In one of the previous episodes, I disconnected the >> power to the oscillator that drives the antenna plate, and opened the >> loop for the feedback damping. There was no significant change in the >> output, which led me at the time to conclude that there must either be >> something wrong with the electronics board, >> or some sort of electrical/magnetic pick-up. Despite a lot of >> diddling around, I couldn't determine a cause, and eventually, the >> system settled down without my having done anything specific to fixing >> it. And, neither theory fits well with this current episode, which >> started when I mechanically disurbed the sensor a little by adjusting >> the leveling. >> >> So, do I have a poltergeist detector when I thought I had a >> seismometer? I threw together a web page that shows the onset of the >> problem, as well as short time intervals before and after the problem >> started this time. If anyone cares to take a look at it and offer >> their thoughts (or condolences), I'd like to hear them. >> >> http://home.twcny.rr.com/lwconklin/Seismograph_Noise_Problem.html >> >> Larry Conklin >> Liverpool, NY >> lconklin@............ >> >> >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: ChrisAtUpw@....... Date: Sun, 10 Feb 2008 13:17:03 EST In a message dated 10/02/2008, PETERS_RD@.......... writes: I've been able now to give enough thought to your comments about "potholes" to provide the following response. Chris 'hit the nail on the head' with his statement "... to cope with discrete steps in the zero level". In other words, if the term is at all appropriate, it is not your 'average' pothole as found in northern climate highways where temperatures are at times routinely below freezing. The 'potholes of seismic type' are 'diffusive' in terms of both temperature and stress. Hi Brett, This raises another point about practical seismometer performance. 'Instantaneous' shifts in the zero level generate wide bandwidth high amplitudes spikes in a velocity feedback loop. These have to be applied using a coil with a high inductance and can saturate the electronics. Using magnet + plate damping avoids this. Regards, Chris Chapman
In a message dated 10/02/2008, PETERS_RD@.......... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2> =20   I've been able now to give enough thought to your comments about=20 "potholes" to
provide the following response.
Chris 'hit the nail on= the=20 head' with his statement "... to cope with discrete steps in
the zero=20 level".  In other words, if the term is at all appropriate, it is not= =20 your
'average' pothole as found in northern climate highways where=20 temperatures are at times
routinely below freezing.  The 'potholes= of=20 seismic type' are 'diffusive' in terms of
both temperature and=20 stress.
Hi Brett,
 
    This raises another point about=20 practical seismometer performance. 'Instantaneous' shifts in the zero l= evel=20 generate wide bandwidth high amplitudes spikes in a velocity feedback l= oop.=20 These have to be applied using a coil with a high inductance and c= an=20 saturate the electronics. Using magnet + plate damping avoids this.
 
    Regards,
 
    Chris Chapman
Subject: Geophone From: "Dale Hardy" photon1@........... Date: Mon, 11 Feb 2008 12:30:43 +1100 Hi, I am going to add a geophone to my station and just would like ideas = on how best to place one. Thanks Dale
Hi, I am going to add a geophone to my = station and=20 just would like ideas on how best to place one.
Thanks
Dale
Subject: Re: Geophone From: John Lahr johnjan@........ Date: Sun, 10 Feb 2008 18:02:04 -0800 At 05:30 PM 2/10/2008, you wrote: >Hi, I am going to add a geophone to my station and just would like >ideas on how best to place one. >Thanks >Dale Dale, Could you provide a few more details about the geophone and your setting? John __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: Brett Nordgren Brett3mr@............. Date: Sun, 10 Feb 2008 21:37:36 -0500 Randall and Chris, Sorry to be slow in responding to your messages, but you and Chris have given me much to think about and it's going to take a few days more of thinking to digest it all. One open issue that I would like to get pinned down is getting a rough idea of how large these effects are relative to the overall spring forces. I think that Chris had implied that they could be of the same order of magnitude, which I am finding very hard to visualize. Also in his message today I think he was implying that the spring can undergo steplike changes which contain high frequency components. If too large, they could be deadly--see centering discussion below. In particular I am mainly interested in the effects which will occur with the spring under constant tension--not moving significantly. I find that I need to try to separate the fundamental spring-noise issues which will always be present from ones that can be addressed by manufacturing and design techniques such as limiting spring stress, ageing, heat cycling, material choice, etc. For example, I'd heard stories of leaf-spring designs that popped and crackled when they were first assembled and which then, over time, would quiet down to an acceptable noise level. However a noise process that is fundamental and always present would be of greater concern. As an engineer, creep itself does not concern me, so long as it is acceptably slow and not too noisy. Being able to quantify what one might expect to see would be helpful in trying to design something. New subject: Both you and Chris had previously written of the idea of using feedback to help maintain instrument centering. I came up with the following, which if correct has some interesting implications. "The goal of maintaining centering by the use of feedback can be restated as the goal of using feedback to make the instrument insensitive to the unwanted 'noise' forces which would tend to push it off center. When trying to do this, however, a problem unfortunately arises of the 'no free lunch' class, which in fact has nothing directly to do with feedback. The (vertical) instrument simply can't distinguish where an input force is coming from. Is it from the spring getting weaker as the temperature rises, from buoyancy-force changes with the barometer, from spring creep or is it the acceleration-related force from the very low frequency geological signal you wanted to observe? To the extent that you succeed in reducing the instrument's sensitivity to the 'noise' forces you also reduce its sensitivity to the signal force. This can be restated as the well accepted generalization: 'feedback does not affect the signal to noise ratio'. (assuming, of course, that the added feedback components are noise free) However there is one hope. If you can assign F as a frequency below which you will not be looking for signals, you can say that anything changing at rates significantly below F, is noise. This in turn allows you to roll off the instrument sensitivity to forces having frequencies below F and to some extent favor signal over more slowly-varying noise. I am confident that is the reason why commercial instruments aren't designed to have large responses to acceleration/force down to very low frequencies. Instead they are designed to establish a compromise between letting through sufficiently low-frequency seismic signals to be useful, while at the same time resisting the much larger, though more slowly changing, instrument 'noise' forces. That may also explain why so much effort has to go into reducing the noise generators at their source, by using exotic alloys in leaf spring suspensions, maintaining constant (usually low) ambient pressure, and attempting to maintain the temperature as constant as possible, etc." Brett At 09:14 AM 2/10/2008 -0500, you wrote: >Brett, > I've been able now to give enough thought to your comments about > "potholes" to >provide the following response. >Chris 'hit the nail on the head' with his statement "... to cope with >discrete steps in >the zero level". In other words, if the term is at all appropriate, it is >not your >'average' pothole as found in northern climate highways where temperatures >are at times >routinely below freezing. The 'potholes of seismic type' are 'diffusive' >in terms of >both temperature and stress. > There is a paper of mine at http://arxiv.org/html/physics/0307016 >titled "Harmonic oscillator potential to describe internal >dissipation". As discussed >there, the potential function is not fixed. As the seismometer mass moves >back and >forth, Actually in a force-balance instrument the mass does very little moving, which should be an advantage. You are trading physical movement of the spring-mass for electrical 'movement' in the feedback elements. >the equilibrium position, to which it would go if motion were suppressed, >shifts >back and forth. This is the basis for hysteresis--reason the term >'hysteretic damping' >is appropriate. > The problem with this hysteresis is that the mesoanelastic steps > associated with it >are not themselves fixed. Can the amplitude distribution of these steps be predicted? >My study of creep mentioned earlier is proof positive of that >fact. What happens is the strain energy that accumulates at >polycrystalline grain >boundaries causes a rearrangement of the atoms (redistribution of the >defect structures) >when various thresholds are exceeded. Such is the nature of >work-hardening. In primary >creep (exponential variation), the material is trying to arrest the >changes brought about >by the external forcing. 'Success' in so doing results in a conversion to >secondary >(linear variation) creep. If the temperature were zero--end of >story. But temperature >serves to undo the hardening and so a 'balance' results between hardening >and softening. >If the stress levels become large enough, the defect structural >reorganizations become >much bigger, resulting in cracks and eventual fatigue failure. Truly, >what I'm >discussing is one of the most important and yet still mysterious of scientific >phenomena. Its complexity has so far prohibited understanding of the >processes from >first principles. > Randall __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: ChrisAtUpw@....... Date: Sun, 10 Feb 2008 23:45:35 EST In a message dated 11/02/2008, Brett3mr@............. writes: Randall and Chris, Sorry to be slow in responding to your messages, but you and Chris have given me much to think about and it's going to take a few days more of thinking to digest it all. One open issue that I would like to get pinned down is getting a rough idea of how large these effects are relative to the overall spring forces. I think that Chris had implied that they could be of the same order of magnitude, which I am finding very hard to visualize. Hi Brett, You have to make a spring arrangement such that it exactly balances the mass, but has a very slow rate of change of force with position, a few % at most. Hence the somewhat exotic spring arrangements used in seismometers. Also in his message today I think he was implying that the spring can undergo steplike changes which contain high frequency components. If too large, they could be deadly--see centering discussion below. In particular I am mainly interested in the effects which will occur with the spring under constant tension--not moving significantly. Hooke's Law is only an approximation. You get a time dependant component and creep. The creep is noisy and also time dependant. The changes tend to be steps in the characteristic and these decrease with time after the load is applied. New steps may be excited by quakes. The step changes can give problems with velocity feedback circuits - they tend to generate spikes. I find that I need to try to separate the fundamental spring-noise issues which will always be present from ones that can be addressed by manufacturing and design techniques such as limiting spring stress, ageing, heat cycling, material choice, etc. For example, I'd heard stories of leaf-spring designs that popped and crackled when they were first assembled and which then, over time, would quiet down to an acceptable noise level. However a noise process that is fundamental and always present would be of greater concern. All common / practical spring materials are like this. You have the electronic noise, the thermal noise of the sensor itself, the hysteretic noise and the background seismic noise. As an engineer, creep itself does not concern me, so long as it is acceptably slow and not too noisy. Being able to quantify what one might expect to see would be helpful in trying to design something. New subject: Both you and Chris had previously written of the idea of using feedback to help maintain instrument centering. I came up with the following, which if correct has some interesting implications. "The goal of maintaining centering by the use of feedback can be restated as the goal of using feedback to make the instrument insensitive to the unwanted 'noise' forces which would tend to push it off center. When trying to do this, however, a problem unfortunately arises of the 'no free lunch' class, which in fact has nothing directly to do with feedback. The (vertical) instrument simply can't distinguish where an input force is coming from. Is it from the spring getting weaker as the temperature rises, from buoyancy-force changes with the barometer, from spring creep or is it the acceleration-related force from the very low frequency geological signal you wanted to observe? To the extent that you succeed in reducing the instrument's sensitivity to the 'noise' forces you also reduce its sensitivity to the signal force. This can be restated as the well accepted generalization: 'feedback does not affect the signal to noise ratio'. (assuming, of course, that the added feedback components are noise free) Yes you can. You can either re-zero mechanically with a small motor to keep the system in range or use an integrated signal as force feedback. If you integrate the output to say 500 seconds for a 50 second period instrument, you can keep the mean position centred without significantly effecting the 50 second response. This will take out most drifts. With a velocity output, the very long period signals are small. I am confident that is the reason why commercial instruments aren't designed to have large responses to acceleration / force down to very low frequencies. Instead they are designed to establish a compromise between letting through sufficiently low-frequency seismic signals to be useful, while at the same time resisting the much larger, though more slowly changing, instrument 'noise' forces. That may also explain why so much effort has to go into reducing the noise generators at their source, by using exotic alloys in leaf spring suspensions, maintaining constant (usually low) ambient pressure, and attempting to maintain the temperature as constant as possible, etc." See Wielandt's references on psn for feedback seismometer design. Seismometers are usually designed to give a velocity law output directly using quite complicated feedback loops - this is 'traditional'. High sensitivity seismometers usually have periods between 60 and 120 seconds and this covers most surface wave periods of maybe 15 to 40 seconds. A few types go to 360 seconds. To cover all the Earth Eigenmodes, you have to go to about 2,000 seconds. Regards, Chris Chapman
In a message dated 11/02/2008, Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Randall=20 and Chris,

Sorry to be slow in responding to your messages, but you= and=20 Chris have given me much to think about and it's going to take a few days=20= more=20 of thinking to digest it all.

One open issue that I would like to g= et=20 pinned down is getting a rough idea of how large these effects are relativ= e to=20 the overall spring forces.  I think that Chris had implied that they=20 could be of the same order of magnitude, which I am finding very hard to=20 visualize. 
Hi Brett,
 
    You have to make a spring arrangement such that= it=20 exactly balances the mass, but has a very slow rate of change of force with=20 position, a few % at most. Hence the somewhat exotic spring arrangements use= d in=20 seismometers.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Also in=20 his message today I think he was implying that the spring can undergo step= like=20 changes
which contain high frequency components.  If too large, t= hey=20 could be deadly--see centering discussion below.  In particular I am=20 mainly interested in the effects which will occur with the spring under=20 constant tension--not moving significantly.
    Hooke's Law is only an approximation. You get a= =20 time dependant component and creep. The creep is noisy and also time dependa= nt.=20 The changes tend to be steps in the characteristic and these decrease with t= ime=20 after the load is applied. New steps may be excited by quakes. The step chan= ges=20 can give problems with velocity feedback circuits - they tend to generate=20 spikes.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I find=20 that I need to try to separate the fundamental spring-noise issues which w= ill=20 always be present from ones that can be addressed by manufacturing and des= ign=20 techniques such as limiting spring stress, ageing, heat cycling, material=20 choice, etc.  For example, I'd heard stories of leaf-spring designs t= hat=20 popped and crackled when they were first assembled and which then, over ti= me,=20 would quiet down to an acceptable noise level.  However a noise proce= ss=20 that is fundamental and always present would be of greater concern. =20
    All common / practical spring materials are lik= e=20 this. You have the electronic noise, the thermal noise of the sensor itself,= the=20 hysteretic noise and the background seismic noise.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>As an=20 engineer, creep itself does not concern me, so long as it is acceptably sl= ow=20 and not too noisy.  Being able to quantify what one might expect to s= ee=20 would be helpful in trying to design
something.

New subject: Bo= th=20 you and Chris had previously written of the idea of using feedback to help= =20 maintain instrument centering.  I came up with the following, which i= f=20 correct has some interesting implications.

"The goal of maintaining= =20 centering by the use of feedback can be restated as the goal of using feed= back=20 to make the instrument insensitive to the unwanted 'noise' forces which wo= uld=20 tend to push it off center.

When trying to do this, however, a prob= lem=20 unfortunately arises of the 'no free lunch' class, which in fact has nothi= ng=20 directly to do with feedback. The (vertical) instrument simply can't=20 distinguish where an input force is coming from.  Is it from the spri= ng=20 getting weaker as the temperature rises, from buoyancy-force changes with=20= the=20 barometer, from spring creep or is it the acceleration-related force from=20= the=20 very low frequency geological signal you wanted to observe?  To the=20 extent that you succeed in reducing the instrument's sensitivity to the=20 'noise' forces you also reduce its sensitivity to the signal force. =20= This=20 can be restated as the well accepted generalization:  'feedback does=20= not=20 affect the signal to noise ratio'. (assuming, of course, that the added=20 feedback components are noise free)
    Yes you can. You can either re-zero mechanicall= y=20 with a small motor to keep the system in range or use an integrated signal a= s=20 force feedback. If you integrate the output to say 500 seconds for a 50 seco= nd=20 period instrument, you can keep the mean position centred without significan= tly=20 effecting the 50 second response. This will take out most drifts.=20= With=20 a velocity output, the very long period signals are small.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I am=20 confident that is the reason why commercial instruments aren't designed to= =20 have large responses to acceleration / force down to very low=20 frequencies.  Instead they are designed to establish a compromise bet= ween=20 letting through sufficiently low-frequency seismic signals to be useful, w= hile=20 at the same time resisting the much larger, though more slowly changing,=20 instrument 'noise' forces.  That may also explain why so much effort=20= has=20 to go into reducing the noise generators at their source, by using exotic=20 alloys in leaf spring suspensions, maintaining constant
(usually low)=20 ambient pressure, and attempting to maintain the temperature as constant a= s=20 possible, etc."
    See Wielandt's references on psn for=20 feedback seismometer design. Seismometers are usually designed to give=20= a=20 velocity law output directly using quite complicated feedback loops - this i= s=20 'traditional'. High sensitivity seismometers usually have periods between 60= and=20 120 seconds and this covers most surface wave periods of maybe 15 to 40 seco= nds.=20 A few types go to 360 seconds. To cover all the Earth Eigenmodes, you have t= o go=20 to about 2,000 seconds. 
 
    Regards,
 
    Chris Chapman
Subject: Re: Seismograph noise problem From: ChrisAtUpw@....... Date: Mon, 11 Feb 2008 00:01:14 EST In a message dated 10/02/2008, lconklin@............ writes: Thanks for your suggestions. I haven't yet made any serious attempt to work the current manifestation of this problem, mostly for lack of new ideas for something new to try. Hi Larry, You have to approach fault finding step by step. 1 Check the PSU lines for DC level and AC noise first. 2 Visually check all solder joints with a magnifying glass. These are the commonest problems. 3 When the system is noisy, disconnect the oscillator drive, observe any change in the trace and then connect it again. Also measure the DC level on the TP output of the first opamp. 4 Check the two sensors for operation. 5 Assuming that here is no significant change, disconnect the drive again, short the input and observe the output and DC level changes. Try unplugging the sensors in sequence 6 If you can't use a freezer can, try pushing / tapping components with a plastic rod. 7 Definitely check for crevice corrosion under solder joints. 8 Clean and put vaseline on the input plugs. Nickel and particularly chrome plugs develop tough oxide coatings in the damp. 9 You can brush coat the circuit tracks with polyurethane single pack varnish. You can solder through it if necessary. Because you have changed the opamp does not mean that the new opamp is good! When I change opamps, I usually fit a plug in holder. You can wreck an opamp by overheating it during soldering. Regards, Chris Chapman
In a message dated 10/02/2008, lconklin@............ writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Thanks=20 for your suggestions.  I haven't yet made any serious attempt to
= work=20 the current manifestation of this problem, mostly for lack of new
idea= s=20 for something new to try.
Hi Larry,
 
    You have to approach fault finding step by=20 step.
 
    1 Check the PSU lines for DC level and AC noise= =20 first.
    2 Visually check all solder joints with a=20 magnifying glass. These are the commonest problems.
    3 When the system is noisy, disconnect the=20 oscillator drive, observe any change in the trace and then connect it again.= =20 Also measure the DC level on the TP output of the first opamp.
    4 Check the two sensors for operation.
    5 Assuming that here is no significant change,=20 disconnect the drive again, short the input and observe the output and DC le= vel=20 changes. Try unplugging the sensors in sequence
    6 If you can't use a freezer can, try pushing /= =20 tapping components with a plastic rod.
    7 Definitely check for crevice corrosion under=20 solder joints.
    8 Clean and put vaseline on the input plugs. Ni= ckel=20 and particularly chrome plugs develop tough oxide coatings in the damp.
    9 You can brush coat the circuit tracks with=20 polyurethane single pack varnish. You can solder through it if necessary.
    
    Because you have changed the opamp does not mea= n=20 that the new opamp is good! When I change opamps, I usually fit a plug in=20 holder. You can wreck an opamp by overheating it during soldering.
 
    Regards,
 
    Chris Chapman
 
Subject: Re: Seismograph noise problem From: ChrisAtUpw@....... Date: Mon, 11 Feb 2008 00:13:31 EST In a message dated 10/02/2008 15:40:02 GMT Standard Time, lconklin@............ writes: One thing that your comments encourage me to revisit is the way the cover over the sensor is made. It is made of 1/4/inch particle board and a little heavy on the heavy side. I is just sitting on the base frame of the sensor, held down by it's own weight. There are soft plastic feet attached where the contact is made to the frame. Hi Larry, You want to make a cover which rests on the floor NOT on the seismometer base. Put a single sheet of bubble wrap over it with the corners folded in. 1/4" particle board won't give much thermal protection. Regards, Chris
In a message dated 10/02/2008 15:40:02 GMT Standard Time,=20 lconklin@............ writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>One=20 thing that your comments encourage me to revisit is the way the
cover=20= over=20 the sensor is made.  It is made of 1/4/inch particle board
and a=20 little heavy on the heavy side.  I is just sitting on the base
fr= ame=20 of the sensor, held down by it's own weight.  There are soft
plas= tic=20 feet attached where the contact is made to the=20 frame. 
Hi Larry,
 
    You want to make a cover which rests on the flo= or=20 NOT on the seismometer base. Put a single sheet of bubble wrap over it with=20= the=20 corners folded in. 1/4" particle board won't give much thermal protection.
    Regards,
    Chris
Subject: Re: Geophone From: "Dale Hardy" photon1@........... Date: Mon, 11 Feb 2008 17:25:36 +1100 Hello John, actually there are 2 units, the geophones are from Larry, L15 used ones. One will be on a hillside of conglomerate, 20mtr above sea-level, the other at sea-level on a sand flat. Both have houses nearby. regards Dale ----- Original Message ----- From: "John Lahr" To: Sent: Monday, February 11, 2008 1:02 PM Subject: Re: Geophone > At 05:30 PM 2/10/2008, you wrote: >>Hi, I am going to add a geophone to my station and just would like ideas >>on how best to place one. >>Thanks >>Dale > > Dale, > > Could you provide a few more details about the geophone and your setting? > > John > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.2 - > Release Date: 10/02/2008 12:00 AM > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Geophone From: John Lahr johnjan@........ Date: Sun, 10 Feb 2008 22:39:35 -0800 Dale, In both cases, could you burry the geophones at least 18-inches deep? Perhaps on the hillside there are some areas with at least that much soil. Should be easy in the sand. John At 10:25 PM 2/10/2008, you wrote: >Hello John, >actually there are 2 units, the geophones are from Larry, L15 used ones. >One will be on a hillside of conglomerate, 20mtr above >sea-level, the other at sea-level on a sand flat. >Both have houses nearby. >regards >Dale > > > > >----- Original Message ----- From: "John Lahr" >To: >Sent: Monday, February 11, 2008 1:02 PM >Subject: Re: Geophone > > >>At 05:30 PM 2/10/2008, you wrote: >>>Hi, I am going to add a geophone to my station and just would like >>>ideas on how best to place one. >>>Thanks >>>Dale >> >>Dale, >> >>Could you provide a few more details about the geophone and your setting? >> >>John >> >>__________________________________________________________ >> >>Public Seismic Network Mailing List (PSN-L) >> >>To leave this list email PSN-L-REQUEST@.............. with the body >>of the message (first line only): unsubscribe >>See http://www.seismicnet.com/maillist.html for more information. >> >> >>-- >>No virus found in this incoming message. >>Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: >>269.20.2 - Release Date: 10/02/2008 12:00 AM >> > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with the body >of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Geophone From: "Dale Hardy" photon1@........... Date: Mon, 11 Feb 2008 17:43:59 +1100 John, yes, burying in either location is not a problem Dale ----- Original Message ----- From: "John Lahr" To: Sent: Monday, February 11, 2008 5:39 PM Subject: Re: Geophone > Dale, > > In both cases, could you burry the geophones at least 18-inches deep? > Perhaps on the hillside > there are some areas with at least that much soil. Should be easy in the > sand. > > John > > At 10:25 PM 2/10/2008, you wrote: >>Hello John, >>actually there are 2 units, the geophones are from Larry, L15 used ones. >>One will be on a hillside of conglomerate, 20mtr above sea-level, the >>other at sea-level on a sand flat. >>Both have houses nearby. >>regards >>Dale __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: Brett Nordgren Brett3mr@............. Date: Mon, 11 Feb 2008 08:17:33 -0500 Chris At 11:45 PM 2/10/2008 -0500, you wrote: >In a message dated 11/02/2008, Brett Nordgren writes: >Hi Brett, > > You have to make a spring arrangement such that it exactly balances > the mass, but has a very slow rate of change of force with position, a > few % at most. Hence the somewhat exotic spring arrangements used in > seismometers. Agreed The example case I've been analyzing uses a 2 sec period. >Hooke's Law is only an approximation. You get a time dependant component >and creep. The creep is noisy and also time dependant. The changes tend to >be steps in the characteristic and these decrease with time after the load >is applied. New steps may be excited by quakes. The step changes can give >problems with velocity feedback circuits - they tend to generate spikes. How noisy? How large steps/spikes? What is their assumed spectrum? > All common / practical spring materials are like this. You have the > electronic noise, the thermal noise of the sensor itself, the hysteretic > noise and the background seismic noise. >When trying to do this, however, a problem unfortunately arises of the 'no >free lunch' class, which in fact has nothing directly to do with feedback. >The (vertical) instrument simply can't distinguish where an input force is >coming from. Is it from the spring getting weaker as the temperature >rises, from buoyancy-force changes with the barometer, from spring creep >or is it the acceleration-related force from the very low frequency >geological signal you wanted to observe? To the extent that you succeed >in reducing the instrument's sensitivity to the 'noise' forces you also >reduce its sensitivity to the signal force. This can be restated as the >well accepted generalization: 'feedback does not affect the signal to >noise ratio'. (assuming, of course, that the added feedback components are >noise free) > Yes you can. You can either re-zero mechanically with a small motor > to keep the system in range or use an integrated signal as force > feedback. If you integrate the output to say 500 seconds for a 50 second > period instrument, you can keep the mean position centred without > significantly effecting the 50 second response. This will take out most > drifts. With a velocity output, the very long period signals are small. That was exactly what I was suggesting; that if you could assign a frequency F below which you didn't want to see data you might be able to do feedback centering. Your example suggests that F is a bit below 1/50sec. What if you wanted to make an instrument which was sensitive to 1/500sec and below. It is only to the degree that you are willing to limit your low-end response that you have a chance of using feedback to perform centering, and then, only if the 'noise' forces are of lower frequency than your signals. To have been properly precise, I should have said '*In any frequency band* feedback does not change the S/N ratio.' Incidentally, the process of mechanical re-zeroing, if automated or done in a systematic way, can be crudely treated as just another very low frequency feedback branch. >I am confident that is the reason why commercial instruments aren't >designed to have large responses to acceleration / force down to very low >frequencies. Instead they are designed to establish a compromise between >letting through sufficiently low-frequency seismic signals to be useful, >while at the same time resisting the much larger, though more slowly >changing, instrument 'noise' forces. That may also explain why so much >effort has to go into reducing the noise generators at their source, by >using exotic alloys in leaf spring suspensions, maintaining constant >(usually low) ambient pressure, and attempting to maintain the temperature >as constant as possible, etc." > See Wielandt's references on psn for feedback seismometer design. > Seismometers are usually designed to give a velocity law output directly > using quite complicated feedback loops - this is 'traditional'. High > sensitivity seismometers usually have periods between 60 and 120 seconds > and this covers most surface wave periods of maybe 15 to 40 seconds. A > few types go to 360 seconds. To cover all the Earth Eigenmodes, you have > to go to about 2,000 seconds. Which again raises the issue; in the 2000 sec instrument, how do you propose to use feedback to maintain centering in the presence of 500sec 'noises'? The very reason for the 60 or 120 or 360 sec limits is to allow the instruments to 'filter out' lower frequency noise. Also the choice of using a response that is flat to velocity, rather than to force/acceleration, is having the significant effect of attenuating the influence of force-noise below the low frequency cutoff. Regards, Brett You can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Seismograph noise problem From: Roger Sparks rsparks@.......... Date: Mon, 11 Feb 2008 06:35:25 -0800 Hi Larry, The description of your seismometer seems very similar to mine, except for the mount of the sensor cover. I drilled three holes in the concrete floor, then put expansion bolts in. The result is three 1/4 inch bolts extending about 2 inches above the rug. On top of these three bolts I laid a 3/4 inch thick particle board large enough to support the seismometer cover. I stepped on the board both to seat it and to ensure that the supporting bolts were solid. As I recall, I re tightened the bolts after the first step-on, and repeated the procedure. I took the precaution of supporting the seismometer cover with three support points, to prevent rocking of the cover. It sounds like you accomplished the same thing with flexible/soft cover supports. My seismometer goes inside of the cover. I am very satisfied with the mounting now. You can see my occasional postings from Ellensburg, Wash. on the PSN web site. Good luck, Roger > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 2 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Re: Seismograph noise problem > From: Larry Conklin > Date: Sun, 10 Feb 2008 10:39:43 -0500 > > Hi Roger, > > I it very interesting that you have had a similar problem, and I > appreciate your suggestions. I my case, the sensor in in the basement, > sitting on a concrete floor. Several years ago I epoxied three small > aluminum plates to the floor for the settling screws to sit on. My > concern at the time was that turning the leveling screw against the > concrete was grinding into the floor, leaving concrete dust under the > screw. One of the probable flaws in my construction is that the > leveling screw is very small (#4) and more than likely not really firm > enough. But, when I'm not being "haunted" the thing performs pretty > well. Seems like problems stemming from the mechanical design shouldn't > be episodic the way I have having them. I am using a 3 point mount, and > the other two feet (base of the triangle) are sturdier. > > One thing that your comments encourage me to revisit is the way the > cover over the sensor is made. It is made of 1/4/inch particle board > and a little heavy on the heavy side. I is just sitting on the base > frame of the sensor, held down by it's own weight. There are soft > plastic feet attached where the contact is made to the frame. I don't > normally make a point of pressing everything down to reseat things after > i adjust it. Never occurred to me to do that. One thing I did try > since this last episode started was to put a little piece of tape under > each foot, to introduce a little "sqisshyness" to prevent the kind of > "micro-rocking" that you apparently had. I didn't see any obvious > difference. > > Guess I'm going to have to embark on a real science project. > > Larry > > > > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: seismometer performance From: Randall Peters PETERS_RD@.......... Date: Mon, 11 Feb 2008 10:26:27 -0500 Confusion about noise limitations of a seismic instrument results largely from misconceptions about how even a perfect instrument behaves. It is universally appreciated that a low natural period is needed, but the nature and the reason for this are not so widely understood. That the sensitivity is proportional to the square of the mechanical period is easy to understand in the case of a simple pendulum. Remember that what excites the pendulum (and every other seismometer) is acceleration. For drive frequencies below the natural period, the angle in radians through which the pendulum gets displaced is a measure of the acceleration. No matter the detector type, its best placement is at the bottom of the pendulum. For a displacement sensor, the output signal is proportional to the acceleration, since the displacement of the bob equals the pendulum length times the measured angle, for angles much less than the 57.3 degrees of a radian (always true). The displacement sensor output is proportional to the length of the pendulum in this case, according to the definition of angle. Further, according to the well known expression for the period of a simple pendulum (two pi times the square root of its length divided by the earth's field, 'little g') we see that the size of the displacement (which determines the sensitivity of the instrument when noise is present) is governed by the square of the period. It can be shown from the mathematics describing every seismometer (by solving its equation of motion derived from Newton's 2nd law) that this is a general result. In other words, every mechanical oscillator configured to behave as a seismometer will be limited in sensitivity according to the square of the natural period. It is important to understand that the instrument's sensitivity to the external excitation is not the only thing to which a seismometer responds. Just as the ideal response involves the square of the period, so the sensitivity of an instrument to its own internal structural changes is likewise proportional to the square of its natural period. It is for this reason (undesirable motions due to internal changes) that virtually all long-period seismometers must use feedback. What feedback is able to accomplish depends on its type. The common commercial force feedback methodology is one in which a very powerful feedback force is employed, using an actuator. The actuator force is tailored to provide the desired 'flat to velocity' output while at the same time providing the desired near critical damping. This synergetic combination of (i) mechanical part and (ii) electronic feedback part -- amounts to something brand new; I will here call it the super-duper-seismometer. For earthquake-only measurements, the force-balance instruments have proven worthy of the title super-seismometer. Nothing else compares favorably with their performance capabilities in the frequency range where they have been fine-tuned to excel. In the frequency range where research is increasingly directed (realm of earth hum and even lower), the super-duper-seismometer has a fatal flaw. Its flat to velocity sensing scheme willl never allow the signals of increasing interest to be seen above noise. There is an alternative feedback scheme that is not thus limited. It is one of 'soft-force feedback' to serve an entirely different function than force-balance. Force-balance 'morphs' a spring into something effectively altogether different--making in effect a 'soft spring having long period' out of a hard spring of astatic type. In the soft-force approach the long period is realized by the time-tested means first used by Lucien LaCoste. As LaCoste discovered in the 1930's, a spring with a period of 20 s is inherently prone to instabilities (through sensitivity to internal structural changes as a key factor, mentioned above). The adverse influences of its imperfections are greatly reduced if the spring is of zero-length. If this zero-length (effectively soft) spring can be gently manipulated so as to stay within an acceptable range of operation, as dictated by the sensor's requirements; then it will be super-sensitive without the noise limitations of the super-duper system. The means to 'manipulate' are not difficult. One way is to continually 'babysit' the instrument and make slight manual tilt adjustments when there is a slow wandering away from the operating point. Of course we all have other things to do, including sleep. But Allan Jones has used a motor/sensor subsystem on some of his horizontal instruments to accomplish this automatically. In my case, I have done the same thing on a vertical by using the original magnet/coil (Faraday law) detector of my Sprengnether vertical--except operating as an actuator instread of a detector. The error signal to accomplish the task is provided by small currents through the coil, their amounts being determined by a long time constant integrator of the output from the displacement sensor with which I modifed the instrument. Incidently, I understand that the very first automated feedback instrument was similar, except hydraulic in nature, using the flow of huge amounts of water to adjust the tilt of the 'pier'. Why is the soft-feedback better? I think on two accounts--the first already mentioned (fatal flaw of velocity sensing). The 2nd involves the nature of the imperfections. It is better to let the spring continually evolve into its "own best' equilibrium, as opposed to strongly manipulating the system with a strong force into the state that is dictated by the feedback network. To use an old expression, it's not good to mess with mother nature. A primary reason that strong-force feedback evolved the way it did is because of the sensor used. It is a capacitive, gap-varying type in which there is virtually no mechanical dynamic range. Thus force balance (almost no inertial mass movement) is necessary if the system is to have any decent sensitivity. By contrast, an area-varying capacitive sensor of the type that I patented can have a large mechanical dynamic range. Thus the mass can be allowed to evolve positionally through small amounts in the manner mentioned above. One other thing I want to mention in closing this discussion. The instrument with strong-force feedback is a 'whole new beast'. It behaves like a non-feedback instrument having a substantially lengthened period. It is not possible by passive electronic means (system without an actuator) to accomplish what is done by means of the electronic feedback forcing. Lowering the corner frequency of the amplifier in a passive system by an amount x does not give rise to the same improvement as lowering the natural mechanical frequency by the same x. The latter gives rise to an x-squared improvement in sensitivity; whereas the former has no chance of being similarly effective--because the electronics must be virtually linear if it is to be acceptable. Randall Subject: Re: Geophone From: ChrisAtUpw@....... Date: Mon, 11 Feb 2008 11:22:35 EST In a message dated 11/02/2008 06:25:56 GMT Standard Time, photon1@........... writes: Hello John, actually there are 2 units, the geophones are from Larry, L15 used ones. One will be on a hillside of conglomerate, 20mtr above sea-level, the other at sea-level on a sand flat. Both have houses nearby. Hi Dale, Check the units for the correct damping resistors. You need about 2.7 K Ohms total for a L15B, allowing for any parallel input resistors on your amplifier board. I aways use metal film resistors. Seal both ends of the 6 core screened connecting cable with silicone rubber to stop it 'breathing'. You will need to seal the top of the units and the cable entry points, if you bury them. You can get an odour free silicone rubber for this. DON'T use the sort which smells strongly of acetic acid - vinegar. You may have to seal the cable entry on the opposite side if they are not in a string. Don't leave any cropped wires exposed. Adhesive Heatshrink and be very useful here and for joining cables.. They should be set level using the spirit level supplied and the arrow should point true North. Alternatively, you could mount them in the bottom of a vertical pipe, but this is more expensive. We can buy an adhesive mastic which never sets called Blu-Tack / White-Tack, from stationers. It is used for attaching paper to notice boards. It is very good for sealing a seismometer case. Regards, Chris Chapman
In a message dated 11/02/2008 06:25:56 GMT Standard Time,=20 photon1@........... writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Hello=20 John,
actually there are 2 units, the geophones are from Larry, L15 use= d=20 ones.
One will be on a hillside of conglomerate, 20mtr above=20 sea-level,  the other
at sea-level on a sand flat.
Both have=20 houses nearby.
Hi Dale,
 
    Check the units for the correct damping resisto= rs.=20 You need about 2.7 K Ohms total for a L15B, allowing for any parallel input=20 resistors on your amplifier board. I aways use metal film resistors.
    Seal both ends of the 6 core screened=20 connecting cable with silicone rubber to stop it 'breathing'.
    You will need to seal the top of the units and=20= the=20 cable entry points, if you bury them. You can get an odour free silicone rub= ber=20 for this. DON'T use the sort which smells strongly of acetic acid - vinegar.= You=20 may have to seal the cable entry on the opposite side if they are not in a=20 string. Don't leave any cropped wires exposed. Adhesive Heatshrink and be ve= ry=20 useful here and for joining cables..
    They should be set level using the spirit level= =20 supplied and the arrow should point true North. 
    Alternatively, you could mount them in the bott= om=20 of a vertical pipe, but this is more expensive.
    We can buy an adhesive mastic which never sets=20 called Blu-Tack / White-Tack, from stationers. It is used for attaching pape= r to=20 notice boards. It is very good for sealing a seismometer case.
 
    Regards,
 
    Chris Chapman
Subject: Re: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Mon, 11 Feb 2008 12:23:56 -0500 Hi Chris, I think I will put your list of suggestions in my "great minds think alike" file. I have tried all of your first 6 suggestions, albeit not since this latest episode started. Regarding corrosion under solder joints, I haven't really checked thoroughly for that yet, but the board looks very clean. Re. your and Roger's comments about the cover, It will take me a little time to build a new one. In the mean time, I think I will try putting some sort of shims under the edges of it so that it is supported by the floor rather than the sensor frame, to see what happens. I already have some cloth wrapped around the base to keep drafts from getting under the cover. One other thing that I'd be interested in hearing your thoughts on is the fact that the "noise" isn't really as random as I'd expect from something like bad solder joints and such. If you look at the data I posted, especially from the LF channel, there definitely seems to be a dominant component with a period of around 20 seconds or so. I've got too many irons in the fire right now to devote full time to debugging this, but I plan to revisit all of your suggestions. Aside with messing with the cover a little, the other very easy test will be to disconnect the oscillator to see what happens. I still have an old test data file from the last time I tried it, and it doesn't look much different from what I saw then with everything hooked up, or now. Larry > Hi Larry, > > You have to approach fault finding step by step. > > 1 Check the PSU lines for DC level and AC noise first. > 2 Visually check all solder joints with a magnifying glass. These > are the commonest problems. > 3 When the system is noisy, disconnect the oscillator drive, observe > any change in the trace and then connect it again. Also measure the DC > level on the TP output of the first opamp. > 4 Check the two sensors for operation. > 5 Assuming that here is no significant change, disconnect the drive > again, short the input and observe the output and DC level changes. Try > unplugging the sensors in sequence > 6 If you can't use a freezer can, try pushing / tapping components > with a plastic rod. > 7 Definitely check for crevice corrosion under solder joints. > 8 Clean and put vaseline on the input plugs. Nickel and particularly > chrome plugs develop tough oxide coatings in the damp. > 9 You can brush coat the circuit tracks with polyurethane single > pack varnish. You can solder through it if necessary. > > Because you have changed the opamp does not mean that the new opamp > is good! When I change opamps, I usually fit a plug in holder. You can > wreck an opamp by overheating it during soldering. > > Regards, > > Chris Chapman > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: seismometer performance From: Brett Nordgren Brett3mr@............. Date: Mon, 11 Feb 2008 13:56:59 -0500 Randall, I just finished the the 3rd major revision and expansion of my overview of seismometer feedback, which may possibly present some of the issues we have been discussing from a slightly different perspective. What I try to do is, without much math, and depending mostly on frequency response graphs, conceptually build up a force-balance instrument, starting with a simple spring-mass. As a test case I use the parameters of Sean-Thomas Morrissey's STM-8, though the approach can be directly applied to any feedback vertical, or even pendulum design. In the process, my goal has been to convey a solid general sense of what feedback can and cannot do when applied to seismic sensors and provide an understanding of how design parameters relate to performance. It is at http://bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf about 2.4MB At 10:26 AM 2/11/2008 -0500, you wrote: >Confusion about noise limitations of a seismic instrument results largely >from misconceptions >about how even a perfect instrument behaves. It is universally >appreciated that a low >natural period is needed, but the nature and the reason for this are not >so widely >understood. >That the sensitivity is proportional to the square of the mechanical period is >easy to understand in the case of a simple pendulum. Remember that what >excites the pendulum >(and every other seismometer) is acceleration. For drive frequencies >below the natural >period, the angle in radians through which the pendulum gets displaced is >a measure of the >acceleration. >No matter the detector type, its best placement is at the bottom of the >pendulum. For a displacement sensor, the output signal is proportional to >the acceleration, >since the displacement of the bob equals the pendulum length times the >measured angle, for >angles much less than the 57.3 degrees of a radian (always true). The >displacement sensor >output is proportional to the length of the pendulum in this case, >according to the >definition of angle. Further, according to the well known expression for >the period of a >simple pendulum (two pi times the square root of its length divided by the >earth's field, >'little g') we see that the size of the displacement (which determines the >sensitivity of the >instrument when noise is present) is governed by the square of the >period. It can be shown >from the mathematics describing every seismometer (by solving its equation >of motion derived >from Newton's 2nd law) that this is a general result. In other words, >every mechanical >oscillator configured to behave as a seismometer will be limited in >sensitivity according to >the square of the natural period. > > It is important to understand that the instrument's sensitivity to > the external >excitation is not the only thing to which a seismometer responds. Just as >the ideal response >involves the square of the period, so the sensitivity of an instrument to >its own internal >structural changes is likewise proportional to the square of its natural >period. It is for >this reason (undesirable motions due to internal changes) that virtually >all long-period >seismometers must use feedback. Completely agree. > What feedback is able to accomplish depends on its type. The common > commercial force >feedback methodology is one in which a very powerful feedback force is >employed, using an >actuator. The actuator force is tailored to provide the desired 'flat to >velocity' output >while at the same time providing the desired near critical damping. This >synergetic >combination of (i) mechanical part and (ii) electronic feedback part -- >amounts to something >brand new; I will here call it the super-duper-seismometer. For >earthquake-only >measurements, the force-balance instruments have proven >worthy of the title super-seismometer. Nothing else compares favorably >with their >performance capabilities in the frequency range where they have been >fine-tuned to excel. > In the frequency range where research is increasingly directed > (realm of earth hum and >even lower), the super-duper-seismometer has a fatal flaw. Its flat to >velocity sensing >scheme willl never allow the signals of increasing interest to be seen >above noise. If by 'noise' you mean internal instrument noise such as from spring imperfections or sensor noise, then it's not clear that extending the instrument's low frequency response will improve the relationship between signals of interest and the instrument noise. Noise arising from places 'deeper' in the circuit may possibly be affected, though. > There >is an alternative feedback scheme that is not thus limited. It is one of >'soft-force >feedback' to serve an entirely different function than >force-balance. Force-balance 'morphs' >a spring into something effectively altogether different--making in effect >a 'soft spring >having long period' out of a hard spring of astatic type. In the >soft-force approach the >long period is realized by the time-tested means first used by Lucien >LaCoste. As LaCoste >discovered in the 1930's, a spring with a period of 20 s is inherently >prone to instabilities >(through sensitivity to internal structural changes as a key factor, >mentioned above). The >adverse influences of its imperfections are greatly reduced if the spring >is of zero-length. >If this zero-length (effectively soft) spring can be gently manipulated so >as to stay within >an acceptable range of operation, as dictated by the sensor's >requirements; then it will be >super-sensitive without the noise limitations of the super-duper >system. The means to >'manipulate' are not difficult. One way is to continually 'babysit' the >instrument and make >slight manual tilt adjustments when there is a slow wandering away from >the operating point. >Of course we all have other things to do, including sleep. But Allan >Jones has used a >motor/sensor subsystem on some of his horizontal instruments to accomplish >this >automatically. In my case, I have done the same thing on a vertical by >using the original >magnet/coil (Faraday law) detector of my Sprengnether vertical--except >operating as an >actuator instread of a detector. The error signal to accomplish the task >is provided by >small currents through the coil, their amounts being determined by a long >time constant >integrator of the output from the displacement sensor with which I modifed >the instrument. >Incidently, I understand that the very first >automated feedback instrument was similar, >except hydraulic in nature, using the flow of huge amounts of water to >adjust the tilt of the >'pier'. What you are describing is indeed feedback. In fact even the systematic manual readjusting of the tilt effects back to zero, say once per hour or even once per day, can be analyzed as a very rough approximation of a linear feedback branch. What threw me was the use of the term 'soft' in describing the process. The process as described corresponds to feedback with very high 'loop gain' which is the usual measure of feedback strength. Your soft feedback is also very strong feedback. What is characteristic, though, of the process is that it is only applied at very low frequencies, presumably lower than any data being collected. > Why is the soft-feedback better? I think on two accounts--the first > already mentioned >(fatal flaw of velocity sensing). The 2nd involves the nature of the >imperfections. It is >better to let the spring continually evolve into its "own best' >equilibrium, as opposed to >strongly manipulating the system with a strong force into the state that >is dictated by the >feedback network. To use an old expression, it's not good to mess with >mother nature. > A primary reason that strong-force feedback evolved the way it did > is because of the >sensor used. It is a capacitive, gap-varying type in which there is >virtually no mechanical >dynamic range. Though which is also quite sensitive and low noise relative to its size. >Thus force balance (almost no inertial mass movement) is necessary if the >system is to have any decent sensitivity. By contrast, an area-varying >capacitive sensor of >the type that I patented can have a large mechanical dynamic range. Thus >the mass can be >allowed to evolve positionally through small amounts in the manner >mentioned above. > One other thing I want to mention in closing this discussion. The > instrument with >strong-force feedback is a 'whole new beast'. It behaves like a >non-feedback instrument >having a substantially lengthened period. It is not possible by passive >electronic means >(system without an actuator) to accomplish what is done by means of the >electronic feedback >forcing. Lowering the corner frequency of the amplifier in a passive >system by an amount x >does not give rise to the same improvement as lowering the natural >mechanical frequency by >the same x. The latter gives rise to an x-squared improvement in >sensitivity; whereas the >former has no chance of being similarly effective--because the electronics >must be virtually >linear if it is to be acceptable. > Randall Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: feedback semantics From: Randall Peters PETERS_RD@.......... Date: Mon, 11 Feb 2008 18:18:31 -0500 Brett, I am not very familiar with the terminology used in the world of engineering controls. My term 'soft' for the feedback scheme that I have used seemed reasonable to me for the following reasons: (i) it is as you noted, happerning at a much lower frequency than most of the signals of interest (say teleseisms at 20 s period, and (ii) it is nowhere near as powerful as the forces required to do force-balance; i.e., keep the mass from ostensibly moving. You mention the matter of using feedback with a pendulum. I can't imagine a reasonably simple pendulum for seismic purposes where feedback would ever be necessary. The primary source of motion at very low frequencies is the change in shape of the earth. Every mass part of our planet contributes to the local field, and so a plumb bob provides information concerning eigenmodes and tides (as the VolksMeter has demonstrated). Your question about my use of the word 'noise' relative to force balance systems--anything that works with the derivative of the position of the inertial mass (flat to velocity sensor) will fail to see earth motions at really long periods (starting around a few thousand seconds or even less). Even though the period of the VolksMeter's simple pendulum is only about 1 s, it is well suited to the study of earth changes happening over days, months, and even years. Randall Subject: Re: Seismograph noise problem From: ChrisAtUpw@....... Date: Mon, 11 Feb 2008 18:53:34 EST In a message dated 11/02/2008, lconklin@............ writes: Regarding corrosion under solder joints, I haven't really checked thoroughly for that yet, but the board looks very clean. Hi Larry, I had a whole Sony TV with crevice corrosion. The joints looked perfect, but you could peel them off a black corrosion coat on the circuit strips. I had to unsolder, clean and resolder every joint on the **** board. Re. your and Roger's comments about the cover, It will take me a little time to build a new one. Putting the cover on the floor isolates the seismometer from pneumatic effects. I use 2" Celotex, but it isn't cheap. Bubble wrap can also be very useful in reducing temperature changes and drafts .... One other thing that I'd be interested in hearing your thoughts on is the fact that the "noise" isn't really as random as I'd expect from something like bad solder joints and such. If you look at the data I posted, especially from the LF channel, there definitely seems to be a dominant component with a period of around 20 seconds or so. I had noted that. It looked as if you were experiencing greatly increased gain, rather than just random noise. This could be resistors, solder joints, diodes or the opamp. Do measure the DC levels on TP. Does the Red/Green LED ever light up? The NE5534 does take about 0.5 micro A to drive it - quite thirsty... Try tapping the components? Unsoldering C49 would isolate everything downstream of the first two opamps. Could there be any strong radio signals at 2 / 4 / 8 / 12 MHz? You do have two radio receivers on the input... Electricity Utility time switches work off radio signals on the power lines. Try connecting an audio amplifier to the circuit before the integrator and listening with headphones? I have solved some noise problems this way. I was getting quite large random pulses which seemed to be real, not instrumental. When I listened, I heard a heavy lorry approaching a sunken drain grating on the corner of the local main road.... I've got too many irons in the fire right now to devote full time to debugging this, but I plan to revisit all of your suggestions. Aside with messing with the cover a little, the other very easy test will be to disconnect the oscillator to see what happens. I still have an old test data file from the last time I tried it, and it doesn't look much different from what I saw then with everything hooked up, or now. I would expect there to be a simple fault which is sensitive to humidity - since heating the board reduced the signal. Good Luck! Regards, Chris Chapman
In a message dated 11/02/2008, lconklin@............ writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>Regarding corrosion under solder joints, I haven't really checked= =20
thoroughly for that yet, but the board looks very clean.
Hi Larry,
 
    I had a whole Sony TV with crevice=20 corrosion. The joints looked perfect, but you could peel them off a bla= ck=20 corrosion coat on the circuit strips. I had to unsolder, clean and reso= lder=20 every joint on the **** board.
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>Re. your=20 and Roger's comments about the cover, It will take me a little
time to= =20 build a new one. 
    Putting the cover on the floor isolates the=20 seismometer from pneumatic effects. I use 2" Celotex, but it isn't cheap. Bu= bble=20 wrap can also be very useful in reducing temperature changes and=20 drafts ....
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>One=20 other thing that I'd be interested in hearing your thoughts on is
the=20= fact=20 that the "noise" isn't really as random as I'd expect from
something l= ike=20 bad solder joints and such.  If you look at the data I
posted,=20 especially from the LF channel, there definitely seems to be a
dominan= t=20 component with a period of around 20 seconds or so.
    I had noted that. It looked as if you were=20 experiencing greatly increased gain, rather than just random noise. This cou= ld=20 be resistors, solder joints, diodes or the opamp.
    Do measure the DC levels on TP. Does the Red/Gr= een=20 LED ever light up?
    The NE5534 does take about 0.5 micro A to drive= it=20 - quite thirsty...
    Try tapping the components?
    Unsoldering C49 would isolate everything downst= ream=20 of the first two opamps.
    Could there be any strong radio signals at 2 /=20= 4 /=20 8 / 12 MHz? You do have two radio receivers on the input... Electricity Util= ity=20 time switches work off radio signals on the power lines.
    Try connecting an audio amplifier to the circui= t=20 before the integrator and listening with headphones? I have solved some nois= e=20 problems this way. I was getting quite large random pulses which seemed to b= e=20 real, not instrumental. When I listened, I heard a heavy lorry approaching a= =20 sunken drain grating on the corner of the local main road....
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I've got=20 too many irons in the fire right now to devote full time to debugging this= ,=20 but I plan to revisit all of your suggestions.  Aside with messing wi= th=20 the cover a little, the other very easy test will be
to disconnect the= =20 oscillator to see what happens.  I still have an old test data file f= rom=20 the last time I tried it, and it doesn't look much different from what I s= aw=20 then with everything hooked up, or now.
    I would expect there to be a simple fault which= is=20 sensitive to humidity - since heating the board reduced the signal. Good=20 Luck!
 
    Regards,
 
    Chris Chapman
 
Subject: Re: Seismograph noise problem From: Larry Conklin lconklin@............ Date: Mon, 11 Feb 2008 20:27:39 -0500 Yeah, I've thought about resoldering the entire **** board too, but it's not my first choice of things to try. When I tried to bake out the board under an incandescent lamp that one time, I did seem to get some improvement, but it certainly wasn't very impressive. Regarding the apparent non-randomness of the noise. I had the thought that dampness had gotten into one of the gain pots resulting in a larrge increase in the gain. But, despite the high noise level, I am still able to record quakes and they produce records that are just about the amplitude I would expect. I got a record of the mid-atlantic quake that was good enough that I was able to set the phase picks. Even when the thing is running acceptably, I still notice the same 20 second or so hump spectrum. I do monitor the leveling test point continuously. I put a zero center meter on it so that I better center the leveling. I added a readout of the voltage at the test point to my data logging program. I have a line from the test point connected to a spare channel on my A/D converter. Several of your other suggestions are things I wouldn't have thought of. Tapping in with headphones would be interesting to try in any event. I'm in a residential area not far from a busy street, and I have no doubt that I'm getting a lot of higher frequency noise from traffic and such. I can see a definite dinural variation, quieter at night, noiseier during the day. But I see no variation whatsoever for days on end when the thing is acting up. Interesting. As I have been typing this, the excess noise has diminished very substantially over the span of about 15 minutes, and has stayed pretty low ever since. It would be a sort of Murphy's law in reverse if just when I have been getting motivated to make an all out attack on the problem, it went away spontaneously. Wouldn't be the first time. At any rate, you've given me a lot of food for thought, for which I thank you. Larry ChrisAtUpw@....... wrote: > In a message dated 11/02/2008, lconklin@............ writes: > > Regarding corrosion under solder joints, I haven't really checked > thoroughly for that yet, but the board looks very clean. > > Hi Larry, > > I had a whole Sony TV with crevice corrosion. The joints looked > perfect, but you could peel them off a black corrosion coat on the > circuit strips. I had to unsolder, clean and resolder every joint on the > **** board. > > Re. your and Roger's comments about the cover, It will take me a little > time to build a new one. > > Putting the cover on the floor isolates the seismometer from > pneumatic effects. I use 2" Celotex, but it isn't cheap. Bubble wrap can > also be very useful in reducing temperature changes and drafts .... > > One other thing that I'd be interested in hearing your thoughts on is > the fact that the "noise" isn't really as random as I'd expect from > something like bad solder joints and such. If you look at the data I > posted, especially from the LF channel, there definitely seems to be a > dominant component with a period of around 20 seconds or so. > > I had noted that. It looked as if you were experiencing greatly > increased gain, rather than just random noise. This could be resistors, > solder joints, diodes or the opamp. > Do measure the DC levels on TP. Does the Red/Green LED ever light up? > The NE5534 does take about 0.5 micro A to drive it - quite thirsty... > Try tapping the components? > Unsoldering C49 would isolate everything downstream of the first two > opamps. > Could there be any strong radio signals at 2 / 4 / 8 / 12 MHz? You > do have two radio receivers on the input... Electricity Utility time > switches work off radio signals on the power lines. > Try connecting an audio amplifier to the circuit before the > integrator and listening with headphones? I have solved some noise > problems this way. I was getting quite large random pulses which seemed > to be real, not instrumental. When I listened, I heard a heavy lorry > approaching a sunken drain grating on the corner of the local main road.... > > I've got too many irons in the fire right now to devote full time to > debugging this, but I plan to revisit all of your suggestions. > Aside with messing with the cover a little, the other very easy test > will be > to disconnect the oscillator to see what happens. I still have an > old test data file from the last time I tried it, and it doesn't > look much different from what I saw then with everything hooked up, > or now. > > I would expect there to be a simple fault which is sensitive to > humidity - since heating the board reduced the signal. Good Luck! > > Regards, > > Chris Chapman > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: ChrisAtUpw@....... Date: Mon, 11 Feb 2008 22:43:08 EST In a message dated 11/02/2008, Brett3mr@............. writes: >Hooke's Law is only an approximation. You get a time dependant component >and creep. The creep is noisy and also time dependant. The changes tend to >be steps in the characteristic and these decrease with time after the load >is applied. New steps may be excited by quakes. The step changes can give >problems with velocity feedback circuits - they tend to generate spikes. How noisy? How large steps/spikes? What is their assumed spectrum? Hi Brett, My experience is that the steps can be well above the normal noise level. If they are smaller, they probably don't matter. They are a step function with the appropriate spectrum. The frequency varied greatly from several per second after stressing the spring to an odd one per hour or less after an extended stabilisation period. Springs for seismometers go through extended preparation to reduce / measure the noise. I don't know the full details. > All common / practical spring materials are like this. You have the > electronic noise, including maybe 1/f noise, the thermal noise of the sensor itself, the hysteretic > noise and the background seismic noise. That was exactly what I was suggesting; that if you could assign a frequency F below which you didn't want to see data you might be able to do feedback centering. Your example suggests that F is a bit below 1/50 Hz. What if you wanted to make an instrument which was sensitive to 1/500 Hz and below. It is only to the degree that you are willing to limit your low-end response that you have a chance of using feedback to perform centering, and then, only if the 'noise' forces are of lower frequency than your signals. It is more usual to get very long periods by feedback + integration, maybe numerical? > See Wielandt's references on psn for feedback seismometer design. > Seismometers are usually designed to give a velocity law output directly > using quite complicated feedback loops - this is 'traditional'. High > sensitivity seismometers usually have periods between 60 and 120 seconds > and this covers most surface wave periods of maybe 15 to 40 seconds. A > few types go to 360 seconds. To cover all the Earth Eigenmodes, you have > to go to about 2,000 seconds. Which again raises the issue; in the 2000 sec instrument, how do you propose to use feedback to maintain centering in the presence of 500sec 'noises'? The very reason for the 60 or 120 or 360 sec limits is to allow the instruments to 'filter out' lower frequency noise. Also the choice of using a response that is flat to velocity, rather than to force/acceleration, is having the significant effect of attenuating the influence of force-noise below the low frequency cutoff. Reducing the noise and drift to allow 1000 second responses was what made the Streckeisen STS-1 so difficult to make and so expensive. I would advise using a digital measuring / feedback system to do this for the long periods involved. It is possible to greatly reduce the drift components. By temperature cycling and measuring the result, it is possible to remove a lot of the thermal drift. You hermetically seal the case to keep the gas density constant. With reference to _http://bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf_ (http://bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf) describing feedback systems: >> The difficulty comes when we want to tightly control the frequency response of such a device, or equally important, accurately know its phase response or time delays over the band of frequencies of interest, which is essential to do if its data are to be compared with data from other instruments. Another difficulty comes when we try to maintain the proper centering of the mass in the presence of slow changes in the device or its surroundings. These could arise from changes in temperature, slow changes in ground tilt, earth tides, or in the case of a vertical instrument, spring creep, as well as from numerous other potential sources. In a sensitive instrument such changes could be great enough to move its output completely out of range before mechanical adjustments can be made. Feedback, properly applied, can be used both to shape the instrument response and also to counter some of the effects of slowly-applied errors. Finally, feedback will have the effect of greatly reducing the motion of the mass in response to seismic ground motion. This means that with feedback we might be able to use a displacement transducer which has quite a small range of operation, but which, in return, could be very sensitive. In addition, by limiting the sensor motion we can greatly reduce the effect of transducer and other system nonlinearities. It should be noted that we will be looking here at a feedback system which senses the apparent position of the seismic mass and then feeds back a signal which is used to apply a force to the mass to counter any changes. If we consider a pendulum sensor system, the response is proportional to the square of the period. If you take a 2 second pendulum and reduce the restoring force to give a 20 second system, should you get 100x the response for signals already in the passband? Why should a synthesised feedback response to obtain a longer period result in a much smaller response to the ground motion? You seem to consider that requiring an increased position sensitivity is an advantage. Since we are already at or beyond the easy measurement / stability limit at maybe 10 nm, getting an increased sensitivity / lower instrument noise with a comparable stability is an expensive pain in the backside. There is just no problem in measuring quite large position changes in principle. There are increasing problems in trying to measure smaller changes. If you use a DC path from your position sensor through a long period integrator to the feedback transducer, you can in theory remove ~all position drifts. However, this might require a high current output or a power opamp. You don't need very much gain, but maybe a separate feedback coil? You seem to be adding a high pass filter to the system and then trying to get long period / low drift performance?? A capacitative position sensor system can have a very high linearity. What other system nonlinearities were you considering that could be relevant? See _http://physics.mercer.edu/hpage/peters.html_ (http://physics.mercer.edu/hpage/peters.html) Improving seismometer performance..... Regards, Chris Chapman
In a message dated 11/02/2008, Brett3mr@............. writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>>Hooke's Law is only an approximation. You get a time dependan= t=20 component
>and creep. The creep is noisy and also time dependant. T= he=20 changes tend to
>be steps in the characteristic and these decrease=20= with=20 time after the load
>is applied. New steps may be excited by quakes= ..=20 The step changes can give
>problems with velocity feedback circuits= -=20 they tend to generate spikes.

How noisy?  How large=20 steps/spikes?  What is their assumed spectrum?
Hi Brett,
 
    My experience is that the steps can be wel= l=20 above the normal noise level. If they are smaller, they probably don't matte= r.=20 They are a step function with the appropriate spectrum.
    The frequency varied greatly from several per=20 second after stressing the spring to an odd one per hour or less after an=20 extended stabilisation period. Springs for seismometers go through exte= nded=20 preparation to reduce / measure the noise. I don't know the full=20 details. 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>>     All common / practical spring materials a= re=20 like this. You have the
> electronic noise, including maybe 1/f noi= se,=20 the thermal noise of the sensor itself, the hysteretic
> noise and=20= the=20 background seismic noise.

That was exactly what I was suggesting; t= hat=20 if you could assign a
frequency F below which you didn't want to see d= ata=20 you might be able to do
feedback centering.  Your example suggest= s=20 that F is a bit below
1/50 Hz.  What if you wanted to make an=20 instrument which was sensitive to
1/500 Hz and below.  It is only= to=20 the degree that you are willing to limit
your low-end response that yo= u=20 have a chance of using feedback to perform
centering, and then, only i= f=20 the 'noise' forces are of lower frequency than
your=20 signals.
    It is more usual to get very long periods by=20 feedback + integration, maybe numerical?
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2> >     See Wielandt's references on psn fo= r=20 feedback seismometer design.
> Seismometers are usually designed to= =20 give a velocity law output directly
> using quite complicated feedb= ack=20 loops - this is 'traditional'. High
> sensitivity seismometers usua= lly=20 have periods between 60 and 120 seconds
> and this covers most surf= ace=20 wave periods of maybe 15 to 40 seconds. A
> few types go to 360=20 seconds. To cover all the Earth Eigenmodes, you have
> to go to abo= ut=20 2,000 seconds.

Which again raises the issue; in the 2000 sec=20 instrument, how do you
propose to use feedback to maintain centering i= n=20 the presence of 500sec
'noises'?  The very reason for the 60 or 1= 20=20 or 360 sec limits is to allow
the instruments to 'filter out' lower=20 frequency noise.  Also the choice of
using a response that is fla= t to=20 velocity, rather than to
force/acceleration, is having the significant= =20 effect of attenuating the
influence of force-noise below the low frequ= ency=20 cutoff.
    Reducing the noise and drift to allow 1000= =20 second responses was what made the Streckeisen STS-1 so difficult to ma= ke=20 and so expensive. I would advise using a digital measuring / feedback system= to=20 do this for the long periods involved. It is possible to greatly reduce the=20 drift components. By temperature cycling and measuring the result, it i= s=20 possible to remove a lot of the thermal drift. You hermetically seal the cas= e to=20 keep the gas density constant. 
 
     With reference to http:/= /bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf =20 describing feedback systems:
 
>>    The difficulty comes when we want to=20 tightly control the frequency response of such a device, or
equally=20 important, accurately know its phase response or time delays over the band o= f=20 frequencies of
interest, which is essential to do if its data are to be=20 compared with data from other instruments.
Another difficulty comes when=20= we=20 try to maintain the proper centering of the mass in the presence of
slow=20 changes in the device or its surroundings. These could arise from changes in= =20 temperature, slow
changes in ground tilt, earth tides, or in the case of=20= a=20 vertical instrument, spring creep, as well as from
numerous other potenti= al=20 sources. In a sensitive instrument such changes could be great enough to
= move=20 its output completely out of range before mechanical adjustments can be made= ..=20 Feedback,
properly applied, can be used both to shape the instrument resp= onse=20 and also to counter some of the
effects of slowly-applied errors. Finally= ,=20 feedback will have the effect of greatly reducing the motion
of the mass=20= in=20 response to seismic ground motion. This means that with feedback we might be= =20 able to
use a displacement transducer which has quite a small range of=20 operation, but which, in return, could
be very sensitive. In addition, by= =20 limiting the sensor motion we can greatly reduce the effect of
transducer= and=20 other system nonlinearities. It should be noted that we will be looking here= at=20 a
feedback system which senses the apparent position of the seismic mass=20= and=20 then feeds back a signal
which is used to apply a force to the mass to=20 counter any changes.
 
    If we consider a pendulum sensor system, the=20 response is proportional to the square of the period. If you take a 2 second= =20 pendulum and reduce the restoring force to give a 20 second system, should y= ou=20 get 100x the response for signals already in the passband?
 
    Why should a synthesised feedback=20 response to obtain a longer period result in a much smaller respon= se=20 to the ground motion?
 
    You seem to consider that requiring an increase= d=20 position sensitivity is an advantage. Since we are already at or beyond = ;the=20 easy measurement / stability limit at maybe 10 nm, getting an increased= =20 sensitivity / lower instrument noise with a comparable stability is an=20 expensive pain in the backside. There is just no problem in measuring q= uite=20 large position changes in principle. There are increasing problems in trying= to=20 measure smaller changes.
 
   If you use a DC path from your position sensor throug= h a=20 long period integrator to the feedback transducer, you can in=20 theory remove ~all position drifts. However, this might require a high=20 current output or a power opamp. You don't need very much gain, but maybe a=20 separate feedback coil?
 
    You seem to be adding a high pass filter to the= =20 system and then trying to get long period / low drift performance??
 
    A capacitative position sensor system can have=20= a=20 very high linearity. What other system nonlinearities were you considering t= hat=20 could be relevant?
 
    See http://physics.mercer.e= du/hpage/peters.html Improving=20 seismometer performance.....
 
    Regards,
 
    Chris Chapman
Subject: BAJA CALIFORNIA, MEXICO Aftershocks From: "Jerry Payton" gpayton880@....... Date: Tue, 12 Feb 2008 14:24:53 -0600 Forgive me for asking, but it normal to have so many after shocks after a 5.4 EQ such as BAJA CALIFORNIA, MEXICO has had since the 9th?
Forgive me for asking, but it normal to have so many after shocks = after a=20 5.4 EQ such as BAJA CALIFORNIA, MEXICO has had since the=20 9th?
Subject: Re: BAJA CALIFORNIA, MEXICO Aftershocks From: Bob Hancock carpediem1@......... Date: Tue, 12 Feb 2008 17:15:24 -0700 Jerry - The problem is the ability to see all of the aftershocks normally generated by a seismic event. On the header of the site most of us use to view various events world wide, it states: Latest Earthquakes Magnitude 2.5 or Greater in the United States and Adjacent Areas and Magnitude 4.0 or Greater in the Rest of the World - Last 7 days You can see events down to M 2.5 on this list because the Baja events were adjacent to Southern California. If you go to the map of California and Nevada that shows recent event, and then click on one pf the squares that show the recent Baja events, you will find the following link near the bottom of the page: List of Earthquakes on this Map (with MAP) This link will give you a much more complete list of events, some even less that M 1.0 The variable is having access to the information on all the aftershocks. Bob Hancock On 2/12/08 1:24 PM, "Jerry Payton" wrote: > Forgive me for asking, but it normal to have so many after shocks after a 5.4 > EQ such as BAJA CALIFORNIA, MEXICO has had since the 9th? > Re: BAJA CALIFORNIA, MEXICO Aftershocks Jerry= -

The problem is the ability to see all of the aftershocks normally generated= by a seismic event.  On the header of the site most of us use to view = various events world wide, it states:

Latest Earthquakes Magnitude 2.5 or Greater in the United States and = Adjacent Areas and Magnitude 4.0 or Greater in the Rest of the World - Last = 7 days

You can see events down to M 2.5 on this list because the Baja events were = adjacent to Southern California.  If you go to the map of California an= d Nevada that shows recent event, and then click on one pf the squares that = show the recent Baja events, you will find the following link near the botto= m of the page:

List of Earthquakes on this Map (with MAP)

This link will give you a much more complete list of events, some even less= that M 1.0

The variable is having access to the information on all the aftershocks.
Bob Hancock





On 2/12/08 1:24 PM, "Jerry Payton" <gpayton880@.......> wro= te:

Forgive me for asking, but it normal to have so many af= ter shocks after a 5.4 EQ such as BAJA CALIFORNIA, MEXICO has had since the = 9th?


 Subject: Re: BAJA CALIFORNIA, MEXICO Aftershocks From: "Jerry Payton" gpayton880@....... Date: Tue, 12 Feb 2008 18:23:09 -0600 Re: BAJA CALIFORNIA, MEXICO AftershocksThank you, Bob. Yes, I have seen that other URL, but not in this case. I was just amazed by the number listed, as you say, above 2.5. Even the ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA complex does not seem to have this many. As usual, I was just curious! Best regards, Jerry ----- Original Message ----- From: Bob Hancock To: psn-l@.............. Sent: Tuesday, February 12, 2008 6:15 PM Subject: Re: BAJA CALIFORNIA, MEXICO Aftershocks Jerry - The problem is the ability to see all of the aftershocks normally generated by a seismic event. On the header of the site most of us use to view various events world wide, it states: Latest Earthquakes Magnitude 2.5 or Greater in the United States and Adjacent Areas and Magnitude 4.0 or Greater in the Rest of the World - Last 7 days You can see events down to M 2.5 on this list because the Baja events were adjacent to Southern California. If you go to the map of California and Nevada that shows recent event, and then click on one pf the squares that show the recent Baja events, you will find the following link near the bottom of the page: List of Earthquakes on this Map (with MAP) This link will give you a much more complete list of events, some even less that M 1.0 The variable is having access to the information on all the aftershocks. Bob Hancock On 2/12/08 1:24 PM, "Jerry Payton" wrote: Forgive me for asking, but it normal to have so many after shocks after a 5.4 EQ such as BAJA CALIFORNIA, MEXICO has had since the 9th? Re: BAJA CALIFORNIA, MEXICO Aftershocks
Thank you, Bob.  Yes, I have seen that other URL, but = not in this=20 case.  I was just amazed by the number listed, as you say, above = 2.5. =20 Even the ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA complex does not seem = to have=20 this many. 
 
As usual, I was just curious!
 
Best regards,
Jerry
 
 
----- Original Message -----=20
From: Bob = Hancock=20
Sent: Tuesday, February 12, 2008 6:15 PM
Subject: Re: BAJA CALIFORNIA, MEXICO Aftershocks

Jerry -

The problem is the ability to = see all of=20 the aftershocks normally generated by a seismic event.  On the = header of=20 the site most of us use to view various events world wide, it=20 states:

Latest Earthquakes Magnitude 2.5 or Greater = in the=20 United States and Adjacent Areas and Magnitude 4.0 or Greater in the = Rest of the=20 World - Last 7 days

You can see=20 events down to M 2.5 on this list because the Baja events were adjacent = to=20 Southern California.  If you go to the map of California and Nevada = that=20 shows recent event, and then click on one pf the squares that show the = recent=20 Baja events, you will find the following link near the bottom of the=20 page:

List of Earthquakes on this Map (with=20 MAP)

This link will give you a much more = complete list of=20 events, some even less that M 1.0

The variable is having access = to the=20 information on all the aftershocks.

Bob = Hancock





On=20 2/12/08 1:24 PM, "Jerry Payton" <gpayton880@.......>=20 wrote:
Forgive me for asking, but it normal to have = so many=20 after shocks after a 5.4 EQ such as BAJA CALIFORNIA, MEXICO has had = since the=20 9th?


Subject: Re: nature of the mesoscopic nonlinearity From: Brett Nordgren Brett3mr@............. Date: Tue, 12 Feb 2008 22:46:55 -0500 Chris, At 10:43 PM 2/11/2008 -0500, you wrote: >In a message dated 11/02/2008, Brett Nordgren writes: > >How noisy? How large steps/spikes? What is their assumed spectrum? > >Hi Brett, > > My experience is that the steps can be well above the normal noise > level. If they are smaller, they probably don't matter. They are a step > function with the appropriate spectrum. > The frequency varied greatly from several per second after stressing > the spring to an odd one per hour or less after an extended stabilisation > period. Springs for seismometers go through extended preparation to > reduce / measure the noise. I don't know the full details. That is reassuring. My greatest concern was for effects which persisted indefinitely. > > All common / practical spring materials are like this. You have the > > electronic noise, including maybe 1/f noise, the thermal noise of the > sensor itself, the hysteretic > > noise and the background seismic noise. > >That was exactly what I was suggesting; that if you could assign a >frequency F below which you didn't want to see data you might be able to do >feedback centering. Your example suggests that F is a bit below >1/50 Hz. What if you wanted to make an instrument which was sensitive to >1/500 Hz and below. It is only to the degree that you are willing to limit >your low-end response that you have a chance of using feedback to perform >centering, and then, only if the 'noise' forces are of lower frequency than >your signals. > > It is more usual to get very long periods by feedback + integration, > maybe numerical? If you are speaking of integral feedback, it *reduces* the low frequency response and somewhat raises the low frequency rolloff frequency, hence shortening the 'period' slightly, though one can't really talk of a 'period' when you are describing something more complex than a simple resonant device, i.e. one which has multiple poles in its transfer function. In the STM-8 adding the integral branch raises the low frequency rolloff you get from using derivative feedback alone, from 0.007 Hz to 0.011 Hz, which you can see in the 'FISS' paper. However, it is the derivative feedback which effectively improves the low frequency response, by flattening and widening the velocity response curve. In a real sense, it improves both low frequency and high frequency responses. Numerical integration looks interesting. What I think I need to make it work is a D/A with something like 24-bit resolution and correspondingly low noise. Haven't looked too hard, and haven't found any. > > See Wielandt's references on psn for feedback seismometer design. > > Seismometers are usually designed to give a velocity law output directly > > using quite complicated feedback loops - this is 'traditional'. High > > sensitivity seismometers usually have periods between 60 and 120 seconds > > and this covers most surface wave periods of maybe 15 to 40 seconds. A > > few types go to 360 seconds. To cover all the Earth Eigenmodes, you have > > to go to about 2,000 seconds. > >Which again raises the issue; in the 2000 sec instrument, how do you >propose to use feedback to maintain centering in the presence of 500sec >'noises'? The very reason for the 60 or 120 or 360 sec limits is to allow >the instruments to 'filter out' lower frequency noise. Also the choice of >using a response that is flat to velocity, rather than to >force/acceleration, is having the significant effect of attenuating the >influence of force-noise below the low frequency cutoff. > Reducing the noise and drift to allow 1000 second responses was what > made the Streckeisen STS-1 so difficult to make and so expensive. I would > advise using a digital measuring / feedback system to do this for the > long periods involved. It is possible to greatly reduce the drift > components. By temperature cycling and measuring the result, it is > possible to remove a lot of the thermal drift. You hermetically seal the > case to keep the gas density constant. My understanding was that the 360 second low-end response of the STS-1 was about as good as you can get, while still maintaining instrument noise below earth noise, and it required using every possible scheme to reduce and slow internal noise sources. That also raises the interesting question, whether some of that 'low earth noise' isn't exactly what you are looking to measure. > With reference to > http://bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf > describing feedback systems: > > >> The difficulty comes when we want to tightly control the frequency > response of such a device, or >equally important, accurately know its phase response or time delays over >the band of frequencies of >interest, which is essential to do if its data are to be compared with >data from other instruments. >Another difficulty comes when we try to maintain the proper centering of >the mass in the presence of >slow changes in the device or its surroundings. These could arise from >changes in temperature, slow >changes in ground tilt, earth tides, or in the case of a vertical >instrument, spring creep, as well as from >numerous other potential sources. In a sensitive instrument such changes >could be great enough to >move its output completely out of range before mechanical adjustments can >be made. Feedback, >properly applied, can be used both to shape the instrument response and >also to counter some of the >effects of slowly-applied errors. Finally, feedback will have the effect >of greatly reducing the motion >of the mass in response to seismic ground motion. This means that with >feedback we might be able to >use a displacement transducer which has quite a small range of operation, >but which, in return, could >be very sensitive. In addition, by limiting the sensor motion we can >greatly reduce the effect of >transducer and other system nonlinearities. It should be noted that we >will be looking here at a >feedback system which senses the apparent position of the seismic mass and >then feeds back a signal >which is used to apply a force to the mass to counter any changes. > > If we consider a pendulum sensor system, the response is proportional > to the square of the period. If you take a 2 second pendulum and reduce > the restoring force to give a 20 second system, should you get 100x the > response for signals already in the passband? Not sure how you are proposing to reduce the restoring force. If you are suggesting feedback, it actually doesn't act in that way. It effectively applies a very large velocity-damping force on the pendulum in a very linear manner. The result is that the low frequency corner is lower and the high frequency corner is higher than the original single peak at 2 seconds. In a sense the system is still acting as a 2 second pendulum but one which is extremely overdamped. see 'FISS' > Why should a synthesised feedback response to obtain a longer period > result in a much smaller response to the ground motion? The simple answer: Because (negative) feedback always acts to lower the instrument sensitivity to position, velocity and acceleration, (excepting in a few pathological cases). A complete answer involves actually doing the computations for a particular case and examining the results such as is done in 'FISS'. > You seem to consider that requiring an increased position > sensitivity is an advantage. Don't know about *requiring* greater sensitivity, but obtaining greater sensitivity allows for better signal/noise where the noise is that which arises in the measurement circuitry and its connections, the C/D converter, for example. In general improving s/n should allow expanding the performance envelope. >Since we are already at or beyond the easy measurement / stability limit >at maybe 10 nm, getting an increased sensitivity / lower instrument noise >with a comparable stability is an expensive pain in the backside. There is >just no problem in measuring quite large position changes in principle. >There are increasing problems in trying to measure smaller changes. Not exactly following here. Can you try this from a different angle. Incidentally, I often use the terms 'stability' and 'noise' to describe inverse aspects of the same thing. > If you use a DC path from your position sensor through a long period > integrator to the feedback transducer, you can in theory remove ~all > position drifts. Yes, but when you call it a long-period integrator you imply that there is no DC path. It only integrates down to the frequency corresponding to the 'long period' An integrator which integrates down to DC would be have to be called an 'infinite' period integrator. In practice 10,000 seconds or somewhat longer might be possible with a very good capacitor. Anyone for digital? Also, position drifts which occur more rapidly than DC (which I trust includes most of them:-) are only partially cancelled by integration depending on their frequency content. The slower they are, the more they are cancelled. >However, this might require a high current output or a power opamp. You >don't need very much gain, but maybe a separate feedback coil? When I did the calculations using typical 'noise' forces, I found that you indeed had to have quite high loop gain to reduce their effects to be below the small, higher frequency acceleration forces you are trying to observe, . > You seem to be adding a high pass filter to the system and then > trying to get long period / low drift performance?? If you are talking about adding a 0.002Hz high-pass filter to the output to camouflage drift, it works, but I don't believe that's the best approach. However I was analyzing the STM-8 which uses that. A better solution might be with 'better' feedback. > A capacitative position sensor system can have a very high > linearity. What other system nonlinearities were you considering that > could be relevant? Primarily the position sensor system. That would include, of course, the C/D converter as well as the capacitor. When you say very high linearity are you implying 1%, 0.1%, 0.01%....? Have any measurements been made? My concern is that even with fairly small nonlinearity, large amplitude, higher frequency signals can mix to generate small low-frequency difference signals which could possibly confound measurements attempted down at very low frequencies. Only with specific linearity figures could one rule in/out that effect by calculating its magnitude. Also the spring in a vertical, or pendulum geometry might possibly add nonlinearity. Certainly in good clocks it is a concern though quite probably not here. > See > http://physics.mercer.edu/hpage/peters.html > Improving seismometer performance..... > Regards, Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: when feedback is not needed From: Randall Peters PETERS_RD@.......... Date: Wed, 13 Feb 2008 12:08:23 -0500 Recent discussions of force feedback have mentioned pendulums. I hope that these were thoughts directed only toward horizontal instruments of the 'garden gate' variety (not what I call a pendulum); since I can't imagine a reason for ever wanting to go to that degree of difficulty with a 'simple' pendulum such as in the VolksMeter. The direction of a simple static pendulum does not migrate to any great extent. Its very low frequency response is determined by shape changes of the earth that do not exceed tens of microradians. The exception to this claim applies only to the case of a detector with a very limited mechanical dynamic range, such as a gap varying capacitive sensor. With the area-varying array used by the VoksMeter it is unlikely that force balance or any other type of feedback should ever be needed. Randall Subject: Re: nature of the mesoscopic nonlinearity From: ChrisAtUpw@....... Date: Wed, 13 Feb 2008 14:17:08 EST In a message dated 2008/02/13, Brett3mr@............. writes: > > It is more usual to get very long periods by feedback + integration, > > maybe numerical? > > If you are speaking of integral feedback, it *reduces* the low frequency > response and somewhat raises the low frequency rolloff frequency, hence > shortening the 'period' slightly, though one can't really talk of a > 'period' when you are describing something more complex than a simple > resonant device, i.e. one which has multiple poles in its transfer > function. In the STM-8 adding the integral branch raises the low frequency > rolloff you get from using derivative feedback alone, from 0.007 Hz to > 0.011 Hz, which you can see in the 'FISS' paper. However, it is the > derivative feedback which effectively improves the low frequency response, > by flattening and widening the velocity response curve. In a real sense, > it improves both low frequency and high frequency responses. > > Numerical integration looks interesting. What I think I need to make it > work is a D/A with something like 24-bit resolution and correspondingly low > noise. Haven't looked too hard, and haven't found any. There are some about. > My understanding was that the 360 second low-end response of the STS-1 was > about as good as you can get, while still maintaining instrument noise > below earth noise, and it required using every possible scheme to reduce > and slow internal noise sources. The STS-2 goes to this. Particular versions of the STS-1 would go out to 1,000 seconds. It is a very hard way to get this performance! > That also raises the interesting question, whether some of that 'low earth > noise' isn't exactly what you are looking to measure. There is a lot of earth noise down to the Eigenmodes, which are interesting in themselves. Transient signals occur which look very like quake precursors. > > If we consider a pendulum sensor system, the response is proportional > > > to the square of the period. If you take a 2 second pendulum and reduce > > the restoring force to give a 20 second system, should you get 100x the > > response for signals already in the passband? > > Not sure how you are proposing to reduce the restoring force. If you are > suggesting feedback, it actually doesn't act in that way. Positive feedback does and it will reduce the period. It effectively > applies a very large velocity-damping force on the > pendulum in a very linear manner. The result is that the low frequency corner > is lower and > the high frequency corner is higher than the original single peak at 2 > seconds. In a sense the system is still acting as a 2 second pendulum but > one which is extremely overdamped. see 'FISS' > > > Why should a synthesised feedback response to obtain a longer period > > result in a much smaller response to the ground motion? > > The simple answer: Because (negative) feedback always acts to lower the > instrument sensitivity to position, velocity and acceleration, (excepting > in a few pathological cases). A complete answer involves actually doing > the computations for a particular case and examining the results such as is > done in 'FISS'. > > > You seem to consider that requiring an increased position > > sensitivity is an advantage. > > Don't know about *requiring* greater sensitivity, but obtaining greater > sensitivity allows for better signal/noise where the noise is that which > arises in the measurement circuitry and its connections, the C/D converter, > for example. In general improving s/n should allow expanding the > performance envelope. > > >Since we are already at or beyond the easy measurement / stability limit > >at maybe 10 nm, getting an increased sensitivity / lower instrument noise > >with a comparable stability is an expensive pain in the backside. There is > >just no problem in measuring quite large position changes in principle. > >There are increasing problems in trying to measure smaller changes. > > Not exactly following here. Can you try this from a different > angle. Incidentally, I often use the terms 'stability' and 'noise' to > describe inverse aspects of the same thing. You are using a position sensor, which will have a measurement range and a noise level which limits what you can sense. I am enquiring what resolution you can get. The practical limit is likely to be set above this by thermal varriations. > > If you use a DC path from your position sensor through a long period > > integrator to the feedback transducer, you can in theory remove ~all > > position drifts. > > Yes, but when you call it a long-period integrator you imply that there is > no DC path. It only integrates down to the frequency corresponding to the > 'long period'. An integrator which integrates down to DC would be have to > be called an 'infinite' period integrator. In practice 10,000 seconds or > somewhat longer might be possible with a very good capacitor. Anyone for > digital? Also, position drifts which occur more rapidly than DC (which I > trust includes most of them:-) are only partially cancelled by integration > depending on their frequency content. The slower they are, the more they > are cancelled. No. They can go down to DC. Randal uses one on his Sprengnether. See my reference. You have a large resistance onto the negative input of a FET opamp and a capacitor (+ resistor?) in the feedback loop. > > You seem to be adding a high pass filter to the system and then > > trying to get long period / low drift performance?? > > If you are talking about adding a 0.002Hz high-pass filter to the output to > camouflage drift, it works, but I don't believe that's the best > approach. However I was analyzing the STM-8 which uses that. A better > solution might be with 'better' feedback. > > > A capacitative position sensor system can have a very high > > linearity. What other system nonlinearities were you considering that > > could be relevant? > > Primarily the position sensor system. That would include, of course, the > C/D converter as well as the capacitor. When you say very high linearity > are you implying 1%, 0.1%, 0.01%....? Have any measurements been made? My guesstimate would be in the 0.1% region, probably better. It will depend mostly on the precision of the physical sensor construction. The linearity over a small range will be extreme. My > concern is that even with fairly small nonlinearity, large > amplitude, > higher frequency signals can mix to generate small low-frequency difference > signals which could possibly confound measurements attempted down at very > low frequencies. Only with specific linearity figures could one rule > in/out that effect by calculating its magnitude. Also the spring in a > vertical, or pendulum geometry might possibly add nonlinearity. I would not expect even moderate quakes to generate serious non linearity. You are more likely to run out of detector range. The angles are less than 2 degrees. Regards, Chris In a me= ssage dated 2008/02/13, Brett3mr@............. writes:

>     It= is more usual to get very long periods by feedback + integration,
> maybe numerical?

If you are speaking of integral feedback, it *reduces* the low frequency response and somewhat raises the low frequency rolloff frequency, hence
shortening the 'period' slightly, though one can't really talk of a
'period' when you are describing something more complex than a simple
resonant device, i.e. one which has multiple poles in its transfer
function.  In the STM-8 adding the integral branch raises the low frequ= ency
rolloff you get from using derivative feedback alone, from 0.007 Hz to
0.011 Hz, which you can see in the 'FISS' paper.  However, it is the derivative feedback which effectively improves the low frequency response, <= BR> by flattening and widening the velocity response curve.  In a real sens= e,
it improves both low frequency and high frequency responses.

Numerical integration looks interesting.  What I think I need to make i= t
work is a D/A with something like 24-bit resolution and correspondingly low=20=
noise.  Haven't looked too hard, and haven't found any.

       There are some about.

My understanding was that the 3= 60 second low-end response of the STS-1 was
about as good as you can get, while still maintaining instrument noise
below earth noise, and it required using every possible scheme to reduce and slow internal noise sources.


       The STS-2 goes to this. Particular ver= sions of the STS-1 would go out to 1,000 seconds. It is a very hard way to g= et this performance!

That also raises the interestin= g question, whether some of that 'low earth
noise' isn't exactly what you are looking to measure.


       There is a lot of earth noise down to=20= the Eigenmodes, which are interesting in themselves. Transient signals occur= which look very like quake precursors.

>     If= we consider a pendulum sensor system, the response is proportional
> to the square of the period. If you take a 2 second pendulum and reduce=
> the restoring force to give a 20 second system, should you get 100x the=
> response for signals already in the passband?

Not sure how you are proposing to reduce the restoring force.  If you a= re
suggesting feedback, it actually doesn't act in that way.


    Positive feedback does and it will reduce the period.

        It effectively
applies a very large velocity-damping force on=20= the pendulum in a very linear manner.  The result is that the low frequ= ency corner is lower and
the high frequency corner is higher than the original single peak at 2
seconds.  In a sense the system is still acting as a 2 second pendulum=20= but
one which is extremely overdamped. see 'FISS'

>      Why should a synthesised feedback respons= e to obtain a longer period
> result in a much smaller response to the ground motion?

The simple answer: Because (negative) feedback always acts to lower the
instrument sensitivity to position, velocity and acceleration, (excepting in a few pathological cases).  A complete answer involves actually doin= g
the computations for a particular case and examining the results such as is=20=
done in 'FISS'.

>      You seem to consider that requiring an in= creased position
> sensitivity is an advantage.

Don't know about *requiring* greater sensitivity, but obtaining greater
sensitivity allows for better signal/noise where the noise is that which arises in the measurement circuitry and its connections, the C/D converter,=20=
for example.  In general improving s/n should allow expanding the
performance envelope.

>Since we are already at or beyond the easy measurement / stability limit=
>at maybe 10 nm, getting an increased sensitivity / lower instrument nois= e
>with a comparable stability is an expensive pain in the backside. There=20= is
>just no problem in measuring quite large position changes in principle.=20=
>There are increasing problems in trying to measure smaller changes.

Not exactly following here.  Can you try this from a different
angle.  Incidentally, I often use the terms 'stability' and 'noise' to=20=
describe inverse aspects of the same thing.


       You are using a position sensor, which= will have a measurement range and a  noise level which limits what you= can sense. I am enquiring what resolution you can get. The practical limit=20= is likely to be set above this by thermal varriations.

>     If= you use a DC path from your position sensor through a long period
> integrator to the feedback transducer, you can in theory remove ~all > position drifts.

Yes, but when you call it a long-period integrator you imply that there is <= BR> no DC path.  It only integrates down to the frequency corresponding to=20= the
'long period'.  An integrator which integrates down to DC would be have= to
be called an 'infinite' period integrator.  In practice 10,000 seconds=20= or
somewhat longer might be possible with a very good capacitor.  Anyone f= or
digital?  Also, position drifts which occur more rapidly than DC (which= I
trust includes most of them:-) are only partially cancelled by integration <= BR> depending on their frequency content.  The slower they are, the more th= ey
are cancelled.


       No. They can go down to DC. Randal use= s one on his Sprengnether. See my reference. You have a large resistance ont= o the negative input of a FET opamp and a capacitor (+ resistor?) in the fee= dback loop.

>    &nb= sp; You seem to be adding a high pass filter to the system and then
> trying to get long period / low drift performance??

If you are talking about adding a 0.002Hz high-pass filter to the output to=20=
camouflage drift, it works, but I don't believe that's the best
approach.  However I was analyzing the STM-8 which uses that.  A b= etter
solution might be with 'better' feedback.

>      A capacitative position sensor system can= have a very high
> linearity. What other system nonlinearities were you considering that <= BR> > could be relevant?

Primarily the position sensor system.  That would include, of course,&n= bsp; the
C/D converter as well as the capacitor.  When you say very high lineari= ty
are you implying 1%, 0.1%, 0.01%....?  Have any measurements been made?=  


    My guesstimate would be in the 0.1% region, probably bett= er. It will depend mostly on the precision of the physical sensor constructi= on. The linearity over a small range will be extreme.

       My
concern is that even with fairly small nonlinearity, large amplitu= de,
higher frequency signals can mix to generate small low-frequency difference=20=
signals which could possibly confound measurements attempted down at very low frequencies.  Only with specific linearity figures could one rule <= BR> in/out that effect by calculating its magnitude.  Also the spring in a=20=
vertical, or pendulum geometry might possibly add nonlinearity.

       I would not expect even moderate quakes= to generate serious non linearity. You are more likely to run out of detect= or range. The angles are less than 2 degrees.

       Regards,

       Chris Subject: How much mass ? From: jonfr@......... Date: Wed, 13 Feb 2008 15:49:50 -0500 (EST) Hi all I am continuing to planning the build of an lechman sensor. But I am wondering what the ideal mass is going to have to be. But I am hoping for at as many seconds as I can. Preferably around 20 seconds. But only if I can. Regards. Jón Frímann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: How much mass ? From: ChrisAtUpw@....... Date: Wed, 13 Feb 2008 22:07:36 EST In a message dated 2008/02/13, jonfr@......... writes: > Hi all > I am continuing to planning the build of an Lehman sensor. But I am > wondering what the ideal mass is going to have to be. But I am hoping for > at as many seconds as I can. Preferably around 20 seconds.=20 Hi Jon, The mass is not important in a Lehman, only the length between the=20 hinge and the centre of mass =3D L ~56 cm. You need to keep the arm rigid bu= t=20 light. Between 1/2 and 1 kg is about right, certainly no more. We use brass=20= rod. I=20 use 3" x 1" Aluminum U channel, 1/8" Al plate and SS bolts. The magnets are=20 NdFeB, 1" square x 1/8" thick for the sensor and 1" x 1/2" x 1/4" thick for=20= the=20 damper, 4 off each type Have a look at our Lehman school seismometer. The dimensions and=20 construction are shown. Don't use any of the constructions shown on psn. See= =20 http://www.bgs.ac.uk/education/school_seismology/seismometer.html I don't suppose that you are feeling rich, but MUTR sell them for=20= =A3290=20 + carriage. ~IK 33,282 + carriage. I don't know about your import duty or tax. This=20 includes the sensor, the electronics and the PSU. It plugs into a PC compute= r and=20 runs under AmaSeis. You can get 30 seconds, although they only claim 20. Let me know if you need more information. Regards, Chris Chapman =20 In a me= ssage dated 2008/02/13, jonfr@......... writes:

Hi all
I am continuing to planning the build of an Lehman sensor. But I am
wondering what the ideal mass is going to have to be. But I am hoping for at as many seconds as I can. Preferably around 20 seconds.


Hi Jon,

       The mass is not important in a Lehman,=20= only the length between the hinge and the centre of mass =3D L ~56 cm. You n= eed to keep the arm rigid but light. Between 1/2 and 1 kg is about right, ce= rtainly no more. We use brass rod. I use 3" x 1" Aluminum U channel, 1/8" Al= plate and SS bolts. The magnets are NdFeB, 1" square x 1/8" thick for the s= ensor and 1" x 1/2" x 1/4" thick for the damper, 4 off each type

       Have a look at our Lehman school seismo= meter. The dimensions and construction are shown. Don't use any of the const= ructions shown on psn. See http://www.bgs.ac.uk/education/school_seismology/= seismometer.html
       I don't suppose that you are feeling ri= ch, but MUTR sell them for =A3290 + carriage.
~IK 33,282 + carriage. I don't know about your import duty or tax. This incl= udes the sensor, the electronics and the PSU. It plugs into a PC computer an= d runs under AmaSeis. You can get 30 seconds, although they only claim 20.
       Let me know if you need more informatio= n.

       Regards,

       Chris Chapman Subject: RE: How much mass ? From: "Steve Hammond" shammon1@............. Date: Thu, 14 Feb 2008 00:29:57 -0800 Hi, Jon, I like to use the old style Lehman design. The device I built = with the best results was the PSN San Jose Lehmans which used a 1-in square aluminum rod L=3D 80cm and 80-ounce lead mass. They had a natural period = of 20-seconds with minimal setup effort. The total boom length was 100cm = and they used a brass plate mounted at the end of the boom for the damping. = I was very happy with the performance. One of the issues you will face is = the selection of the gauge of the upper support wire. I tried to use #8 = machine (piano) wire but it kept breaking during use. I increased the wire gauge = to #10 machine wire and the wire life was about 1-year before rust causes = the wire to snap under tension.=20 =20 When I moved here to Aptos, California I was forced to reduce the length = of the boom to L=3D60cm because of limited space as seen in the photos in = the link below and the resulting natural period is now typically 10-12 = seconds. Needless to say, the performance these Lehmans are marginal and I live = near the ocean and the wave action causes them to osculate during storms. = When I have the time I'm going to pull them out and build one L=3D80cm device.=20 =20 My suggestion is to use the calculation seen on this list (sorry I don't have the calculation for a natural period of a garden gate Lehman at = hand. Maybe somebody on the list does??) to determine the boom length you = desire. Then plan the design based on that calculation. You said you wanted a = device with a period of 20-second and as pointed out below by Chris, L is based = on the length of the boom measured from the pivot point to the center of = the mass weight (Chris, do you have this calculation??). I have found that setting the device up this way also reduces the impact of ground = deformation (boom does not remains level and centered) over time which improves the overall operation of the device keeping the boom off the stops.=20 http://pw2.netcom.com/~shammon1/AptosStn.htm =20 =20 Regards, Steve Hammond Aptos California, PSN San Jose. =20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of ChrisAtUpw@....... Sent: Wednesday, February 13, 2008 7:08 PM To: psn-l@.............. Subject: Re: How much mass ? In a message dated 2008/02/13, jonfr@......... writes: Hi all I am continuing to planning the build of an Lehman sensor. But I am wondering what the ideal mass is going to have to be. But I am hoping = for at as many seconds as I can. Preferably around 20 seconds.=20 Hi Jon, The mass is not important in a Lehman, only the length between = the hinge and the centre of mass =3D L ~56 cm. You need to keep the arm = rigid but light. Between 1/2 and 1 kg is about right, certainly no more. We use = brass rod. I use 3" x 1" Aluminum U channel, 1/8" Al plate and SS bolts. The magnets are NdFeB, 1" square x 1/8" thick for the sensor and 1" x 1/2" x 1/4" thick for the damper, 4 off each type Have a look at our Lehman school seismometer. The dimensions and construction are shown. Don't use any of the constructions shown on psn. = See http://www.bgs.ac.uk/education/school_seismology/seismometer.html I don't suppose that you are feeling rich, but MUTR sell them for =A3290 + carriage. ~IK 33,282 + carriage. I don't know about your import duty or tax. This includes the sensor, the electronics and the PSU. It plugs into a PC computer and runs under AmaSeis. You can get 30 seconds, although they = only claim 20. Let me know if you need more information. Regards, Chris Chapman=20 Message
Hi,=20 Jon, I like to use the old style Lehman design. The device I built = with the=20 best results was the PSN San Jose Lehmans which used a 1-in square = aluminum=20 rod L=3D 80cm and 80-ounce lead mass. They had a natural = period of=20 20-seconds with minimal setup effort. The total boom length was 100cm=20 and they used a brass plate mounted at the end of the = boom for=20 the damping. I was very happy with the performance. One of the issues = you will=20 face is the selection of the gauge of the upper support wire. = I tried to=20 use #8 machine (piano) wire but it kept breaking during use. I increased = the=20 wire gauge to #10 machine wire and the wire life was about = 1-year=20 before rust causes the wire to snap under = tension. 
 
When I=20 moved here to Aptos, California I was forced to reduce the length of the = boom to=20 L=3D60cm because of limited space as seen in the photos in the link = below and the=20 resulting natural period is now typically 10-12 seconds. Needless to = say, the=20 performance these Lehmans are marginal and I live near the = ocean and=20 the wave action causes them to osculate during storms. When I have the = time I'm=20 going to pull them out and build one L=3D80cm device. =
 
My=20 suggestion is to use the calculation seen on this list (sorry I don't = have the=20 calculation for a natural period of a garden gate Lehman at hand. = Maybe=20 somebody on the list does??) to determine the boom length you desire. = Then plan=20 the design based on that calculation. You said you wanted a device with = a period=20 of 20-second and as pointed out below by Chris, L is based on the length = of the=20 boom measured from the pivot point to the center of the mass weight = (Chris, do=20 you have this calculation??). I have found that setting the device = up this=20 way also reduces the impact of ground deformation (boom does not=20 remains level and centered) over time which improves the overall = operation=20 of the device keeping the boom off the stops. 
http://pw2.netcom.c= om/~shammon1/AptosStn.htm
 
 
Regards, Steve Hammond Aptos California,  PSN San=20 Jose.
 
 -----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@............... On Behalf Of=20 ChrisAtUpw@.......
Sent: Wednesday, February 13, 2008 7:08 = PM
To: psn-l@..............
Subject: Re: How much = mass=20 ?

In a message dated 2008/02/13, jonfr@......... = writes:

Hi all
I am continuing to planning the build of an = Lehman=20 sensor. But I am
wondering what the ideal mass is going to have = to be.=20 But I am hoping for
at as many seconds as I can. Preferably = around 20=20 seconds.


Hi=20 Jon,

       The mass is not = important in=20 a Lehman, only the length between the hinge and the centre of mass =3D = L ~56 cm.=20 You need to keep the arm rigid but light. Between 1/2 and 1 kg is = about right,=20 certainly no more. We use brass rod. I use 3" x 1" Aluminum U channel, = 1/8" Al=20 plate and SS bolts. The magnets are NdFeB, 1" square x 1/8" thick for = the=20 sensor and 1" x 1/2" x 1/4" thick for the damper, 4 off each=20 type

       Have a look at our = Lehman=20 school seismometer. The dimensions and construction are shown. Don't = use any=20 of the constructions shown on psn. See=20 = http://www.bgs.ac.uk/education/school_seismology/seismometer.html
&nbs= p;     =20 I don't suppose that you are feeling rich, but MUTR sell them for = =A3290 +=20 carriage.
~IK 33,282 + carriage. I don't know about your import = duty or=20 tax. This includes the sensor, the electronics and the PSU. It plugs = into a PC=20 computer and runs under AmaSeis. You can get 30 seconds, although they = only=20 claim 20.

       Let me know if = you need=20 more information.

      =20 Regards,

       Chris = Chapman=20
Subject: Re: How much mass ? From: ChrisAtUpw@....... Date: Thu, 14 Feb 2008 09:49:04 EST In a message dated 2008/02/14, shammon1@............. writes: > Hi, Jon, I like to use the old style Lehman design. The device I built with > the best results was the PSN San Jose Lehmans which used a 1-in square > aluminum rod L= 80cm and 80-ounce lead mass. They had a natural period of > 20-seconds with minimal setup effort. The total boom length was 100cm and they used a > brass plate mounted at the end of the boom for the damping. I was very happy > with the performance. One of the issues you will face is the selection of > the gauge of the upper support wire. I tried to use #8 machine (piano) wire but > it kept breaking during use. I increased the wire gauge to #10 machine wire > and the wire life was about 1-year before rust causes the wire to snap under > tension. Hi Steve, If you use D'Addario piano wire, it comes protected with Nickel plating. Use either Aluminum or Copper plate for the damper. Al works, but 1/16" Cu is better. I use 1" square x 1/8" thick NdFeB magnets for the sensor and 1" x 1/2" x 1/4" thick NdFeB magnets for the damper, four off in both cases. A N/S pair on one 1/4" backing plate faces a S/N pair on the other backing plate. The backing plates are held in position by 1/4" zinc plated mild steel bolts. This greatly reduces any stray field. Put the coil on the arm and the magnet on the base. If you put a magnet on the arm, you will pick up a lot of magnetic noise from the house wiring, passing trains and lorries etc. > When I moved here to Aptos, California I was forced to reduce the length of > the boom to L=60cm because of limited space as seen in the photos in the > link below and the resulting natural period is now typically 10-12 seconds. > Needless to say, the performance these Lehmans are marginal and I live near the > ocean and the wave action causes them to osculate during storms. You should be able to get 30 seconds out of a 60 cm arm quite OK. Most period limitations are caused by a poor lower suspension, such as a point in a cup or knife edge. It improves the period if you put the mass at the end of the arm. Use 3/4" square or round Al tube for the arm - definitely not solid. You want to keep the arm light but rigid compared to the mass. I use 15 mm SS water pipe + plumbing fittings The bottom hinge should be ball on a plane or crossed cylinder. You put the SS ball on the upright and the SS / WC plane / SS blade the end of the arm. For WC rod, you can use 1/8" Tungsten Carbide drill shanks, with the vertical on the upright. See www.smallparts.com. You can also buy type 416 SS 1/4" shoulder bolts from McMaster Carr. www.mcmaster.com If you construct a double T frame similar to http://www.bgs.ac.uk/education/school_seismology/seismometer.html you can set up the system and then trim the response - all adjustments are sequential, not inter related like on the psn designs. This makes setup and adjustment far easier. The red block is a support, with a horizontal damping blade and the sliding damping magnet is placed on the bottom frame. The coil is fixed to the outside end and swings between the other magnet block. The diagonal Al support tube prevents rotation. I used 3" x 1" Al U Channel with triangular 6" x 6" x 1/8" Al plates to support the joint in the prototype. This is easy to make and to set up. I use 1/4" SS bolts. > My suggestion is to use the calculation seen on this list to determine the > boom length you desire. Then plan the design based on that calculation. You > said you wanted a device with a period of 20-second and as pointed out below > by Chris, L is based on the length of the boom measured from the pivot point > to the center of the mass weight (Chris, do you have this calculation?). I > have found that setting the device up this way also reduces the impact of > ground deformation (boom does not remains level and centered) over time which > improves the overall operation of the device keeping the boom off the stops. > http://pw2.netcom.com/~shammon1/AptosStn.htm If the distance between the hinge and the centre of mass is L metres and the suspension angle is A, the period T = 2xPixSqrt(L / (9.81 x sin(A))) I use 0.56 m which would give a 1.5 sec pendulum if held vertically. A is ~1/3 degree. Alnico magnets are now quite expensive. NdFeB magnets are much cheaper and give a much higher output. For damper and coil designs - click on Lehman at http://jclahr.com/science/psn/chapman/ Make the damping blade wide so that it covers both magnets at all times as shown. There is also an alternative design under muventures. The boom does not have to be level, but it should be adjusted parallel with the lower frame. Then you can simply slide the damping magnet further over the horizontal damping blade to adjust the damping. You adjust the whole rigid frame to centre the arm and to set the period. I use three SS plates glued to the concrete floor for the screw adjusters. I glued SS bearings into the end of the adjust bolts. Then they don't move about / wander when you adjust them. The SS mounting nuts are glued to the underside of the frame. Regards, Chris Chapman In a me= ssage dated 2008/02/14, shammon1@............. writes:

Hi, Jon, I like to use the old= style Lehman design. The device I built with the best results was the PSN S= an Jose Lehmans which used a 1-in square aluminum rod L=3D 80cm and 80-ounce= lead mass. They had a natural period of 20-seconds with minimal setup effor= t. The total boom length was 100cm and they used a brass plate mounted at th= e end of the boom for the damping. I was very happy with the performance. On= e of the issues you will face is the selection of the gauge of the upper sup= port wire. I tried to use #8 machine (piano) wire but it kept breaking durin= g use. I increased the wire gauge to #10 machine wire and the wire life was=20= about 1-year before rust causes the wire to snap under tension.

Hi Steve,

       If you use D'Addario piano wire, it com= es protected with Nickel plating.
       Use either Aluminum or Copper plate for= the damper. Al works, but 1/16" Cu is better.
       I use 1" square x 1/8" thick NdFeB magn= ets for the sensor and 1" x 1/2" x 1/4" thick NdFeB magnets for the damper,=20= four off in both cases. A N/S pair on one 1/4" backing plate faces a S/N pai= r on the other backing plate. The backing plates are held in position by 1/4= " zinc plated mild steel bolts. This greatly reduces any stray field.
       Put the coil on the arm and the magnet=20= on the base. If you put a magnet on the arm, you will pick up a lot of magne= tic noise from the house wiring, passing trains and lorries etc.

When I moved here to Aptos, Ca= lifornia I was forced to reduce the length of the boom to L=3D60cm because o= f limited space as seen in the photos in the link below and the resulting na= tural period is now typically 10-12 seconds. Needless to say, the performanc= e these Lehmans are marginal and I live near the ocean and the wave action c= auses them to osculate during storms.


       You should be able to get 30 seconds o= ut of a 60 cm arm quite OK. Most period limitations are caused by a poor low= er suspension, such as a point in a cup or knife edge. It improves the perio= d if you put the mass at the end of the arm.
       Use 3/4" square or round Al tube for th= e arm - definitely not solid. You want to keep the arm light but rigid compa= red to the mass. I use 15 mm SS water pipe + plumbing fittings
       The bottom hinge should be ball on a pl= ane or crossed cylinder. You put the SS ball on the upright and the SS / WC=20= plane / SS blade the end of the arm. For WC rod, you can use 1/8" Tungsten C= arbide drill shanks, with the vertical on the upright. See www.smallparts.co= m. You can also buy type 416 SS 1/4" shoulder bolts from McMaster Carr. www.= mcmaster.com
       If you construct a double T frame simil= ar to http://www.bgs.ac.uk/education/school_seismology/seismometer.html you=20= can set up the system and then trim the response - all adjustments are seque= ntial, not inter related like on the psn designs. This makes setup and adjus= tment far easier. The red block is a support, with a horizontal damping blad= e and the sliding damping magnet is placed on the bottom frame. The coil is=20= fixed to the outside end and swings between the other magnet block. The diag= onal Al support tube prevents rotation.
       I used 3" x 1" Al U Channel with triang= ular 6" x 6" x 1/8" Al plates to support the joint in the prototype. This is= easy to make and to set up. I use 1/4" SS bolts.

My suggestion is to use the c= alculation seen on this list to determine the boom length you desire. Then p= lan the design based on that calculation. You said you wanted a device with=20= a period of 20-second and as pointed out below by Chris, L is based on the l= ength of the boom measured from the pivot point to the center of the mass we= ight (Chris, do you have this calculation?). I have found that setting the d= evice up this way also reduces the impact of ground deformation (boom does n= ot remains level and centered) over time which improves the overall operatio= n of the device keeping the boom off the stops.
http://pw2.netcom.= com/~shammon1/AptosStn.htm


       If the distance between the hinge and=20= the centre of mass is L metres and the suspension angle is A, the period T=20= =3D 2xPixSqrt(L / (9.81 x sin(A))) I use 0.56 m which would give a 1.5 sec p= endulum if held vertically. A is ~1/3 degree.
       Alnico magnets are now quite expensive.= NdFeB magnets are much cheaper and give a much higher output. For damper an= d coil designs - click on Lehman at http://jclahr.com/science/psn/chapman/ M= ake the damping blade wide so that it covers both magnets at all times as sh= own.
       There is also an alternative design und= er muventures.
       The boom does not have to be level, but= it should be adjusted parallel with the lower frame. Then you can simply sl= ide the damping magnet further over the horizontal damping blade to adjust t= he damping.
       You adjust the whole rigid frame to cen= tre the arm and to set the period. I use three SS plates glued to the concre= te floor for the screw adjusters. I glued SS bearings into the end of the ad= just bolts. Then they don't move about / wander when you adjust them. The SS= mounting nuts are glued to the underside of the frame.

       Regards,

       Chris Chapman Subject: RE: How much mass ? From: "Stephen Hammond" shammon1@............. Date: Thu, 14 Feb 2008 09:37:46 -0800 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of ChrisAtUpw@....... Sent: Thursday, February 14, 2008 6:49 AM To: psn-l@.............. Subject: Re: How much mass ? In a message dated 2008/02/14, shammon1@............. writes: See comment below: Hi, Jon, I like to use the old style Lehman design. The device I built with the best results was the PSN San Jose Lehmans which used a 1-in square aluminum rod L= 80cm and 80-ounce lead mass. They had a natural period of 20-seconds with minimal setup effort. The total boom length was 100cm and they used a brass plate mounted at the end of the boom for the damping. I was very happy with the performance. One of the issues you will face is the selection of the gauge of the upper support wire. I tried to use #8 machine (piano) wire but it kept breaking during use. I increased the wire gauge to #10 machine wire and the wire life was about 1-year before rust causes the wire to snap under tension. Hi Steve, If you use D'Addario piano wire, it comes protected with Nickel plating. Use either Aluminum or Copper plate for the damper. Al works, but 1/16" Cu is better. I use 1" square x 1/8" thick NdFeB magnets for the sensor and 1" x 1/2" x 1/4" thick NdFeB magnets for the damper, four off in both cases. A N/S pair on one 1/4" backing plate faces a S/N pair on the other backing plate. The backing plates are held in position by 1/4" zinc plated mild steel bolts. This greatly reduces any stray field. Put the coil on the arm and the magnet on the base. If you put a magnet on the arm, you will pick up a lot of magnetic noise from the house wiring, passing trains and lorries etc. Update 2/14/08: Thanks Chris, I'll try mounting the coil on the boom in the next revision. I never wanted to deal with the lead wires off the rear of the boom. Do you have any tips for frictionless lead wires? Steve H. When I moved here to Aptos, California I was forced to reduce the length of the boom to L=60cm because of limited space as seen in the photos in the link below and the resulting natural period is now typically 10-12 seconds. Needless to say, the performance these Lehmans are marginal and I live near the ocean and the wave action causes them to osculate during storms. You should be able to get 30 seconds out of a 60 cm arm quite OK. Most period limitations are caused by a poor lower suspension, such as a point in a cup or knife edge. It improves the period if you put the mass at the end of the arm. Use 3/4" square or round Al tube for the arm - definitely not solid. You want to keep the arm light but rigid compared to the mass. I use 15 mm SS water pipe + plumbing fittings The bottom hinge should be ball on a plane or crossed cylinder. You put the SS ball on the upright and the SS / WC plane / SS blade the end of the arm. For WC rod, you can use 1/8" Tungsten Carbide drill shanks, with the vertical on the upright. See www.smallparts.com. You can also buy type 416 SS 1/4" shoulder bolts from McMaster Carr. www.mcmaster.com If you construct a double T frame similar to http://www.bgs.ac.uk/education/school_seismology/seismometer.html you can set up the system and then trim the response - all adjustments are sequential, not inter related like on the psn designs. This makes setup and adjustment far easier. The red block is a support, with a horizontal damping blade and the sliding damping magnet is placed on the bottom frame. The coil is fixed to the outside end and swings between the other magnet block. The diagonal Al support tube prevents rotation. I used 3" x 1" Al U Channel with triangular 6" x 6" x 1/8" Al plates to support the joint in the prototype. This is easy to make and to set up. I use 1/4" SS bolts. My suggestion is to use the calculation seen on this list to determine the boom length you desire. Then plan the design based on that calculation. You said you wanted a device with a period of 20-second and as pointed out below by Chris, L is based on the length of the boom measured from the pivot point to the center of the mass weight (Chris, do you have this calculation?). I have found that setting the device up this way also reduces the impact of ground deformation (boom does not remains level and centered) over time which improves the overall operation of the device keeping the boom off the stops. http://pw2.netcom.com/~shammon1/AptosStn.htm If the distance between the hinge and the centre of mass is L metres and the suspension angle is A, the period T = 2xPixSqrt(L / (9.81 x sin(A))) I use 0.56 m which would give a 1.5 sec pendulum if held vertically. A is ~1/3 degree. Alnico magnets are now quite expensive. NdFeB magnets are much cheaper and give a much higher output. For damper and coil designs - click on Lehman at http://jclahr.com/science/psn/chapman/ Make the damping blade wide so that it covers both magnets at all times as shown. There is also an alternative design under muventures. The boom does not have to be level, but it should be adjusted parallel with the lower frame. Then you can simply slide the damping magnet further over the horizontal damping blade to adjust the damping. You adjust the whole rigid frame to centre the arm and to set the period. I use three SS plates glued to the concrete floor for the screw adjusters. I glued SS bearings into the end of the adjust bolts. Then they don't move about / wander when you adjust them. The SS mounting nuts are glued to the underside of the frame. Regards, Chris Chapman

 =

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of ChrisAtUpw@.......
Sent: = Thursday, February 14, = 2008 6:49 AM
To: = psn-l@..............
Subject: Re: How much = mass ?

 

In a message dated = 2008/02/14, shammon1@............. writes:
See comment = below:

= Hi, Jon, I like to use the old style Lehman design. The device I built with the = best results was the PSN San Jose Lehmans which used a 1-in square aluminum = rod L=3D 80cm and 80-ounce lead mass. They had a natural period of 20-seconds = with minimal setup effort. The total boom length was 100cm and they used a = brass plate mounted at the end of the boom for the damping. I was very happy = with the performance. One of the issues you will face is the selection of the = gauge of the upper support wire. I tried to use #8 machine (piano) wire but it = kept breaking during use. I increased the wire gauge to #10 machine wire and = the wire life was about 1-year before rust causes the wire to snap under = tension.

=

Hi Steve,

       If you use D'Addario piano wire, it = comes protected with Nickel plating.
       Use either Aluminum or Copper plate = for the damper. Al works, but 1/16" Cu is better.
       I use 1" square x 1/8" = thick NdFeB magnets for the sensor and 1" x 1/2" x 1/4" thick = NdFeB magnets for the damper, four off in both cases. A N/S pair on one = 1/4" backing plate faces a S/N pair on the other backing plate. The backing = plates are held in position by 1/4" zinc plated mild steel bolts. This = greatly reduces any stray field.
       Put the coil on the arm and the = magnet on the base. If you put a magnet on the arm, you will pick up a lot of = magnetic noise from the house wiring, passing trains and lorries etc.

 

Update = = 2/14/08: Thanks Chris, I’ll try mounting the = coil on the boom in the next revision. I never wanted to deal with the lead = wires off the rear of the boom. Do you have any tips for frictionless lead = wires?

Steve H. =




= When I moved here to Aptos, California I was forced to reduce the length of the = boom to L=3D60cm because of limited space as seen in the photos in the link = below and the resulting natural period is now typically 10-12 seconds. Needless to = say, the performance these Lehmans are marginal and I live near the ocean and = the wave action causes them to osculate during storms. =

=

       You should be = able to get 30 seconds out of a 60 cm arm quite OK. Most period limitations are = caused by a poor lower suspension, such as a point in a cup or knife edge. It = improves the period if you put the mass at the end of the arm.
       Use 3/4" square or round Al = tube for the arm - definitely not solid. You want to keep the arm light but rigid compared to the mass. I use 15 mm SS water pipe + plumbing fittings
       The bottom hinge should be ball on = a plane or crossed cylinder. You put the SS ball on the upright and the SS / WC = plane / SS blade the end of the arm. For WC rod, you can use 1/8" Tungsten = Carbide drill shanks, with the vertical on the upright. See www.smallparts.com. = You can also buy type 416 SS 1/4" shoulder bolts from McMaster Carr. www.mcmaster.com
       If you construct a double T frame = similar to http://www.bgs.ac.uk/education/school_seismology/seismometer.html you = can set up the system and then trim the response - all adjustments are = sequential, not inter related like on the psn designs. This makes setup and = adjustment far easier. The red block is a support, with a horizontal damping blade and = the sliding damping magnet is placed on the bottom frame. The coil is fixed = to the outside end and swings between the other magnet block. The diagonal Al = support tube prevents rotation.
       I used 3" x 1" Al U = Channel with triangular 6" x 6" x 1/8" Al plates to support the joint = in the prototype. This is easy to make and to set up. I use 1/4" SS = bolts.


My suggestion is to use = the calculation seen on this list to determine the boom length you desire. = Then plan the design based on that calculation. You said you wanted a device = with a period of 20-second and as pointed out below by Chris, L is based on the = length of the boom measured from the pivot point to the center of the mass = weight (Chris, do you have this calculation?). I have found that setting the = device up this way also reduces the impact of ground deformation (boom does not = remains level and centered) over time which improves the overall operation of = the device keeping the boom off the stops.
http://pw2.netcom.c= om/~shammon1/AptosStn.htm



       If the distance = between the hinge and the centre of mass is L metres and the suspension angle is = A, the period T =3D 2xPixSqrt(L / (9.81 x sin(A))) I use 0.56 m which would = give a 1.5 sec pendulum if held vertically. A is ~1/3 degree.
       Alnico magnets are now quite = expensive. NdFeB magnets are much cheaper and give a much higher output. For damper = and coil designs - click on Lehman at http://jclahr.com/science/psn/chapman/ = Make the damping blade wide so that it covers both magnets at all times as = shown.
       There is also an alternative design = under muventures.
       The boom does not have to be level, = but it should be adjusted parallel with the lower frame. Then you can simply = slide the damping magnet further over the horizontal damping blade to adjust the = damping.
       You adjust the whole rigid frame to = centre the arm and to set the period. I use three SS plates glued to the = concrete floor for the screw adjusters. I glued SS bearings into the end of the = adjust bolts. Then they don't move about / wander when you adjust them. The SS mounting nuts are glued to the underside of the frame.

       Regards,

       Chris = Chapman =

Subject: new style vertical seismometer From: Randall Peters PETERS_RD@.......... Date: Thu, 14 Feb 2008 13:56:00 -0500 Those of you who like to build things might want to try your hand at a new design for the old LaCoste spring vertical seismometer. Internal friction that limits performance has with previous designs been mainly concentrated in both (i) spring, and (ii) axis. My design can radically reduce the hinge force influence, which should improve performance. A prototype is pictured at http://physics.mercer.edu/hpage/new-z.html The key to the smaller reaction forces at the hinge (pair of ball-point pens) is to add an angled boom appendage that allows the zero-length spring itself to be vertical, as opposced to the usual orientation (inclined)--and to place the inertial masses such that the center of mass is close to where the spring passes through the split region of the horizontal segment of the boom. Although the prototype is shown with an SDC array to sense displacement, the instrument can be configured to operate with a magnet/coil (Faraday-law) velocity sensor. Randall Subject: Re: How much mass ? From: ChrisAtUpw@....... Date: Thu, 14 Feb 2008 16:37:52 EST In a message dated 2008/02/14, shammon1@............. writes: > Put the coil on the arm and the magnet on the base. If you put a=20 > magnet on the arm, you will pick up a lot of magnetic noise from the house= =20 > wiring, passing trains and lorries etc. > Update 2/14/08: Thanks Chris, I=E2=80=99ll try mounting the coil on the bo= om in the=20 > next revision. I never wanted to deal with the lead wires off the rear of=20= the=20 > boom. Do you have any tips for frictionless lead wires?=20 Hi Steve, I mount two 2 mm banana sockets on the end of the arm and two nearby=20 on the frame. I use a ~4" loop of 38 AWG polyurethane insulated copper wire=20 soldered between two 2 mm banana plugs. You can solder the insulated wire=20 directly with a hot iron - the insulation just melts. I coat the plugs with=20= Vaseline=20 after soldering and before insertion. The wires are bent to form a vertical=20 'hairpin' V. This has very little effect on the mechanical balance and a low= =20 electrical resistance. I use twin core braid screened microphone cable to co= nnect=20 up. You can use gold plated D twin plastic connectors. You can also mount=20 insulated pins on the arm and frame and solder wires directly, but dismounti= ng=20 and adjusting the arm is easier if you can just unplug the connectors. The biggest improvement that you could make would be to replace the=20 point in a cup lower support with a 1/4" SS ball bearing on the end of the=20 mounting bolt and stick a SS blade flat or a WC triangle on the end of the a= rm.=20 This would enable you to extend the period to at least 20 seconds.=20 An alternative would be to buy a 1/8" tungsten carbide drill bit and=20 cut the shank in two. This would give you two cylinders for a crossed cylind= er=20 rolling suspension. The vertical goes on the frame. Both systems work well. I don't know where point in a cup or knife edge 'bearings' originated= ,=20 but they automatically fail in use as you overload the tip / edge and they=20 then limit the performance. The 'knife edge' bearings used in chemical balan= ces=20 don't actually have a knife edge! The 60 degree triangle is lapped to a tiny= =20 radius cylinder rolling on a flat. I did a rough comparison with the output of a coil using a U Alnico=20 magnet and a Quad of NdFeB bar magnets on 1/4" backing plates. The improveme= nt=20 was > x10. My original coil was about 6,000 turns, but I have reduced this t= o=20 2,000 to keep the output from overloading my amplifier on the lowest gain=20 setting. See drawings on http://jclahr.com/science/psn/chapman/lehman/index.= html I hope that this helps. Regards, Chris Chapman =20 In a me= ssage dated 2008/02/14, shammon1@............. writes:

     &= nbsp; Put the coil on the arm and the magnet on the base. If you put a magne= t on the arm, you will pick up a lot of magnetic noise from the house wiring= , passing trains and lorries etc.
Update 2/14/08: Thanks Chris, I=E2=80=99ll try mounting the coil on the boo= m in the next revision. I never wanted to deal with the lead wires off the r= ear of the boom. Do you have any tips for frictionless lead wires?

Hi Steve,

       I mount two 2 mm banana sockets on the=20= end of the arm and two nearby on the frame. I use a ~4" loop of 38 AWG polyu= rethane insulated copper wire soldered between two 2 mm banana plugs. You ca= n solder the insulated wire directly with a hot iron - the insulation just m= elts. I coat the plugs with Vaseline after soldering and before insertion. T= he wires are bent to form a vertical 'hairpin' V. This has very little effec= t on the mechanical balance and a low electrical resistance. I use twin core= braid screened microphone cable to connect up. You can use gold plated D tw= in plastic connectors. You can also mount insulated pins on the arm and fram= e and solder wires directly, but dismounting and adjusting the arm is easier= if you can just unplug the connectors.

       The biggest improvement that you could=20= make would be to replace the point in a cup lower support with a 1/4" SS bal= l bearing on the end of the mounting bolt and stick a SS blade flat or a WC=20= triangle on the end of the arm. This would enable you to extend the period t= o at least 20 seconds.
       An alternative would be to buy a 1/8" t= ungsten carbide drill bit and cut the shank in two. This would give you two=20= cylinders for a crossed cylinder rolling suspension. The vertical goes on th= e frame. Both systems work well.
       I don't know where point in a cup or kn= ife edge 'bearings' originated, but they automatically fail in use as you ov= erload the tip / edge and they then limit the performance. The 'knife edge'=20= bearings used in chemical balances don't actually have a knife edge! The 60=20= degree triangle is lapped to a tiny radius cylinder rolling on a flat.

       I did a rough comparison with the outpu= t of a coil using a U Alnico magnet and a Quad of NdFeB bar magnets on 1/4"=20= backing plates. The improvement was > x10. My original coil was about 6,0= 00 turns, but I have reduced this to 2,000 to keep the output from overloadi= ng my amplifier on the lowest gain setting. See drawings on http://jclahr.co= m/science/psn/chapman/lehman/index.html

       I hope that this helps.

       Regards,

       Chris Chapman Subject: Re: new style vertical seismometer From: "meredith lamb" paleoartifact@......... Date: Thu, 14 Feb 2008 22:34:22 -0700 Hi Randall, Any possiblity of a close up of the ball point hinge arrangement? The picture can't define what anchors the pen assembly or in which direction, or what the ball points contacts. Either way it "looks" like it might be a little difficult to initially set up; i.e., the spring would have to be adjusted just right for it to be reasonably consistently stable. I suppose you've also tried having the ball points resting atop the cross rectangular piece at one time or the other....but I'd guess the pressure is too much there. Thanks, Meredith Lamb On Thu, Feb 14, 2008 at 11:56 AM, Randall Peters wrote: > Those of you who like to build things might want to try your hand at a new > design for the old > LaCoste spring vertical seismometer. Internal friction that limits > performance has with > previous designs been mainly concentrated in both (i) spring, and (ii) > axis. My design can > radically reduce the hinge force influence, which should improve > performance. A prototype is > pictured at http://physics.mercer.edu/hpage/new-z.html > The key to the smaller reaction forces at the hinge (pair of > ball-point pens) is to add an angled > boom appendage that allows the zero-length spring itself to be vertical, > as opposced to the usual > orientation (inclined)--and to place the inertial masses such that the > center of mass is close to where the > spring passes through the split region of the horizontal segment of the > boom. > Although the prototype is shown with an SDC array to sense > displacement, the instrument can be > configured to operate with a magnet/coil (Faraday-law) velocity sensor. > > Randall > >
Hi Randall,
 
Any possiblity of a close up of the ball point hinge arrangement?  The picture can't define
what anchors the pen assembly or in which direction, or what the ball points contacts.
 
Either way it "looks" like it might be a little difficult to initially set up; i.e., the spring would
have to be adjusted just right for it to be reasonably consistently stable.
 
I suppose you've also tried having the ball points resting atop the cross rectangular piece
at one time or the other....but I'd guess the pressure is too much there.
 
Thanks, Meredith Lamb
  
On Thu, Feb 14, 2008 at 11:56 AM, Randall Peters <PETERS_RD@..........> wrote:
Those of you who like to build things might want to try your hand at a new design for the old
LaCoste spring vertical seismometer.  Internal friction that limits performance has with
previous designs been mainly concentrated in both (i) spring, and (ii) axis.  My design can
radically reduce the hinge force influence, which should improve performance. A prototype is
pictured at  http://physics.mercer.edu/hpage/new-z.html
    The key to the smaller reaction forces at the hinge (pair of ball-point pens) is to add an angled
boom appendage that allows the zero-length spring itself to be vertical, as opposced to the usual
orientation (inclined)--and to place the inertial masses such that the center of mass is close to where the
spring passes through the split region of the horizontal segment of the boom.
   Although the prototype is shown with an SDC array to sense displacement, the instrument can be
configured to operate with a magnet/coil (Faraday-law) velocity sensor.

   Randall


Subject: Explosives vs. calibration From: "Fikke, Audun" Audun.Fikke@......... Date: Fri, 15 Feb 2008 11:09:10 +0100 All, I've just learned that during easter the harbour will be opened up with explsives, 2km from where I live (Stavanger/Norway). They will be using 120metric tonnes of explosives. I belive they will do it in one blast. I don't have confirmation on type of explosives yet (TNT,dynamite,C4,firecrackers....) Does anybody have an idea if this could be used as a benchmark for my seismometer in regards to get a usable calibration? I'm thinking Velocity/Accelleration/Displacement? =20 regards Audun http://vindkast.no =20 =20
All,
I've just = learned=20 that during easter the harbour will be opened up with explsives, = 2km from=20 where I live (Stavanger/Norway).
They will be = using=20 120metric tonnes of explosives. I belive they will do it in one blast. I = don't=20 have confirmation on type of explosives yet=20 (TNT,dynamite,C4,firecrackers....)
Does anybody = have an idea=20 if this could be used as a benchmark for my seismometer in regards = to get a=20 usable calibration? I'm thinking=20 Velocity/Accelleration/Displacement?
 
regards
Audun
http://vindkast.no
 
 
Subject: Re: feedback semantics From: Brett Nordgren Brett3mr@............. Date: Fri, 15 Feb 2008 10:24:19 -0500 Randall, No problem. My only issue had been that I was interpreting 'soft' as meaning 'low loop gain' and because of that had privately dismissed the concept without pursuing it. In fact, you are describing a feedback approach which has low/no loop gain at the mid-band frequencies you are hoping to observe, though the integral feedback should become quite strong and effective at sufficiently low frequencies. Regarding the centering forces required, it's my feeling that they are not all that small. For example, in the STM-8 example, 1 degC changes the spring force by about 10 dynes, which I believe is quite large compared to the forces you might be wanting to measure. I reread your June 2005 paper which referenced the Sprengnether setup and now understand much better that you were describing 'integral only' feedback. I was hoping to use that as a sample case in my analysis programs to better understand how it performs. In particular, the program would need to know the main instrument parameters most of which I can find, assuming it was an S-5100-V, except I'd need to know what natural frequency you had set it up for?. And do I understand correctly in Figure 3 that "Sensor output" is where you are obtaining your instrument output, with a sensitivity of about 2000V/m? Regards, Brett At 06:18 PM 2/11/2008 -0500, you wrote: >Brett, > I am not very familiar with the terminology used in the world of > engineering controls. >My term 'soft' for the feedback scheme that I have used seemed reasonable >to me for the >following reasons: (i) it is as you noted, happerning at a much lower >frequency than most of >the signals of interest (say teleseisms at 20 s period, and (ii) it is >nowhere near as >powerful as the forces required to do force-balance; i.e., keep the mass >from ostensibly >moving. > You mention the matter of using feedback with a pendulum. I can't > imagine a reasonably >simple pendulum for seismic purposes where feedback would ever be >necessary. The primary >source of motion at very low frequencies is the change in shape of the >earth. Every mass >part of our planet contributes to the local field, and so a plumb bob >provides information >concerning eigenmodes and tides (as the VolksMeter has demonstrated). > Your question about my use of the word 'noise' relative to force balance >systems--anything that works with the derivative of the position of the >inertial mass (flat >to velocity sensor) will fail to see earth motions at really long periods >(starting around a >few thousand seconds or even less). Even though the period of the >VolksMeter's simple >pendulum is only about 1 s, it is well suited to the study of earth >changes happening over >days, months, and even years. > > Randall My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: nature of the mesoscopic nonlinearity From: Brett Nordgren Brett3mr@............. Date: Fri, 15 Feb 2008 12:15:04 -0500 Chris, At 02:17 PM 2/13/2008 -0500, you wrote: >>Numerical integration looks interesting. What I think I need to make it >>work is a D/A with something like 24-bit resolution and correspondingly low >>noise. Haven't looked too hard, and haven't found any. > > There are some about. Any suggestions as to what manufacturers to check? >>My understanding was that the 360 second low-end response of the STS-1 was >>about as good as you can get, while still maintaining instrument noise >>below earth noise, and it required using every possible scheme to reduce >>and slow internal noise sources. > > The STS-2 goes to this. Particular versions of the STS-1 would go > out to 1,000 seconds. It is a very hard way to get this performance! Given the fundamental noise issues in any vertical, I think it's the only way. >>That also raises the interesting question, whether some of that 'low earth >>noise' isn't exactly what you are looking to measure. > > There is a lot of earth noise down to the Eigenmodes, which are > interesting in themselves. Transient signals occur which look very like > quake precursors. Those transients worry me just a little. >> > If we consider a pendulum sensor system, the response is proportional >> > to the square of the period. If you take a 2 second pendulum and reduce >> > the restoring force to give a 20 second system, should you get 100x the >> > response for signals already in the passband? >> >>Not sure how you are proposing to reduce the restoring force. If you are >>suggesting feedback, it actually doesn't act in that way. > > Positive feedback does and it will reduce the period. Sounds like an oscillator to me. > It effectively >>applies a very large velocity-damping force on the pendulum in a very >>linear manner. The result is that the low frequency corner is lower and >>the high frequency corner is higher than the original single peak at 2 >>seconds. In a sense the system is still acting as a 2 second pendulum but >>one which is extremely overdamped. see 'FISS' >> >> > Why should a synthesised feedback response to obtain a longer period >> > result in a much smaller response to the ground motion? >> >>The simple answer: Because (negative) feedback always acts to lower the >>instrument sensitivity to position, velocity and acceleration, (excepting >>in a few pathological cases). A complete answer involves actually doing >>the computations for a particular case and examining the results such as is >>done in 'FISS'. >> >> > You seem to consider that requiring an increased position >> > sensitivity is an advantage. > > You are using a position sensor, which will have a measurement > range and a noise level which limits what you can sense. I am enquiring > what resolution you can get. The practical limit is likely to be set > above this by thermal varriations. Using the same C/D device, a little better than the SDC, maybe 5-10x the displacement sensitivity depending on the plate size, so 5-10x S/N. I have been scratching my head as to how to characterize C/D quantization noise relative to feedback. I'm sure as you apply feedback, reducing the sensitivity, the displacement corresponding to one C/D step also reduces, so S/N from that source shouldn't get worse. I need to think about this more. My approach to the thermal problem is to try to keep the thermal changes small and very slow, below the low-end response of the system. But that implies that the system *has* a low end limit, i.e. that its force-response will be low near zero frequency. >> > If you use a DC path from your position sensor through a long period >> > integrator to the feedback transducer, you can in theory remove ~all >> > position drifts. >> >>Yes, but when you call it a long-period integrator you imply that there is >>no DC path. . > > No. They can go down to DC. Randal uses one on his Sprengnether. > See my reference. You have a large resistance onto the negative input of > a FET opamp and a capacitor (+ resistor?) in the feedback loop. You are sooooo right. I went back and looked at my proposed circuit, which is similar to what Randall was using, and found that, indeed, with a particular capacitor I'd tested it should integrate down to something below a microHertz. >> > A capacitative position sensor system can have a very high >> > linearity. What other system nonlinearities were you considering that >> > could be relevant? >> >>Primarily the position sensor system. That would include, of course, the >>C/D converter as well as the capacitor. When you say very high linearity >>are you implying 1%, 0.1%, 0.01%....? Have any measurements been made? > > > My guesstimate would be in the 0.1% region, probably better. It will > depend mostly on the precision of the physical sensor construction. The > linearity over a small range will be extreme. OK, sometime I'll play around with numbers in that range and see what happens. > My >>concern is that even with fairly small nonlinearity, large amplitude, >>higher frequency signals can mix to generate small low-frequency difference >>signals which could possibly confound measurements attempted down at very >>low frequencies. Only with specific linearity figures could one rule >>in/out that effect by calculating its magnitude. Also the spring in a >>vertical, or pendulum geometry might possibly add nonlinearity. > > > I would not expect even moderate quakes to generate serious non > linearity. You are more likely to run out of detector range. The angles > are less than 2 degrees. Yes, you don't usually notice a vertical pendulum swinging very far in response to distant quakes, do you. Regards, Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: How much mass ? From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Fri, 15 Feb 2008 19:12:51 +0000 Hi The teacher how is helping me building the seismometer wants to know what type of material is best to use in the seismometer. He was wondering about iron or steel, maybe aluminum. But as I am not sure so I was unable to give him good answer. He was also wondering about the arm that holds them mass up, what it should me made out of. I am going to use the BGS design, as it has the configuration numbers that the teacher needs to build the seismometer. Thanks in advance for the help. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: How much mass ? From: ChrisAtUpw@....... Date: Fri, 15 Feb 2008 14:59:44 EST In a message dated 2008/02/15, jonfr@......... writes: > The teacher how is helping me building the seismometer wants to know > what type of material is best to use in the seismometer. He was > wondering about iron or steel, maybe aluminum. But as I am not sure so I > was unable to give him good answer. He was also wondering about the arm > that holds them mass up, what it should me made out of. > > I am going to use the BGS design, as it has the configuration numbers > that the teacher needs to build the seismometer. Hi Jon, I suggest that you download and read ftp://ftp.bgs.ac.uk/pubload/schoolseismology/SEP_CD/SSS_instructions_v1.pdf The original version used 2.5" or 3" x 1" U Channel Aluminum for the frame and 1/8" Al plate for the corners. It used 6mm SS bolts. You can buy 1/8" / 3mm Tungsten Carbide drills and use the shanks for the bearings This should give you some ideas anyway! Regards, Chris Chapman In a me= ssage dated 2008/02/15, jonfr@......... writes:

The teacher how is helping me b= uilding the seismometer wants to know
what type of material is best to use in the seismometer. He was
wondering about iron or steel, maybe aluminum. But as I am not sure so I
was unable to give him good answer. He was also wondering about the arm
that holds them mass up, what it should me made out of.

I am going to use the BGS design, as it has the configuration numbers
that the teacher needs to build the seismometer.


Hi Jon,

       I suggest that you download and read ft= p://ftp.bgs.ac.uk/pubload/schoolseismology/SEP_CD/SSS_instructions_v1.pdf        The original version used 2.5" or 3" x=20= 1" U Channel Aluminum for the frame and  1/8" Al plate for the corners.= It used 6mm SS bolts.
       You can buy 1/8" / 3mm Tungsten Carbide= drills and use the shanks for the bearings

       This should give you some ideas anyway!=

       Regards,

       Chris Chapman Subject: Re: seismometer performance From: Bobhelenmcclure@....... Date: Fri, 15 Feb 2008 21:13:05 EST Hi all, Brett, you did a beautiful job with your paper on force feedback. I can almost understand it! One issue discussed but unresolved is how to handle drift. Have you ever looked at the efforts of one of our PSN members, Allan Coleman. He has built a number of force feedback sensors of both horizontal and vertical types. His designs feature the use of motors to recenter the pendulum. His website is: http://mysite.verizon.net/ressczez/homebuilt_seismometers/ You can also access it from a link in: http://www.jclahr.com/science/psn Look for "Allan Coleman's seismometer designs". Force rebalance is a necessity for network sensors. All need a flat response that is known and stable. As for me, there is too much involved circuitry to cope with. I choose to use conventional open loop sensors of known period and damping, and then to make their response flat and broadband using my inverse filter program, "WQFilter.exe". This utility is available for download from http://jclahr.com/science/psn/mcclure/sac/index.html Regards, Bob PSN Station REM Locust Valley, NY ************** The year's hottest artists on the red carpet at the Grammy Awards. Go to AOL Music. (http://music.aol.com/grammys?NCID=aolcmp00300000002565) Hi all,

  Brett, you did a beautiful job with your paper on force feedback. I c= an almost understand it! One issue discussed but unresolved is how to handle= drift. Have you ever looked at the efforts of one of our PSN members, Allan= Coleman. He has built a number of force feedback sensors of both horizontal= and vertical types. His designs feature the use of motors to recenter the p= endulum.

  His website is:

  http://mysite.verizon.net/ressczez/homebuilt_seismometers/

  You can also access it from a link in:

  http://www.jclahr.com/science/psn

  Look for "Allan Coleman's seismometer designs".

  Force rebalance is a necessity for network sensors. All need a flat r= esponse that is known and stable. As for me, there is too much involved circ= uitry to cope with. I choose to use conventional open loop sensors of known=20= period and damping, and then to make their response flat and broadband using= my inverse filter program, "WQFilter.exe". This utility is available for do= wnload from

  http://jclahr.com/science/psn/mcclure/sac/index.html

Regards,

Bob
PSN Station REM
Locust Valley, NY


**************
The year's hottest art= ists on the red carpet at the Grammy Awards. Go to AOL Music.
(http= ://music.aol.com/grammys?NCID=3Daolcmp00300000002565) Subject: Re: nature of the mesoscopic nonlinearity From: ChrisAtUpw@....... Date: Fri, 15 Feb 2008 21:29:34 EST In a message dated 2008/02/15, Brett3mr@............. writes: > >>Numerical integration looks interesting. What I think I need to make it > >>work is a D/A with something like 24-bit resolution and correspondingly > low > >>noise. Haven't looked too hard, and haven't found any. > > > > There are some about. > > Any suggestions as to what manufacturers to check? Texas, Burr-Brown They do 20 bit single channel, DAC1220E. Most of the 24 bit ones seem to be audio codecs. I don't know what their error or stability are like. > > The STS-2 goes to this. Particular versions of the STS-1 would go > > out to 1,000 seconds. It is a very hard way to get this performance! > > Given the fundamental noise issues in any vertical, I think it's the only > way. Only because you are using a particular feedback loop method involving velocity feedback. If you measure the position and relate the movement digitally, you should not have problems over period. > > There is a lot of earth noise down to the Eigenmodes, which are > > interesting in themselves. Transient signals occur which look very like > > quake precursors. > > Those transients worry me just a little. What worries you about them? I find the prospect both interesting and exciting! The crust of the Earth is being continually cyclically flexed by the Sun and the Moon. It would be very surprising if there were NO transients! You also get Earth Hum. > >>Not sure how you are proposing to reduce the restoring force. If you are > >>suggesting feedback, it actually doesn't act in that way. > > > > Positive feedback does and it will increase the period. > > Sounds like an oscillator to me. Then you may be misunderstanding something. There is no reason why you should not provide a weaker spring / seek to reduce the force required to move the mass by feedback. You can certainly get an oscillator this way, but only if you generate a net positive force, not reduce a negative one. > > You are using a position sensor, which will have a measurement > > range and a noise level which limits what you can sense. I am enquiring > > what resolution you can get. The practical limit is likely to be set > > above this by thermal variations. > > Using the same C/D device, a little better than the SDC, maybe 5-10x the > displacement sensitivity depending on the plate size, so 5-10x S/N. I > have been scratching my head as to how to characterize C/D quantization > noise relative to feedback. I'm sure as you apply feedback, reducing the > sensitivity, the displacement corresponding to one C/D step also reduces, > so S/N from that source shouldn't get worse. I need to think about this > more. If you apply strong feedback, the detector will not 'know' anything about it, but the mass movement for a given quake amplitude will be decreased. You will be requiring increased resolution and this conflicts with stability / drift. You can fit fixed capacitors to the system and then measure the actual output noise that you get. This is what we did with Barzilai's circuit and the sine wave circuit. I don't see how you can calculate it. The digital method is inferior due to it's sensitivity to tiny variations in timing. > >> > A capacitative position sensor system can have a very high > >> > linearity. What other system nonlinearities were you considering that > >> > could be relevant? > >> > >>Primarily the position sensor system. That would include, of course, the > >>C/D converter as well as the capacitor. When you say very high linearity > >>are you implying 1%, 0.1%, 0.01%....? Have any measurements been made? > > > > My guesstimate would be in the 0.1% region, but probably better. It > will > > depend mostly on the precision of the physical sensor construction. The > > linearity over a small range will be extreme. > > OK, sometime I'll play around with numbers in that range and see what > happens. Regards, Chris In a me= ssage dated 2008/02/15, Brett3mr@............. writes:

>>Numerical integration l= ooks interesting.  What I think I need to make it
>>work is a D/A with something like 24-bit resolution and correspondin= gly low
>>noise.  Haven't looked too hard, and haven't found any.
>
>        There are some about.

Any suggestions as to what manufacturers to check?


       Texas, Burr-Brown They do 20 bit singl= e channel, DAC1220E. Most of the 24 bit ones seem to be audio codecs. I don'= t know what their error or stability are like.

>    &nb= sp;   The STS-2 goes to this. Particular versions of the STS-1 wou= ld go
> out to 1,000 seconds. It is a very hard way to get this performance!
Given the fundamental noise issues in any vertical, I think it's the only wa= y.


       Only because you are using a particula= r feedback loop method involving velocity feedback. If you measure the posit= ion and relate the movement digitally, you should not have problems over per= iod.

>    &nb= sp;   There is a lot of earth noise down to the Eigenmodes, which=20= are
> interesting in themselves. Transient signals occur which look very like=
> quake precursors.

Those transients worry me just a little.


       What worries you about them? I find th= e prospect both interesting and exciting! The crust of the Earth is being co= ntinually cyclically flexed by the Sun and the Moon. It would be very surpri= sing if there were NO transients! You also get Earth Hum.

>>Not sure how you are pr= oposing to reduce the restoring force.  If you are
>>suggesting feedback, it actually doesn't act in that way.
>
>    Positive feedback does and it will increase the perio= d.

Sounds like an oscillator to me.


       Then you may be misunderstanding somet= hing. There is no reason why you should not provide a weaker spring / seek t= o reduce the force required to move the mass by feedback. You can certainly=20= get an oscillator this way, but only if you generate a net positive force, n= ot reduce a negative one.

>    &nb= sp;   You are using a position sensor, which will have a measureme= nt
> range and a noise level which limits what you can sense. I am enquiring=
> what resolution you can get. The practical limit is likely to be set > above this by thermal variations.

Using the same C/D device, a little better than the SDC, maybe 5-10x the displacement sensitivity depending on the plate size, so 5-10x S/N.  I=20=
have been scratching my head as to how to characterize C/D quantization
noise relative to feedback.  I'm sure as you apply feedback, reducing t= he
sensitivity, the displacement corresponding to one C/D step also reduces, so S/N from that source shouldn't get worse.  I need to think about thi= s more.


       If you apply strong feedback, the dete= ctor will not 'know' anything about it, but the mass movement for a given qu= ake amplitude will be decreased. You will be requiring increased resolution=20= and this conflicts with stability / drift.
       You can fit fixed capacitors to the sys= tem and then measure the actual output noise that you get. This is what we d= id with Barzilai's circuit and the sine wave circuit. I don't see how you ca= n calculate it. The digital method is inferior due to it's sensitivity to ti= ny variations in timing.

>> >   =    A capacitative position sensor system can have a very high
>> > linearity. What other system nonlinearities were you consideri= ng that
>> > could be relevant?
>>
>>Primarily the position sensor system.  That would include, of c= ourse, the
>>C/D converter as well as the capacitor.  When you say very high= linearity
>>are you implying 1%, 0.1%, 0.01%....?  Have any measurements be= en made?
>
>     My guesstimate would be in the 0.1% region, but= probably better. It will
> depend mostly on the precision of the physical sensor construction. The=
> linearity over a small range will be extreme.

OK, sometime I'll play around with numbers in that range and see what happen= s.


       Regards,

       Chris Subject: RE: new style vertical seismometer From: Michael Kimzey mckimzey@........... Date: Fri, 15 Feb 2008 21:57:42 -0500 Great design, Dr. Peters. =20 A question, though. The web page mentions a feedback system to increase th= e period. What would such a system look like? - Mike > Date: Thu, 14 Feb 2008 13:56:00 -0500 > From: PETERS_RD@.......... > Subject: new style vertical seismometer > To: psn-l@.............. >=20 > Those of you who like to build things might want to try your hand at a ne= w design for the old > LaCoste spring vertical seismometer. Internal friction that limits perfo= rmance has with > previous designs been mainly concentrated in both (i) spring, and (ii) ax= is. My design can > radically reduce the hinge force influence, which should improve performa= nce. A prototype is > pictured at http://physics.mercer.edu/hpage/new-z.html > The key to the smaller reaction forces at the hinge (pair of ball-po= int pens) is to add an angled > boom appendage that allows the zero-length spring itself to be vertical, = as opposced to the usual > orientation (inclined)--and to place the inertial masses such that the ce= nter of mass is close to where the > spring passes through the split region of the horizontal segment of the b= oom. > Although the prototype is shown with an SDC array to sense displaceme= nt, the instrument can be > configured to operate with a magnet/coil (Faraday-law) velocity sensor. >=20 > Randall >=20
Great design, Dr= .. Peters. 

A question, though.  The web page mentions a f= eedback system to increase the period.  What would such a system look = like?

- Mike



> Date:= Thu, 14 Feb 2008 13:56:00 -0500
> From: PETERS_RD@..........
>= Subject: new style vertical seismometer
> To: psn-l@..............>
> Those of you who like to build things might want to try you= r hand at a new design for the old
> LaCoste spring vertical seismome= ter. Internal friction that limits performance has with
> previous d= esigns been mainly concentrated in both (i) spring, and (ii) axis. My desi= gn can
> radically reduce the hinge force influence, which should imp= rove performance. A prototype is
> pictured at http://physics.mercer= ..edu/hpage/new-z.html
> The key to the smaller reaction forces a= t the hinge (pair of ball-point pens) is to add an angled
> boom appe= ndage that allows the zero-length spring itself to be vertical, as opposced= to the usual
> orientation (inclined)--and to place the inertial mas= ses such that the center of mass is close to where the
> spring passe= s through the split region of the horizontal segment of the boom.
> = Although the prototype is shown with an SDC array to sense displacement,= the instrument can be
> configured to operate with a magnet/coil (Fa= raday-law) velocity sensor.
>
> Randall
>
= Subject: Re: seismometer performance From: Brett Nordgren Brett3mr@............. Date: Fri, 15 Feb 2008 22:40:57 -0500 At 09:13 PM 2/15/2008 -0500, you wrote: >Hi all, > > Brett, you did a beautiful job with your paper on force feedback. I can > almost understand it! One issue discussed but unresolved is how to handle > drift. Have you ever looked at the efforts of one of our PSN members, > Allan Coleman. He has built a number of force feedback sensors of both > horizontal and vertical types. His designs feature the use of motors to > recenter the pendulum. Bob, Thanks for the kind words. Yes, I had studied what Allan was doing, though I should go back and see what's new. He's had some very interesting ideas. I completely agree that some form of mechanical rebalancing process will be essential, extremely so in a vertical. The real value of using feedback to aid in centering is to reduce how often you need to mechanically rebalance, and minimize zero point drift between adjustments. If you think about it, any systematic mechanical rebalancing of the system is also feedback, though it sometimes involves a human in the feedback loop, and it will be a little hard to describe well with numbers. If carried down to low enough frequency, integral feedback can go a long way toward resisting instrument drift. This is 'just' a matter of making the instrument force/acceleration response approach zero at very low frequencies. Unfortunately, there is dirty little secret about using R-C integral feedback to resist drift error forces, and that is evident when the integrator is 'straining' to cancel a fairly strong unbalance force, in which event there will be a substantial voltage across the integrating capacitor. The cap. has a temperature coefficient of C which is of the same order of magnitude as the Temp. Coeff. of a steel spring i.e. pretty large. Since in a feedback integrator the charge, Q in the cap. changes relatively slowly and can be considered to be constant as a first approximation, if its capacitance goes up with temperature, its voltage goes down in proportion because of Q=CV thus introducing its own rather large drift effect. It will only work as expected if the system is already reasonably well balanced mechanically making the voltage across the cap. not too large. Allan's got the right approach. Thanks for Allan's links. I'll go take a look. Brett > His website is: > > http://mysite.verizon.net/ressczez/homebuilt_seismometers/ > > You can also access it from a link in: > > http://www.jclahr.com/science/psn > > Look for "Allan Coleman's seismometer designs". > > Force rebalance is a necessity for network sensors. All need a flat > response that is known and stable. As for me, there is too much involved > circuitry to cope with. I choose to use conventional open loop sensors of > known period and damping, and then to make their response flat and > broadband using my inverse filter program, "WQFilter.exe". This utility > is available for download from > > http://jclahr.com/science/psn/mcclure/sac/index.html > >Regards, > >Bob >PSN Station REM >Locust Valley, NY > > >************** >The year's hottest artists on the red carpet at the Grammy Awards. Go to >AOL Music. >(http://music.aol.com/grammys?NCID=aolcmp00300000002565) My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: How much mass ? From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 16 Feb 2008 14:57:20 +0000 Hi Thanks for this. I have printed out the guide to show the teacher. It is cheaper for me build it then buy it.=20 Regards. J=F3n Fr=EDmann. On Fri, 2008-02-15 at 14:59 -0500, ChrisAtUpw@....... wrote: > In a message dated 2008/02/15, jonfr@......... writes: >=20 > > The teacher how is helping me building the seismometer wants to know > > what type of material is best to use in the seismometer. He was > > wondering about iron or steel, maybe aluminum. But as I am not sure > > so I > > was unable to give him good answer. He was also wondering about the > > arm > > that holds them mass up, what it should me made out of. > >=20 > > I am going to use the BGS design, as it has the configuration > > numbers > > that the teacher needs to build the seismometer. >=20 >=20 > Hi Jon, >=20 > I suggest that you download and read > ftp://ftp.bgs.ac.uk/pubload/schoolseismology/SEP_CD/SSS_instructions_v1.p= df > The original version used 2.5" or 3" x 1" U Channel Aluminum > for the frame and 1/8" Al plate for the corners. It used 6mm SS > bolts.=20 > You can buy 1/8" / 3mm Tungsten Carbide drills and use the > shanks for the bearings=20 >=20 > This should give you some ideas anyway! >=20 > Regards, >=20 > Chris Chapman=20 __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: new style vertical seismometer From: ChrisAtUpw@....... Date: Sat, 16 Feb 2008 10:23:15 EST In a message dated 2008/02/14, PETERS_RD@.......... writes: > Those of you who like to build things might want to try your hand at a new > design for the old LaCoste spring vertical seismometer. Hi Randall, I note that you mention using a zero length spring. The extension springs that you can buy do not have such a high preload - usually about 1/3 of that required. Are you winding your own? What hard counterface are you using for the WC 1 mm bearings? They have quite a restricted load carrying capacity (100 gm?), but, unlike the Volksmeter, the seismic mass is quite heavy. How does the seismometer cope with vertical inertial loads of up to 0.1 g and horizontal loads of an appreciable fraction of this? How do you avoid overloading these very small bearings? What is supposed to maintain the horizontal positional stability? While a vertical seismometer is only sensitive to vertical loads, it experiences both vertical and horizontal displacements while in operation. Regards, Chris Chapman In a me= ssage dated 2008/02/14, PETERS_RD@.......... writes:

Those of you who like to build=20= things might want to try your hand at a new design for the old LaCoste sprin= g vertical seismometer.


Hi Randall,

       I note that you mention using a zero le= ngth spring. The extension springs that you can buy do not have such a high=20= preload - usually about 1/3 of that required. Are you winding your own?

       What hard counterface are you using for= the WC 1 mm bearings? They have quite a restricted load carrying capacity (= 100 gm?), but, unlike the Volksmeter, the seismic mass is quite heavy.

       How does the seismometer cope with vert= ical inertial loads of up to 0.1 g and horizontal loads of an appreciable fr= action of this? How do you avoid overloading these very small bearings? What= is supposed to maintain the horizontal positional stability? While a vertic= al seismometer is only sensitive to vertical loads, it experiences both vert= ical and horizontal displacements while in operation.   

       Regards,

       Chris Chapman Subject: FW: Explosives vs. calibration From: "Fikke, Audun" Audun.Fikke@......... Date: Sat, 16 Feb 2008 18:11:02 +0100 =20 All, I've just learned that during easter our harbour will be opened up with explsives, 2km from where I live (Stavanger/Norway). They will be using 120metric tonnes of explosives.=20 Does anybody have an idea if this could be used as a benchmark for my seismometer in regards to get a usable calibration? I'm thinking down the road of Velocity/Accelleration/Displacement? =20 The guys involved in the blast must have some calculations ready as part of the pre job planning/safety. And I can contact them if you guys think It's worth pursuing. regards Audun =20 __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: seismometer performance From: ChrisAtUpw@....... Date: Sat, 16 Feb 2008 12:28:23 EST In a message dated 2008/02/16, Brett3mr@............. writes: > If carried down to low enough frequency, integral feedback can go a long > way toward resisting instrument drift. This is 'just' a matter of making > the instrument force / acceleration response approach zero at very low > frequencies. > > Unfortunately, there is dirty little secret about using R-C integral > feedback to resist drift error forces, and that is evident when the > integrator is 'straining' to cancel a fairly strong unbalance force, in > which event there will be a substantial voltage across the integrating > capacitor. The cap. has a temperature coefficient of C which is of the > same order of magnitude as the Temp. Coeff. of a steel spring i.e. pretty > large. Since in a feedback integrator the charge, Q in the cap. changes > relatively slowly and can be considered to be constant as a first > approximation, if its capacitance goes up with temperature, its voltage > goes down in proportion because of Q=CV thus introducing its own rather > large drift effect. It will only work as expected if the system is already > reasonably well balanced mechanically making the voltage across the cap. > not too large. Hi Brett, You have four drifts here. The change in the magnet strength with temperature, the changes in the coil with temperature and the change in the capacitor with temperature. The magnet strength is decreasing, the coil area and resistance are increasing and the capacitance is decreasing with increasing T. I don't know to what extent these can be chosen to cancel? However, you only have to put the low pass frequency below the minimum response frequency, but this could give problems with 1000 second instruments. Regards, Chris Chapman In a me= ssage dated 2008/02/16, Brett3mr@............. writes:

If carried down to low enough f= requency, integral feedback can go a long
way toward resisting instrument drift.  This is 'just' a matter of maki= ng
the instrument force / acceleration response approach zero at very low
frequencies.

Unfortunately, there is dirty little secret about using R-C integral
feedback to resist drift error forces, and that is evident when the
integrator is 'straining' to cancel a fairly strong unbalance force, in
which event there will be a substantial voltage across the integrating
capacitor.  The cap. has a temperature coefficient of C which is of the=
same order of magnitude as the Temp. Coeff. of a steel spring i.e. pretty large.  Since in a feedback integrator the charge, Q in the cap. change= s
relatively slowly and can be considered to be constant as a first
approximation, if its capacitance goes up with temperature, its voltage
goes down in proportion because of Q=3DCV thus introducing its own rather large drift effect.  It will only work as expected if the system is alr= eady
reasonably well balanced mechanically making the voltage across the cap. not too large.


Hi Brett,

       You have four drifts here. The change i= n the magnet strength with temperature, the changes in the coil with tempera= ture and the change in the capacitor with temperature. The magnet strength i= s decreasing, the coil area and resistance are increasing and the capacitanc= e is decreasing with increasing T. I don't know to what extent these can be=20= chosen to cancel? However, you only have to put the low pass frequency below= the minimum response frequency, but this could give problems with 1000 seco= nd instruments.

       Regards,

       Chris Chapman
 Subject: Re: FW: Explosives vs. calibration From: ChrisAtUpw@....... Date: Sat, 16 Feb 2008 12:38:33 EST In a message dated 2008/02/16, Audun.Fikke@......... writes: > I've just learned that during easter our harbour will be opened up with > explsives, 2km from where I live (Stavanger/Norway). They will be using > 120metric tonnes of explosives. > Does anybody have an idea if this could be used as a benchmark for my > seismometer in regards to get a usable calibration? I'm thinking down > the road of Velocity/Accelleration/Displacement? Hi Audun, You don't say what seismometer you are using? I would be inclined to pack up and take my seismometer on holiday at that time. I regard 120 tons of HE at 2 km as far too close for comfort for either of us. Regards, Chris Chapman In a me= ssage dated 2008/02/16, Audun.Fikke@......... writes:

I've just learned that during e= aster our harbour will be opened up with explsives, 2km from where I live (S= tavanger/Norway). They will be using 120metric tonnes of explosives.
Does anybody have an idea if this could be used as a benchmark for my
seismometer in regards to get a usable calibration? I'm thinking down
the road of Velocity/Accelleration/Displacement?


Hi Audun,

       You don't say what seismometer you are=20= using? I would be inclined to pack up and take my seismometer on holiday at=20= that time. I regard 120 tons of HE at 2 km as far too close for comfort for=20= either of us.

       Regards,

       Chris Chapman Subject: Re: seismometer performance From: Brett Nordgren Brett3mr@............. Date: Sat, 16 Feb 2008 13:50:42 -0500 Hi Chris, At 12:28 PM 2/16/2008 -0500, you wrote: >In a message dated 2008/02/16, Brett3mr@............. writes: > >>If carried down to low enough frequency, integral feedback can go a long >>way toward resisting instrument drift. This is 'just' a matter of making >>the instrument force / acceleration response approach zero at very low >>frequencies. >> >>Unfortunately, there is dirty little secret about using R-C integral >>feedback to resist drift error forces, and that is evident when the >>integrator is 'straining' to cancel a fairly strong unbalance force, in >>which event there will be a substantial voltage across the integrating >>capacitor. The cap. has a temperature coefficient of C which is of the >>same order of magnitude as the Temp. Coeff. of a steel spring i.e. pretty >>large. Since in a feedback integrator the charge, Q in the cap. changes >>relatively slowly and can be considered to be constant as a first >>approximation, if its capacitance goes up with temperature, its voltage >>goes down in proportion because of Q=CV thus introducing its own rather >>large drift effect. It will only work as expected if the system is already >>reasonably well balanced mechanically making the voltage across the cap. >>not too large. > > >Hi Brett, > > You have four drifts here. The change in the magnet strength with > temperature, the changes in the coil with temperature and the change in > the capacitor with temperature. The magnet strength is decreasing, the > coil area and resistance are increasing and the capacitance is decreasing > with increasing T. I don't know to what extent these can be chosen to > cancel? However, you only have to put the low pass frequency below the > minimum response frequency, but this could give problems with 1000 second > instruments. Yes, I agree the forcing coil/magnet also introduce effects similar to what I was describing for the integrator capacitor; except that you can avoid the coil resistance issues by using a current driver. It's obvious that you can't depend on electronic feedback to do all your centering, forever, but must occasionally turn a screw to unload the feedback loop. Thanks for your thoughts, Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: seismometer performance From: ChrisAtUpw@....... Date: Sat, 16 Feb 2008 17:28:45 EST In a message dated 2008/02/16, Brett3mr@............. writes: > Yes, I agree the forcing coil/magnet also introduce effects similar to what > > I was describing for the integrator capacitor; except that you can avoid > the coil resistance issues by using a current driver. It's obvious that > you can't depend on electronic feedback to do all your centering, forever, > but must occasionally turn a screw to unload the feedback loop. Hi Brett, My train of thought was to either compensate or to drastically reduce the main error drifts. I use a small thermostat circuit to keep crystal temperatures constant to better than 0.1 C Deg. I could wrap one nicely around a capacitor. If you used an electromagnet, you could keep the field constant to a few ppm. An alternative would be to control the temperature of the magnets. The biggest drift is likely that of a steel spring. Can you get Ni-SpanC wire? sheet? I can get Invar wire, but not Elinvar at the moment. Regards, Chris Chapman In a me= ssage dated 2008/02/16, Brett3mr@............. writes:

Yes, I agree the forcing coil/m= agnet also introduce effects similar to what
I was describing for the integrator capacitor; except that you can avoid the coil resistance issues by using a current driver.  It's obvious tha= t
you can't depend on electronic feedback to do all your centering, forever, <= BR> but must occasionally turn a screw to unload the feedback loop.
=

Hi Brett,

       My train of thought was to either compe= nsate or to drastically reduce the main error drifts. I use a small thermost= at circuit to keep crystal temperatures constant to better than 0.1 C Deg. I= could wrap one nicely around a capacitor. If you used an electromagnet, you= could keep the field constant to a few ppm. An alternative would be to cont= rol the temperature of the magnets.
       The biggest drift is likely that of a s= teel spring. Can you get Ni-SpanC wire? sheet? I can get Invar wire, but not= Elinvar at the moment.

       Regards,

       Chris Chapman Subject: Re: FW: Explosives vs. calibration<<< Hmmmm........ From: "Jim ODonnell" geophysics@.......... Date: Sun, 17 Feb 2008 00:44:49 GMT Audun- You may be looking at ~M3.5+ at 2km which is rather Awesome.... See Prof John Louie's chart at UNR relating EQ Mag to seismic energy Yie= ld: = = http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html It depends on the coupling and if it is a ripple shot rather than 1 big = bang. <<<<<<<<<< Jim Jim O'Donnell = Geological/Geophysical Consultant GEOTECHNICAL APPLICATIONS 702.293.5664 geophysics@.......... 702.281.9081 cell jimo17@........ -- "Fikke, Audun" wrote: All, I've just learned that during easter our harbour will be opened up with explsives, 2km from where I live (Stavanger/Norway). They will be using 120metric tonnes of explosives. = Does anybody have an idea if this could be used as a benchmark for my seismometer in regards to get a usable calibration? I'm thinking down the road of Velocity/Accelleration/Displacement? The guys involved in the blast must have some calculations ready as part= of the pre job planning/safety. And I can contact them if you guys think= It's worth pursuing. regards Audun __________________________________________________________ Public Seismic Network Mailing List (PSN-L) See http://www.seismicnet.com/maillist.html for more information.

Audun- You may be looking at ~M3.5+ at 2km which is rather = ;Awesome....
See Prof John Louie's chart at UNR relating EQ Mag to se= ismic energy Yield: 

http://www.seismo.unr.edu/ftp/pub= /louie/class/100/magnitude.html

It depends on the coupling and if it is a ripple shot rather than 1 b= ig bang.
<<<<<<<<<<   Jim
=

          &nbs= p;       Jim O'Donnell   &n= bsp; 
        Geological= /Geophysical Consultant
       &nb= sp;   GEOTECHNICAL APPLICATIONS
702.293.5664  &nb= sp; geophysics@..........
702.281.9081 cell   jimo17@j= uno.com

-- "Fikke, Audun" <Audun.Fikke@.........> wrote:

All,
I've just learned that during easter our harbour will b= e opened up with
explsives, 2km from where I live (Stavanger/Norway).=
They will be using 120metric tonnes of explosives.
Does anybody = have an idea if this could be used as a benchmark for my
seismometer = in regards to get a usable calibration? I'm thinking down
the road of= Velocity/Accelleration/Displacement?

The guys involved in the bl= ast must have some calculations ready as part
of the pre job planning= /safety. And I can contact them if you guys think
It's worth pursuing= ..

regards
Audun

_______________________________________= ___________________

Public Seismic Network Mailing List (PSN-L)
To leave this list email PSN-L-REQUEST@.............. with
the= body of the message (first line only): unsubscribe
See http://www.se= ismicnet.com/maillist.html for more information.

Subject: Re: when feedback is not needed From: Barry Lotz barry_lotz@............. Date: Sat, 16 Feb 2008 16:49:01 -0800 (PST) Randall Something has confused me about the volksmeter or the SG sensor. For a passive sensor I always thought the response of the sensor dropped by (I forget the db slope) for frequencies below the natural frequency of the sensor. Therefore I would think the output would have to amplified accordingly for low frequencies. Is the noise amplified also? Is the drop-off mathematically known so the amplification can be correctly compensated? I didn't think a simple intergator in the output of the SG provided a simple flat response of output vs frequency. Regards Barry Randall Peters wrote: Recent discussions of force feedback have mentioned pendulums. I hope that these were thoughts directed only toward horizontal instruments of the 'garden gate' variety (not what I call a pendulum); since I can't imagine a reason for ever wanting to go to that degree of difficulty with a 'simple' pendulum such as in the VolksMeter. The direction of a simple static pendulum does not migrate to any great extent. Its very low frequency response is determined by shape changes of the earth that do not exceed tens of microradians. The exception to this claim applies only to the case of a detector with a very limited mechanical dynamic range, such as a gap varying capacitive sensor. With the area-varying array used by the VoksMeter it is unlikely that force balance or any other type of feedback should ever be needed. Randall begin:vcard n:Peters;Randall tel;work:(478)301-2747 x-mozilla-html:FALSE url:http://physics.mercer.edu/hpage/peters.html org:Mercer University;Physics Department adr:;;1400 Coleman Ave.;Macon;Georgia;31207;USA version:2.1 email;internet:peters_rd@.......... title:Professor and Chairman fn:Randall Peters PhD end:vcard
Randall
Something has confused me about the volksmeter or the SG sensor. For a passive sensor I always thought the response of the sensor dropped by (I forget the db slope) for frequencies below the natural frequency of the sensor. Therefore I would think the output would have to amplified accordingly for low frequencies. Is the noise amplified also? Is the drop-off mathematically known so the amplification can be correctly compensated? I didn't think a simple intergator in the output of the SG provided a simple flat response of output vs frequency.
Regards
Barry


Randall Peters <PETERS_RD@..........> wrote:
Recent discussions of force feedback have mentioned pendulums. I hope that these were thoughts directed only toward horizontal
instruments of the 'garden gate' variety (not what I call a pendulum); since I can't imagine a reason for ever wanting to go to
that degree of difficulty with a 'simple' pendulum such as in the VolksMeter. The direction of a simple static pendulum does
not migrate to any great extent. Its very low frequency response is determined by shape changes of the earth that do not exceed
tens of microradians. The exception to this claim applies only to the case of a detector with a very limited mechanical dynamic
range, such as a gap varying capacitive sensor. With the area-varying array used by the VoksMeter it is unlikely that force
balance or any other type of feedback should ever be needed.
Randall

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tel;work:(478)301-2747
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url:http://physics.mercer.edu/hpage/peters.html
org:Mercer University;Physics Department
adr:;;1400 Coleman Ave.;Macon;Georgia;31207;USA
version:2.1
email;internet:peters_rd@..........
title:Professor and Chairman
fn:Randall Peters PhD
end:vcard

Subject: Re: seismometer performance From: Brett Nordgren Brett3mr@............. Date: Sat, 16 Feb 2008 20:24:02 -0500 Hi Chris, If you're interested in Ni-Span-C you might find this of interest. http://bnordgren.org/seismo/ni-span-c_alloy_902.pdf I think you can get if from Special Metals Corp. I see that they have some kind of operation in the UK, so it might be worth a call. I don't know how much you can specify regarding the heat treatment, especially in sample/prototype quantities. It's likely that you would have to find someone in the area who does that and have them do the heat treating to your specs. It is not quite as strong as spring steel, so you'd need to take that into consideration when designing the spring to avoid having it take a set (as well as doing all sorts of other interesting nonlinear things). It's obvious that constructing a low T.C. spring is not for the faint of heart. Regarding temperature control, you might be able to control the entire device fairly well if it's not too large. I had an oven circuit in one of our power supplies that would control to about 1/1000 deg C, though the thermal design of the oven meant that the actual regulation was a good deal poorer. I'd imagine you could control a small copper box to a fraction of a degree. That's one good reason for designing small. Brett At 05:28 PM 2/16/2008 -0500, you wrote: >In a message dated 2008/02/16, Brett3mr@............. writes: > >>Yes, I agree the forcing coil/magnet also introduce effects similar to what >>I was describing for the integrator capacitor; except that you can avoid >>the coil resistance issues by using a current driver. It's obvious that >>you can't depend on electronic feedback to do all your centering, forever, >>but must occasionally turn a screw to unload the feedback loop. > > >Hi Brett, > > My train of thought was to either compensate or to drastically > reduce the main error drifts. I use a small thermostat circuit to keep > crystal temperatures constant to better than 0.1 C Deg. I could wrap one > nicely around a capacitor. If you used an electromagnet, you could keep > the field constant to a few ppm. An alternative would be to control the > temperature of the magnets. > The biggest drift is likely that of a steel spring. Can you get > Ni-SpanC wire? sheet? I can get Invar wire, but not Elinvar at the moment. > > Regards, > > Chris Chapman My e-mail address above should be working, but if not you can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: when feedback is not needed From: ChrisAtUpw@....... Date: Sat, 16 Feb 2008 22:54:19 EST In a message dated 2008/02/17, barry_lotz@............. writes: > Something has confused me about the volksmeter or the SG sensor. For a > passive sensor I always thought the response of the sensor dropped by (I forget > the db slope) for frequencies below the natural frequency of the sensor. > Therefore I would think the output would have to amplified accordingly for low > frequencies. Is the noise amplified also? Is the drop-off mathematically known > so the amplification can be correctly compensated? I didn't think a simple > intergator in the output of the SG provided a simple flat response of output vs > frequency. Hi Barry, If you use a velocity sensor, the output falls off below resonance at x100 per decade and stays level above resonance. However, both the SG and the Volksmeter use position sensors which fall off at x10 per decade below resonance. Hence you can extend the period by about 1000 and still get an OK noise level, using a really low noise system. Your 0.9 Hz Volksmeter really will work out to 1000 second periods. They also fall off x10 per decade above resonance..... but you can also compensate OK for that. See Brett's recent posting on feedback systems? http://bnordgren.org/seismo/feedback_in_seismic_sensors3.pdf Regards, Chris Chapman In a me= ssage dated 2008/02/17, barry_lotz@............. writes:

Something has confused me about= the volksmeter or the SG sensor. For a passive sensor I always thought the=20= response of the sensor dropped by (I forget the db slope) for frequencies be= low the natural frequency of the sensor. Therefore I would think the output=20= would have to amplified accordingly for low frequencies. Is the noise amplif= ied also? Is the drop-off mathematically known so the amplification can be c= orrectly compensated? I didn't think a simple intergator in the output of th= e SG provided a simple flat response of output vs frequency.

Hi Barry,

       If you use a velocity sensor, the outpu= t falls off below resonance at x100 per decade and stays level above resonan= ce. However, both the SG and the Volksmeter use position sensors which fall=20= off at x10 per decade below resonance. Hence you can extend the period by ab= out 1000 and still get an OK noise level, using a really low noise system. Y= our 0.9 Hz Volksmeter really will work out to 1000 second periods. They also= fall off x10 per decade above resonance..... but you can also compensate OK= for that.
       See Brett's recent posting on feedback=20= systems?
       http://bnordgren.org/seismo/feedback_in= _seismic_sensors3.pdf

       Regards,

       Chris Chapman Subject: profound instrument differences From: Randall Peters PETERS_RD@.......... Date: Sun, 17 Feb 2008 08:56:42 -0500 It appears I haven't been clear (or emphatic) enough in stating the profound differences between a vertical seismometer and a pendulum operating as (i) typical horizontal seismometer and/or (ii) tiltmeter. A simple pendulum does not require feedback; moreover, when monitored with a position rather than velocity sensor, there is no falloff in sensitivity whatsoever when the frequency is below its natural frequency (unless one stupidly insists on the use of a velocity sensor, which for periods greater than a few thousand seconds WILL NEVER WORK!). Why so many are OBSESSED with velocity sensing for everything labeled a seismic instrument is beyond my ability to comprehend! The acceleration that begins to become the most important component of what drives a pendulum at low frequencies (below 1000 s period) is that component of the earth's field ( magnitude g = 9.8 m/s^2) that is perpendicular to the case of the instrument; i.e., tilt. To see that there is no loss of sensitivity as frequency goes toward zero, simply look at my latest paper titled "Study of Tides with a Pendulum" at http://physics.mercer.edu/hpage/tidal.html It's not as though I'm talking about some recent discovery. The great Lord Kelvin, with his understudy George Darwin (son of the famous Charles) used a pendulum with optical displacement sensing more than a century ago to try and understand the influence of the Moon on our planet. (There is an animated gif (halfway down the page) at http://en.wikipedia.org/wiki/Tide which might help you to understand how the Moon could influence by more than just the conventional sense of the tidal force. The offset of the center of the earth from the barycenter by about 0.8 times the radius--causes the earth to be 'whipped around' with a sidereal period of 27.3 days--bound to be important but mostly unstudied). In similar manner, with Jim Shirley of JPL I tried with a pendulum (predecessor to the VolksMeter) to understand what happens to the earth because of this, over periods measured in months. What we observed in a time interval measuring about 1.5 years is very DIFFICULT to understand. Kelvin couldn't figure it out, nor could we. And it has nothing to do with electronics limitations imposed on the instrument. What the pendulum was measuring [without frequency limitations in the realm of interest (months to years)] was the exceedingly complex physical changes to its shape that occur in the earth. None of the greats of physics past would have fallen into the `rut' has snared the world of seismology ('hung up' on a particular type of detector to monitor the motion). I once heard `rut' defined as a 'coffin with the ends kicked out'. (applicable to those who refuse to consider anything other than a detector that responds to the time rate of change of position of the inertial mass of a seismometer--otherwise called 'velocity sensor'). So why then am I interested in feedback, which is necessary for a vertical, but not for a pendulum? Because I (like so many of the rest of you) would like to see earthquakes from all over the world, as small as technology will allow. The simple pendulum would be a GREAT candidate for so doing if I had a facility to hold one whose length were 10 m (or even longer). As compared to the VolksMeter, it would be 100 times more sensitive in every frequency range. (For tide studies it doesn't need that sensitivity; but for 20 s period teleseisms, it does.) Unlike the vertical that has become standard (influenced greatly by LaCoste), an ordinary pendulum is not capable of simple mechanical 'period lengthening' by means of structural rearrangement. But what makes any pendulum superior to any vertical seismometer--is its ability to look at REALLY low frequencies in a way that will ALWAYS be impossible for a vertical. The bottom line is that we need to finally understand that different frequency regimes call for different instruments! There never will be a single instrument labeled the SEISMIC-DO-ALL; since the physics refuses to cooperate. Randall Subject: Re: profound instrument differences From: Brett Nordgren Brett3mr@............. Date: Sun, 17 Feb 2008 10:26:41 -0500 Randall, At 08:56 AM 2/17/2008 -0500, you wrote: >It appears I haven't been clear (or emphatic) enough in stating the >profound differences between a vertical seismometer and a >pendulum operating as (i) typical horizontal seismometer and/or (ii) >tiltmeter. > > Unlike the vertical that has become standard (influenced greatly by > LaCoste), an ordinary pendulum is not capable of simple >mechanical 'period lengthening' by means of structural rearrangement. But >what makes any pendulum superior to any vertical >seismometer--is its ability to look at REALLY low frequencies in a way >that will ALWAYS be impossible for a vertical. The >bottom line is that we need to finally understand that different frequency >regimes call for different instruments! >There never will be a single instrument labeled the SEISMIC-DO-ALL; since >the physics refuses to cooperate. > Randall Randall, This morning I had an idea which might possibly be an approach to improving pendulum performance by using feedback, and I think it would act in a way which would meet with your approval. Start with a 300mm pendulum which is hung from a pivot which can be moved horizontally by electronics. ('noisless' motor and leadscrew? or possibly black magic might be necessary) Measure the pendulum angle relative to reference vertical (SDC sensor with static plates attached to the moving pivot?). Then apply feedback to move the pivot so as to keep the measured angle as close to zero as possible. Clearly, there are a multitude of practical issues to solve before you'd ever have something useful, but I believe that a design based on such a concept could possibly have a number of properties which are consistent with the performance characteristices you have set out, and which, in addition, might provide significantly improved linearity. I've only thought about this for a few minutes, so please let me know what fundamental errors you see. Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: feedback pendulum possibility From: Randall Peters PETERS_RD@.......... Date: Sun, 17 Feb 2008 12:16:24 -0500 Brett, Your idea may be worth pursuing--moving the pendulum support horizontally so as to null the response. Moving the pendulum support can emulate a horizontal acceleration, but it cannot null tilt. Tilting the case of the instrument would allow to null both ground acceleration and tilt, but it would require a very powerful actuator--not consistent with a 'noiseless' motor/leadscrew. You mention the feedback as a means to improve linearity, but I don't think that is really an issue. The pole/zero features of the feedback network could presumably morph the short pendulum into an equivalent long pendulum?? If so, then it would be a means to improve teleseismic sensitivity. But I don't see any need for such feedback at really low frequencies. A mechanical means for nulling the low-frequency tilt variations would be to move the static plates of the sensor so as to produce a null output; but this does not influence the dynamics of the pendulum itself. Thus I don't see it having any advantage over a high-pass filter with a low corner frequency. Perhaps you see some advantage to a combination; i.e., moving both the pivot and the stationary sensor plates (one for short periods, the other for long periods?) After all, sensitivity is not the show-stopper for hugely long periods when using a displacement sensor whose electronics desn't wander. My guess is that the inherent stability of a feedback system involving a pendulum would be greater than that of conventional instruments--because of the inherent stability of the pendulum itself. And I gather that your background in controls is adequate to the task Physicists are trained in Fourier transform mathematics instead of the Laplace transform. I cringe at the thought of this 'old dog' trying to lean that 'new trick'. I do know a lot about pendulums, though-maybe having done more experiments of diverse type than anybody else, either alive or dead. So we might try to pursue something collectively, if you're interested--and if there is also interest from some student(s) here in pursuing the matter. (I work fiarly regularly with engineering majors on senior design projects). Randall Subject: Seismograph Noise Probelm From: Larry Conklin lconklin@............ Date: Sun, 17 Feb 2008 12:38:12 -0500 Hi Chris, Roger, Thought you might be interested in knowing the outcome of my noise quest. The thing did quiet back down and is now running as well as or better than it ever has. The suggestion regarding the wisdom of resting the cover on the sensor frame looks like it may have been the key. I did shim up the cover with a couple of strips of wood so that it is now effectively resting on the floor. Initially there wasn't much change, but within a couple of hours or so, the noise started to subside, and it has been quiet as a church mouse for several days. I am definitely going to make a new cover, probably out of styrafoam insulation board. It's light, a good insulator and easy to work with. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: profound instrument differences From: Barry Lotz barry_lotz@............. Date: Sun, 17 Feb 2008 09:52:06 -0800 (PST) Randall It seems that there are two measurements being discussed (horizontal accelerations due to teleseismic events and tilting of the sensor). Accelerometers are designed with a high natural frequency since they are suited to measure displacements below this frequency. Tilting a accelerometer will measure that portion of gravity induced. I think accelerations from a teleseismic events are very very small. I can see how a simple pendulum will act as a tilt meter if one can remove the possibly changes from temperature, soil moisture gradients ( when sensor is not on bedrock) etc If a pendulum were very long (as you mentioned) I also believe the measurement of displacement relative to the support would measure the earth displacement from a teleseismic event .It seems to me that bodies at rest tend to stay at rest unless an external force is applied to them (like the restoring force of a short period pendulum which is not allowed to tilt). One would have to correct for the drop off in sensitivity by post processing or with real time electronics or math. Regards Barry Randall Peters wrote: moreover, when monitored with a position rather than velocity sensor, there is no falloff in sensitivity whatsoever when the frequency is below its natural frequency (unless one stupidly insists on the use of a velocity sensor, which for periods greater than a few thousand seconds WILL NEVER WORK!). The simple pendulum would be a GREAT candidate for so doing if I had a facility to hold one whose length were 10 m (or even longer). As compared to the VolksMeter, it would be 100 times more sensitive in every frequency range. (For tide studies it doesn't need that sensitivity; but for 20 s period teleseisms, it does.) Randall begin:vcard n:Peters;Randall tel;work:(478)301-2747 x-mozilla-html:FALSE url:http://physics.mercer.edu/hpage/peters.html org:Mercer University;Physics Department adr:;;1400 Coleman Ave.;Macon;Georgia;31207;USA version:2.1 email;internet:peters_rd@.......... title:Professor and Chairman fn:Randall Peters PhD end:vcard
Randall
It seems that there are two measurements being discussed (horizontal accelerations due to teleseismic events and tilting of the sensor). Accelerometers are designed with a high natural frequency since they are suited to measure displacements below this frequency. Tilting a accelerometer will measure that portion of gravity induced. I think accelerations from a teleseismic events are very very small. I can see how a simple pendulum will act as a tilt meter  if one can remove the possibly changes from temperature, soil moisture gradients ( when sensor is not on bedrock) etc 
If a pendulum were very long (as you mentioned) I also believe the measurement of displacement relative to the support would measure the earth displacement from a teleseismic event .It seems to me that bodies at rest tend to stay at rest unless an external force is applied to them (like the restoring force of a short period pendulum which is not allowed to tilt). One would have to correct for the drop off in sensitivity by post processing or with real time electronics or math.
Regards
Barry


Randall Peters <PETERS_RD@..........> wrote:
<clip>
moreover, when monitored with a position rather than velocity sensor, there is no falloff in sensitivity whatsoever when the
frequency is below its natural frequency (unless one stupidly insists on the use of a velocity sensor, which for periods
greater than a few thousand seconds WILL NEVER WORK!).
 
<clip>
 
The simple
pendulum would be a GREAT candidate for so doing if I had a facility to hold one whose length were 10 m (or even longer). As
compared to the VolksMeter, it would be 100 times more sensitive in every frequency range. (For tide studies it doesn't need
that sensitivity; but for 20 s period teleseisms, it does.)
Randall


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Subject: Re: Seismograph Noise Probelm From: ChrisAtUpw@....... Date: Sun, 17 Feb 2008 13:11:03 EST In a message dated 2008/02/17, lconklin@............ writes: > I am definitely going to make a new cover, probably out of styrafoam > insulation board. It's light, a good insulator and easy to work with. Hi there, Can I recommend Celotex? It has a styrofoam core covered by two very thin sheets of glass scrim and an Al foil topcoat is then added. This makes it impervious to water, resistant to handling damage and easy to clean. You can stick it together using foam grouting. You can get it in a wide range of thicknesses. Regards, Chris Chapman In a me= ssage dated 2008/02/17, lconklin@............ writes:

I am definitely going to make a= new cover, probably out of styrafoam
insulation board.  It's light, a good insulator and easy to work with.<= /BLOCKQUOTE>

Hi there,

       Can I recommend Celotex? It has a styro= foam core covered by two very thin sheets of glass scrim and an Al foil topc= oat is then added. This makes it impervious to water, resistant to handling=20= damage and easy to clean. You can stick it together using foam grouting. You= can get it in a wide range of thicknesses.

       Regards,

       Chris Chapman Subject: Re: Seismograph Noise Probelm From: Larry Conklin lconklin@............ Date: Sun, 17 Feb 2008 13:56:40 -0500 Thanks Chris, Sounds like the ideal answer. Larry ChrisAtUpw@....... wrote: > In a message dated 2008/02/17, lconklin@............ writes: > >> I am definitely going to make a new cover, probably out of styrafoam >> insulation board. It's light, a good insulator and easy to work with. > > > Hi there, > > Can I recommend Celotex? It has a styrofoam core covered by two > very thin sheets of glass scrim and an Al foil topcoat is then added. > This makes it impervious to water, resistant to handling damage and easy > to clean. You can stick it together using foam grouting. You can get it > in a wide range of thicknesses. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: instrument physics From: Randall Peters PETERS_RD@.......... Date: Sun, 17 Feb 2008 14:04:41 -0500 Barry, I'm not sure what it is you're trying to say about accelerometers. Just like any other `seismic' instrument, what they DIRECTLY respond to is ACCELERATION, not displacement. For frequencies of excitation less than the natural frequency of the accelerometer, the displacement can be obtained from the measured acceleration (steady state) by dividing by the square of the frequency; i.e., via the connection between displacement and acceleration. Indeed, the natural frequency of a proper accelerometer (which measures acceleration) will always be higher than the acceleration one is trying to measure (from which displacement could be obtained), so that (i) the signal is easily observed and/or (ii) no correction for the transfer function involving roll-off is necessary. The closest thing to a displacement measuring device is what historically has been called a 'vibrometer'--where the natural frequency of the instrument is much smaller than the motions to which it responds due to acceleration of the case which houses it. In other words, your comments about displacement are focused in exactly the wrong frequency-direction. (Details for all of this are to be found in "Methods of experimental physics", classical methods, Vol I, ed. by I. Estermann, ed.-in-chief L. Marton, p. 93 (1959). One needs to always keep in mind that we're not dealing with a 'chicken or egg' debate. THE FUNDAMENTAL quantity is acceleration that gives rise to velocity that in turn gives rise to displacement. Going the other way makes no physical sense, according to Newton first, and Einstein last. About your statement 'bodies at rest ....', --this of Newton's famous laws of mechanics (first law, a qualitative statement) is most certainly consistent with his quantitative (quintessential) 2nd law--the basis for describing every classical system that exists. The 2nd law he formulated not in terms of acceleration but rather (genius that he was) in terms of the time rate of change of momentum (which for constant mass gives the famous F = m a. His more general result is able to also describe rocket systems where the mass changes.) Notice that the LAW does not involve velocity, NOR does it involve DISPLACEMENT, except to the extent that acceleration ultimately gives rise to changes in these other state variables. The `god of dynamics' is acceleration; and no other state variable can ever usurp its place of rulership. The challenge to conceptual understanding of these problems is centuries old, and all us physics professionals struggle to correct the misconeptions about motion that our students bring into the classroom. Maybe at the bottom line one has to master the equations Newton gave us (in terms of the calculus describing his 2nd law) before the matter really makes sense. Randall Subject: Re: profound instrument differences From: "Charles R. Patton" charles.r.patton@........ Date: Sun, 17 Feb 2008 13:03:42 -0800 Brett, There is another possibility rather than the moving pivot as you describe. Keeping in mind that the basic pendulum period is due to the change in height of the bob during the swing that sets the period, then if we flatten the swing, the period will increase. Therefore starting with the concept that the upper pivot, rather than the customary shape, a point on a flat supporting surface, is a flat rolling on a curved surface. If this curved surface is such that the height of pendulum is constant over the swing, then the period is infinite. Obviously a bit much. It also has the problem that the surface is not round, but increasingly steep off the center, a recipe for slipping. So we marry that with the old Rollamite bearings, to prevent side slip, and put on (immerse in?) lots of lubricant to prevent stiction. Of course this then comes back to the current discussion about macroscopic metal hysteresis, but I suggest that the Rollamite bearings in this case will be very fine wires just sufficient to prevent side slip, not large springs supporting the mass of the pendulum, so the macroscopic properties will not intrude. Regards, Charles R. Patton Brett Nordgren wrote: > Randall, > > At 08:56 AM 2/17/2008 -0500, you wrote: >> It appears I haven't been clear (or emphatic) enough in stating the >> profound differences between a vertical seismometer and a >> pendulum operating as (i) typical horizontal seismometer and/or (ii) >> tiltmeter. > >> > >> Unlike the vertical that has become standard (influenced greatly >> by LaCoste), an ordinary pendulum is not capable of simple >> mechanical 'period lengthening' by means of structural >> rearrangement. But what makes any pendulum superior to any vertical >> seismometer--is its ability to look at REALLY low frequencies in a >> way that will ALWAYS be impossible for a vertical. The >> bottom line is that we need to finally understand that different >> frequency regimes call for different instruments! >> There never will be a single instrument labeled the SEISMIC-DO-ALL; >> since the physics refuses to cooperate. >> Randall > > > Randall, > > This morning I had an idea which might possibly be an approach to > improving pendulum performance by using feedback, and I think it would > act in a way which would meet with your approval. > > Start with a 300mm pendulum which is hung from a pivot which can be > moved horizontally by electronics. ('noisless' motor and leadscrew? or > possibly black magic might be necessary) Measure the pendulum angle > relative to reference vertical (SDC sensor with static plates attached > to the moving pivot?). Then apply feedback to move the pivot so as to > keep the measured angle as close to zero as possible. > > Clearly, there are a multitude of practical issues to solve before > you'd ever have something useful, but I believe that a design based on > such a concept could possibly have a number of properties which are > consistent with the performance characteristices you have set out, and > which, in addition, might provide significantly improved linearity. > > I've only thought about this for a few minutes, so please let me know > what fundamental errors you see. > > Brett > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: curved support for pendulum From: Randall Peters PETERS_RD@.......... Date: Sun, 17 Feb 2008 16:57:02 -0500 Charles, Yours is a splendid idea! Except we need to avoid rolling components because of their 'killer' friction. I view the application of your idea as follows. Imagine the (primary) pendulum axis to be at the top of a rod that is being driven at its bottom like an inverted (secondary) pendulum by a feedback network. If the length of this secondary pendulum is carefully selected, and its motion is phase-matched to that of the primary pendulum--then as you say, the effective period can be much longer than that of the primary pendulum swinging from a fixed support.. Of course the arrangement will not work without feedback; however, the feedback should allow the the short pendulum to be morphed into an equivalent longer pendulum. Voila--increased sensitivity! Randall. Subject: similar to a folded pendulum except using feedback From: Randall Peters PETERS_RD@.......... Date: Sun, 17 Feb 2008 17:14:25 -0500 Charles, In effect, what you have described, is to take advantage of the same property that is used by the folded pendulum, which comprises both a `regular' pendulum and also an 'inverted pendulum. Separated from each other and connected by a rigid horizontal boom, their relative influence ('restoring' from the one, and 'destoring' from the other) is determined by how close the inertial mass is placed to one or the other. Because the folded pendulum can be made to have a very long period, upper valuve being limited by mesoanelastic complexity, it appears clear then, that the feedback drive of the primary pendulum by an inverted secondary one is capable (for ideal meaterials) of very long period indeed, and therefore very great sensitivity. Moreover, since the adverse effects of material problems can be essentially eliminated by means of the feedback, I see this as a really attractive idea to try and demonstrate! Are there any takers? (meaning folks like Brett who know how to make control systems work right). Randall Subject: Re: similar to a folded pendulum except using feedback From: Brett Nordgren Brett3mr@............. Date: Sun, 17 Feb 2008 22:16:26 -0500 Randall At 05:14 PM 2/17/2008 -0500, you wrote: >Charles, > In effect, what you have described, is to take advantage of the same > property that is used by the folded pendulum, which >comprises both a `regular' pendulum and also an 'inverted >pendulum. Separated from each other and connected by a rigid >horizontal boom, their relative influence ('restoring' from the one, and >'destoring' from the other) is determined by how close >the inertial mass is placed to one or the other. > Because the folded pendulum can be made to have a very long period, > upper valuve being limited by mesoanelastic complexity, >it appears clear then, that the feedback drive of the primary pendulum by >an inverted secondary one is capable (for ideal >meaterials) of very long period indeed, and therefore very great >sensitivity. Moreover, since the adverse effects of material >problems can be essentially eliminated by means of the feedback, I see >this as a really attractive idea to try and demonstrate! >Are there any takers? (meaning folks like Brett who know how to make >control systems work right). > Randall Always happy to help, especially if someone would like to volunteer for the construction part. Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: instrument physics From: ChrisAtUpw@....... Date: Sun, 17 Feb 2008 23:12:38 EST In a message dated 2008/02/17, PETERS_RD@.......... writes: Hi Randall, I hear what you say about pendulums and agree with it. However, I am having a little bit of a problem in relating this to seismometers, in which the principle is that the mass stays still - it is the Earth which moves / accelerates! Before we try to reinvent the wheel, perhaps we should consider the history of past seismometer and linkage types? A simple vertical pendulum depends for the resonant period on the length of it's suspension. It is desirable to keep this ~1 second , ~25 cm, on grounds of physical size, ease of construction and freedom from environmental effects. We can keep about this size, but get much longer periods if we use either a garden gate suspension, a Romberg linkage or a Folded pendulum construction. However, the gg uses two flexures and the other designs use at least 4 sets of flexures, which can, but not necessarily do, limit their performance. Won't this seriously muck up your suspension flex loss problems, Randall? The reason why you are using ball on a plane bearings for the Volksmeter? The Australians claim to have got about 90 seconds from a folded pendulum. However, in practical experiments making up simple FP constructions, it seemed to be difficult to get beyond about 10 seconds. Both the Teds found similar problems. And there is still the huge tilt sensitivity. I do wonder if the Aussies left something a bit critical out of their write up? Historically, the period of simple pendulums has been varied by reducing the vertical force on the mass. This has been done with a vertically mounted spring under the mass, by fitting repelling magnets on the mass and on the ground and by providing a solenoid field to attract some iron attached to the mass. 2 second Willmore vertical seismometers were extended to about 20 seconds with a spring and there are several other examples applied to inverted pendulums. There is no reason in principle why you could not feed a fraction of a position signal back to a vertical coil mounted on the mass, to directly reduce the horizontal centring force. I would expect to be able to get x3, maybe x10 increase in the period this way. This is an example of positive feedback less than that required to make the pendulum oscillate. An analogy would be to reduce the strength of the spring in a vertical seismometer. Note that some quite complicated and critical spring designs have used for LaCoste and Streckeisen vertical seismometers. The 'trick' here is to offset the gravitational load in such a way that the force change for a small vertical movement is also very small. Regarding loss in suspension systems, the sequence for reducing the loss appears to be Cardan single wires/foils, crossed wires/foils, ball on a plane, crossed cylinders and best of all, rolling wires/foils. Note that I have deliberately missed out point in a cup and knife edge suspensions, which are both profoundly unsatisfactory. In a message dated 2008/02/17, charles.r.patton@........ writes: > There is another possibility rather than the moving pivot as you describe. > Keeping in mind that the basic pendulum period is due to the change in > height of the bob during the swing that sets the period, then if we flatten the > swing, the period will increase. Therefore starting with the concept that the > upper pivot, rather than the customary shape, a point on a flat supporting > surface, is a flat rolling on a curved > surface. If this curved surface is such that the height of pendulum is > constant over the swing, then the period is infinite. Obviously a bit much. It > also has the problem that the surface is not round, but increasingly steep > off the center, a recipe for slipping. I am having great difficulty in visualising this. It seems that the bearing plate would have to rotate in the opposite sense to the pendulum? It is not just the height change that matters; the angle is also important. So we marry > that with the old Rollamite bearings, to prevent side slip, and > put on > (immerse in?) lots of lubricant to prevent stiction. Uh Uh! Any liquid lubricant will really foul up such a suspension! Liquid flow and surface tension spring to mind. The contact friction is highly variable between lubricated rolling surfaces. You might try fluon spray or dry moly, or rely in the oxide coating. Regards, Chris Chapman In a me= ssage dated 2008/02/17, PETERS_RD@.......... writes:

Hi Randall,

       I hear what you say about pendulums and= agree with it. However, I am having a little bit of a problem in relating t= his to seismometers, in which the principle is that the mass stays still - i= t is the Earth which moves / accelerates!

       Before we try to reinvent the wheel, pe= rhaps we should consider the history of  past seismometer and linkage t= ypes?

       A simple vertical pendulum depends for=20= the resonant period on the length of it's suspension. It is desirable to kee= p this ~1 second , ~25 cm, on grounds of physical size, ease of construction= and freedom from environmental effects.

       We can keep about this size, but get mu= ch longer periods if we use either a garden gate suspension, a Romberg linka= ge or a Folded pendulum construction. However, the gg uses two flexures and=20= the other designs use at least 4 sets of flexures, which can, but not necess= arily do, limit their performance. Won't this seriously muck up your suspens= ion flex loss problems, Randall? The reason why you are using ball on a plan= e bearings for the Volksmeter?

       The Australians claim to have got about= 90 seconds from a folded pendulum. However, in practical experiments making= up simple FP constructions, it seemed to be difficult to get beyond about 1= 0 seconds. Both the Teds found similar problems. And there is still the huge= tilt sensitivity. I do wonder if the Aussies left something a bit critical=20= out of their write up?

       Historically, the period of simple pend= ulums has been varied by reducing the vertical force on the mass. This has b= een done with a vertically mounted spring under the mass, by fitting repelli= ng magnets on the mass and on the ground and by providing a solenoid field t= o attract some iron attached to the mass.

       2 second Willmore vertical seismometers= were extended to about 20 seconds with a spring and there are several other= examples applied to inverted pendulums.

       There is no reason in principle why you= could not feed a fraction of a position signal back to a vertical coil moun= ted on the mass, to directly reduce the horizontal centring force. I would e= xpect to be able to get x3, maybe x10 increase in the period this way. This=20= is an example of positive feedback less than that required to make the pendu= lum oscillate. An analogy would be to reduce the strength of the spring in a= vertical seismometer.

       Note that some quite complicated and cr= itical spring designs have used for LaCoste and Streckeisen vertical seismom= eters. The 'trick' here is to offset the gravitational load in such a way th= at the force change for a small vertical movement is also very small.

       Regarding loss in suspension systems, t= he sequence for reducing the loss appears to be Cardan single wires/foils, c= rossed wires/foils, ball on a plane, crossed cylinders and best of all, roll= ing wires/foils. Note that I have deliberately missed out point in a cup and= knife edge suspensions, which are both profoundly unsatisfactory.

In a message dated 2008/02/17, charles.r.patton@........ writes:

There is another possibility ra= ther than the moving pivot as you describe.  Keeping in mind that the b= asic pendulum period is due to the change in height of the bob during the sw= ing that sets the period, then if we flatten the swing, the period will incr= ease.  Therefore starting with the concept that the upper pivot, rather= than the customary shape, a point on a flat supporting surface, is a flat r= olling on a curved
surface.  If this curved surface is such that the height of pendulum is= constant over the swing, then the period is infinite.  Obviously a bit= much.  It also has the problem that the surface is not round, but incr= easingly steep off the center, a recipe for slipping. 

    I am having great difficulty in visualising this. It seem= s that the bearing plate would have to rotate in the opposite sense to the p= endulum? It is not just the height change that matters; the angle is also im= portant.

So we marry
that with the old=20= Rollamite bearings, to prevent side slip, and put on
(immerse in?) lots of lubricant to prevent stiction
.

       Uh Uh! Any liquid lubricant will reall= y foul up such a suspension! Liquid flow and surface tension spring to mind= .. The contact friction is highly variable between lubricated rolling surface= s. You might try fluon spray or dry moly, or rely in the oxide coating.

       Regards,

       Chris Chapman Subject: Re: pivots vs bearing structures From: Charles Patton charles.r.patton@........ Date: Sun, 17 Feb 2008 21:08:51 -0800 Randall, I understand the folded pendulums you mention, but I want to touch on several related subjects. Back of the napkin pendulum length for 10 secs is about 1000 inches. A one inch swing would be a ˝ milli-inch rise. This gives me a bit of feel/insight on possible error mechanisms. It strikes me that one general problem with flexures is that they are not a pivot in the sense of having a known axis like a bearing does. I haven’t totally worked out the ramifications, but I’m sure this is the reason many amateurs have problems taking Lehman style instruments to long periods. Even if they’re not using flexures, pivot points are a round point that also may or may not have a constant point of rotation, depending whether it is rotating in a pocket or rolling on the surface of its pivot support, so the length may well be getting shorter as it rotates and a shorter length on the beam equates to the weight dropping, not rising as is necessary for stability and so the distance to un-stability is around ˝ a milli-inch. So the way I perceive it, a big problem is having a system where the axis of rotation remains constant, quite accurately. Unfortunately the only solutions I keep coming back to are bearing style things. So then the question becomes, “Can a bearing be made that has low loss?” But a concurrent question is do I really need a very low amount of loss? I know recent discussions have experimented with crossed pivots of extremely low loss. Why? The immediate next step will be to add a damper to get to something close to critical damping. My understanding is that the only reason to have low loss is to be able to use lots of feedback to lengthen the period. But if the period can be achieved directly, and it includes some damping, so what? In my mind, the important item is hysteresis/stiction. As bearings and bearing surfaces can easily be ground to a ten-thousandth or even better, 10 or 20 second period structures should be in reach. Back to possible structures. The structure I originally presented is probably not possible geometrically. But one that is obviously possible is as follows. Imagine a hollow cylinder (like a pipe) that has been centerless ground to be round. Now take a high density rod like lead or tungsten and center it down the axis of the cylinder with fine adjustment screws so you can offset the center of gravity by a fraction of a thousandth. (The hollow cylinder construction is to reduce the rotational moment of inertia.) Now place this cylinder on a surface plate (again a commonly available object that can be obtained flat to fractions of a ten-thousandth.) that is level better than a ten-thousandth per inch. Use very fine steel (a few thousandths) wire as Rollamite bands. The cylinder should roll to center the mass down. So lets assume a three inch dia. pipe. That’s roughly 10 inches circumference, or 2.5 inches to 90 degrees, and raising the mass by the amount of the off-center that could be easily set to 1 mill. Easily greater than 10 seconds rotation period? Once you have that structure in mind, chop off ž of the cylinder not in contact with the surface plate. As long as the center of mass is below the center of rotation this has become an upside down pendulum that is stable on the surface place and the rotational inertia has been reduced to a minimum. The position sensor is placed to monitor the mass at the ‘top’ of this pendulum. Just some more idle musings. Regards, Charles R. Patton Randall Peters wrote: > Charles, > In effect, what you have described, is to take advantage of the same property that is used by the folded pendulum, which > comprises both a `regular' pendulum and also an 'inverted pendulum. Separated from each other and connected by a rigid > horizontal boom, their relative influence ('restoring' from the one, and 'destoring' from the other) is determined by how close > the inertial mass is placed to one or the other. > Because the folded pendulum can be made to have a very long period, upper valuve being limited by mesoanelastic complexity, > it appears clear then, that the feedback drive of the primary pendulum by an inverted secondary one is capable (for ideal > meaterials) of very long period indeed, and therefore very great sensitivity. Moreover, since the adverse effects of material > problems can be essentially eliminated by means of the feedback, I see this as a really attractive idea to try and demonstrate! > Are there any takers? (meaning folks like Brett who know how to make control systems work right). > Randall __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: instrument physics From: Charles Patton charles.r.patton@........ Date: Sun, 17 Feb 2008 21:42:45 -0800 Hi Chris, I agree with the liquid flow question, but I'm not certain I understand the "...The contact friction is highly variable between lubricated rolling surfaces." Are you thinking about surface tension of variable areas of contact on a non-immersed contact pair? Wouldn't that basically disappear if there was total immersion of wetted surfaces and the oil doesn't use fiberous fillers (such as greases) to thicken it? Regards, Charles R. Patton P.S. I agree with you that I don't know how to fashion the bearing I was proposing -- a half baked idea in formation, I guess. But in a separate post I do visit a variation that I think is possible using as a starting point the idea of controlling the height change of a mass to control the period. I would definitely build it without oil first, then dunk it to see what happens! ChrisAtUpw@....... wrote: .... > So we marry >> that with the old Rollamite bearings, to prevent side slip, and put on >> (immerse in?) lots of lubricant to prevent stiction > . > > Uh Uh! Any liquid lubricant will really foul up such a > suspension! Liquid flow and surface tension spring to mind. The contact > friction is highly variable between lubricated rolling surfaces. You > might try fluon spray or dry moly, or rely in the oxide coating. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: ChrisAtUpw@....... 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Date: Mon, 18 Feb 2008 03:28:24 EST In a message dated 2008/02/18, charles.r.patton@........ writes: > Hi Chris, > I agree with the liquid flow question, but I'm not certain I understand > the "...The contact friction is highly variable between lubricated > rolling surfaces." Are you thinking about surface tension of variable > areas of contact on a non-immersed contact pair? Wouldn't that > basically disappear if there was total immersion of wetted surfaces and > the oil doesn't use fiberous fillers (such as greases) to thicken it? Surface tension is likely to be the least of your worries. Grease is a mixture of varios types of soap and oil. A few specialist greases have powder fillers. Moly grease for instance and chassis grease. They prevent metal to metal contact for various reasons. If you roll a bearing very slowly, you get full metal to metal contact with very high friction. Increase the speed and the surfaces start to separate on a thin film of oil and the friction drops dramatically. The viscosity of oil is pressure dependant and varies from a thin fluid to the consistency of solid pitch. It is also time dependant. The rolling surfaces also deform elastically with increasing load and the contact area increases. > P.S. I agree with you that I don't know how to fashion the bearing I was > proposing -- a half baked idea in formation, I guess. But in a separate > post I do visit a variation that I think is possible using as a starting > point the idea of controlling the height change of a mass to control the > period. I would definitely build it without oil first, then dunk it to > see what happens! I doubt that you will be too happy with the result. There will be quite large viscous losses as fluid flows from and into the rolling contact area. This will be highly rate and temperature dependant and non linear. Regards, Chris Chapman In a me= ssage dated 2008/02/18, charles.r.patton@........ writes:

Hi Chris,
I agree with the liquid flow question, but I'm not certain I understand
the "...The contact friction is highly variable between lubricated
rolling surfaces."  Are you thinking about surface tension of variable=20=
areas of contact on a non-immersed contact pair?  Wouldn't that
basically disappear if there was total immersion of wetted surfaces and
the oil doesn't use fiberous fillers (such as greases) to thicken it?=

       Surface tension is likely to be the le= ast of your worries.

       Grease is a mixture of varios types of=20= soap and oil. A few specialist greases have powder fillers. Moly grease for=20= instance and chassis grease. They prevent metal to metal contact for various= reasons.

       If you roll a bearing very slowly, you=20= get full metal to metal contact with very high friction. Increase the speed=20= and the surfaces start to separate on a thin film of oil and the friction dr= ops dramatically. The viscosity of oil is pressure dependant and varies from= a thin fluid to the consistency of solid pitch. It is also time dependant.=20= The rolling surfaces also deform elastically with increasing load and the co= ntact area increases.

P.S. I agree with you that I do= n't know how to fashion the bearing I was
proposing -- a half baked idea in formation, I guess.  But in a separat= e
post I do visit a variation that I think is possible using as a starting point the idea of controlling the height change of a mass to control the   period. I would definitely build it without oil first, then dunk it t= o
see what happens!


       I doubt that you will be too happy with= the result. There will be quite large viscous losses as fluid flows from an= d into the rolling contact area. This will be highly rate and temperature de= pendant and non linear.

       Regards,

       Chris Chapman Subject: Re: profound instrument differences From: Brett Nordgren Brett3mr@............. Date: Mon, 18 Feb 2008 08:20:29 -0500 Charles, Earlier I had been trying to visualize such an arrangement and had come to the conclusion that I wasn't going to be able to find one, which then pushed me toward the idea of the driven pivot system. Can you give me a bit more detail on the geometry you're thinking of. I can fairly easily draw it up on the CAD program, which can be used to plot the locus of the pendulum with as much accuracy as you'd like. When I tried using the description below, I couldn't construct anything that looked right. Speaking of Rollamite pivots. I am personally convinced that they appear to be quite attractive. One symmetrical design has very low (nearly zero) restoring force, and they are likely to suffer much less from the hysteresis effects you see in commercial crossed-foil bearings such as I believe were used in some high-end sensors (STS-1?). In particular, when using the thinnest foil which can safely carry the expected load, the bending stresses in the foils are very low and the volume of material under stress is also tiny; both contributing to minimizing losses. Like anything else, the proof is in the testing, but I think the chances of it working well are good enough to justify the time required. The only down-sides that I can see is that they might be less stiff than other pivot designs relative to side loads and moments, and you would have to make sure that their environment was kept clean to avoid getting dust in the works. Regards, Brett At 01:03 PM 2/17/2008 -0800, you wrote: >Brett, > >There is another possibility rather than the moving pivot as you >describe. Keeping in mind that the basic pendulum period is due to the >change in height of the bob during the swing that sets the period, then if >we flatten the swing, the period will increase. Therefore starting with >the concept that the upper pivot, rather than the customary shape, a point >on a flat supporting surface, is a flat rolling on a curved surface. If >this curved surface is such that the height of pendulum is constant over >the swing, then the period is infinite. Obviously a bit much. It also >has the problem that the surface is not round, but increasingly steep off >the center, a recipe for slipping. So we marry that with the old >Rollamite bearings, to prevent side slip, and put on (immerse in?) lots of >lubricant to prevent stiction. Of course this then comes back to the >current discussion about macroscopic metal hysteresis, but I suggest that >the Rollamite bearings in this case will be very fine wires just >sufficient to prevent side slip, not large springs supporting the mass of >the pendulum, so the macroscopic properties will not intrude. > >Regards, > >Charles R. Patton __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: folded variant with feedback From: Randall Peters PETERS_RD@.......... Date: Mon, 18 Feb 2008 08:21:59 -0500 What I'm envisioning is not significantly different than the folded pendulum in terms of the physics involved. Before describing it in more detail, let me respond to your comments, Chris. Yes, one approach that has been used is to place a spring at the bottom to 'soften' the restoring force of gravity acting on the pendulum. Although in principle o.k., in fact it has been shown to be unacceptable, due to the dastardly properties of springs. There is no need for such a spring to accomplish the same result. In the case of the so-called folded pendulum, there are really two pendulums--one that is 'usual', the other that is inverted. The usual one of the pair behaves in normal manner; i.e., if disturbed, gravity restores it to equilibrium. The inverted one behaves in just the opposite manner, and provides for a much greater linear response than is possible by using positive feedback by means of a spring at the bottom of a single pendulum. Because one pendulum is trying to 'restore' to equilibrium whereas the other one ('destoring') is trying to take the system away from equilibrium--the net effect of these competing forces is a system with a longer period. It can be taken all the way to infinite period and beyond (critical point in which conversion from stable equilibrium to unstable equilibrium occurs). Just like any long period seismometer, the material properties limit how far one can go in the direction of long-period until it becomes operationally unacceptable (enough to make a preacher cuss).. The difference between what I've bee discussing and the usual folded pendulum without feedback is the following. Instead of two obvious pendulums as with the folded, there is a single (usual) pendulum hanging from the drive component of the feedback system which is itself functioning as the inverted pendulum. In other words, the axis at the top of this drive component (holding the pivot for the usual pendulum) is of approximately the same length as the primary pendulum. As the pendulum swings to the right, its axis on the drive (inverted pendulum) swings to the left. If the inverted pendulum were of infiinite length (horizontal motion as was first discussed as a feedback means) all that the drive would accomplish is to excite the primary pendulum via acceleration. On the other hand, for the two pendulums swinging in precise phase opposition, the net effect is one of a single pendulum with a longer period. The phase opposition of the two pendulums is guaranteed in the case of the folded pendulum because the two are rigidly connected. Which pendulum is more effective in controlling the period dependends on how close the mass is on the horizontal connecting boom to the one pendulum or the other. Get too close to the inverted pendulum and the system goes unstable (goes beyond the critical point). Where my idea differs from the traditional folded pendulum has to do with the 'connection' between the two pendulums. There is no 'flexibility' of that connection in the traditional system. With the feedback arrangement I've described, there is variable 'coupling' determined by the nature of the feedback circuit's pole/zero architecture. Control of the phase between the two units should be for engineers given to this business 'what floats their boat'. I see again in one of Chris' statements the extreme difficulty most everyone of us has when it comes to conceptual understanding of a seismometer. Yes, Newton's first law says that an object at rest wants to remain at rest'. This inertial property of matter is often misunderstood because not enough attention is given to the part of the statement that I left off; i.e., ...remain at rest unless acted upon by a force. Einstein showed us that there doesn't have to be a force acting directly on the seismic (inertial) mass. Indeed, it is the acceleration of the case that is responsible for response. The mass is trying by Newton's first law to remain in place as the case is moved. But it cannot remain fixed!!!!! As the case moves, there is an unbalanced force on the mass that results. With the pendulum, the mass trying to stay at a fixed point and the case moved to a different point--means that there is a deflection of the pendulum. There is no difference to be realized from this and some force applied directly to the inertial mass with the case unmoved. Einstein's principle of relativity says that we cannot distinguish between the two. One can think about the response in the following way. When the case moves, the inertial mass tries to remain fixed, but it cannot remain that way ostensibly for longer than 1/4th the period of the mechanical oscillator of which it is a part. After all, if the system did not oscillate, we're engaging in complete foolishness to talk about sensitivity being proportional to the square of the natural period. One can acceptably estimate the amount of relative motion between mass and case as follows (I'm trying to avoid detailed math for those of you who are frightened by it) Allow me just one foundational feature that you must accept on faith if you can't follow the math. For an object moving at constant acceleration, the distance traveled goes like the square of the time during which it accelerates. Since acceleration of the inertial mass cannot be avoided as the result of case movement, we see immediately that the amount of motion (instrument sensitivity) is proportional to the square of the period of the instrument. Why, because for only about 1/4th of the period of the system can the mass be assumed to be moving with a 'constant' acceleration. For those who want to believe that the inertial mass does not accelerate (total misunderstanding of the physics of Newton's laws applied to a seismometer)--think about the following. The inertial mass is incapable of functioning without oscillatory motion (even though we try with critical damping to suppress the transient parts). Oscillation means 'back and forth', which in turn means acceleration that is also back and forth oppositely directed to displacement. There can be no displacement of the inertial mass relative to the case without a corresponding acceleration of the ineretial mass. It is not at rest, and never can be totally at rest! To place one's emphasis on the displacement as opposed to the acceleration is to 'get the cart before the horese'. Acceleration is fundament; displacement is not! How many variants of this discussion are necessary before folks finally GET IT (the physics). Hey, you amateurs are not the only confused ones. Many of the professional seismologists with whom I've interacted do not have a conceptual understanding of how a seismometer works. It they did, they wouldn't 'worship the god of velocity sensing'. Randall Subject: oops, a wrong phase statement From: Randall Peters PETERS_RD@.......... Date: Mon, 18 Feb 2008 08:33:14 -0500 Where I mentioned ....swings to the right .....axis ...to the left -- is wrong. I was thinking at the time about the opposite angular deflections of the two pendulums in the folded pendulum case. Subject: Re: pivots vs bearing structures From: tchannel1@............ Date: Mon, 18 Feb 2008 08:21:16 -0700 Hi Charles and Others, I have a small shop and love to build new things, some work, some don't, but I always learn in doing. I can not picture your idea, could you send me a sketch? I have made a couple of the Folded Pendulums sensors and found the concept very promising. If I can I would like to try your idea in the shop. Ted ----- Original Message ----- From: "Charles Patton" To: Sent: Sunday, February 17, 2008 10:08 PM Subject: Re: pivots vs bearing structures > Randall, > I understand the folded pendulums you mention, but I want to touch on > several related subjects. Back of the napkin pendulum length for 10 secs > is about 1000 inches. A one inch swing would be a ˝ milli-inch rise. > This gives me a bit of feel/insight on possible error mechanisms. It > strikes me that one general problem with flexures is that they are not a > pivot in the sense of having a known axis like a bearing does. I haven’t > totally worked out the ramifications, but I’m sure this is the reason many > amateurs have problems taking Lehman style instruments to long periods. > Even if they’re not using flexures, pivot points are a round point that > also may or may not have a constant point of rotation, depending whether > it is rotating in a pocket or rolling on the surface of its pivot support, > so the length may well be getting shorter as it rotates and a shorter > length on the beam equates to the weight dropping, not rising as is > necessary for stability and so the distance to un-stability is around ˝ a > milli-inch. > > So the way I perceive it, a big problem is having a system where the axis > of rotation remains constant, quite accurately. Unfortunately the only > solutions I keep coming back to are bearing style things. So then the > question becomes, “Can a bearing be made that has low loss?” But a > concurrent question is do I really need a very low amount of loss? I know > recent discussions have experimented with crossed pivots of extremely low > loss. Why? The immediate next step will be to add a damper to get to > something close to critical damping. My understanding is that the only > reason to have low loss is to be able to use lots of feedback to lengthen > the period. But if the period can be achieved directly, and it includes > some damping, so what? In my mind, the important item is > hysteresis/stiction. As bearings and bearing surfaces can easily be > ground to a ten-thousandth or even better, 10 or 20 second period > structures should be in reach. > > Back to possible structures. The structure I originally presented is > probably not possible geometrically. But one that is obviously possible > is as follows. Imagine a hollow cylinder (like a pipe) that has been > centerless ground to be round. Now take a high density rod like lead or > tungsten and center it down the axis of the cylinder with fine adjustment > screws so you can offset the center of gravity by a fraction of a > thousandth. (The hollow cylinder construction is to reduce the rotational > moment of inertia.) Now place this cylinder on a surface plate (again a > commonly available object that can be obtained flat to fractions of a > ten-thousandth.) that is level better than a ten-thousandth per inch. Use > very fine steel (a few thousandths) wire as Rollamite bands. The cylinder > should roll to center the mass down. So lets assume a three inch dia. > pipe. That’s roughly 10 inches circumference, or 2.5 inches to 90 > degrees, and raising the mass by the amount of the off-center that could > be easily set to 1 mill. Easily greater than 10 seconds rotation period? > Once you have that structure in mind, chop off ž of the cylinder not in > contact with the surface plate. As long as the center of mass is below > the center of rotation this has become an upside down pendulum that is > stable on the surface place and the rotational inertia has been reduced to > a minimum. The position sensor is placed to monitor the mass at the ‘top’ > of this pendulum. > Just some more idle musings. > Regards, > Charles R. Patton > > > Randall Peters wrote: >> Charles, >> In effect, what you have described, is to take advantage of the same >> property that is used by the folded pendulum, which >> comprises both a `regular' pendulum and also an 'inverted pendulum. >> Separated from each other and connected by a rigid >> horizontal boom, their relative influence ('restoring' from the one, and >> 'destoring' from the other) is determined by how close >> the inertial mass is placed to one or the other. >> Because the folded pendulum can be made to have a very long period, >> upper valuve being limited by mesoanelastic complexity, >> it appears clear then, that the feedback drive of the primary pendulum by >> an inverted secondary one is capable (for ideal >> meaterials) of very long period indeed, and therefore very great >> sensitivity. Moreover, since the adverse effects of material >> problems can be essentially eliminated by means of the feedback, I see >> this as a really attractive idea to try and demonstrate! >> Are there any takers? (meaning folks like Brett who know how to make >> control systems work right). >> Randall > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: "Charles R. Patton" charles.r.patton@........ Date: Mon, 18 Feb 2008 09:22:59 -0800 Hi Ted, See: www.myeclectic.info/RollingPendulum.jpg It's about 350 KB so you can download it at your leisure. The "Rollamite" like wires primarily keep the orientation of the cylinder under control. They are also likely to make the cylinder less likely to hang or stick due to dust and lint ( the relatively high pressure of the wires will cut through many of the contaminants. I recommend non-magnetic parts, lead, brass, aluminum so that the changing magnetic field of the earth is not a factor. (It might not be anyway, but I believe in trying to head off some variables from the start.) Hope this makes the idea a bit clearer. Regards, Charles Patton tchannel1@............ wrote: > Hi Charles and Others, I have a small shop and love to build new > things, some work, some don't, but I always learn in doing. > I can not picture your idea, could you send me a sketch? I have made > a couple of the Folded Pendulums sensors and found the concept very > promising. > If I can I would like to try your idea in the shop. > > Ted > > > ----- Original Message ----- From: "Charles Patton" > > To: > Sent: Sunday, February 17, 2008 10:08 PM > Subject: Re: pivots vs bearing structures > > >> Randall, >> I understand the folded pendulums you mention, but I want to touch on >> several related subjects. Back of the napkin pendulum length for 10 >> secs is about 1000 inches. A one inch swing would be a ˝ milli-inch >> rise. This gives me a bit of feel/insight on possible error >> mechanisms. It strikes me that one general problem with flexures is >> that they are not a pivot in the sense of having a known axis like a >> bearing does. I haven’t totally worked out the ramifications, but >> I’m sure this is the reason many amateurs have problems taking Lehman >> style instruments to long periods. Even if they’re not using >> flexures, pivot points are a round point that also may or may not >> have a constant point of rotation, depending whether it is rotating >> in a pocket or rolling on the surface of its pivot support, so the >> length may well be getting shorter as it rotates and a shorter length >> on the beam equates to the weight dropping, not rising as is >> necessary for stability and so the distance to un-stability is around >> ˝ a milli-inch. >> >> So the way I perceive it, a big problem is having a system where the >> axis of rotation remains constant, quite accurately. Unfortunately >> the only solutions I keep coming back to are bearing style things. >> So then the question becomes, “Can a bearing be made that has low >> loss?” But a concurrent question is do I really need a very low >> amount of loss? I know recent discussions have experimented with >> crossed pivots of extremely low loss. Why? The immediate next step >> will be to add a damper to get to something close to critical >> damping. My understanding is that the only reason to have low loss >> is to be able to use lots of feedback to lengthen the period. But if >> the period can be achieved directly, and it includes some damping, so >> what? In my mind, the important item is hysteresis/stiction. As >> bearings and bearing surfaces can easily be ground to a >> ten-thousandth or even better, 10 or 20 second period structures >> should be in reach. >> >> Back to possible structures. The structure I originally presented is >> probably not possible geometrically. But one that is obviously >> possible is as follows. Imagine a hollow cylinder (like a pipe) that >> has been centerless ground to be round. Now take a high density rod >> like lead or tungsten and center it down the axis of the cylinder >> with fine adjustment screws so you can offset the center of gravity >> by a fraction of a thousandth. (The hollow cylinder construction is >> to reduce the rotational moment of inertia.) Now place this cylinder >> on a surface plate (again a commonly available object that can be >> obtained flat to fractions of a ten-thousandth.) that is level better >> than a ten-thousandth per inch. Use very fine steel (a few >> thousandths) wire as Rollamite bands. The cylinder should roll to >> center the mass down. So lets assume a three inch dia. pipe. That’s >> roughly 10 inches circumference, or 2.5 inches to 90 degrees, and >> raising the mass by the amount of the off-center that could be easily >> set to 1 mill. Easily greater than 10 seconds rotation period? Once >> you have that structure in mind, chop off ž of the cylinder not in >> contact with the surface plate. As long as the center of mass is >> below the center of rotation this has become an upside down pendulum >> that is stable on the surface place and the rotational inertia has >> been reduced to a minimum. The position sensor is placed to monitor >> the mass at the ‘top’ of this pendulum. >> Just some more idle musings. >> Regards, >> Charles R. Patton >> >> >> Randall Peters wrote: >>> Charles, >>> In effect, what you have described, is to take advantage of the >>> same property that is used by the folded pendulum, which >>> comprises both a `regular' pendulum and also an 'inverted pendulum. >>> Separated from each other and connected by a rigid >>> horizontal boom, their relative influence ('restoring' from the one, >>> and 'destoring' from the other) is determined by how close >>> the inertial mass is placed to one or the other. >>> Because the folded pendulum can be made to have a very long >>> period, upper valuve being limited by mesoanelastic complexity, >>> it appears clear then, that the feedback drive of the primary >>> pendulum by an inverted secondary one is capable (for ideal >>> meaterials) of very long period indeed, and therefore very great >>> sensitivity. Moreover, since the adverse effects of material >>> problems can be essentially eliminated by means of the feedback, I >>> see this as a really attractive idea to try and demonstrate! >>> Are there any takers? (meaning folks like Brett who know how to >>> make control systems work right). >>> Randall >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body >> of the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: ChrisAtUpw@....... Date: Mon, 18 Feb 2008 18:19:46 EST In a message dated 2008/02/18, charles.r.patton@........ writes: > See: www.myeclectic.info/RollingPendulum.jpg > Hi Charles, Cast iron surface plates do corrode, but you could maybe treat it with an organic inhibitor? The thermal expansion properties will need to be very similar, or changes in the wire may try to rotate the cylinder. The wire / cylinder circle will have a high friction tending to prevent any slippage, which is a +. Maybe use an all SS construction with SS foil instead of wire? You can buy 30" rolls of 2 thou SS foil from www.ksmetals.com You could use two end foils and one double width central foil wrapped half way around the cylinder just and stuck on at the top? Have you given any thought as to what sensor and / or feedback transducer could be used, please? Regards, Chris Chapman In a me= ssage dated 2008/02/18, charles.r.patton@........ writes:

See: www.myeclectic.info/Rollin= gPendulum.jpg

Hi Charles,

       Cast iron surface plates do corrode, bu= t you could maybe treat it with an organic inhibitor?

       The thermal expansion properties will n= eed to be very similar, or changes in the wire may try to rotate the cylinde= r. The wire / cylinder circle will have a high friction tending to prevent a= ny slippage, which is a +. 
       Maybe use an all SS construction with S= S foil instead of wire? You can buy 30" rolls of 2 thou SS foil from www.ksm= etals.com You could use two end foils and one double width central foil wrap= ped half way around the cylinder just and stuck on at the top?

       Have you given any thought as to what s= ensor and / or feedback transducer could be used, please?

       Regards,

       Chris Chapman
 Subject: Re: pivots vs bearing structures From: tchannel1@............ Date: Mon, 18 Feb 2008 17:20:29 -0700 Charles, Yes the .jpg helps... Please can you now explain how a pendulum is attached, or to which part it is attached? Ted ----- Original Message ----- From: "Charles R. Patton" To: Sent: Monday, February 18, 2008 10:22 AM Subject: Re: pivots vs bearing structures > Hi Ted, > See: > www.myeclectic.info/RollingPendulum.jpg > It's about 350 KB so you can download it at your leisure. > The "Rollamite" like wires primarily keep the orientation of the cylinder > under control. They are also likely to make the cylinder less likely to > hang or stick due to dust and lint ( the relatively high pressure of the > wires will cut through many of the contaminants. I recommend non-magnetic > parts, lead, brass, aluminum so that the changing magnetic field of the > earth is not a factor. (It might not be anyway, but I believe in trying > to head off some variables from the start.) > > Hope this makes the idea a bit clearer. > Regards, > Charles Patton > > tchannel1@............ wrote: >> Hi Charles and Others, I have a small shop and love to build new things, >> some work, some don't, but I always learn in doing. >> I can not picture your idea, could you send me a sketch? I have made a >> couple of the Folded Pendulums sensors and found the concept very >> promising. >> If I can I would like to try your idea in the shop. >> >> Ted >> >> >> ----- Original Message ----- From: "Charles Patton" >> >> To: >> Sent: Sunday, February 17, 2008 10:08 PM >> Subject: Re: pivots vs bearing structures >> >> >>> Randall, >>> I understand the folded pendulums you mention, but I want to touch on >>> several related subjects. Back of the napkin pendulum length for 10 >>> secs is about 1000 inches. A one inch swing would be a ˝ milli-inch >>> rise. This gives me a bit of feel/insight on possible error mechanisms. >>> It strikes me that one general problem with flexures is that they are >>> not a pivot in the sense of having a known axis like a bearing does. I >>> haven’t totally worked out the ramifications, but I’m sure this is the >>> reason many amateurs have problems taking Lehman style instruments to >>> long periods. Even if they’re not using flexures, pivot points are a >>> round point that also may or may not have a constant point of rotation, >>> depending whether it is rotating in a pocket or rolling on the surface >>> of its pivot support, so the length may well be getting shorter as it >>> rotates and a shorter length on the beam equates to the weight dropping, >>> not rising as is necessary for stability and so the distance to >>> un-stability is around ˝ a milli-inch. >>> >>> So the way I perceive it, a big problem is having a system where the >>> axis of rotation remains constant, quite accurately. Unfortunately the >>> only solutions I keep coming back to are bearing style things. So then >>> the question becomes, “Can a bearing be made that has low loss?” But a >>> concurrent question is do I really need a very low amount of loss? I >>> know recent discussions have experimented with crossed pivots of >>> extremely low loss. Why? The immediate next step will be to add a >>> damper to get to something close to critical damping. My understanding >>> is that the only reason to have low loss is to be able to use lots of >>> feedback to lengthen the period. But if the period can be achieved >>> directly, and it includes some damping, so what? In my mind, the >>> important item is hysteresis/stiction. As bearings and bearing >>> surfaces can easily be ground to a ten-thousandth or even better, 10 or >>> 20 second period structures should be in reach. >>> >>> Back to possible structures. The structure I originally presented is >>> probably not possible geometrically. But one that is obviously possible >>> is as follows. Imagine a hollow cylinder (like a pipe) that has been >>> centerless ground to be round. Now take a high density rod like lead or >>> tungsten and center it down the axis of the cylinder with fine >>> adjustment screws so you can offset the center of gravity by a fraction >>> of a thousandth. (The hollow cylinder construction is to reduce the >>> rotational moment of inertia.) Now place this cylinder on a surface >>> plate (again a commonly available object that can be obtained flat to >>> fractions of a ten-thousandth.) that is level better than a >>> ten-thousandth per inch. Use very fine steel (a few thousandths) wire >>> as Rollamite bands. The cylinder should roll to center the mass down. >>> So lets assume a three inch dia. pipe. That’s roughly 10 inches >>> circumference, or 2.5 inches to 90 degrees, and raising the mass by the >>> amount of the off-center that could be easily set to 1 mill. Easily >>> greater than 10 seconds rotation period? Once you have that structure in >>> mind, chop off ž of the cylinder not in contact with the surface plate. >>> As long as the center of mass is below the center of rotation this has >>> become an upside down pendulum that is stable on the surface place and >>> the rotational inertia has been reduced to a minimum. The position >>> sensor is placed to monitor the mass at the ‘top’ of this pendulum. >>> Just some more idle musings. >>> Regards, >>> Charles R. Patton >>> >>> >>> Randall Peters wrote: >>>> Charles, >>>> In effect, what you have described, is to take advantage of the >>>> same property that is used by the folded pendulum, which >>>> comprises both a `regular' pendulum and also an 'inverted pendulum. >>>> Separated from each other and connected by a rigid >>>> horizontal boom, their relative influence ('restoring' from the one, >>>> and 'destoring' from the other) is determined by how close >>>> the inertial mass is placed to one or the other. >>>> Because the folded pendulum can be made to have a very long period, >>>> upper valuve being limited by mesoanelastic complexity, >>>> it appears clear then, that the feedback drive of the primary pendulum >>>> by an inverted secondary one is capable (for ideal >>>> meaterials) of very long period indeed, and therefore very great >>>> sensitivity. Moreover, since the adverse effects of material >>>> problems can be essentially eliminated by means of the feedback, I see >>>> this as a really attractive idea to try and demonstrate! >>>> Are there any takers? (meaning folks like Brett who know how to make >>>> control systems work right). >>>> Randall >>> __________________________________________________________ >>> >>> Public Seismic Network Mailing List (PSN-L) >>> >>> To leave this list email PSN-L-REQUEST@.............. with the body of >>> the message (first line only): unsubscribe >>> See http://www.seismicnet.com/maillist.html for more information. >>> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body of >> the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: "Charles R. Patton" charles.r.patton@........ Date: Mon, 18 Feb 2008 18:09:01 -0800 Ted, The whole thing is an upside down pendulum. Think about a rocking chair. It has the same properties as this cylinder. The center of mass of the body sitting in the chair is below the center of the circle formed by the rockers on the floor. So the top of the rocker and the person rock back-and-forth on the floor. Now imagine that the floor is jerked by some force such as an earthquake. The mass of the body in the chair stays in place but the rockers stay in contact with the floor but they assume a “rocked” position. Now the chair will rock back and forth over the new position. So by analogy, due to inertia this rolling pendulum will tend to stay in position while the plate is moved, but due to the contact with the plate the cylinder will be rotated. The result will be that the weight will want to roll back to restore the weight to its lowest point so the cylinder will rock until it dissipates the potential energy transferred to it by the plate displacement. This is exactly what happens to a normal pendulum. The bob stays in place while the support pivot moves in synchronization with the floor, so if the bob position relative to the floor is measured, it yields the displacement due to the seismic event. In exactly the same way the rolling cylinder’s position will be displaced relative to the floor/surface plate in proportion to the seismic event. (It’s interesting to note that you can have a free 2X gain simply by monitoring the position of the top of the cylinder rather than the axis of it.) What complicates this rolling pendulum is that it will also have significant rotational inertia. So it lowers the resonant frequency a bit from what might be expected by the weight unbalance distance plugged into a simple pendulum equation based on T=2*Pi*Sqrt(l/g). (Recognize that this equation only works on small angles and assumes all weight is concentrated at the bob point. Furthermore, in some ways it obscures the relation of the swing angle vs. the height change of the bob weight by talking about the length of the pendulum. The length is only important in that as it increases, it reduces the amount the weight is lifted vs the distance the pendulum swings. The cylinder pendulum brings to the fore that the weight is lifting by very small amounts as the pendulum swings.) You don’t even need sine/cosines to do the simple math for this one. Imagine a 1000” pendulum. Now swing it 1”. What’s the lift? Since the numbers are so big, just take the square root of the sum of the squares (the old Pythagorean theorem) and subtract the pendulum length. (Sqrt ( 1000^2 + 1^2)) – 1000 = 0.0005” (The purists out there may hate me as this isn’t set up geometrically correct, but it’s simple and quick and close enough that I can’t measure the difference without a laser interferometer.) So to tweak the cylinder pendulum into a 10 second period you’ll need to be able to tweak the center of mass to something like 0.007 inch off center (not likely with my micrometer!) But the rocking period comes to the rescue. Just keep tweaking until the period is about right. Go too far and the cylinder will want to topple, i.e., rotate 180 degrees and come to a rest. In practical terms it will have some of the same problems all long period pendulums do—notably the sensitivity to tilt inherent in long period pendulums. As Randall points out, friction is critical. An important consequence of the weight height changing very little for long periods is that the restoring force – that force trying to return the pendulum bob or cylinder back to its resting point is being reduced to very small numbers. And that change in resting point is the very item being measured for indication of a seismic event. The one thing that this should have over standard pendulums is it’s ability to handle big seismic displacements, perhaps plus/minus two inches or so for a three inch cylinder. Potentially another advantage would be better temperature stability due to the geometric symmetry not present in a Lehman for instance. The simple test will be to build it, give it a gentle shove and see if it can approach a 10 or 20 second period of rocking back and forth. Another point I want to mention is that I’m sure the “Rollamite” wires are critical for another reason. At a microscopic level, the surfaces of the plate and cylinder, even if mirror polished, will have hills and valleys that will want to “lock” the cylinder to a position due to the low restoring force mentioned above. The wires will have only point contacts that I feel will help ameliorate the problem, so although Chris mentions thin foils, I lean in the direction of thinking fine wire is better. Hope this helps, Charles Patton tchannel1@............ wrote: > Charles, Yes the .jpg helps... Please can you now explain how a > pendulum is attached, or to which part it is attached? > Ted > ----- Original Message ----- From: "Charles R. Patton" > > To: > Sent: Monday, February 18, 2008 10:22 AM > Subject: Re: pivots vs bearing structures > > >> Hi Ted, >> See: >> www.myeclectic.info/RollingPendulum.jpg >> It's about 350 KB so you can download it at your leisure. >> The "Rollamite" like wires primarily keep the orientation of the >> cylinder under control. They are also likely to make the cylinder >> less likely to hang or stick due to dust and lint ( the relatively >> high pressure of the wires will cut through many of the contaminants. >> I recommend non-magnetic parts, lead, brass, aluminum so that the >> changing magnetic field of the earth is not a factor. (It might not >> be anyway, but I believe in trying to head off some variables from >> the start.) >> >> Hope this makes the idea a bit clearer. >> Regards, >> Charles Patton >> >> tchannel1@............ wrote: >>> Hi Charles and Others, I have a small shop and love to build new >>> things, some work, some don't, but I always learn in doing. >>> I can not picture your idea, could you send me a sketch? I have >>> made a couple of the Folded Pendulums sensors and found the concept >>> very promising. >>> If I can I would like to try your idea in the shop. >>> >>> Ted >>> >>> >>> ----- Original Message ----- From: "Charles Patton" >>> >>> To: >>> Sent: Sunday, February 17, 2008 10:08 PM >>> Subject: Re: pivots vs bearing structures >>> >>> >>>> Randall, >>>> I understand the folded pendulums you mention, but I want to touch >>>> on several related subjects. Back of the napkin pendulum length >>>> for 10 secs is about 1000 inches. A one inch swing would be a ˝ >>>> milli-inch rise. This gives me a bit of feel/insight on possible >>>> error mechanisms. It strikes me that one general problem with >>>> flexures is that they are not a pivot in the sense of having a >>>> known axis like a bearing does. I haven’t totally worked out the >>>> ramifications, but I’m sure this is the reason many amateurs have >>>> problems taking Lehman style instruments to long periods. Even if >>>> they’re not using flexures, pivot points are a round point that >>>> also may or may not have a constant point of rotation, depending >>>> whether it is rotating in a pocket or rolling on the surface of its >>>> pivot support, so the length may well be getting shorter as it >>>> rotates and a shorter length on the beam equates to the weight >>>> dropping, not rising as is necessary for stability and so the >>>> distance to un-stability is around ˝ a milli-inch. >>>> >>>> So the way I perceive it, a big problem is having a system where >>>> the axis of rotation remains constant, quite accurately. >>>> Unfortunately the only solutions I keep coming back to are bearing >>>> style things. So then the question becomes, “Can a bearing be made >>>> that has low loss?” But a concurrent question is do I really need >>>> a very low amount of loss? I know recent discussions have >>>> experimented with crossed pivots of extremely low loss. Why? The >>>> immediate next step will be to add a damper to get to something >>>> close to critical damping. My understanding is that the only >>>> reason to have low loss is to be able to use lots of feedback to >>>> lengthen the period. But if the period can be achieved directly, >>>> and it includes some damping, so what? In my mind, the important >>>> item is hysteresis/stiction. As bearings and bearing surfaces can >>>> easily be ground to a ten-thousandth or even better, 10 or 20 >>>> second period structures should be in reach. >>>> >>>> Back to possible structures. The structure I originally presented >>>> is probably not possible geometrically. But one that is obviously >>>> possible is as follows. Imagine a hollow cylinder (like a pipe) >>>> that has been centerless ground to be round. Now take a high >>>> density rod like lead or tungsten and center it down the axis of >>>> the cylinder with fine adjustment screws so you can offset the >>>> center of gravity by a fraction of a thousandth. (The hollow >>>> cylinder construction is to reduce the rotational moment of >>>> inertia.) Now place this cylinder on a surface plate (again a >>>> commonly available object that can be obtained flat to fractions of >>>> a ten-thousandth.) that is level better than a ten-thousandth per >>>> inch. Use very fine steel (a few thousandths) wire as Rollamite >>>> bands. The cylinder should roll to center the mass down. So lets >>>> assume a three inch dia. pipe. That’s roughly 10 inches >>>> circumference, or 2.5 inches to 90 degrees, and raising the mass by >>>> the amount of the off-center that could be easily set to 1 mill. >>>> Easily greater than 10 seconds rotation period? Once you have that >>>> structure in mind, chop off ž of the cylinder not in contact with >>>> the surface plate. As long as the center of mass is below the >>>> center of rotation this has become an upside down pendulum that is >>>> stable on the surface place and the rotational inertia has been >>>> reduced to a minimum. The position sensor is placed to monitor the >>>> mass at the ‘top’ of this pendulum. >>>> Just some more idle musings. >>>> Regards, >>>> Charles R. Patton >>>> >>>> >>>> Randall Peters wrote: >>>>> Charles, >>>>> In effect, what you have described, is to take advantage of >>>>> the same property that is used by the folded pendulum, which >>>>> comprises both a `regular' pendulum and also an 'inverted >>>>> pendulum. Separated from each other and connected by a rigid >>>>> horizontal boom, their relative influence ('restoring' from the >>>>> one, and 'destoring' from the other) is determined by how close >>>>> the inertial mass is placed to one or the other. >>>>> Because the folded pendulum can be made to have a very long >>>>> period, upper valuve being limited by mesoanelastic complexity, >>>>> it appears clear then, that the feedback drive of the primary >>>>> pendulum by an inverted secondary one is capable (for ideal >>>>> meaterials) of very long period indeed, and therefore very great >>>>> sensitivity. Moreover, since the adverse effects of material >>>>> problems can be essentially eliminated by means of the feedback, I >>>>> see this as a really attractive idea to try and demonstrate! >>>>> Are there any takers? (meaning folks like Brett who know how to >>>>> make control systems work right). >>>>> Randall >>>> __________________________________________________________ >>>> >>>> Public Seismic Network Mailing List (PSN-L) >>>> >>>> To leave this list email PSN-L-REQUEST@.............. with the body >>>> of the message (first line only): unsubscribe >>>> See http://www.seismicnet.com/maillist.html for more information. >>>> >>> >>> __________________________________________________________ >>> >>> Public Seismic Network Mailing List (PSN-L) >>> >>> To leave this list email PSN-L-REQUEST@.............. with the body >>> of the message (first line only): unsubscribe >>> See http://www.seismicnet.com/maillist.html for more information. >>> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body >> of the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: Brett Nordgren Brett3mr@............. Date: Mon, 18 Feb 2008 21:50:54 -0500 Chris At 09:08 PM 2/17/2008 -0800, you wrote: >Randall, >I understand the folded pendulums you mention, but I want to touch on=20 >several related subjects. Back of the napkin pendulum length for 10 secs= =20 >is about 1000 inches. A one inch swing would be a =BD milli-inch=20 >rise. This gives me a bit of feel/insight on possible error=20 >mechanisms. It strikes me that one general problem with flexures is that= =20 >they are not a pivot in the sense of having a known axis like a bearing=20 >does. I haven=92t totally worked out the ramifications, but I=92m sure= this=20 >is the reason many amateurs have problems taking Lehman style instruments= =20 >to long periods. Even if they=92re not using flexures, pivot points are a= =20 >round point that also may or may not have a constant point of rotation,=20 >depending whether it is rotating in a pocket or rolling on the surface of= =20 >its pivot support, so the length may well be getting shorter as it rotates= =20 >and a shorter length on the beam equates to the weight dropping, not=20 >rising as is necessary for stability and so the distance to un-stability=20 >is around =BD a milli-inch. Both those issues were of great interest to pendulum clock makers. The=20 latter was studed by no less of an authority than Pierre-Simon LaPlace who= =20 came to two conclusions. First, a (very) small radius would be better than= =20 a knife-edge. Second, it might even be possible to consider a roller. He= =20 studied the geometry and concluded that the deviation from pendulum arc=20 circularity was a small fraction of the edge radius. That and very=20 thorough analyses of flexure suspensions, including effective pivot point=20 and nonlinear losses are covered in detail in the most excellent book by=20 A. L. Rawlings "The Science of Clocks & Watches 3rd edition, 1993" ISBN 0= =20 950 9621 3 9 which is a revised and annotated version of the 1948=20 edition. See:=20 http://www.ubr.com/clocks/clocks-and-time-horological-books/clocks-and-time-= new-books-and-reviews/the-science-of-clocks-amp-watches.aspx=20 It may not be in print but I have seen them, used, priced from $35 to $67=20 through Amazon and Barnes & Noble. Anyone who is serious about suspension= =20 design should have this book. >So the way I perceive it, a big problem is having a system where the axis= =20 >of rotation remains constant, quite accurately. Unfortunately the only=20 >solutions I keep coming back to are bearing style things. So then the=20 >question becomes, =93Can a bearing be made that has low loss?=94 But a=20 >concurrent question is do I really need a very low amount of loss? I know= =20 >recent discussions have experimented with crossed pivots of extremely low= =20 >loss. Why? The immediate next step will be to add a damper to get to=20 >something close to critical damping. My understanding is that the only=20 >reason to have low loss is to be able to use lots of feedback to lengthen= =20 >the period. But if the period can be achieved directly, and it includes=20 >some damping, so what? In my mind, the important item is=20 >hysteresis/stiction. As bearings and bearing surfaces can easily be=20 >ground to a ten-thousandth or even better, 10 or 20 second period=20 >structures should be in reach. For displacement-to-force feedback and possibly for other configurations, I= =20 believe you are exactly right. The main reason for having low pivot loss=20 is to make it 'easy' for the feedback to do its job, resulting in higher=20 loop gain. In general the pivot losses in such an instrument should have=20 very little effect on the instrument performance. Consider that the STS-1= =20 used bearings which I believe had a relatively poor hysteresis spec., yet=20 its performance was considered to be pretty good. >Back to possible structures. The structure I originally presented is=20 >probably not possible geometrically. But one that is obviously possible=20 >is as follows. Imagine a hollow cylinder (like a pipe) that has been=20 >centerless ground to be round. Now take a high density rod like lead or=20 >tungsten and center it down the axis of the cylinder with fine adjustment= =20 >screws so you can offset the center of gravity by a fraction of a=20 >thousandth. (The hollow cylinder construction is to reduce the rotational= =20 >moment of inertia.) Now place this cylinder on a surface plate (again a=20 >commonly available object that can be obtained flat to fractions of a=20 >ten-thousandth.) that is level better than a ten-thousandth per inch. Use= =20 >very fine steel (a few thousandths) wire as Rollamite bands. The cylinder= =20 >should roll to center the mass down. So lets assume a three inch dia.=20 >pipe. That=92s roughly 10 inches circumference, or 2.5 inches to 90=20 >degrees, and raising the mass by the amount of the off-center that could=20 >be easily set to 1 mill. Easily greater than 10 seconds rotation=20 >period? Once you have that structure in mind, chop off =BE of the cylinder= =20 >not in contact with the surface plate. As long as the center of mass is=20 >below the center of rotation this has become an upside down pendulum that= =20 >is stable on the surface place and the rotational inertia has been reduced= =20 >to a minimum. The position sensor is placed to monitor the mass at the=20 >=91top=92 of this pendulum. >Just some more idle musings. Regards, Brett __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: "meredith lamb" paleoartifact@......... Date: Mon, 18 Feb 2008 20:32:24 -0700 Hi Charles and all, ONLY on the light side....your rocking chair analogy sure brings back the most unusal memory I have of a quake that occurred in 1969 in the Portual-Morocco area, M7.8; that I "felt" in the Denver, Colorado area. I was asleep in a rocking chair, when I had the feeling I was moving (or rocking), and rolled my head over to check on a makeshift drum recorder I had running....it was synchronizing the slow movement with a hooked up seismometer I had in operation. For the rocking chair "seismometer"; in effect, I was the "mass" ! I did just lay there and watched awhile.....it was a unforgettable experience. Your project meets with my rolling approval... Take care, Meredith On 2/18/08, Charles R. Patton wrote: > Ted, > The whole thing is an upside down pendulum. Think about a rocking > chair. It has the same properties as this cylinder. (snip) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: tchannel1@............ Date: Mon, 18 Feb 2008 21:27:57 -0700 Charles, Thanks, I think I understand the idea. If I have other question I will ask. Ted ----- Original Message ----- From: "Charles R. Patton" To: Sent: Monday, February 18, 2008 7:09 PM Subject: Re: pivots vs bearing structures > Ted, > The whole thing is an upside down pendulum. Think about a rocking chair. > It has the same properties as this cylinder. The center of mass of the > body sitting in the chair is below the center of the circle formed by the > rockers on the floor. So the top of the rocker and the person rock > back-and-forth on the floor. Now imagine that the floor is jerked by some > force such as an earthquake. The mass of the body in the chair stays in > place but the rockers stay in contact with the floor but they assume a > “rocked” position. Now the chair will rock back and forth over the new > position. So by analogy, due to inertia this rolling pendulum will tend > to stay in position while the plate is moved, but due to the contact with > the plate the cylinder will be rotated. The result will be that the weight > will want to roll back to restore the weight to its lowest point so the > cylinder will rock until it dissipates the potential energy transferred to > it by the plate displacement. This is exactly what happens to a normal > pendulum. The bob stays in place while the support pivot moves in > synchronization with the floor, so if the bob position relative to the > floor is measured, it yields the displacement due to the seismic event. > In exactly the same way the rolling cylinder’s position will be displaced > relative to the floor/surface plate in proportion to the seismic event. > (It’s interesting to note that you can have a free 2X gain simply by > monitoring the position of the top of the cylinder rather than the axis of > it.) What complicates this rolling pendulum is that it will also have > significant rotational inertia. So it lowers the resonant frequency a bit > from what might be expected by the weight unbalance distance plugged into > a simple pendulum equation based on T=2*Pi*Sqrt(l/g). (Recognize that > this equation only works on small angles and assumes all weight is > concentrated at the bob point. Furthermore, in some ways it obscures the > relation of the swing angle vs. the height change of the bob weight by > talking about the length of the pendulum. The length is only important in > that as it increases, it reduces the amount the weight is lifted vs the > distance the pendulum swings. The cylinder pendulum brings to the fore > that the weight is lifting by very small amounts as the pendulum swings.) > You don’t even need sine/cosines to do the simple math for this one. > Imagine a 1000” pendulum. Now swing it 1”. What’s the lift? Since the > numbers are so big, just take the square root of the sum of the squares > (the old Pythagorean theorem) and subtract the pendulum length. (Sqrt ( > 1000^2 + 1^2)) – 1000 = 0.0005” > (The purists out there may hate me as this isn’t set up geometrically > correct, but it’s simple and quick and close enough that I can’t measure > the difference without a laser interferometer.) > > So to tweak the cylinder pendulum into a 10 second period you’ll need to > be able to tweak the center of mass to something like 0.007 inch off > center (not likely with my micrometer!) But the rocking period comes to > the rescue. Just keep tweaking until the period is about right. Go too > far and the cylinder will want to topple, i.e., rotate 180 degrees and > come to a rest. > In practical terms it will have some of the same problems all long period > pendulums do—notably the sensitivity to tilt inherent in long period > pendulums. As Randall points out, friction is critical. An important > consequence of the weight height changing very little for long periods is > that the restoring force – that force trying to return the pendulum bob or > cylinder back to its resting point is being reduced to very small numbers. > And that change in resting point is the very item being measured for > indication of a seismic event. The one thing that this should have over > standard pendulums is it’s ability to handle big seismic displacements, > perhaps plus/minus two inches or so for a three inch cylinder. > Potentially another advantage would be better temperature stability due to > the geometric symmetry not present in a Lehman for instance. The simple > test will be to build it, give it a gentle shove and see if it can > approach a 10 or 20 second period of rocking back and forth. Another > point I want to mention is that I’m sure the “Rollamite” wires are > critical for another reason. At a microscopic level, the surfaces of the > plate and cylinder, even if mirror polished, will have hills and valleys > that will want to “lock” the cylinder to a position due to the low > restoring force mentioned above. The wires will have only point contacts > that I feel will help ameliorate the problem, so although Chris mentions > thin foils, I lean in the direction of thinking fine wire is better. > > Hope this helps, > Charles Patton > > tchannel1@............ wrote: >> Charles, Yes the .jpg helps... Please can you now explain how a >> pendulum is attached, or to which part it is attached? >> Ted >> ----- Original Message ----- From: "Charles R. Patton" >> >> To: >> Sent: Monday, February 18, 2008 10:22 AM >> Subject: Re: pivots vs bearing structures >> >> >>> Hi Ted, >>> See: >>> www.myeclectic.info/RollingPendulum.jpg >>> It's about 350 KB so you can download it at your leisure. >>> The "Rollamite" like wires primarily keep the orientation of the >>> cylinder under control. They are also likely to make the cylinder less >>> likely to hang or stick due to dust and lint ( the relatively high >>> pressure of the wires will cut through many of the contaminants. I >>> recommend non-magnetic parts, lead, brass, aluminum so that the changing >>> magnetic field of the earth is not a factor. (It might not be anyway, >>> but I believe in trying to head off some variables from the start.) >>> >>> Hope this makes the idea a bit clearer. >>> Regards, >>> Charles Patton >>> >>> tchannel1@............ wrote: >>>> Hi Charles and Others, I have a small shop and love to build new >>>> things, some work, some don't, but I always learn in doing. >>>> I can not picture your idea, could you send me a sketch? I have made >>>> a couple of the Folded Pendulums sensors and found the concept very >>>> promising. >>>> If I can I would like to try your idea in the shop. >>>> >>>> Ted >>>> >>>> >>>> ----- Original Message ----- From: "Charles Patton" >>>> >>>> To: >>>> Sent: Sunday, February 17, 2008 10:08 PM >>>> Subject: Re: pivots vs bearing structures >>>> >>>> >>>>> Randall, >>>>> I understand the folded pendulums you mention, but I want to touch on >>>>> several related subjects. Back of the napkin pendulum length for 10 >>>>> secs is about 1000 inches. A one inch swing would be a ˝ milli-inch >>>>> rise. This gives me a bit of feel/insight on possible error >>>>> mechanisms. It strikes me that one general problem with flexures is >>>>> that they are not a pivot in the sense of having a known axis like a >>>>> bearing does. I haven’t totally worked out the ramifications, but I’m >>>>> sure this is the reason many amateurs have problems taking Lehman >>>>> style instruments to long periods. Even if they’re not using flexures, >>>>> pivot points are a round point that also may or may not have a >>>>> constant point of rotation, depending whether it is rotating in a >>>>> pocket or rolling on the surface of its pivot support, so the length >>>>> may well be getting shorter as it rotates and a shorter length on the >>>>> beam equates to the weight dropping, not rising as is necessary for >>>>> stability and so the distance to un-stability is around ˝ a >>>>> milli-inch. >>>>> >>>>> So the way I perceive it, a big problem is having a system where the >>>>> axis of rotation remains constant, quite accurately. Unfortunately >>>>> the only solutions I keep coming back to are bearing style things. So >>>>> then the question becomes, “Can a bearing be made that has low loss?” >>>>> But a concurrent question is do I really need a very low amount of >>>>> loss? I know recent discussions have experimented with crossed pivots >>>>> of extremely low loss. Why? The immediate next step will be to add a >>>>> damper to get to something close to critical damping. My >>>>> understanding is that the only reason to have low loss is to be able >>>>> to use lots of feedback to lengthen the period. But if the period can >>>>> be achieved directly, and it includes some damping, so what? In my >>>>> mind, the important item is hysteresis/stiction. As bearings and >>>>> bearing surfaces can easily be ground to a ten-thousandth or even >>>>> better, 10 or 20 second period structures should be in reach. >>>>> >>>>> Back to possible structures. The structure I originally presented is >>>>> probably not possible geometrically. But one that is obviously >>>>> possible is as follows. Imagine a hollow cylinder (like a pipe) that >>>>> has been centerless ground to be round. Now take a high density rod >>>>> like lead or tungsten and center it down the axis of the cylinder with >>>>> fine adjustment screws so you can offset the center of gravity by a >>>>> fraction of a thousandth. (The hollow cylinder construction is to >>>>> reduce the rotational moment of inertia.) Now place this cylinder on >>>>> a surface plate (again a commonly available object that can be >>>>> obtained flat to fractions of a ten-thousandth.) that is level better >>>>> than a ten-thousandth per inch. Use very fine steel (a few >>>>> thousandths) wire as Rollamite bands. The cylinder should roll to >>>>> center the mass down. So lets assume a three inch dia. pipe. That’s >>>>> roughly 10 inches circumference, or 2.5 inches to 90 degrees, and >>>>> raising the mass by the amount of the off-center that could be easily >>>>> set to 1 mill. Easily greater than 10 seconds rotation period? Once >>>>> you have that structure in mind, chop off ž of the cylinder not in >>>>> contact with the surface plate. As long as the center of mass is below >>>>> the center of rotation this has become an upside down pendulum that is >>>>> stable on the surface place and the rotational inertia has been >>>>> reduced to a minimum. The position sensor is placed to monitor the >>>>> mass at the ‘top’ of this pendulum. >>>>> Just some more idle musings. >>>>> Regards, >>>>> Charles R. Patton >>>>> >>>>> >>>>> Randall Peters wrote: >>>>>> Charles, >>>>>> In effect, what you have described, is to take advantage of the >>>>>> same property that is used by the folded pendulum, which >>>>>> comprises both a `regular' pendulum and also an 'inverted pendulum. >>>>>> Separated from each other and connected by a rigid >>>>>> horizontal boom, their relative influence ('restoring' from the one, >>>>>> and 'destoring' from the other) is determined by how close >>>>>> the inertial mass is placed to one or the other. >>>>>> Because the folded pendulum can be made to have a very long >>>>>> period, upper valuve being limited by mesoanelastic complexity, >>>>>> it appears clear then, that the feedback drive of the primary >>>>>> pendulum by an inverted secondary one is capable (for ideal >>>>>> meaterials) of very long period indeed, and therefore very great >>>>>> sensitivity. Moreover, since the adverse effects of material >>>>>> problems can be essentially eliminated by means of the feedback, I >>>>>> see this as a really attractive idea to try and demonstrate! >>>>>> Are there any takers? (meaning folks like Brett who know how to make >>>>>> control systems work right). >>>>>> Randall >>>>> __________________________________________________________ >>>>> >>>>> Public Seismic Network Mailing List (PSN-L) >>>>> >>>>> To leave this list email PSN-L-REQUEST@.............. with the body of >>>>> the message (first line only): unsubscribe >>>>> See http://www.seismicnet.com/maillist.html for more information. >>>>> >>>> >>>> __________________________________________________________ >>>> >>>> Public Seismic Network Mailing List (PSN-L) >>>> >>>> To leave this list email PSN-L-REQUEST@.............. with the body of >>>> the message (first line only): unsubscribe >>>> See http://www.seismicnet.com/maillist.html for more information. >>>> >>> >>> __________________________________________________________ >>> >>> Public Seismic Network Mailing List (PSN-L) >>> >>> To leave this list email PSN-L-REQUEST@.............. with the body of >>> the message (first line only): unsubscribe >>> See http://www.seismicnet.com/maillist.html for more information. >>> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body of >> the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: pivots vs bearing structures From: "Charles R. Patton" charles.r.patton@........ Date: Mon, 18 Feb 2008 20:30:32 -0800 Hi Chris, Sorry for the out of sequence reply – I read Ted’s question first, but I definitely want to comment on your items: So your points in order: >Cast iron surface plates do corrode, but you could maybe treat it with an organic inhibitor? --- Although I know there are cast iron surface plates, I envisioned using a standard machine shop granite surface block. Also there’s a strong possibility that pieces of plate glass – not standard window pane glass that is float made – rather plate glass, some of which is even polished. Old science experiments often recommended pieces of plate glass for interferometer experiments. So they have to be reasonably flat and for this experiment might be more than sufficient. You’d only need a slab about 4” x 4”, which a glass shop would probably give you from their scrap bin. Additionally, both glass and granite, especially granite are harder than cast iron and unlike cast iron, don’t corrode or oxidize. Obviously the glass will gradually flow out of alignment being a super-cooled liquid, but that’s a discussion for another day and a few years down the pike! Some approximate numbers Mild steel 120 HB Cast iron 200 18-8 (304) stainless steel 1250 HB Glass 1550 HB Hardened tool steel 1500 - 1900 HB So my feeling is that a granite surface plate would be best, but you’d be dealing with some bulk and weight that has to include a method of leveling to 0.0001”. So as a compromise, glass plate on a steel platform with leveling screws. >The thermal expansion properties will need to be very similar, or changes in the wire may try to rotate the cylinder. The wire / cylinder circle will have a high friction tending to prevent any slippage, which is a +. --- The wire length expansion falls problem falls out of the equation as long as the two bands are of equal length and expansion. Un-equality shows up as a twist in the axis of the cylinder, i.e., if the cylinder is along a N-S line, it starts to rotate to an E-W line. This may or may not result in an apparent rotation with relation to the sensor, but the cylinder will just roll to place it’s center of gravity down. For the same reason, just make sure the “tails” of the wires are of equal length, then the expansion just shows up as a change in tension, but no movement. > Maybe use an all SS construction with SS foil instead of wire? You can buy 30" rolls of 2 thou SS foil from www.ksmetals.com You could use two end foils and one double width central foil wrapped half way around the cylinder just and stuck on at the top? --- This is probably the area of most uncertainty. The first and biggest pause about using foil is the problem of obtaining bands without ripples on the edge that I’m certain would spell disaster for this scheme. You can’t just cut them with a scissors – any scallop at all would be a monstrous stiction point. So if they were to be used, they’d probably have to be etched out of a larger sheet, certainly a viable and standard method for many products, but in small or one-off prototyping, a big pain requiring masks and somebody who can etch steel, whereas wire that has been drawn is typically very consistent over long distances. Also as I touched on in my reply to Ted, I think that the higher pressure of a line contact from the wire is more likely to ignore certain types of surface imperfections and contaminations. > Have you given any thought as to what sensor and / or feedback transducer could be used, please? --- I think Randall’s SDC is a perfect candidate. Stick the movable plate on the top of the cylinder, like a rooster’s comb and put sensor plates (supported by the surface plate) on each side. Randall’s SDCs can sense standard pendulum movements and as I mentioned to Ted, the cylinder would have an inherent 2X gain over the simple pendulum. I would like to make one more point about temperature immunity. A full cylinder, while having the drawback of more rotational inertia, should have outstanding thermal stability. Although the diameter would increase significantly (in terms of normal seismometer criteria) the symmetrical nature should only change the distance of the mass balance point, not cause it to cross over and in effect overturn the cylinder. This would certainly be true if rather than build the cylinder exactly according to my sketch, use aluminum bolts (assuming an aluminum cylinder) that are threaded into the cylinder and go across the diameter. This way something that is supported by those cross members will be very stable in its reference to the cylinder axis, even as the cylinder expands and contracts. So although the period may change a bit, it doesn’t flip or have any reason to change rest position. For sake of construction, assuming a 3” aluminum cylinder, use 4 pieces of a 3 ˝” 6/32 or 8/32 flat head bolts. Drill opposing clearance holes across the diameter, rotate 90 degrees and slightly offset along the axis and drill two more. Now countersink two adjacent holes (two that are 90 degrees apart). Repeat on the other end of the cylinder. The countersunk holes will be the down side of the cylinder. Start bolt into the countersunk hole, add two nuts, push bolt through center weight, add two more nuts, push bolt through opposite hole, add last nut. The first nut is tightened up to hold flat-head tight to cylinder. The next two hold the weight nearly centered, and the last two nuts clamp the free end of the bolt to the opposite side of the cylinder. Repeat three more times. A thermally expansion balanced design. Regards, Charles Patton __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: From: "Ted Rogers" tedr@........... Date: Tue, 19 Feb 2008 15:31:02 +1100 Charles, You could create the same "rolling" effect by having 2 narrow plates a = short distance apart on the upper edge of each a shallow curve of about = 1000' radius. On these you sit a ground and polished rod of, say, 2" = (~50mm). I'm sure this would give the same effect as your cylinder, the = only problem being of course - the creation of the curves. The = measurement of any movement of the rod could be done by some sort of = optical sensor looking either up or down passed a narrower extension of = the rod, or even a flat reflective surface attached to one end of the = rod... Regards Ted
Charles,
 
You could create the same "rolling" = effect by=20 having 2 narrow plates a short distance apart on the upper edge of = each a=20 shallow curve of about 1000' radius. On these you sit a ground and = polished rod=20 of, say, 2" (~50mm). I'm sure this would give the same effect as your = cylinder,=20 the only problem being of course - the creation of the curves.=20 The measurement of any movement of the rod could be done by some = sort of=20 optical sensor looking either up or down passed a narrower extension of = the rod,=20 or even a flat reflective surface attached to one end of the=20 rod...
 
Regards
 
Ted
 
<tedr@...........>
Subject: Re: From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 01:34:41 EST In a message dated 2008/02/19, tedr@........... writes: > You could create the same "rolling" effect by having 2 narrow plates a > short distance apart on the upper edge of each a shallow curve of about 1000' > radius. On these you sit a ground and polished rod of, say, 2" (~50mm). I'm sure > this would give the same effect as your cylinder, the only problem being of > course - the creation of the curves. Hi Ted, You could probably get this sort of curvature most easily by flexing a flat plate? It is approximately 0.75 thou for a 6" long plate! Part of the problem is having large area contacts. This is most easily corrected with either strips of foil or wires. Regards, Chris Chapman In a me= ssage dated 2008/02/19, tedr@........... writes:

You could create the same "roll= ing" effect by having 2 narrow plates a short distance apart on the upper ed= ge of each a shallow curve of about 1000' radius. On these you sit a ground=20= and polished rod of, say, 2" (~50mm). I'm sure this would give the same effe= ct as your cylinder, the only problem being of course - the creation of the=20= curves.


Hi Ted,

       You could probably get this sort of cur= vature most easily by flexing a flat plate? It is approximately 0.75 thou fo= r a 6" long plate!

       Part of the problem is having large are= a contacts. This is most easily corrected with either strips of foil or wire= s.

       Regards,

       Chris Chapman Subject: Re: pivots vs bearing structures From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 02:05:01 EST In a message dated 2008/02/19, Brett3mr@............. writes: > Both those issues were of great interest to pendulum clock makers. The=20 > latter was studed by no less of an authority than Pierre-Simon LaPlace who= =20 > came to two conclusions. First, a (very) small radius would be better tha= n=20 > a knife-edge. Second, it might even be possible to consider a roller. He= =20 > studied the geometry and concluded that the deviation from pendulum arc=20 > circularity was a small fraction of the edge radius. That and very=20 > thorough analyses of flexure suspensions, including effective pivot point=20 > and nonlinear losses are covered in detail in the most excellent book by=20 > A. L. Rawlings "The Science of Clocks & Watches 3rd edition, 1993"=20 Hi Brett, I dug out my copy, but it is unfortunately silent on many of the=20 suspensions that we might want to use. In particular, the rolling wire/foil=20= types=20 have an accurate centre of rotation, extremely low hysteretic loss and ALSO=20 have ZERO TORQUE. The variation of stiffness and torque are two of the probl= ems=20 of Cardan single foil suspensions, but crossed wires/foils are a bit better.= =20 =20 > >So the way I perceive it, a big problem is having a system where the axis= =20 > >of rotation remains constant, quite accurately. Unfortunately the only=20 > >solutions I keep coming back to are bearing style things. So then the=20 > >question becomes, =E2=80=9CCan a bearing be made that has low loss?=E2= =80=9D =20 Categorically yes. But a > concurrent question is do I really need a very low amount of=20 > loss? I know recent discussions have experimented with crossed pivots of=20 > extremely low=20 > >loss. Why? The immediate next step will be to add a damper to get to=20 > >something close to critical damping. My understanding is that the only=20 > >reason to have low loss is to be able to use lots of feedback to lengthen= =20 > >the period. But if the period can be achieved directly, and it includes=20 > >some damping, so what? In my mind, the important item is=20 > >hysteresis/stiction. As bearings and bearing surfaces can easily be=20 > >ground to a ten-thousandth or even better, 10 or 20 second period=20 > >structures should be in reach. Again yes. You need to measure movements down to nano metres, so you=20 need extremely low hysteresis / stiction -.whatever system you use. Feedback= =20 will not compensate for this. > For displacement-to-force feedback and possibly for other configurations,=20= I=20 >=20 > believe you are exactly right. The main reason for having low pivot loss=20 > is to make it 'easy' for the feedback to do its job, resulting in higher=20 > loop gain. In general the pivot losses in such an instrument should have=20 > very little effect on the instrument performance. Consider that the STS-1= =20 > used bearings which I believe had a relatively poor hysteresis spec., yet=20 > its performance was considered to be pretty good. Don't know where you get this from. The STS-1 used crossed foils. The= =20 problems of making the STS-1 eventually lead to it's replacement!=20 > >Back to possible structures. The structure I originally presented is=20 > >probably not possible geometrically. But one that is obviously possible=20 > >is as follows. Imagine a hollow cylinder (like a pipe) that has been=20 > >centerless ground to be round. Now take a high density rod like lead or=20 > >tungsten and center it down the axis of the cylinder with fine adjustment= =20 > >screws so you can offset the center of gravity by a fraction of a=20 > >thousandth.=20 Let's define out objectives. We don't want extreme periods, just mayb= e=20 10 seconds instead of 1 second. Trying to get very long periods makes the=20 task increasingly difficult and the small anelastic effects become major=20 problems, as do thermal variations / expansions. I am fairly confident that you could extend the period by using=20 feedback to SOFTEN the suspension forces of a standard vertical pendulum. Ra= ndall=20 can then keep his 1 mm WC low loss bearings - no problem. Regards, Chris Chapman =20 In a me= ssage dated 2008/02/19, Brett3mr@............. writes:

Both those issues were of great= interest to pendulum clock makers.  The
latter was studed by no less of an authority than Pierre-Simon LaPlace who <= BR> came to two conclusions.  First, a (very) small radius would be better=20= than
a knife-edge.  Second, it might even be possible to consider a roller.&= nbsp; He
studied the geometry and concluded that the deviation from pendulum arc
circularity was a small fraction of the edge radius.  That and very thorough analyses of flexure suspensions, including effective pivot point and nonlinear losses are covered in detail in the most excellent book =20= by
A. L. Rawlings "The Science of Clocks & Watches  3rd edition, 1993"=


Hi Brett,

       I dug out my copy, but it is unfortunat= ely silent on many of the suspensions that we might want to use. In particul= ar, the rolling wire/foil types have an accurate centre of rotation, extreme= ly low hysteretic loss and ALSO have ZERO TORQUE. The variation of stiffness= and torque are two of the problems of Cardan single foil suspensions, but c= rossed wires/foils are a bit better.

>So the way I perceive it,=20= a big problem is having a system where the axis
>of rotation remains constant, quite accurately.  Unfortunately the=20= only
>solutions I keep coming back to are bearing style things.  So then=20= the
>question becomes, =E2=80=9CCan a bearing be made that has low loss?=E2= =80=9D 


    Categorically yes.

       But a
concurrent question is do I really need a very low amount of= loss?  I know recent discussions have experimented with crossed pivots= of extremely low
>loss.  Why?  The immediate next step will be to add a damper t= o get to
>something close to critical damping.   My understanding is tha= t the only
>reason to have low loss is to be able to use lots of feedback to lengthe= n
>the period.  But if the period can be achieved directly, and it inc= ludes
>some damping, so what?  In my mind, the important item is
>hysteresis/stiction.   As bearings and bearing surfaces can ea= sily be
>ground to a ten-thousandth or even better, 10 or 20 second period
>structures should be in reach.


       Again yes. You need to measure movemen= ts down to nano metres, so you need extremely low hysteresis / stiction -.wh= atever system you use. Feedback will not compensate for this.

For displacement-to-force feedb= ack and possibly for other configurations, I
believe you are exactly right.  The main reason for having low pivot lo= ss
is to make it 'easy' for the feedback to do its job, resulting in higher loop gain.  In general the pivot losses in such an instrument should ha= ve
very little effect on the instrument performance.  Consider that the ST= S-1
used bearings which I believe had a relatively poor hysteresis spec., yet its performance was considered to be pretty good.


       Don't know where you get this from. Th= e STS-1 used crossed foils. The problems of making the STS-1 eventually lead= to it's replacement!

>Back to possible structures= ..  The structure I originally presented is
>probably not possible geometrically.  But one that is obviously pos= sible
>is as follows.  Imagine a hollow cylinder (like a pipe) that has be= en
>centerless ground to be round.  Now take a high density rod like le= ad or
>tungsten and center it down the axis of the cylinder with fine adjustmen= t
>screws so you can offset the center of gravity by a fraction of a
>thousandth.


       Let's define out objectives. We don't=20= want extreme periods, just maybe 10 seconds instead of 1 second. Trying to g= et very long periods makes the task increasingly difficult and the small ane= lastic effects become major problems, as do thermal variations / expansions.=

       I am fairly confident that you could ex= tend the period by using feedback to SOFTEN the suspension forces of a stand= ard vertical pendulum. Randall can then keep his 1 mm WC low loss bearings -= no problem.

    Regards,

    Chris Chapman Subject: Re: folded variant with feedback From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 02:51:26 EST In a message dated 2008/02/18, PETERS_RD@.......... writes: > What I'm envisioning is not significantly different from the folded > pendulum in terms of the physics involved. > Before describing it in more detail, let me respond to your comments, Chris. > Yes, one approach that has been used is to place a spring at the bottom to > 'soften' the restoring force of gravity acting on the pendulum. Although in > principle o.k., in fact it has been shown to be unacceptable, due to the > dastardly properties of springs. There is no need for such a spring to > accomplish the same result. I note that you have not commented using magnetic repulsion which has been shown to work! > In the case of the so-called folded pendulum, there are really two > pendulums--one that is 'usual', the other that is inverted. The usual one of > the pair behaves in normal manner; i.e., if disturbed, gravity restores it to > equilibrium. The inverted one behaves in just the opposite manner, and > provides for a much greater linear response than is possible by using positive > feedback by means of a spring at the bottom of a single pendulum. > Because one pendulum is trying to 'restore' to equilibrium whereas the > other one ('destoring') is trying to take the system away from equilibrium--the > net effect of these competing forces is a system with a longer period. It > can be taken all the way to infinite period and beyond (critical point in which > conversion from stable equilibrium to unstable equilibrium occurs). Just > like any long period seismometer, the material properties limit how far one can > go in the direction of long-period until it becomes operationally > unacceptable (enough to make a preacher cuss). Several non-preachers have been cussing over the practicalities of trying to get a folded pendulum to work OK beyond 10 seconds. With four hinges, you seem to run into suspension stability / hysteresis problems. > The difference between what I've been discussing and the usual folded > pendulum without feedback is the following. Instead of two obvious pendulums > as with the folded, there is a single (usual) pendulum hanging from the drive > component of the > feedback system which is itself functioning as the inverted pendulum. In > other words, the axis at the top of this drive component (holding the pivot for > the usual pendulum) is of approximately the same length as the primary > pendulum. > As the pendulum swings to the right, its axis on the drive (inverted > pendulum) swings to the left. If the inverted pendulum were of infinite length > (horizontal motion as was first discussed as a feedback means) all that the drive > would accomplish is > to excite the primary pendulum via acceleration. On the other hand, for the > two pendulums swinging in precise phase opposition, the net effect is one of > a single pendulum with a longer period. > The phase opposition of the two pendulums is guaranteed in the case of > the folded pendulum because the two are rigidly connected. Which pendulum is > more effective in controlling the period depends on how close the mass is on > the horizontal connecting boom to the one pendulum or the other. Get too > close to the inverted pendulum and the system goes unstable (goes beyond the > critical point). Sure, but it seems to be difficult in practice and you still have an extremely high tilt sensitivity. > Where my idea differs from the traditional folded pendulum has to do > with the 'connection' between the two pendulums. > There is no 'flexibility' of that connection in the traditional system. > With the feedback arrangement I've described, there is variable 'coupling' > determined by the nature of the feedback circuit's pole/zero architecture. > Control of the phase between the two units should be for engineers given to this > business 'what floats their boat'. OK. But you will have a driven support and a long period pendulum. What you will NOT have is the 1 second reference pendulum, so I where are getting the signal to drive the support? > I see again in one of Chris' statements the extreme difficulty most > everyone of us has when it comes to conceptual understanding of a seismometer. > Yes, Newton's first law says that an object at rest wants to remain at rest'. > This inertial property of matter is often misunderstood because not enough > attention is given to the part of the statement that I left off; i.e., > ...remain at rest unless acted upon by a force. Rather my point? > Einstein showed us that there doesn't have to be a force acting > directly on the seismic (inertial) mass. Indeed, it is the acceleration of the case > that is responsible for response. The mass is trying by Newton's first law to > remain in place as the > case is moved. But it cannot remain fixed! As the case moves, there is an > unbalanced force on the mass that results. With the pendulum, the mass trying > to stay at a fixed point and the case moved to a different point - means that > there is a deflection of the pendulum. There is no difference to be realized > from this and some force applied directly to the inertial mass with the case > unmoved. Einstein's principle of relativity says that we cannot distinguish > between the two. My understanding of Einstein's work would not entirely support this. You are driving the case and looking at the relative response of the pendulum. You are not driving the pendulum. It will have a lower dynamic energy. > One can think about the response in the following way. When the case > moves, the inertial mass tries to remain fixed, but it cannot remain that way > ostensibly for longer than 1/4th the period of the mechanical oscillator of > which it is a part. After > all, if the system did not oscillate, we're engaging in complete foolishness > to talk about sensitivity being proportional to the square of the natural > period. Again, one of my concerns. If you drive the case of a 1 Hz pendulum at 10Hz, 20 Hz you will get a direct amplitude response. The pendulum will not be able to respond. It is the pendulum in the gravitational field which oscillates / fails to respond. > One can acceptably estimate the amount of relative motion between mass > and case as follows (I'm trying to avoid detailed math for those of you who > are frightened by it) Allow me just one foundational feature that you must > accept on faith if you > can't follow the math. For an object moving at constant acceleration, the > distance travelled goes like the square of the time during which it > accelerates. Since acceleration of the inertial mass cannot be avoided as the result > of case movement, we see immediately that the amount of motion (instrument > sensitivity) is proportional to the square of the period of the instrument. > Why, because for only about 1/4th of the period of the system can the mass > be assumed to be moving with a 'constant' acceleration. > For those who want to believe that the inertial mass does not accelerate > (total misunderstanding of the physics of Newton's laws applied to a > seismometer) - think about the following. The inertial mass is incapable of > functioning without oscillatory > motion (even though we try with critical damping to suppress the transient > parts). Oscillation means 'back and forth', which in turn means acceleration > that is also back and forth oppositely directed to displacement. There can be > no displacement of the inertial mass relative to the case without a > corresponding acceleration of the inertial mass. It is not at rest, and never can be > totally at rest! To place one's emphasis on the displacement as opposed to > the acceleration is to 'get the cart before the horse'. Acceleration is > fundament; displacement is not! We used to have a first year dynamics demonstration apparatus. It was a horizontal glass sheet supported by four horizontal hinge links at the corners. On the top, there were four sprung wires attached around the edges. The dynamic 'pucks' were short brass cylinders with a chamber in the top for dry ice. The dry ice (CO2) sublimated slowly and provided the gas drive for the bearing on the circular base (The glass was polished flat and the bottom of the puck was also lapped flat.) In operation, there was ~zero friction between the pucks and the glass. There was a stationary illuminated white perspex sheet underneath with a coarse grid ruled on it. In operation, you could sit two pucks on the glass and then move the glass in either X or Y direction and the two pucks stayed fixed in space relative to the grid. If no force or acceleration is applied to the mass, it just doesn't move. To 'fire' one puck at the other, you put the target one in the centre of the glass sheet, put the other one up against the spring wire at one end and pushed the glass sheet. The motion of the two pucks was then independent of any motion of the glass sheet until one or both bounced off the sprung wires at the edges. You could fit an O ring to one puck to demonstrate different coefficients of restitution. Cold rubber doesn't bounce too well. I suspect that you could make a fairly good demonstration horizontal seismometer this way. Use a couple of small magnets to provide the centralising force and detect the relative motion of the puck and the baseplate. If you used two pairs of magnets or bar magnets, you could probably get ~single axis motion? Or maybe a thin leaf spring? It should be fairly easy to get a 20 second period or longer. You could damp the system magnetically if you made the puck from copper or fitted a Cu disk to the top. Maybe use battery 'pointer' lasers and mirrors to project the motion onto a wall or ceiling? > How many variants of this discussion are necessary before folks finally > GET IT (the physics). Hey, you amateurs are not the only confused ones. > Many of the professional seismologists with whom I've interacted do not have a > conceptual understanding of how a seismometer works. It they did, they > wouldn't 'worship the god of velocity sensing'. Don't be too hard on them. Not all seismologists have the physics training to design or to understand a seismometer. And once a particular 'system' has been adopted (for good historical reasons) and thousands of seismometer years of data collected, it would take a huge effort to change the system. Remember that digital recording is only maybe 25 years old and we are still updating older systems. But wanting to, being able to and finding useful / publishable results at periods out to 2,000 seconds could just change all this. I suspect that if we are ever to be able to predict the severe quakes, this is the region to try to do it, where the crust is being cycled by the Earth tides twice a day. That and determining the precise location, depth and timing (or cessation) of nearby small quakes. Regards, Chris In a me= ssage dated 2008/02/18, PETERS_RD@.......... writes:

What I'm envisioning is not sig= nificantly different from the folded pendulum in terms of the physics involv= ed.
Before describing it in more detail, let me respond to your comments, Chris.=
  Yes, one approach that has been used is to place a spring at the bott= om to 'soften' the restoring force of gravity acting on the pendulum. =20= Although in principle o.k., in fact it has been shown to be unacceptable, du= e to the dastardly properties of springs.  There is no need for such a=20= spring to accomplish the same result.


       I note that you have not commented usi= ng magnetic repulsion which has been shown to work!

     =20= In the case of the so-called folded pendulum, there are really two pendulums= --one that is 'usual', the other that is inverted. The usual one of the pair= behaves in normal manner; i.e., if disturbed, gravity restores it to equili= brium. The inverted one behaves in just the opposite manner, and provides fo= r a much greater linear response than is possible by using positive feedback= by means of a spring at the bottom of a single pendulum.
   Because one pendulum is trying to 'restore' to equilibrium wher= eas the other one ('destoring') is trying to take the system away from equil= ibrium--the net effect of these competing forces is a system with a longer p= eriod. It can be taken all the way to infinite period and beyond (critical p= oint in which conversion from stable equilibrium to unstable equilibrium occ= urs).  Just like any long period seismometer, the material properties l= imit how far one can go in the direction of long-period until it becomes ope= rationally unacceptable (enough to make a preacher cuss).


       Several non-preachers have been cussin= g over the practicalities of trying to get a folded pendulum to work OK beyo= nd 10 seconds. With four hinges, you seem to run into suspension stability /= hysteresis problems.

    The differen= ce between what I've been discussing and the usual folded pendulum without f= eedback is the following. Instead of two obvious pendulums as with the folde= d, there is a single (usual) pendulum hanging from the drive component of th= e
feedback system which is itself functioning as the inverted pendulum. In oth= er words, the axis at the top of this drive component (holding the pivot for= the usual pendulum) is of approximately the same length as the primary pend= ulum.
As the pendulum swings to the right, its axis on the drive (inverted pendulu= m) swings to the left. If the inverted pendulum were of infinite length (hor= izontal motion as was first discussed as a feedback means) all that the driv= e would accomplish is
to excite the primary pendulum via acceleration.  On the other hand, fo= r the two pendulums swinging in precise phase opposition, the net effect is=20= one of a single pendulum with a longer period.
    The phase opposition of the two pendulums is guaranteed i= n the case of the folded pendulum because the two are rigidly connected.&nbs= p; Which pendulum is more effective in controlling the period depends on how= close the mass is on the horizontal connecting boom to the one pendulum or=20= the other.  Get too close to the inverted pendulum and the system goes=20= unstable (goes beyond the critical point).


       Sure, but it seems to be difficult in=20= practice and you still have an extremely high tilt sensitivity.

   Where my idea diff= ers from the traditional folded pendulum has to do with the 'connection' bet= ween the two pendulums.
There is no 'flexibility' of that connection in the traditional system. = ; With the feedback arrangement I've described, there is variable 'coupling'= determined by the nature of the feedback circuit's pole/zero architecture.&= nbsp; Control of the phase between the two units should be for engineers giv= en to this business 'what floats their boat'.


       OK. But you will have a driven support= and a long period pendulum. What you will NOT have is the 1 second referenc= e pendulum, so I where are getting the signal to drive the support?

    I see again=20= in one of Chris' statements the extreme difficulty most everyone of us has w= hen it comes to conceptual understanding of a seismometer. Yes, Newton's fir= st law says that an object at rest wants to remain at rest'.  This iner= tial property of matter is often misunderstood because not enough attention=20= is given to the part of the statement that I left off; i.e., ...remain at re= st unless acted upon by a force.


       Rather my point?

    Einstein sho= wed us that there doesn't have to be a force acting directly on the seismic=20= (inertial) mass. Indeed, it is the acceleration of the case that is responsi= ble for response. The mass is trying by Newton's first law to remain in plac= e as the
case is moved. But it cannot remain fixed!  As the case moves, there is= an unbalanced force on the mass that results. With the pendulum, the mass t= rying to stay at a fixed point and the case moved to a different point - mea= ns that there is a deflection of the pendulum. There is no difference to be=20= realized from this and some force applied directly to the inertial mass with= the case unmoved. Einstein's principle of relativity says that we cannot di= stinguish between the two.


       My understanding of Einstein's work wo= uld not entirely support this. You are driving the case and looking at the r= elative response of the pendulum. You are not driving the pendulum. It will=20= have a lower dynamic energy.

   One can think abou= t the response in the following way.  When the case moves, the inertial= mass tries to remain fixed, but it cannot remain that way ostensibly for lo= nger than 1/4th the period of the mechanical oscillator of which it is a par= t.  After
all, if the system did not oscillate, we're engaging in complete foolishness= to talk about sensitivity being proportional to the square of the natural p= eriod.


       Again, one of my concerns. If you driv= e the case of a 1 Hz pendulum at 10Hz, 20 Hz you will get a direct amplitude= response. The pendulum will not be able to respond. It is the pendulum in t= he gravitational field which oscillates / fails to respond.

    One can acce= ptably estimate the amount of relative motion between mass and case as follo= ws (I'm trying to avoid detailed math for those of you who are frightened by= it) Allow me just one foundational feature that you must accept on faith if= you
can't follow the math.  For an object moving at constant acceleration,=20= the distance travelled goes like the square of the time during which it acce= lerates.  Since acceleration of the inertial mass cannot be avoided as=20= the result of case movement, we see immediately that the amount of motion (i= nstrument sensitivity) is proportional to the square of the period of the in= strument.
Why, because for only about 1/4th of the period of the system can the mass b= e assumed to be moving with a 'constant' acceleration.
    For those who want to believe that the inertial mass does= not accelerate (total misunderstanding of the physics of Newton's laws appl= ied to a seismometer) - think about the following. The inertial mass is inca= pable of functioning without oscillatory
motion (even though we try with critical damping to suppress the transient p= arts).  Oscillation means 'back and forth', which in turn means acceler= ation that is also back and forth oppositely directed to displacement. There= can be no displacement of the inertial mass relative to the case without a=20= corresponding acceleration of the inertial mass. It is not at rest, and neve= r can be totally at rest! To place one's emphasis on the displacement as opp= osed to the acceleration is to 'get the cart before the horse'.  Accele= ration is fundament; displacement is not!


       We used to have a first year dynamics=20= demonstration apparatus. It was a horizontal glass sheet supported by four h= orizontal hinge links at the corners. On the top, there were four sprung wir= es attached around the edges. The dynamic 'pucks' were short brass cylinders= with a chamber in the top for dry ice. The dry ice (CO2) sublimated slowly=20= and provided the gas drive for the bearing on the circular base (The glass w= as polished flat and the bottom of the puck was also lapped flat.) In operat= ion, there was ~zero friction between the pucks and the glass. There was a s= tationary illuminated white perspex sheet underneath with a coarse grid rule= d on it.
       In operation, you could sit two pucks o= n the glass and then move the glass in either X or Y direction and the two p= ucks stayed fixed in space relative to the grid. If no force or acceleration= is applied to the mass, it just doesn't move. To 'fire' one puck at the oth= er, you put the target one in the centre of the glass sheet, put the other o= ne up against the spring wire at one end and pushed the glass sheet. The mot= ion of the two pucks was then independent of any motion of the glass sheet u= ntil one or both bounced off the sprung wires at the edges. You could fit an= O ring to one puck to demonstrate different coefficients of restitution. Co= ld rubber doesn't bounce too well.

       I suspect that you could make a fairly=20= good demonstration horizontal seismometer this way. Use a couple of small ma= gnets to provide the centralising force and detect the relative motion of th= e puck and the baseplate. If you used two pairs of magnets or bar magnets, y= ou could probably get ~single axis motion?  Or maybe a thin leaf spring= ? It should be fairly easy to get a 20 second period or longer. You could da= mp the system magnetically if you made the puck from copper or fitted a Cu d= isk to the top. Maybe use battery 'pointer' lasers and mirrors to project th= e motion onto a wall or ceiling?

    How many var= iants of this discussion are necessary before folks finally GET IT (the phys= ics).  Hey, you amateurs are not the only confused ones.  Many of=20= the professional seismologists with whom I've interacted do not have a conce= ptual understanding of how a seismometer works.  It they did, they woul= dn't 'worship the god of velocity sensing'.


       Don't be too hard on them. Not all seis= mologists have the physics training to design or to understand a seismometer= .. And once a particular 'system' has been adopted (for good historical reaso= ns) and thousands of seismometer years of data collected, it would take a hu= ge effort to change the system. Remember that digital recording is only mayb= e 25 years old and we are still updating older systems.
       But wanting to, being able to and findi= ng useful / publishable results at periods out to 2,000 seconds could just c= hange all this. I suspect that if we are ever to be able to predict the seve= re quakes, this is the region to try to do it, where the crust is being cycl= ed by the Earth tides twice a day. That and determining the precise location= , depth and timing (or cessation) of nearby small quakes.
      
       Regards,

       Chris Subject: Re: From: "Ted Rogers" tedr@........... Date: Tue, 19 Feb 2008 22:07:20 +1100 Chris, Do you thing that purpose could be served if the rod was a modified = "cotton reel" shape and it rolling on a polished flat plate with a = slight bow in it ? Regards Ted =20 ----- Original Message -----=20 From: ChrisAtUpw@.......... To: psn-l@................. Sent: Tuesday, February 19, 2008 5:34 PM Subject: Re:=20 In a message dated 2008/02/19, tedr@........... writes: You could create the same "rolling" effect by having 2 narrow plates = a short distance apart on the upper edge of each a shallow curve of = about 1000' radius. On these you sit a ground and polished rod of, say, = 2" (~50mm). I'm sure this would give the same effect as your cylinder, = the only problem being of course - the creation of the curves.=20 Hi Ted, You could probably get this sort of curvature most easily by = flexing a flat plate? It is approximately 0.75 thou for a 6" long plate! Part of the problem is having large area contacts. This is most = easily corrected with either strips of foil or wires. Regards, Chris Chapman
Chris,
 
Do you thing that purpose could be = served if the=20 rod was a modified "cotton reel" shape and it rolling on a polished = flat=20 plate with a slight bow in it ?
 
Regards
 
Ted
 
<tedr@...........> 
----- Original Message -----
From:=20 ChrisAtUpw@.......
Sent: Tuesday, February 19, = 2008 5:34=20 PM
Subject: Re:

In a=20 message dated 2008/02/19, tedr@........... writes:

You could create the same "rolling" effect by having 2 = narrow=20 plates a short distance apart on the upper edge of each a shallow = curve of=20 about 1000' radius. On these you sit a ground and polished rod of, = say, 2"=20 (~50mm). I'm sure this would give the same effect as your cylinder, = the only=20 problem being of course - the creation of the curves. =


Hi=20 Ted,

       You could probably = get this=20 sort of curvature most easily by flexing a flat plate? It is = approximately=20 0.75 thou for a 6" long = plate!

      =20 Part of the problem is having large area contacts. This is most easily = corrected with either strips of foil or=20 wires.

      =20 Regards,

       Chris = Chapman=20
Subject: serious pendulum misconceptions From: Randall Peters PETERS_RD@.......... Date: Tue, 19 Feb 2008 08:13:55 -0500 Just because a physical pendulum has a long period does not mean it is useful as a seismometer! For two decades I have been using such an instrument to study internal friction. The period of such a pendulum approaches very long values (easily beyond 20 s), by causing the center of mass to get ever closer to the axis of rotation. The way this is done, of course, is to put mass above the axis as well as below it as in the simple pendulum The long periods of oscillation are possible only for a structure that is very rigid, having a large quality factor in the absence of externally imposed damping. The reason this long period pendulum is not a useful seismometer is very easy to understand from the physics of extended bodies. When you apply a force to an extended body, as opposed to a point mass, the acceleration that results involves both translation and rotation. If the force acts exactly through the center of mass, the result is strictly translation; i.e., rotation is not possible because the moment arm responsible for torque has vanished. In the case of the pendulum, the acceleration of the case is equivalent (in terms of response) to a force in the opposite direction to the acceleration acting directly on the pendulum through the center of mass. As the center of mass approaches the axis, there is no torque with which to produce rotation. Without rotation there is no response. Thus the instrument is not a viable seismometer, even though it is a wonderfully useful tool for studying the influence of defect structures. What this demonstrates is just one more example of the critical need to understand conceptually the physics involved, if one is to build a useful instrument. That physics continues to be 'clouded', even by the 'analogy' you mention Chris--about pucks on a table. The demonstrations that you observed were cases (as appropriate to the discussion of seismic behavior) in which the frequency character of disturbance was much higher than the natural frequency of the analogous seismometer (puck/spring arrangement). The unit was therefore functioning as the 'vibrometer' that I mentioned earlier. The vibrometer works on the basis of the fact (low eignfrequency of the instrument compared to frequency of acceleration disturbance) that there is insignifcant motion of the mass (puck) over the time intervals of external (case) disturbance. This is not the regime for which are trying so hard to improve instrument performance. That regime is at the opposite end of the excitation frequency spectrum. When the case of a seismometer is accelerated at very low frequencies of the earth's motion, there is absolutely no way one can think of the inertial mass remaining at rest!!!!! The mass is connected to something (whether spring or pendulum rod) that serves as a device to keep it centered in the case and which is responsible for the seismometer being a mechanical oscillator. If it were not an oscillator, then there would be no reason to provide eddy current dampers using rare earth magnets. Simply stated, the inertial mass MUST be part of an oscillator IF it is to be a seismometer. If it oscillates, then the mass cannot remain at rest, and there is a repeat interval of time associated with the motion, called the period of oscillation. The finite value of this period is what in turn causes an upper limit on the sensitivity that is governed by the square of the period of oscillation. The reason there is a limit to the amount of relative motion between mass and case (instrument sensitivity) is the FACT that the inertial mass DOES move. There is ABSOLUTELY no way it CANNOT! On a different subject: Chris you mention what I believe to be indeed true--publishable results out to (and beyond) 2000 s could change a great deal in the world of seismmology. It is a virtually unexplored regime. Let me give you an example. I was just yesterday looking at the differences between the N-S and E-W channels of my VolksMeter here in Macon. Because the concrete cylinder that is part of the monolithic pier goes 20 ft into the ground, there is a significant reduction in the thermoelastic tilt that is otherwise seen for instruments sitting on a slab on top of the earth. What is really interesting about the two channel records, for 1 sample per minute over 24 h is the following. Sometimes the two channels are almost completely correlated. Whatever is tilting the pier is the same in both N-S and E-W direction. But there are days in which this is not at all true. A correlation plot shows fascinating loop-the-loops that seem to cycle over a period of several days. Is this something local to middle Georgia, or does it have global features? The answer to this important question can only be provided by networked sensors. What I find remarkable is that a simple pendulum has the potential to do some experiments which cry out for data collection. Anybody who believes that science is in the process of just 'tying up loose ends' to mature understand of nature (whether in physics or any other discipline) is hopelessly naive. It is mind boggling to me the extent to which seismology has only 'scratched the surface' with regard to a true understanding of earth's complex motions. One of the reasons so little understanding has been gained derives from the 'delta function' mentality concerning sensor type for instruments. Randall Subject: Re: pivots vs bearing structures From: Brett Nordgren Brett3mr@............. Date: Tue, 19 Feb 2008 09:00:32 -0500 Chris, At 02:05 AM 2/19/2008 -0500, you wrote: >In a message dated 2008/02/19, Brett Nordgren writes: > >>Both those issues were of great interest to pendulum clock makers. The >>latter was studed by no less of an authority than Pierre-Simon LaPlace who >>came to two conclusions. First, a (very) small radius would be better than >>a knife-edge. Second, it might even be possible to consider a roller. He >>studied the geometry and concluded that the deviation from pendulum arc >>circularity was a small fraction of the edge radius. That and very >>thorough analyses of flexure suspensions, including effective pivot point >>and nonlinear losses are covered in detail in the most excellent book by >>A. L. Rawlings "The Science of Clocks & Watches 3rd edition, 1993" > >Hi Brett, > > I dug out my copy, but it is unfortunately silent on many of the > suspensions that we might want to use. In particular, the rolling > wire/foil types have an accurate centre of rotation, extremely low > hysteretic loss and ALSO have ZERO TORQUE. The variation of stiffness and > torque are two of the problems of Cardan single foil suspensions, but > crossed wires/foils are a bit better. The rolling foil design is the one I like the best, but I would feel better if there were more experimental results to prove it's as good as I think it will be. see: http://bnordgren.org/seismo/zerohng2.pdf > But a >>concurrent question is do I really need a very low amount of loss? I >>know recent discussions have experimented with crossed pivots of extremely low >> >loss. Why? The immediate next step will be to add a damper to get to >> >something close to critical damping. My understanding is that the only >> >reason to have low loss is to be able to use lots of feedback to lengthen >> >the period. But if the period can be achieved directly, and it includes >> >some damping, so what? In my mind, the important item is >> >hysteresis/stiction. As bearings and bearing surfaces can easily be >> >ground to a ten-thousandth or even better, 10 or 20 second period >> >structures should be in reach. > > > Again yes. You need to measure movements down to nano metres, so > you need extremely low hysteresis / stiction -.whatever system you use. > Feedback will not compensate for this. Don't agree with Chris here. Without feedback, mechanical issues are important, but if you have reasonably strong feedback (loop gain), which should be possible at all frequencies in the mid and low region, any *small* effects, linear or non-linear will be made insignificant by the feedback. However, at the highest frequencies, the spring and pivot will influence the performance, because the feedback disappears there. >>For displacement-to-force feedback and possibly for other configurations, I >>believe you are exactly right. The main reason for having low pivot loss >>is to make it 'easy' for the feedback to do its job, resulting in higher >>loop gain. In general the pivot losses in such an instrument should have >>very little effect on the instrument performance. Consider that the STS-1 >>used bearings which I believe had a relatively poor hysteresis spec., yet >>its performance was considered to be pretty good. > > > Don't know where you get this from. The STS-1 used crossed foils. > The problems of making the STS-1 eventually lead to it's replacement! See http://www.c-flex.com/technicaldata.pdf which shows that the crossed-foil bearings take a "set" each time they are rotated which I consider to be a pretty good indication of significant hysteresis. This is consistent with the observation that the foils must undergo considerable bending stress near their points of connection with the sleeves. I believe that C-Flex is the successor to a series of companies which made these bearings and am assuming that Streckeisen used either them, or something very similar in the STS-1. Crossed foils are not necessarily low hysteresis. That's why I'm partial to the rolling foil design. >> >Back to possible structures. The structure I originally presented is >> >probably not possible geometrically. But one that is obviously possible >> >is as follows. Imagine a hollow cylinder (like a pipe) that has been >> >centerless ground to be round. Now take a high density rod like lead or >> >tungsten and center it down the axis of the cylinder with fine adjustment >> >screws so you can offset the center of gravity by a fraction of a >> >thousandth. > > Let's define out objectives. We don't want extreme periods, just > maybe 10 seconds instead of 1 second. Trying to get very long periods > makes the task increasingly difficult and the small anelastic effects > become major problems, as do thermal variations / expansions. > > I am fairly confident that you could extend the period by using > feedback to SOFTEN the suspension forces of a standard vertical pendulum. > Randall can then keep his 1 mm WC low loss bearings - no problem. Chris, can you give a bit more detail about what you're thinking here. (block diagram or such) Almost by definition, any significant positive feedback is going to oscillate. Are you possibly thinking of using 'feed forward', sometimes called 'open loop compensation' here. That's not feedback but is a technique for reducing error effects, usually used to moderately improve performance in combination with the usual negative feedback. I won't say that positive feedback can *never* be of use, but it has to be combined with an even stronger dose of negative feedback in order not to oscillate, and even then you have to be careful. Brett You can always use my mail form at: http://bnordgren.org/contactB.html using your Web browser. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 10:15:01 EST In a message dated 2008/02/19, tedr@........... writes: D> o you think that purpose could be served if the rod was a modified "cotton > reel" shape and it rolling on a polished flat plate with a slight bow in it > ? Hi Ted, This was my idea, but I am not entirely sure how you would go about making it. A cylinder moving in a cylinder would work in principle, but I am not sure about how you would reduce the friction / link the translational and rotational motions. Need to think more carefully. Regards, Chris In a me= ssage dated 2008/02/19, tedr@........... writes:

D
o you think that purpose could= be served if the rod was a modified "cotton reel" shape and it rolling on a= polished flat plate with a slight bow in it ?


Hi Ted,

       This was my idea, but I am not entirely= sure how you would go about making it.
       A cylinder moving in a cylinder would w= ork in principle, but I am not sure about how you would reduce the friction=20= / link the translational and rotational motions. Need to think more carefull= y.

       Regards,

       Chris Subject: Re: From: "Charles R. Patton" charles.r.patton@........ Date: Tue, 19 Feb 2008 08:39:42 -0800 Ted, Yes, that thought had occurred to me, too. One possibility would be to find a flat piece of standard window pane, mount it, and provide tension screws to physically pressure it into the desired curve. After all it is only 0.001" in 1". I think glass would bend that much. Charles Patton Ted Rogers wrote: > Charles, > > You could create the same "rolling" effect by having 2 narrow plates a > short distance apart on the upper edge of each a shallow curve of > about 1000' radius. On these you sit a ground and polished rod of, > say, 2" (~50mm). I'm sure this would give the same effect as your > cylinder, the only problem being of course - the creation of the > curves. The measurement of any movement of the rod could be done by > some sort of optical sensor looking either up or down passed a > narrower extension of the rod, or even a flat reflective surface > attached to one end of the rod... > > Regards > > Ted > > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Curved strip From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 12:05:11 EST In a message dated 2008/02/19, charles.r.patton@........ writes: > One possibility would be to find a flat piece of standard window pane, > mount it, and provide tension screws to physically pressure it into the desired > curve. After all it > is only 0.001" in 1". I think glass would bend that much. Hi Charles, Much less than that. You specified a curve of 1000 ft, presumably the radius. If your strip is 6" long Center deflection = (0.25)^2 / 2000 x 12 inches = 0.000375" Regards, Chris Chapman In a me= ssage dated 2008/02/19, charles.r.patton@........ writes:

One possibility would be to fin= d a flat piece of standard window pane, mount it, and provide tension screws= to physically pressure it into the desired curve.  After all it
is only 0.001" in 1".  I think glass would bend that much.
=

Hi Charles,

       Much less than that. You specified a cu= rve of 1000 ft, presumably the radius.
       If your strip is 6" long
       Center deflection =3D (0.25)^2 / 2000 x= 12 inches =3D 0.000375"

       Regards,

       Chris Chapman Subject: Re: pivots vs bearing structures From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 12:36:08 EST In a message dated 2008/02/19, Brett3mr@............. writes: > The rolling foil design is the one I like the best, but I would feel better > > if there were more experimental results to prove it's as good as I think it > will be. see: http://bnordgren.org/seismo/zerohng2.pdf Hi Brett, In the rundown tests, the rolling foil performed the best. I enclosed a preference list last time I wrote to Charles. > > But a concurrent question is do I really need a very low amount of loss? > I > >>know recent discussions have experimented with crossed pivots of extremely > > >> low loss. Why? The immediate next step will be to add a damper to get > to > >> >something close to critical damping. My understanding is that the only > >> >reason to have low loss is to be able to use lots of feedback to > lengthen > >> >the period. But if the period can be achieved directly, and it includes > >> >some damping, so what? In my mind, the important item is > >> >hysteresis/stiction. As bearings and bearing surfaces can easily be > >> >ground to a ten-thousandth or even better, 10 or 20 second period > >> >structures should be in reach. > >> > > Again yes. You need to measure movements down to nano metres, so > > you need extremely low hysteresis / stiction -.whatever system you use. > > Feedback will not compensate for this. > > Don't agree with Chris here. Without feedback, mechanical issues are > important, but if you have reasonably strong feedback (loop gain), which > should be possible at all frequencies in the mid and low region, any > *small* effects, linear or non-linear will be made insignificant by the > feedback. Sorry but it doesn't. This is one of the known limitations of feedback. It may well alter the scale. > > Don't know where you get this from. The STS-1 used crossed foils. > > The problems of making the STS-1 eventually lead to it's replacement! > > See http://www.c-flex.com/technicaldata.pdf which shows that the > crossed-foil bearings take a "set" each time they are rotated which I > consider to be a pretty good indication of significant hysteresis. This is > consistent with the observation that the foils must undergo considerable > bending stress near their points of connection with the sleeves. I believe > that C-Flex is the successor to a series of companies which made these > bearings and am assuming that Streckeisen used either them, or something > very similar in the STS-1. Crossed foils are not necessarily low > hysteresis. That's why I'm partial to the rolling foil design. This relates to C-Flex bearings. They are not quite the same construction as crossed foils and I would expect there to be some hysteresis. As far as I am aware, Streckeisen were making their own flexures. > > Let's define out objectives. We don't want extreme periods, just > > maybe 10 seconds instead of 1 second. Trying to get very long periods > > makes the task increasingly difficult and the small anelastic effects > > become major problems, as do thermal variations / expansions. > > > > I am fairly confident that you could extend the period by using > > feedback to SOFTEN the suspension forces of a standard vertical pendulum. > > Randall can then keep his 1 mm WC low loss bearings - no problem. > > Chris, can you give a bit more detail about what you're thinking here. > (block diagram or such) Almost by definition, any significant positive > feedback is going to oscillate. Are you possibly thinking of using 'feed > forward', sometimes called 'open loop compensation' here. That's not > feedback but is a technique for reducing error effects, usually used to > moderately improve performance in combination with the usual negative > feedback. Sure. Let's take the garden gate system as an analogy. You alter the suspension angle to alter the centring force relationship and so set the period. The centring force involved is a direct function of the deflection angle for small angles. Therefore you can alter the period either by changing the suspension angle or by reducing the centring force by force feedback. Note that force feedback can be positive or negative. If you overdo the suspension angle variation, the mass falls up against the stops. If you overdo the force feedback, the system may oscillate. > I won't say that positive feedback can *never* be of use, but it has to be > combined with an even stronger dose of negative feedback in order not to > oscillate, and even then you have to be careful. The term feedforward to me indicates a phase advanced signal? > Yes, one approach that has been used is to place a spring at the bottom > to 'soften' the restoring force of gravity acting on the pendulum. Although > in principle o.k., in fact it has been shown to be unacceptable, due to the > dastardly properties of springs. The Willmore IIIs had a period which could be set from 1 to 3 seconds. The Willmore IIICs had an additional de-centring spring which allowed the period to be extended to ~20 seconds. It has been made to work in the UK ! The alternative of providing magnetic repulsion should be a practical possibility for the light Volksmeter suspension. Regards, Chris In a me= ssage dated 2008/02/19, Brett3mr@............. writes:

The rolling foil design is the=20= one I like the best, but I would feel better
if there were more experimental results to prove it's as good as I think it=20=
will be.  see:   http://bnordgren.org/seismo/zerohng2.pdf

Hi Brett,

       In the rundown tests, the rolling foil=20= performed the best. I enclosed a preference list last time I wrote to Charle= s.

> But a concurrent question=20= is do I really need a very low amount of loss?  I
>>know recent discussions have experimented with crossed pivots of ext= remely
>> low loss.  Why?  The immediate next step will be to add a= damper to get to
>> >something close to critical damping.   My understandi= ng is that the only
>> >reason to have low loss is to be able to use lots of feedback t= o lengthen
>> >the period.  But if the period can be achieved directly, a= nd it includes
>> >some damping, so what?  In my mind, the important item is<= BR> >> >hysteresis/stiction.   As bearings and bearing surfac= es can easily be
>> >ground to a ten-thousandth or even better, 10 or 20 second peri= od
>> >structures should be in reach.
>>
>        Again yes. You need to measur= e movements down to nano metres, so
> you need extremely low hysteresis / stiction -.whatever system you use.=
> Feedback will not compensate for this.

Don't agree with Chris here.  Without feedback, mechanical issues are <= BR> important, but if you have reasonably strong feedback (loop gain), which should be possible at all frequencies in the mid and low region, any
*small* effects, linear or non-linear will be made insignificant by the
feedback. 


    Sorry but it doesn't. This is one of the known limitation= s of feedback. It may well alter the scale.
   
>    &n= bsp;   Don't know where you get this from. The STS-1 used crossed=20= foils.
> The problems of making the STS-1 eventually lead to it's replacement!
See http://www.c-flex.com/technicaldata.pdf  which shows that the
crossed-foil bearings take a "set" each time they are rotated which I
consider to be a pretty good indication of significant hysteresis.  Thi= s is
consistent with the observation that the foils must undergo considerable bending stress near their points of connection with the sleeves.  I bel= ieve
that C-Flex is the successor to a series of companies which made these
bearings and am assuming that Streckeisen used either them, or something very similar in the STS-1.  Crossed foils are not necessarily low
hysteresis.  That's why I'm partial to the rolling foil design.<= FONT COLOR=3D"#000000" BACK=3D"#ffffff" style=3D"BACKGROUND-COLOR: #ffffff"= SIZE=3D2 PTSIZE=3D10 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"0">

       This relates to C-Flex bearings. They=20= are not quite the same construction as crossed foils and I would expect ther= e to be some hysteresis. As far as I am aware, Streckeisen were making their= own flexures.

>    &nb= sp;   Let's define out objectives. We don't want extreme periods,=20= just
> maybe 10 seconds instead of 1 second. Trying to get very long periods <= BR> > makes the task increasingly difficult and the small anelastic effects <= BR> > become major problems, as do thermal variations / expansions.
>
>        I am fairly confident that yo= u could extend the period by using
> feedback to SOFTEN the suspension forces of a standard vertical pendulu= m.
> Randall can then keep his 1 mm WC low loss bearings - no problem.

Chris, can you give a bit more detail about what you're thinking here.
(block diagram or such)  Almost by definition, any significant positive=
feedback is going to oscillate.  Are you possibly thinking of using 'fe= ed
forward', sometimes called 'open loop compensation' here.  That's not <= BR> feedback but is a technique for reducing error effects, usually used to
moderately improve performance in combination with the usual negative
feedback.


       Sure. Let's take the garden gate syste= m as an analogy. You alter the suspension angle to alter the centring force=20= relationship and so set the period. The centring force involved is a direct=20= function of the deflection angle for small angles. Therefore you can alter t= he period either by changing the suspension angle or by reducing the centrin= g force by force feedback. Note that force feedback can be positive or negat= ive.
       If you overdo the suspension angle vari= ation, the mass falls up against the stops. If you overdo the force feedback= , the system may oscillate.

I won't say that positive feedb= ack can *never* be of use, but it has to be
combined with an even stronger dose of negative feedback in order not to oscillate, and even then you have to be careful.


       The term feedforward to me indicates a=20= phase advanced signal?

  Yes, one approach that h= as been used is to place a spring at the bottom to 'soften' the restoring fo= rce of gravity acting on the pendulum.  Although in principle o.k., in=20= fact it has been shown to be unacceptable, due to the dastardly properties o= f springs.


       The Willmore IIIs had a period which co= uld be set from 1 to 3 seconds. The Willmore IIICs had an additional de-cent= ring spring which allowed the period to be extended to ~20 seconds. It has b= een made to work in the UK ! The alternative of providing magnetic repulsion= should be a practical possibility for the light Volksmeter suspension.
      
       Regards,

       Chris Subject: Re: Curved strip From: "meredith lamb" paleoartifact@......... Date: Tue, 19 Feb 2008 11:18:54 -0700 Hi Charles & Chris, 2 cents.... A possible partial solution for the 3-4" diameter....use old computer 3" hard (actually ~3.1" or so) drives for the upright rolling "ends", with holding spacers inbetween; and then mount your mass and use the spacers for the screws adjustments. They are light, tough, and have precision diameters and have a nickel plated all over....and they can be also be cut in two if really necessary. Meredith On 2/19/08, ChrisAtUpw@....... wrote: > In a message dated 2008/02/19, charles.r.patton@........ writes: > > > One possibility would be to find a flat piece of standard window pane, > > mount it, and provide tension screws to physically pressure it into the > desired > > curve. After all it > > is only 0.001" in 1". I think glass would bend that much. > > Hi Charles, > > Much less than that. You specified a curve of 1000 ft, presumably the > radius. > If your strip is 6" long > Center deflection = (0.25)^2 / 2000 x 12 inches = 0.000375" > > Regards, > > Chris Chapman > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Digest from 02/18/2008 20:31:02 From: "Randy" rpratt@............. Date: Tue, 19 Feb 2008 12:57:37 -0600 Why not reverse and put the narrow edges on the cylinder. The depressed surface could possibly be ground accurately using the method telescope makers use to grind mirrors to very fine tolerance. Randy ..> ------=_NextPart_000_002C_01C8730C.6F82E430 > Content-Type: text/plain; > charset="iso-8859-1" > Content-Transfer-Encoding: quoted-printable > > Charles, > > You could create the same "rolling" effect by having 2 narrow plates a = > short distance apart on the upper edge of each a shallow curve of about = > 1000' radius. On these you sit a ground and polished rod of, say, 2" = > (~50mm). I'm sure this would give the same effect as your cylinder, the = > only problem being of course - the creation of the curves. The = > measurement of any movement of the rod could be done by some sort of = > optical sensor looking either up or down passed a narrower extension of = > the rod, or even a flat reflective surface attached to one end of the = > rod... > > Regards > > Ted > > ..> __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Curved strips of glass From: "Charles R. Patton" charles.r.patton@........ Date: Tue, 19 Feb 2008 11:21:09 -0800 Chris, I thought I was only specifying a curve of 1000 inches, not 1000 feet., so back to about a 0.003 inch deflection in of a 6 inch long strip. Anyway, I just went out to the garage with a microscope slide, 1.0x3.0x0.055", and supported the ends with Allen wrenches (a line contact) and it deflected about 0.025" before breaking so that converts to 0.0166" (16.6 thousandths) per inch -- well above the postulated 3 or so mills for a 10 second curve. Charles Patton ChrisAtUpw@....... wrote: > In a message dated 2008/02/19, charles.r.patton@........ writes: > >> One possibility would be to find a flat piece of standard window >> pane, mount it, and provide tension screws to physically pressure it >> into the desired curve. After all it >> is only 0.001" in 1". I think glass would bend that much. > > > Hi Charles, > > Much less than that. You specified a curve of 1000 ft, > presumably the radius. > If your strip is 6" long > Center deflection = (0.25)^2 / 2000 x 12 inches = 0.000375" > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Curved strip From: "Charles R. Patton" charles.r.patton@........ Date: Tue, 19 Feb 2008 11:29:06 -0800 Hi Meredith, Most disks were aluminum, but some of the disks were ceramic/glass, especially in the smaller diameters like the 2.5 inch portable drives. Find some of those and you'd have very hard disks. The problem is that although the surface are polished to very good figures, the edges were not, so I'm not sure what the final result would be. But starting with those disks, then polishing them could yield some very good hard edges. Regards, Charles Patton meredith lamb wrote: > Hi Charles & Chris, > > 2 cents.... > > A possible partial solution for the 3-4" diameter....use old computer 3" hard > (actually ~3.1" or so) drives for the upright rolling "ends", with > holding spacers inbetween; and then mount your mass and use the > spacers for the screws adjustments. They are light, tough, and have > precision diameters and have a nickel plated all over....and they can be also > be cut in two if really necessary. > > Meredith > > On 2/19/08, ChrisAtUpw@....... wrote: > >> In a message dated 2008/02/19, charles.r.patton@........ writes: >> >> >>> One possibility would be to find a flat piece of standard window pane, >>> mount it, and provide tension screws to physically pressure it into the >>> >> desired >> >>> curve. After all it >>> is only 0.001" in 1". I think glass would bend that much. >>> >> Hi Charles, >> >> Much less than that. You specified a curve of 1000 ft, presumably the >> radius. >> If your strip is 6" long >> Center deflection = (0.25)^2 / 2000 x 12 inches = 0.000375" >> >> Regards, >> >> Chris Chapman >> >> > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: serious pendulum misconceptions From: ChrisAtUpw@....... Date: Tue, 19 Feb 2008 19:52:31 EST In a message dated 2008/02/19, PETERS_RD@.......... writes: > Just because a physical pendulum has a long period does not mean it is > useful as a seismometer! For two decades I have been using such an instrument to > study internal friction. The period of such a pendulum approaches very long > values (easily beyond 20 s), by causing the center of mass toget ever closer > to the axis of rotation. The way this is done, of course, is to put mass > above the axis as well as below it as in the simple pendulum The long periods of > oscillation are possible > only for a structure that is very rigid, having a large quality factor in > the absence of externally imposed damping. > The reason this long period pendulum is not a useful seismometer is > very easy to understand from the physics of extended bodies. When you apply a > force to an extended body, as opposed to a point mass, the acceleration that > results involves both translation and rotation. If the force acts exactly > through the center of mass, the result is strictly translation; i.e., rotation > is not possible because the moment arm responsible for torque has vanished. > In the case of the pendulum, the acceleration of the case is equivalent > (in terms of response) to a force in the opposite direction to the > acceleration acting directly on the pendulum through the center of mass. As the center > of mass approaches the axis, there is no torque with which to produce > rotation. Without rotation there is no response. Thus the instrument is not a > viable seismometer, even though it is a wonderfully useful tool for studying the > influence of defect structures. Hi Randall, Understood. > What this demonstrates is just one more example of the critical need to > understand conceptually the physics involved, if one is to build a useful > instrument. That physics continues to be 'clouded', even by the 'analogy' you > mention Chris--about pucks on a table. The demonstrations that you observed > were cases > (as appropriate to the discussion of seismic behavior) in which the > frequency character of disturbance was much higher than the natural frequency of the > analogous seismometer (puck/spring arrangement). The unit was therefore > functioning as the 'vibrometer' that I mentioned earlier. My fault. I had not picked up that you were referring to a seismometer when the excitation frequency was below resonance, but were calling it a vibrometer when the excitation frequency was above resonance. The vibrometer works on the basis > of the fact (low eignfrequency of the > instrument compared to frequency of acceleration disturbance) that there is > insignifcant motion of the mass (puck) over the time intervals of external (case) > disturbance. This is not the regime for which are trying so hard to improve > instrument performance. OK > That regime is at the opposite end of the excitation frequency spectrum. > When the case of a seismometer is accelerated at very low frequencies of the > earth's motion, there is absolutely no way one can think of the inertial mass > remaining at rest! The mass is connected to something (whether spring or > pendulum rod) that serves as > a device to keep it centered in the case and which is responsible for the > seismometer being a mechanical oscillator. If it were not an oscillator, then > there would be no reason to provide eddy current dampers using rare earth > magnets. Simply stated, the inertial mass MUST be part of an oscillator IF it > is to be a seismometer. If it oscillates, then the mass cannot remain at > rest, and there is a repeat interval of time associated with the motion, called > the period of oscillation. The finite value of this period is what in turn > causes an upper limit on the sensitivity that is governed by the square of the > period of oscillation. The reason there is a limit to the amount of relative > motion between mass and case (instrument sensitivity) is the FACT that the > inertial mass DOES move. There is ABSOLUTELY no way it CANNOT! Agreed. > On a different subject: > Chris you mention what I believe to be indeed true - publishable results > out to (and beyond) 2000 s could change a great deal in the world of > seismology. It is a virtually unexplored regime. Let me give you an example. I was just > yesterday looking at the differences between the N-S and E-W channels of my > VolksMeter here in Macon. Because the concrete cylinder that is part of the > monolithic pier goes 20 ft into the ground, there is a significant reduction > in the thermoelastic tilt that is otherwise seen for instruments sitting on a > slab on top of the earth. What is really interesting about the two channel > records, for 1 sample per minute over 24 h is the following. Sometimes the > two channels are almost completely correlated. Whatever is tilting the pier is > the same in both N-S and E-W direction. > But there are days in which this is not at all true. A correlation plot > shows fascinating loop-the-loops that seem to cycle over a period of several > days. Is this something local to middle Georgia, or does it have global > features? The answer to this important question can only be provided by > networked sensors. What I find remarkable is that a simple pendulum has the > potential to do some experiments which cry out for data collection. Anybody who > believes that science is in the > process of just 'tying up loose ends' to mature understand of nature > (whether in physics or any other discipline) is hopelessly naive. It is mind > boggling to me the extent to which seismology has only 'scratched the surface' with > regard to a true > understanding of earth's complex motions. One of the reasons so little > understanding has been gained derives from the 'delta function' mentality > concerning sensor type for instruments. Interesting. Which was why I suggested siting an instrument at Eskdalemuir 55.3N 3.2W in the UK, about 81 degrees E from Macon 32.85N -83.68W, or at Walferdange 49.7N 6.2E in Luxembourgh at about 89 degrees E? Eskdalemuir is a good bit further N than Macon. But we still have to motivate the seismologists and get the long period equipment to them. STS-1s are in short supply and STS-2s and Guralp CMG 3T can be ordered in 360 sec version, but the Trillium is limited to 240 seconds. They are all a bit short on period for Earth Eigenmodes. I haven't checked the noise levels. The Scripps Institute seems to be junking their STS-1s?? I suspect that Volksmeters could well make excellent Tsunami detectors, particularly off the west coast of the Americas where the major faults are less than 500 miles offshore and the warning response times need to be just a few minutes.They could pick up the tilt signals from vertical ocean floor changes directly. I am not sure about the likely deflection amplitudes required? I have just been watching a TV program about the Cascadia fault off Canada + USA. They were suggesting movement on the coast of up to a foot and a M 9 quake about 600 miles long. The last quake was in 1700 and the previous one was about 300 years before that. This sounds too close for comfort. In a me= ssage dated 2008/02/19, PETERS_RD@.......... writes:

Just because a physical pendulu= m has a long period does not mean it is useful as a seismometer! For two dec= ades I have been using such an instrument to study internal friction. The pe= riod of such a pendulum approaches very long values (easily beyond 20 s), by= causing the center of mass toget ever closer to the axis of rotation. = The way this is done, of course, is to put mass above the axis as well as b= elow it as in the simple pendulum  The long periods of oscillation are=20= possible
only for a structure that is very rigid, having a large quality factor in th= e absence of externally imposed damping.
     The reason this long period pendulum is not a usefu= l seismometer is very easy to understand from the physics of extended bodies= ..  When you apply a force to an extended body, as opposed to a point ma= ss, the acceleration that results involves both translation and rotation.&nb= sp; If the force acts exactly through the center of mass, the result is stri= ctly translation; i.e., rotation is not possible because the moment arm resp= onsible for torque has vanished.
    In the case of the pendulum, the acceleration of the case= is equivalent (in terms of response) to a force in the opposite direction t= o the acceleration acting directly on the pendulum through the center of mas= s. As the center of mass approaches the axis, there is no torque with which=20= to produce rotation.  Without rotation there is no response.  Thus= the instrument is not a viable seismometer, even though it is a wonderfully= useful tool for studying the influence of defect structures.

Hi Randall,

       Understood.

    What this de= monstrates is just one more example of the critical need to understand conce= ptually the physics involved, if one is to build a useful instrument. =20= That physics continues to be 'clouded', even by the 'analogy' you mention Ch= ris--about pucks on a table.  The demonstrations that you observed were= cases
(as appropriate to the discussion of seismic behavior) in which the frequenc= y character of disturbance was much higher than the natural frequency of the= analogous seismometer (puck/spring arrangement).  The unit was therefo= re
functioning as the 'vibrometer' that I mentioned earlier. 

    My fault. I had not picked up that you were referring to=20= a seismometer when the excitation frequency was below resonance, but were ca= lling it a vibrometer when the excitation frequency was above resonance.

The vibrometer works on the basis
of the fact (low eignfrequency of the instrument compared to frequency o= f acceleration disturbance) that there is insignifcant motion of the mass (p= uck) over the time intervals of external (case) disturbance.  This is n= ot the regime for which are trying so hard to improve instrument performance= ..


    OK

That regime is at the opposite= end of the excitation frequency spectrum.  When the case of a seismome= ter is accelerated at very low frequencies of the earth's motion, there is a= bsolutely no way one can think of the inertial mass remaining at rest! The m= ass is connected to something (whether spring or pendulum rod) that serves a= s
a device to keep it centered in the case and which is responsible for the se= ismometer being a mechanical oscillator.  If it were not an oscillator,= then there would be no reason to provide eddy current dampers using rare ea= rth magnets.  Simply stated, the inertial mass MUST be part of an oscil= lator IF it is to be a seismometer.  If it oscillates, then the mass ca= nnot remain at rest, and there is a repeat interval of time associated with=20= the motion, called the period of oscillation.  The finite value of this= period is what in turn causes an upper limit on the sensitivity that is gov= erned by the square of the period of oscillation. The reason there is a limi= t to the amount of relative motion between mass and case (instrument sensiti= vity) is the FACT that the inertial mass DOES move. There is ABSOLUTELY no w= ay it CANNOT!


       Agreed.

    On a differe= nt subject:

      
Chris you mention what I believ= e to be indeed true - publishable results out to (and beyond) 2000 s could c= hange a great deal in the world of seismology. It is a virtually unexplored=20= regime. Let me give you an example. I was just yesterday looking at the diff= erences between the N-S and E-W channels of my VolksMeter here in Macon. Bec= ause the concrete cylinder that is part of the monolithic pier goes 20 ft in= to the ground, there is a significant reduction in the thermoelastic tilt th= at is otherwise seen for instruments sitting on a slab on top of the earth.&= nbsp; What is really interesting about the two channel records, for 1 sample= per minute over 24 h is the following.  Sometimes the two channels are= almost completely correlated.  Whatever is tilting the pier is the sam= e in both N-S and E-W direction.
    But there are days in which this is not at all true. = ; A correlation plot shows fascinating loop-the-loops that seem to cycle ove= r a period of several days.  Is this something local to middle Georgia,= or does it have global features?  The answer to this important questio= n can only be provided by networked sensors.  What I find remarkable is= that a simple pendulum has the potential to do some experiments which cry o= ut for data collection.  Anybody who believes that science is in the process of just 'tying up loose ends' to mature understand of nature (whethe= r in physics or any other discipline) is hopelessly naive.  It is mind=20= boggling to me the extent to which seismology has only 'scratched the surfac= e' with regard to a true
understanding of earth's complex motions. One of the reasons so little under= standing has been gained derives from the 'delta function' mentality concern= ing sensor type for instruments.


       Interesting.

       Which was why I suggested siting an ins= trument at Eskdalemuir 55.3N 3.2W in the UK, about 81 degrees E from Macon 3= 2.85N -83.68W, or at Walferdange 49.7N 6.2E in Luxembourgh at about 89 degre= es E? Eskdalemuir is a good bit further N than Macon.

       But we still have to motivate the seism= ologists and get the long period equipment to them. STS-1s are in short supp= ly and STS-2s and Guralp CMG 3T can be ordered in 360 sec version, but the T= rillium is limited to 240 seconds. They are all a bit short on period for Ea= rth Eigenmodes. I haven't checked the noise levels. The Scripps Institute se= ems to be junking their STS-1s??

       I suspect that Volksmeters could well m= ake excellent Tsunami detectors, particularly off the west coast of the Amer= icas where the major faults are less than 500 miles offshore and the warning= response times need to be just a few minutes.They could pick up the tilt si= gnals from vertical ocean floor changes directly.  I am not sure about=20= the likely deflection amplitudes required?
       I have just been watching a TV program=20= about the Cascadia fault off Canada + USA. They were suggesting movement on=20= the coast of up to a foot and a M 9 quake about 600 miles long. The last qua= ke was in 1700 and the previous one was about 300 years before that. This so= unds too close for comfort. Subject: Nevada earthquake From: jonfr@......... Date: Thu, 21 Feb 2008 09:54:11 -0500 (EST) Hi all According to EMSC there was a Mw6.3 earthquake in Nevada at 14:16 GMT. I guess that there is an damaged following this event. I don't know yet if my station did record it. Regards. Jón Frímann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Nevada earthquake<<< UT From: "Jim ODonnell" geophysics@.......... Date: Thu, 21 Feb 2008 15:31:06 GMT Probably Not- Not too many folks live in the area- closer to Salt Lake C= ity but still to far away...My jugs are still ringing tho<<<<,Jim Jim O'Donnell = Geological/Geophysical Consultant GEOTECHNICAL APPLICATIONS 702.293.5664 geophysics@.......... 702.281.9081 cell jimo17@........ -- jonfr@......... wrote: Hi all According to EMSC there was a Mw6.3 earthquake in Nevada at 14:16 GMT. I= guess that there is an damaged following this event. I don't know yet if my station did record it. Regards. J=C3=B3n Fr=C3­mann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) See http://www.seismicnet.com/maillist.html for more information. Probably Not- Not too many folks live in the area- closer to Salt = Lake City but still to far away...My jugs are still ringing tho<<&= lt;<,Jim


        &= nbsp;         Jim O'Donnell=     
       &= nbsp;Geological/Geophysical Consultant
     =       GEOTECHNICAL APPLICATIONS
702.293= ..5664    geophysics@..........
702.281.9081 cell  = ; jimo17@........

-- jonfr@......... wrote:
Hi all
According to EMSC there was a Mw6.3 earthquake in Nevada at 14:16 GMT. = I
guess that there is an damaged following this event.

I don't= know yet if my station did record it.

Regards.
J=C3=B3n Fr=C3= ­mann.
__________________________________________________________=

Public Seismic Network Mailing List (PSN-L)

To leave this= list email PSN-L-REQUEST@.............. with
the body of the messag= e (first line only): unsubscribe
See http://www.seismicnet.com/mailli= st.html for more information. Subject: Re: Nevada earthquake<<< UT From: "Jerry Payton" gpayton880@....... Date: Thu, 21 Feb 2008 09:52:43 -0600 FOX NEWS is reporting scattered reports of damages: collapsed building, cracks and goods shaking on shelves in surrounding states. On site reports have been slow in coming and not been shown yet. Jerry ----- Original Message ----- From: Jim ODonnell To: psn-l@.............. Sent: Thursday, February 21, 2008 9:31 AM Subject: Re: Nevada earthquake<<< UT Probably Not- Not too many folks live in the area- closer to Salt Lake City but still to far away...My jugs are still ringing tho<<<<,Jim Jim O'Donnell Geological/Geophysical Consultant GEOTECHNICAL APPLICATIONS 702.293.5664 geophysics@.......... 702.281.9081 cell jimo17@........ -- jonfr@......... wrote: Hi all According to EMSC there was a Mw6.3 earthquake in Nevada at 14:16 GMT. I guess that there is an damaged following this event. I don't know yet if my station did record it. Regards. JĂłn FrĂ­mann. __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
FOX NEWS is reporting scattered reports of damages: collapsed = building,=20 cracks and goods shaking on shelves in surrounding states.  On site = reports=20 have been slow in coming and not been shown yet.
Jerry
 
 
----- Original Message -----=20
From: Jim = ODonnell=20
Sent: Thursday, February 21, 2008 9:31 AM
Subject: Re: Nevada earthquake<<< UT

Probably Not- Not too many folks live in the area- closer = to Salt=20 Lake City but still to far away...My jugs are still ringing=20 tho<<<<,Jim


      &n= bsp;           Jim= =20 O'Donnell=20     
       &nb= sp;Geological/Geophysical=20 Consultant
          = ; GEOTECHNICAL=20 APPLICATIONS
702.293.5664    geophysics@..........
702.28= 1.9081=20 cell   jimo17@........

--=20 jonfr@......... wrote:
Hi=20 all

According to EMSC there was a Mw6.3 earthquake in Nevada at = 14:16=20 GMT. I
guess that there is an damaged following this event.

I = don't=20 know yet if my station did record it.

Regards.
J=C3=B3n=20 Fr=C3­mann.
______________________________________________________= ____

Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email=20 PSN-L-REQUEST@.............. with
the body of the message (first = line only):=20 unsubscribe
See http://www.seismicnet.com/maillist.html for more = information.=20 Subject: 6.0M Nevada From: tchannel1@............ Date: Thu, 21 Feb 2008 12:57:05 -0700 Hi Folks, Things very busy here today. No local damage of course, but I = did feel IT. I was still in bed but awake and thinking I should be = getting up. I felt the room move? I thought it was the wind, and heard a small = noise. I noted the clock at 7:17am our time. We have recently installed a vertical spring sensor at River Glen Jr. = High School which shares the building with the TVMSC Treasure Valley = Math and Science Center. The sensor is on the second floor of a three story building. In two = weeks the school has recorded 7 earthquakes. One of which was 9000 miles = away.=20 They certainly got this one, all the 8th Grader where thrilled. Their = event is posted on PSN as TVMSC Boise Id. Two News station did an on = site interview at the school. Channel 2 and 7. I also recorded in at TCID using my new (Larry's) three channel = Amp/filter. I took a screen shot of the Helicorder and it is very interesting on = it's own. E'mail me and I can send it to you as a .jpg. It's a keeper. Alls-Well here in Boise. Damage reported in Nevada but I have heard of = no injuries. One call to the TV station reported it threw a cat out of a chair..... Cheers Ted

Hi Folks, Things very busy here today. No local damage of course, but = I did=20 feel IT. I was still in bed but awake and thinking I should be getting = up.

I felt the room move? I thought it was the wind, and heard a small = noise. I=20 noted the clock at 7:17am our time.

We have recently installed a vertical spring sensor at River Glen Jr. = High=20 School which shares the building with the TVMSC Treasure Valley Math and = Science=20 Center.

The sensor is on the second floor of a three story building. In two = weeks the=20 school has recorded 7 earthquakes. One of which was 9000 miles away. =

They certainly got this one, all the 8th Grader where = thrilled.=20 Their event is posted on PSN as TVMSC Boise Id. Two News station did an = on site=20 interview at the school.

Channel 2 and 7.

I also recorded in at TCID using my new (Larry=92s) three channel=20 Amp/filter.

I took a screen shot of the Helicorder and it is very interesting on = it=92s=20 own.

E=92mail me and I can send it to you as a .jpg. It=92s a keeper.

Alls-Well here in Boise. Damage reported in Nevada but I have heard = of no=20 injuries.

One call to the TV station reported it threw a cat out of a = chair=85=85=85..

Cheers

Ted

Subject: Re: 6.0M Nevada From: jonfr@......... Date: Thu, 21 Feb 2008 17:16:45 -0500 (EST) Hi CNN has been reporting little damage to houses closest to the earthquake center. Regards. Jón Frímann. > Hi Folks, Things very busy here today. No local damage of course, but I > did feel IT. I was still in bed but awake and thinking I should be getting > up. > > I felt the room move? I thought it was the wind, and heard a small noise. > I noted the clock at 7:17am our time. > > We have recently installed a vertical spring sensor at River Glen Jr. High > School which shares the building with the TVMSC Treasure Valley Math and > Science Center. > > The sensor is on the second floor of a three story building. In two weeks > the school has recorded 7 earthquakes. One of which was 9000 miles away. > > They certainly got this one, all the 8th Grader where thrilled. Their > event is posted on PSN as TVMSC Boise Id. Two News station did an on site > interview at the school. > > Channel 2 and 7. > > I also recorded in at TCID using my new (Larry's) three channel > Amp/filter. > > I took a screen shot of the Helicorder and it is very interesting on it's > own. > > E'mail me and I can send it to you as a .jpg. It's a keeper. > > Alls-Well here in Boise. Damage reported in Nevada but I have heard of no > injuries. > > One call to the TV station reported it threw a cat out of a chair..... > > Cheers > > Ted > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Many Nevada aftershock From: tchannel1@............ Date: Fri, 22 Feb 2008 21:47:47 -0700 Hi Folks, We have been recording many aftershocks following the 6.0M = Nevada Feb. 21st. Several in the 4's and many more 3's. I have not been counting the 3's but around 6 events in 24 hours? I = just looked a the last three events from this area, 3.2M, 3.1M, and 3.2M = in the last few hours. These are about 160 miles or 310km, and the 3's are coming through very = well defined. If these were not so numerous I would be posting each and = every one.=20 With my equipment I rarely record events this small and this numerous. = Too many earthquakes to process ! =20 If I were to process all the ones I am recording from this area, I = would be processing 24hours a day. I am recording with two different sensors. One is a Slinky II, which = works very well, but even better , the latest one, I am calling a Tilt = Meter, which is a very simple 2 second pendulum, hanging down like a = Grandfather Clock. It contains a nice coil, 4000 turns and 4 magnets, = nice, but nothing complex. At any rate this machine is working better than any of my other 10 = efforts. If someone is serious about building an inexpensive, but effective = sensor, contact me and I will share my pictures and design notes. I = think the reason it is working so well is the special coil and the fact = that it uses a simple tilt. I am posting these as TCIDTM. Meanwhile, The school, TVMSC is recording away, using the small copper = vertical sensor, and it is working well for them. They also are = recording many of the 3's aftershock. They sure were happy to see the = 6.0M The school had two TV channels come out and interview the 8th = graders. I was there and and sure was smiling. The reporters ask = several of the kids if they felt it, and each told an account. One = boy, said "Well there I was, just eating my oatmeal, and I felt the = table shake" Another one said "It knotted my cat out of the chair" Perhaps I could get some of the kids to write their experience, and post = them here? I will ask their teacher Ms. Poppenga. Cheers Ted
Hi Folks,  We have been recording = many=20 aftershocks following the 6.0M Nevada Feb. 21st.  Several in the = 4's and=20 many more 3's.
I have not been counting the 3's but = around 6=20 events in 24 hours?   I just looked a the last three events = from this=20 area, 3.2M, 3.1M, and 3.2M in the last few hours.
These are about 160 miles or 310km, and = the 3's are=20 coming through very well defined.  If these were not so = numerous I=20 would be posting each and every one. 
 
With my equipment I rarely record = events this small=20 and this numerous.   Too many earthquakes to process=20 !  
 If I were to process all the ones = I am=20 recording from this area, I would be processing 24hours a = day.
 
I am recording with two different = sensors. =20 One is a Slinky II, which works very well, but even better , the latest=20 one,   I am calling a Tilt Meter, which is a very simple 2 = second=20 pendulum, hanging down like a Grandfather Clock.  It contains a = nice coil,=20 4000 turns and 4 magnets, nice, but nothing complex.
At any rate this machine is working = better than any=20 of my other 10 efforts.
 
If someone is serious about building an = inexpensive, but effective sensor, contact me and I will share my = pictures and=20 design notes.   I think the reason it is working so well is = the=20 special coil and the fact that it uses a simple tilt.   I am = posting=20 these as TCIDTM.
 
Meanwhile,  The school, TVMSC is = recording=20 away, using the small copper vertical sensor, and it is working well for = them.   They also are recording many of the 3's=20 aftershock.    They sure were happy to see the = 6.0M  =20 The school had two TV channels come out and interview the 8th=20 graders.   I was there and and sure was smiling.   = The=20 reporters ask several of the kids if they felt it, and each told an=20 account.   One boy, said "Well there I was, just eating my = oatmeal,=20 and I felt the table shake"    Another one said "It = knotted my=20 cat out of the chair"
 
Perhaps I could get some of the kids to = write their=20 experience, and post them here?    I will ask their = teacher Ms.=20 Poppenga.
 
Cheers
Ted
Subject: Re: Many Nevada aftershock From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 23 Feb 2008 15:10:43 +0000 Hi Do you have any numbers of how many aftershocks you are recording ? By my standards anything less then 100 isn't many. When I get a big earthquake swarm it can take me several weeks to review all the earthquakes. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Many Nevada aftershock From: tchannel1@............ Date: Sat, 23 Feb 2008 08:20:11 -0700 Hi Jon, No I don't have numbers. I am sure they are fewer than you are seeing in your part of the world. However this is the first time for me, being close enough to an earthquake to see small aftershocks..........all very interesting. Ted ----- Original Message ----- From: "Jón Frímann" To: Sent: Saturday, February 23, 2008 8:10 AM Subject: Re: Many Nevada aftershock Hi Do you have any numbers of how many aftershocks you are recording ? By my standards anything less then 100 isn't many. When I get a big earthquake swarm it can take me several weeks to review all the earthquakes. Regards. -- Jón Frímann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Many Nevada aftershock<<< wrote: Hi Jon, No I don't have numbers. I am sure they are fewer than you ar= e = seeing in your part of the world. However this is the first time for m= e, = being close enough to an earthquake to see small aftershocks..........al= l = very interesting. Ted ----- Original Message ----- = From: "J=F3n Fr=EDmann" To: Sent: Saturday, February 23, 2008 8:10 AM Subject: Re: Many Nevada aftershock Hi Do you have any numbers of how many aftershocks you are recording ? By my standards anything less then 100 isn't many. When I get a big earthquake swarm it can take me several weeks to review all the earthquakes. Regards. -- = J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) See http://www.seismicnet.com/maillist.html for more information.

Try UNR seismograph station- Great map of aftershocks.
= Wells ~500 miles north of Las Vegas where I am.....Jim

http://www.seismo.unr.edu/=


          =         Jim O'Donnell  &nbs= p;  
        Geolog= ical/Geophysical Consultant
       = ;    GEOTECHNICAL APPLICATIONS
702.293.5664  = ;  geophysics@..........
702.281.9081 cell   jimo= 17@........

-- <tchannel1@............> wrote:
Hi Jon, &= nbsp; No I don't have numbers.  I am sure they are fewer than = you are
seeing in your part of the world.   However this i= s the first time for me,
being close enough to an earthquake to see = small aftershocks..........all
very interesting.
Ted
----- Ori= ginal Message -----
From: "J=F3n Fr=EDmann" <jonfr@.........><= BR>To: <psn-l@..............>
Sent: Saturday, February 23, 2008= 8:10 AM
Subject: Re: Many Nevada aftershock


Hi

Do = you have any numbers of how many aftershocks you are recording ?

= By my standards anything less then 100 isn't many. When I get a big
e= arthquake swarm it can take me several weeks to review all the
earthq= uakes.

Regards.
--
J=F3n Fr=EDmann
http://www.jonfr.com=
http://earthquakes.jonfr.com
http://www.net303.net
http://www.= mobile-coverage.com/

____________________________________________= ______________

Public Seismic Network Mailing List (PSN-L)
To leave this list email PSN-L-REQUEST@.............. with
the body = of the message (first line only): unsubscribe
See http://www.seismicn= et.com/maillist.html for more information.

______________________= ____________________________________

Public Seismic Network Maili= ng List (PSN-L)

To leave this list email PSN-L-REQUEST@SEISMICNET= ..COM with
the body of the message (first line only): unsubscribe
= See http://www.seismicnet.com/maillist.html for more information.

Subject: Re: Many Nevada aftershock<<< wrote: Hi Jon, No I don't have numbers. I am sure they are fewer than you = are=20 seeing in your part of the world. However this is the first time for = me,=20 being close enough to an earthquake to see small = aftershocks..........all=20 very interesting. Ted ----- Original Message -----=20 From: "J=F3n Fr=EDmann" To: Sent: Saturday, February 23, 2008 8:10 AM Subject: Re: Many Nevada aftershock Hi Do you have any numbers of how many aftershocks you are recording ? By my standards anything less then 100 isn't many. When I get a big earthquake swarm it can take me several weeks to review all the earthquakes. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email PSN-L-REQUEST@.............. with the body of the message (first line only): unsubscribe See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) To leave this list email PSN-L-REQUEST@.............. with=20 the body of the message (first line only): unsubscribe See http://www.seismicnet.com/maillist.html for more information.
Hi Jim,  Thanks, nice = site.
Ted
----- Original Message -----
From:=20 Jim=20 ODonnell
Sent: Saturday, February 23, = 2008 8:39=20 AM
Subject: Re: Many Nevada=20 aftershock<<<<Map of aftershocks

Try UNR seismograph station- Great map of = aftershocks.
Wells ~500=20 miles north of Las Vegas where I am.....Jim

http://www.seismo.unr.edu/

           &n= bsp;      Jim=20 O'Donnell=20 =     
       &nb= sp;Geological/Geophysical=20 = Consultant
          = ; GEOTECHNICAL=20 APPLICATIONS
702.293.5664    geophysics@..........
702.28= 1.9081=20 cell   jimo17@........

-- <tchannel1@............>=20 wrote:
Hi Jon,   No I don't have numbers.  I am sure = they=20 are fewer than you are
seeing in your part of the world.=20   However this is the first time for me,
being close = enough to=20 an earthquake to see small aftershocks..........all
very=20 interesting.
Ted
----- Original Message -----
From: "J=F3n = Fr=EDmann"=20 <jonfr@.........>
To: <psn-l@..............>
Sent: = Saturday,=20 February 23, 2008 8:10 AM
Subject: Re: Many Nevada=20 aftershock


Hi

Do you have any numbers of how many=20 aftershocks you are recording ?

By my standards anything less = then 100=20 isn't many. When I get a big
earthquake swarm it can take me = several weeks=20 to review all the
earthquakes.

Regards.
--
J=F3n=20 = Fr=EDmann
http://www.jonfr.com
http://earthquakes.jonfr.com
http= ://www.net303.net
http://www.mobile-coverage.com/

_____________= _____________________________________________

Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email=20 PSN-L-REQUEST@.............. with
the body of the message (first = line=20 only): unsubscribe
See http://www.seismicnet.com/maillist.html for = more=20 = information.

_____________________________________________________= _____

Public=20 Seismic Network Mailing List (PSN-L)

To leave this list email=20 PSN-L-REQUEST@.............. with
the body of the message (first = line=20 only): unsubscribe
See http://www.seismicnet.com/maillist.html for = more=20 information.

Subject: Long Period Pendulums From: tchannel1@............ Date: Sat, 23 Feb 2008 10:29:12 -0700 Hi Folks, http://www.phy.mtu.edu/~suits/PH3110/pendulums.html This is = a description of different long period pendulums. My goal in building = sensors is to obtain the long period, like 20 seconds, In most cases I = have found this hard to do. I know it can be done, but even with the = Lehman the setup to get to 20 second is, for me difficult. I usually = give up at about 15 seconds. I was pointed to this wed site long ago, and tried my hand at some of = the ideas. I made some prototypes, spending very little time, and had = little success. After thinking about the "Rocking Chair Pendulum" recently discussed, I = saw a similarity between it and one of these Long period pendulums, so I = went back to the shop and made another mock up of the "Nearly Balanced = Pendulum" This time I took a little more time. Using a 48" dowel, I = drilled a pivot hole in the center, inserted a finishing nail into the = pivot hole, attached the nail to a table top, so the dowel would spin = like a propeller. Next I threaded a 1/2" machine bolt, nut onto one = end of the dowel. I timed the period at 2.5 seconds. I threaded = another nut on to the opposite end of the dowel, this time one half the = distance, from the end to the pivot. I timed the period at about 3.5 = seconds. I keep moving the second nut closer to the end of dowel, to = match the first nut which remained at the opposite end of the dowel. = As I move the nut the period got longer and longer. When I reached the = end of the dowel, I got a 20 second period, with very little effort. All this may be old news to some of you, but I found it to be amassing. = Now I need to build another sensor, using this approach. I think I will do another mock up, this time taking great care as to the = pivot and finer adjustments, to see how long a period I can achieve. Thanks, Ted
Hi Folks,  http://www.p= hy.mtu.edu/~suits/PH3110/pendulums.html =20 This is a description of different long period pendulums.   My = goal in=20 building sensors is to obtain the long period, like 20 seconds,  In = most=20 cases I have found this hard to do.   I know it can be done, = but even=20 with the Lehman the setup to get to 20 second is, for me = difficult.  =20 I usually give up at about 15 seconds.
 
I was pointed to this wed site long = ago, and tried=20 my hand at some of the ideas.   I made some prototypes, = spending very=20 little time, and had little success.
After thinking about the "Rocking Chair = Pendulum"=20 recently discussed, I saw a similarity between it and one of these = Long=20 period pendulums, so I went back to the shop and made another mock up of = the=20 "Nearly Balanced Pendulum"    This time I took a little = more=20 time.  Using a 48" dowel, I drilled a pivot hole in the center, = inserted a=20 finishing nail into the pivot hole, attached the nail to a table top, so = the=20 dowel would spin like a propeller.   Next I threaded a 1/2" = machine=20 bolt, nut onto one end of the dowel.   I timed the period at = 2.5=20 seconds.   I threaded another nut on to the opposite end of = the dowel,=20 this time  one half the distance, from the end to the = pivot.   I=20 timed the period at about 3.5 seconds.   I keep moving the = second nut=20 closer to the end of dowel, to match the first nut which remained at the = opposite end of the  dowel.   As I move the nut the = period got=20 longer and longer.  When I reached the end of the dowel, I got a 20 = second=20 period, with very little effort.
 
All this may be old news to some of = you, but I=20 found it to be amassing.   Now I need to build another sensor, = using=20 this approach.
 
I think I will do another mock up, this = time taking=20 great care as to the pivot and finer adjustments, to see how long a = period I can=20 achieve.
 
Thanks,
Ted
Subject: Re: Many Nevada aftershock From: John Lahr johnjan@........ Date: Sat, 23 Feb 2008 11:24:06 -0800 J=F3n, The larger events are listed here: http://earthquake.usgs.gov/eqcenter/recenteqsus/Maps/US2/40.42.-115.-113_eqs= ..php Looks like many small events are not included. John At 07:10 AM 2/23/2008, you wrote: >Hi > >Do you have any numbers of how many aftershocks you are recording ? > >By my standards anything less then 100 isn't many. When I get a big >earthquake swarm it can take me several weeks to review all the >earthquakes. > >Regards. >-- >J=F3n Fr=EDmann >http://www.jonfr.com >http://earthquakes.jonfr.com >http://www.net303.net >http://www.mobile-coverage.com/ > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with >the body of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Long Period Pendulum From: tchannel1@............ Date: Sat, 23 Feb 2008 13:38:03 -0700 Hi Folks, I set up another test in the shop for the "Nearly Balanced = Pendulum" This time I found I could only get about 15 seconds, using a = 48" dowel with a center pivot at 24". Here is what I found: As I moved the top mass closer to the end of the dowel, which countered = the fixed lower mass, the dowel's balance point would start to move from = vertical to horizontal. With no mass on the top, the dowel was vertical, because of the lower = mass. Placing the top mass at about half way up, the top half of the = 48" dowel, the whole thing still remained vertical. As I moved the top = mass higher, the dowel started to favor a 45 degree balance point, and a = longer period, about 6 seconds. The higher I moved the top mass, the longer the period, but now the = balance point was getting close to horizontal. I maxed out at 15 seconds, and the dowel nearly horizontal. If I used = a longer dowel I guess I would get a longer period. Q. 1. This movement from vertical to horizontal, it this expected? or = should it remain vertical as the period get longer? Q 2. Should I get more than 15 seconds, by using finer adjustment of = the top mass? I would think infinite. My goal here, is to keep the dowel vertical, so if I swing it, it will = return to vertical, yet obtain the longest period. With this = experiment, I can keep it vertical, but only achieve less than 10 = seconds period. Of course I want to use the shortest possible, = pendulum, say 48" Not sure if it is my set up, or perhaps my adjustments are still too = coarse, or if this movement from vertical to horizontal is normal. Thanks, Ted
Hi Folks,   I set up another = test in the=20 shop for the "Nearly Balanced Pendulum"   This time I = found I=20 could only get about 15 seconds, using a 48" dowel with a center pivot = at=20 24".   Here is what I found:
 
As I moved the top mass closer to the = end of the=20 dowel, which countered the fixed lower mass, the dowel's balance=20 point would start to move from vertical to horizontal.
 
 
With no mass on the top, the dowel was = vertical,=20 because of the lower mass.   Placing the top mass at about = half way=20 up, the top half of the 48" dowel, the whole thing still remained=20 vertical.  As I moved the top mass higher, the dowel started to = favor a 45=20 degree balance point, and a longer period, about 6 seconds.
The higher I moved the top mass, the = longer the=20 period, but now the balance point was getting close to = horizontal.
 
I maxed out at 15 seconds, and the = dowel nearly=20 horizontal.   If I used a longer dowel I guess I would get a = longer=20 period.
 
Q.  1.  This movement from = vertical to=20 horizontal, it this expected?  or should it remain vertical as the = period=20 get longer?
Q   2.  Should I get = more than 15=20 seconds, by using finer adjustment of the top mass?  I would think=20 infinite.
 
My goal here, is to keep the dowel = vertical, so if=20 I swing it, it will return to vertical, yet obtain the longest = period. =20 With this experiment, I can keep it vertical, but only achieve less than = 10=20 seconds period.   Of course I want to use the shortest = possible,=20 pendulum, say 48"
 
 
Not sure if it is my set up, or perhaps = my=20 adjustments are still too coarse, or if this movement from vertical to=20 horizontal is normal.
 
Thanks, Ted
 
Subject: [Fwd: antique seismograph?] From: Larry Cochrane lcochrane@.............. Date: Sat, 23 Feb 2008 12:49:49 -0800 Hi Everyone, I received the following request for information on an old instrument. I placed the pictures she sent me here: http://www.seismicnet.com/incoming/estate%20sale%201-26-08%20010.JPG http://www.seismicnet.com/incoming/estate%20sale%201-26-08%20015.JPG If you can help Anne please send an email to her directly since see is not on the PSN-L list. Regards, Larry Cochrane Redwood City, PSN -------- Original Message -------- Subject: antique seismograph? Date: Fri, 22 Feb 2008 12:29:15 -0800 (PST) From: Anne Fronk To: lcochrane@.............. I have been searching the net for any information on this instrument. I hope that you or your colleague's will be able to help me in identifying this object. It is very heavy, perhaps 40 pounds and has a metal cover that goes over it. The only label on it says Leitz, no year, no patent pending, nada. The only other talks about the internal clock. Could you please send me in the correct direction? I am in Sonoma County. Thanks Anne __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Many Nevada aftershock From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@......... Date: Sat, 23 Feb 2008 22:19:14 +0000 Hi Thanks for the link, John. This is not that many aftershocks by my standards. But I don't see the 0.0 to 2.5 events there. But there problay are quite many such events happening in that area. Now it is the question if it is possible to spot the next mag 5+ earthquake in that area. But the earthquake are grouping them selfs in such way that I belive that mag 5+ earthquake is going to happen there soon. An high (4.5Hz or 1Hz) sensor is needed to detect the high frequancy earthquakes that are happening there. Long period sensors won't do a good job in detecting them. Regards. --=20 J=F3n Fr=EDmann http://www.jonfr.com http://earthquakes.jonfr.com http://www.net303.net http://www.mobile-coverage.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: NEIC Link Address From: "Steve Hammond" shammon1@............. Date: Sat, 23 Feb 2008 15:48:04 -0800 Would somebody please post the NEIC links that work with Winquake. The one I have stopped working. Thanks, Steve Hammond __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Long Period Pendulum From: John Lahr johnjan@........ Date: Sun, 24 Feb 2008 00:31:45 -0800 Ted, What you are describing is a "physical pendulum." It may have a long period, but it's not a good configuration for monitoring earthquakes because it will not be greatly excited by ground motion. When you made it move, you pressed on just one end. When the ground moves, the central pivot will move and both ends will tend to move with it, which will not cause a rocking motion. Cheers, John At 12:38 PM 2/23/2008, you wrote: >Hi Folks, I set up another test in the shop for the "Nearly >Balanced Pendulum" This time I found I could only get about 15 >seconds, using a 48" dowel with a center pivot at 24". Here is what I found: > >As I moved the top mass closer to the end of the dowel, which >countered the fixed lower mass, the dowel's balance point would >start to move from vertical to horizontal. > > >With no mass on the top, the dowel was vertical, because of the >lower mass. Placing the top mass at about half way up, the top >half of the 48" dowel, the whole thing still remained vertical. As >I moved the top mass higher, the dowel started to favor a 45 degree >balance point, and a longer period, about 6 seconds. >The higher I moved the top mass, the longer the period, but now the >balance point was getting close to horizontal. > >I maxed out at 15 seconds, and the dowel nearly horizontal. If I >used a longer dowel I guess I would get a longer period. > >Q. 1. This movement from vertical to horizontal, it this >expected? or should it remain vertical as the period get longer? >Q 2. Should I get more than 15 seconds, by using finer adjustment >of the top mass? I would think infinite. > >My goal here, is to keep the dowel vertical, so if I swing it, it >will return to vertical, yet obtain the longest period. With this >experiment, I can keep it vertical, but only achieve less than 10 >seconds period. Of course I want to use the shortest possible, >pendulum, say 48" > > >Not sure if it is my set up, or perhaps my adjustments are still too >coarse, or if this movement from vertical to horizontal is normal. > >Thanks, Ted > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Long Period Pendulum From: tchannel1@............ Date: Sun, 24 Feb 2008 08:33:18 -0700 Hi John, I see what you are saying.........On the same subject, still looking at theory, vs., what I found on the mock up. In theory, 1. a pendulum with a pivot in the center, no addition mass on either end, everything is in balance, the propeller like pendulum will remain wherever you move it. 1.1 On the mock up this happens. 2. place a nut on the bottom of the propeller, in theory it should always fall to the bottom, coming to rest vertically. 2.2 On the mock up this happens. 3. Place another nut on the other end of the propeller, this time located at 1/2 the distance from the end to the pivot, 48" propeller with a pivot of 24", with this second nut at 12" from the end. In theory it should fall and come to rest at vertical, but with an extended period. 3.3 On the mock up this happens. 4. Keep moving the top nut closer to the end of the propeller, and leave it at about 2" from the end. In theory it should fall and come to rest at vertical, but with an extended period. 4.4 ON THE MOCK UP IT DOES NOT FALL TO VERTICAL, IT FALLS TO 45 DEGREES After sleeping on it, I THINK, might it be that my pivot hole, is not perfectly centered left to right through the dowel, or that the dowel is not perfectly straight and is warped to the left or right???? As a result this error is evident as the period is extended, and it fall off vertical to compensate?? Thanks, Ted ----- Original Message ----- From: "John Lahr" To: Sent: Sunday, February 24, 2008 1:31 AM Subject: Re: Long Period Pendulum > Ted, > > What you are describing is a "physical pendulum." It may have a long > period, but it's not a good > configuration for monitoring earthquakes because it will not be greatly > excited by ground motion. > When you made it move, you pressed on just one end. When the ground > moves, the central > pivot will move and both ends will tend to move with it, which will not > cause a rocking motion. > > Cheers, > John > > > > At 12:38 PM 2/23/2008, you wrote: >>Hi Folks, I set up another test in the shop for the "Nearly Balanced >>Pendulum" This time I found I could only get about 15 seconds, using a >>48" dowel with a center pivot at 24". Here is what I found: >> >>As I moved the top mass closer to the end of the dowel, which countered >>the fixed lower mass, the dowel's balance point would start to move from >>vertical to horizontal. >> >> >>With no mass on the top, the dowel was vertical, because of the lower >>mass. Placing the top mass at about half way up, the top half of the 48" >>dowel, the whole thing still remained vertical. As I moved the top mass >>higher, the dowel started to favor a 45 degree balance point, and a longer >>period, about 6 seconds. >>The higher I moved the top mass, the longer the period, but now the >>balance point was getting close to horizontal. >> >>I maxed out at 15 seconds, and the dowel nearly horizontal. If I used a >>longer dowel I guess I would get a longer period. >> >>Q. 1. This movement from vertical to horizontal, it this expected? or >>should it remain vertical as the period get longer? >>Q 2. Should I get more than 15 seconds, by using finer adjustment of >>the top mass? I would think infinite. >> >>My goal here, is to keep the dowel vertical, so if I swing it, it will >>return to vertical, yet obtain the longest period. With this experiment, >>I can keep it vertical, but only achieve less than 10 seconds period. Of >>course I want to use the shortest possible, pendulum, say 48" >> >> >>Not sure if it is my set up, or perhaps my adjustments are still too >>coarse, or if this movement from vertical to horizontal is normal. >> >>Thanks, Ted >> > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Long Period Pendulum From: John Lahr johnjan@........ Date: Sun, 24 Feb 2008 08:07:20 -0800 Ted, I suspect that there is some friction between your pivot hole and the stationary nail (or what ever forms the pivot). Obviously with lots of friction the propeller would hold still in any location. With a little, the heavy end would drop down but perhaps not make it all the way to vertical. Also, as you suggest, the hole might not be at the exact center of mass. Cheers, John At 07:33 AM 2/24/2008, you wrote: >Hi John, I see what you are saying.........On the same subject, >still looking at theory, vs., what I found on the mock up. >In theory, >1. a pendulum with a pivot in the center, no addition mass on either >end, everything is in balance, the propeller like pendulum will >remain wherever you move it. >1.1 On the mock up this happens. >2. place a nut on the bottom of the propeller, in theory it should >always fall to the bottom, coming to rest vertically. >2.2 On the mock up this happens. >3. Place another nut on the other end of the propeller, this time >located at 1/2 the distance from the end to the pivot, 48" >propeller with a pivot of 24", with this second nut at 12" from the >end. In theory it should fall and come to rest at vertical, but >with an extended period. >3.3 On the mock up this happens. >4. Keep moving the top nut closer to the end of the propeller, and >leave it at about 2" from the end. In theory it should fall and >come to rest at vertical, but with an extended period. >4.4 ON THE MOCK UP IT DOES NOT FALL TO VERTICAL, IT FALLS TO 45 DEGREES > >After sleeping on it, I THINK, might it be that my pivot hole, is >not perfectly centered left to right through the dowel, or that the >dowel is not perfectly straight and is warped to the left or >right???? As a result this error is evident as the period is >extended, and it fall off vertical to compensate?? > >Thanks, Ted > > > > > >----- Original Message ----- From: "John Lahr" >To: >Sent: Sunday, February 24, 2008 1:31 AM >Subject: Re: Long Period Pendulum > > >>Ted, >> >>What you are describing is a "physical pendulum." It may have a >>long period, but it's not a good >>configuration for monitoring earthquakes because it will not be >>greatly excited by ground motion. >>When you made it move, you pressed on just one end. When the >>ground moves, the central >>pivot will move and both ends will tend to move with it, which will >>not cause a rocking motion. >> >>Cheers, >>John >> >> >> >>At 12:38 PM 2/23/2008, you wrote: >>>Hi Folks, I set up another test in the shop for the "Nearly >>>Balanced Pendulum" This time I found I could only get about 15 >>>seconds, using a 48" dowel with a center pivot at 24". Here is what I found: >>> >>>As I moved the top mass closer to the end of the dowel, which >>>countered the fixed lower mass, the dowel's balance point would >>>start to move from vertical to horizontal. >>> >>> >>>With no mass on the top, the dowel was vertical, because of the >>>lower mass. Placing the top mass at about half way up, the top >>>half of the 48" dowel, the whole thing still remained >>>vertical. As I moved the top mass higher, the dowel started to >>>favor a 45 degree balance point, and a longer period, about 6 seconds. >>>The higher I moved the top mass, the longer the period, but now >>>the balance point was getting close to horizontal. >>> >>>I maxed out at 15 seconds, and the dowel nearly horizontal. If I >>>used a longer dowel I guess I would get a longer period. >>> >>>Q. 1. This movement from vertical to horizontal, it this >>>expected? or should it remain vertical as the period get longer? >>>Q 2. Should I get more than 15 seconds, by using finer >>>adjustment of the top mass? I would think infinite. >>> >>>My goal here, is to keep the dowel vertical, so if I swing it, it >>>will return to vertical, yet obtain the longest period. With this >>>experiment, I can keep it vertical, but only achieve less than 10 >>>seconds period. Of course I want to use the shortest possible, >>>pendulum, say 48" >>> >>> >>>Not sure if it is my set up, or perhaps my adjustments are still >>>too coarse, or if this movement from vertical to horizontal is normal. >>> >>>Thanks, Ted >> >> >>__________________________________________________________ >> >>Public Seismic Network Mailing List (PSN-L) >> >>To leave this list email PSN-L-REQUEST@.............. with the body >>of the message (first line only): unsubscribe >>See http://www.seismicnet.com/maillist.html for more information. > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with the body >of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Fw: Long Period Pendulum From: tchannel1@............ Date: Sun, 24 Feb 2008 12:01:20 -0700 Hi John and All, This is clear to me, because its right in front of me, so I hope you can picture the mock up from my description. My latest attempt go like this; A 48" dowel with a pivot, at 24". Equal mass (two machine nuts) one fixed on the bottom of the propeller, and the top nut adjustable up or down. The goal being to adjust the top nut in the up direction until it near reached the top of the dowel, which would equal the mass and position of the fixed bottom nut. Stopping just short of the end of the dowel should result in a longer period, and still always come to rest at vertical. Earlier all this did happen, but the propeller tended to come to rest at the 2:oo o'clock position, and as the nut moved up the resting position wanted to become horizontal. I though, my pivot hole was off center, just a bit, and that could cause the propeller to become other than vertical. So I added this: I drilled and installed a piece of wire about 12" long into the bottom of the propeller. Now it looks like an inverted "T" and by moving the wire to the left or right, I can bring the propeller back to vertical. The wire shift the weight of the prop. until it hang vertical. After this correction, I continued to move the top nut up to increase the period; I was able to get 45 seconds maximum, but it was unstable. I lowered the top nut a bit, and got 20 seconds, still a bit unstable. I lowered more and got 13 seconds stable and hanging vertical. I have no idea what to do with it now, except to confirm it works, but it is touch-y. A 24" pendulum was extended from 1.5 seconds to 45 seconds max. Thanks, Ted ----- Original Message ----- From: To: Sent: Sunday, February 24, 2008 8:33 AM Subject: Re: Long Period Pendulum > Hi John, I see what you are saying.........On the same subject, still > looking at theory, vs., what I found on the mock up. > In theory, > 1. a pendulum with a pivot in the center, no addition mass on either end, > everything is in balance, the propeller like pendulum will remain wherever > you move it. > 1.1 On the mock up this happens. > 2. place a nut on the bottom of the propeller, in theory it should always > fall to the bottom, coming to rest vertically. > 2.2 On the mock up this happens. > 3. Place another nut on the other end of the propeller, this time located > at 1/2 the distance from the end to the pivot, 48" propeller with a pivot > of 24", with this second nut at 12" from the end. In theory it should > fall and come to rest at vertical, but with an extended period. > 3.3 On the mock up this happens. > 4. Keep moving the top nut closer to the end of the propeller, and leave > it at about 2" from the end. In theory it should fall and come to rest at > vertical, but with an extended period. > 4.4 ON THE MOCK UP IT DOES NOT FALL TO VERTICAL, IT FALLS TO 45 DEGREES > > After sleeping on it, I THINK, might it be that my pivot hole, is not > perfectly centered left to right through the dowel, or that the dowel is > not perfectly straight and is warped to the left or right???? As a > result this error is evident as the period is extended, and it fall off > vertical to compensate?? > > Thanks, Ted > > > > > > ----- Original Message ----- > From: "John Lahr" > To: > Sent: Sunday, February 24, 2008 1:31 AM > Subject: Re: Long Period Pendulum > > >> Ted, >> >> What you are describing is a "physical pendulum." It may have a long >> period, but it's not a good >> configuration for monitoring earthquakes because it will not be greatly >> excited by ground motion. >> When you made it move, you pressed on just one end. When the ground >> moves, the central >> pivot will move and both ends will tend to move with it, which will not >> cause a rocking motion. >> >> Cheers, >> John >> >> >> >> At 12:38 PM 2/23/2008, you wrote: >>>Hi Folks, I set up another test in the shop for the "Nearly Balanced >>>Pendulum" This time I found I could only get about 15 seconds, using a >>>48" dowel with a center pivot at 24". Here is what I found: >>> >>>As I moved the top mass closer to the end of the dowel, which countered >>>the fixed lower mass, the dowel's balance point would start to move from >>>vertical to horizontal. >>> >>> >>>With no mass on the top, the dowel was vertical, because of the lower >>>mass. Placing the top mass at about half way up, the top half of the >>>48" dowel, the whole thing still remained vertical. As I moved the top >>>mass higher, the dowel started to favor a 45 degree balance point, and a >>>longer period, about 6 seconds. >>>The higher I moved the top mass, the longer the period, but now the >>>balance point was getting close to horizontal. >>> >>>I maxed out at 15 seconds, and the dowel nearly horizontal. If I used a >>>longer dowel I guess I would get a longer period. >>> >>>Q. 1. This movement from vertical to horizontal, it this expected? or >>>should it remain vertical as the period get longer? >>>Q 2. Should I get more than 15 seconds, by using finer adjustment of >>>the top mass? I would think infinite. >>> >>>My goal here, is to keep the dowel vertical, so if I swing it, it will >>>return to vertical, yet obtain the longest period. With this experiment, >>>I can keep it vertical, but only achieve less than 10 seconds period. >>>Of course I want to use the shortest possible, pendulum, say 48" >>> >>> >>>Not sure if it is my set up, or perhaps my adjustments are still too >>>coarse, or if this movement from vertical to horizontal is normal. >>> >>>Thanks, Ted >>> >> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body of >> the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Long Period Pendulum From: "Geoff" gmvoeth@........... Date: Sun, 24 Feb 2008 12:20:41 -0700 Howdy tchannel1 & PSN, It seems to me that even tho you get a longer period this way your sensitivity to motion will be greatly reduced because you are using masses that are in opposition to each other. I think in imperative to have the mass be totally out of balance with a pure force that is not a mass. Thus only the sensor mass will be involved in forces relating to accelerational forces. THE restoring forces will dictate the free period. Are you planning to incorporate this pendulous device in some role that is not the sensor itself ?? Maybe i am not picturing your verbose ideas correctly even tho verbosity is necessary in absecense of pictures? Regards; geoff ----- Original Message ----- From: To: "psn" Sent: Saturday, February 23, 2008 1:38 PM Subject: Long Period Pendulum Hi Folks, I set up another test in the shop for the "Nearly Balanced Pendulum" This time I found I could only get about 15 seconds, using a 48" dowel with a center pivot at 24". Here is what I found: As I moved the top mass closer to the end of the dowel, which countered the fixed lower mass, the dowel's balance point would start to move from vertical to horizontal. With no mass on the top, the dowel was vertical, because of the lower mass. Placing the top mass at about half way up, the top half of the 48" dowel, the whole thing still remained vertical. As I moved the top mass higher, the dowel started to favor a 45 degree balance point, and a longer period, about 6 seconds. The higher I moved the top mass, the longer the period, but now the balance point was getting close to horizontal. I maxed out at 15 seconds, and the dowel nearly horizontal. If I used a longer dowel I guess I would get a longer period. Q. 1. This movement from vertical to horizontal, it this expected? or should it remain vertical as the period get longer? Q 2. Should I get more than 15 seconds, by using finer adjustment of the top mass? I would think infinite. My goal here, is to keep the dowel vertical, so if I swing it, it will return to vertical, yet obtain the longest period. With this experiment, I can keep it vertical, but only achieve less than 10 seconds period. Of course I want to use the shortest possible, pendulum, say 48" Not sure if it is my set up, or perhaps my adjustments are still too coarse, or if this movement from vertical to horizontal is normal. Thanks, Ted __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: Brett Nordgren Brett3mr@............. Date: Sun, 24 Feb 2008 15:15:01 -0500 Ted, I think you are finding that simply having long period does not necessarily make a good sensor. What seems to be happening is that you are largely lengthening the period by reducing the restoring force on a distributed pendulum. In the design you describe, that is also having the effect of reducing its horizontal motion sensitivity, pretty much in proportion. Another design which would act in the same way would be a heavy disk with an axle drilled just slightly off-center. It would rotate heavy side down and would oscillate quite slowly, but its sensitivity to horizontal motion would be very small. It might still be fairly sensitive to tilt oscillation, though. Brett At 12:01 PM 2/24/2008 -0700, you wrote: >Hi John and All, This is clear to me, because its right in front of me, >so I hope you can picture the mock up from my description. >My latest attempt go like this; > >A 48" dowel with a pivot, at 24". Equal mass (two machine nuts) one fixed >on the bottom of the propeller, and the top nut adjustable up or down. >The goal being to adjust the top nut in the up direction until it near >reached the top of the dowel, which would equal the mass and position of >the fixed bottom nut. Stopping just short of the end of the dowel should >result in a longer period, and still always come to rest at vertical. > >Earlier all this did happen, but the propeller tended to come to rest at >the 2:oo o'clock position, and as the nut moved up the resting position >wanted to become horizontal. > >I though, my pivot hole was off center, just a bit, and that could cause >the propeller to become other than vertical. >So I added this: I drilled and installed a piece of wire about 12" long >into the bottom of the propeller. Now it looks like an inverted "T" and >by moving the wire to the left or right, I can bring the propeller back to >vertical. The wire shift the weight of the prop. until it hang vertical. > >After this correction, I continued to move the top nut up to increase the >period; I was able to get 45 seconds maximum, but it was unstable. I >lowered the top nut a bit, and got 20 seconds, still a bit unstable. I >lowered more and got 13 seconds stable and hanging vertical. > >I have no idea what to do with it now, except to confirm it works, but it >is touch-y. A 24" pendulum was extended from 1.5 seconds to 45 seconds max. >Thanks, Ted __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: "Geoff" gmvoeth@........... Date: Sun, 24 Feb 2008 13:21:28 -0700 WHAT WOULD be wrong with building a device that is fixed in a level fashion and measure only tilt since distortions stress and strain in the earth will manifest itself as a tilt ? It may be easier and cheaper to do this ? regards; geoff ----- Original Message ----- From: "Brett Nordgren" To: Sent: Sunday, February 24, 2008 1:15 PM Subject: Re: Fw: Long Period Pendulum > Ted, > > I think you are finding that simply having long period does not necessarily > make a good sensor. What seems to be happening is that you are largely > lengthening the period by reducing the restoring force on a distributed > pendulum. In the design you describe, that is also having the effect of > reducing its horizontal motion sensitivity, pretty much in proportion. > > Another design which would act in the same way would be a heavy disk with > an axle drilled just slightly off-center. It would rotate heavy side down > and would oscillate quite slowly, but its sensitivity to horizontal motion > would be very small. It might still be fairly sensitive to tilt > oscillation, though. > > Brett > > At 12:01 PM 2/24/2008 -0700, you wrote: >>Hi John and All, This is clear to me, because its right in front of me, >>so I hope you can picture the mock up from my description. >>My latest attempt go like this; >> >>A 48" dowel with a pivot, at 24". Equal mass (two machine nuts) one fixed >>on the bottom of the propeller, and the top nut adjustable up or down. >>The goal being to adjust the top nut in the up direction until it near >>reached the top of the dowel, which would equal the mass and position of >>the fixed bottom nut. Stopping just short of the end of the dowel should >>result in a longer period, and still always come to rest at vertical. >> >>Earlier all this did happen, but the propeller tended to come to rest at >>the 2:oo o'clock position, and as the nut moved up the resting position >>wanted to become horizontal. >> >>I though, my pivot hole was off center, just a bit, and that could cause >>the propeller to become other than vertical. >>So I added this: I drilled and installed a piece of wire about 12" long >>into the bottom of the propeller. Now it looks like an inverted "T" and >>by moving the wire to the left or right, I can bring the propeller back to >>vertical. The wire shift the weight of the prop. until it hang vertical. >> >>After this correction, I continued to move the top nut up to increase the >>period; I was able to get 45 seconds maximum, but it was unstable. I >>lowered the top nut a bit, and got 20 seconds, still a bit unstable. I >>lowered more and got 13 seconds stable and hanging vertical. >> >>I have no idea what to do with it now, except to confirm it works, but it >>is touch-y. A 24" pendulum was extended from 1.5 seconds to 45 seconds max. >>Thanks, Ted > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: Brett Nordgren Brett3mr@............. Date: Sun, 24 Feb 2008 23:20:35 -0500 Geoff, I believe that the only problem is that the amplitude of tilt oscillations from quakes would be rather small, and they are only associated with some of the phases. But it should definitely be worth a try. Regards, Brett At 01:21 PM 2/24/2008 -0700, you wrote: >WHAT WOULD be wrong with building a >device that is fixed in a level >fashion and measure only tilt since >distortions stress and strain in the earth >will manifest itself as a tilt ? > >It may be easier and cheaper to do this ? > >regards; >geoff __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: ian ian@........... Date: Mon, 25 Feb 2008 07:49:11 +0000 I was playing with something like this but with the pivot near the top end of the rod. The top weight was much bigger than the lower weight in proportion to the lengths of the sections above and below the pivot. That way, you'll get more movement at the bottom end of the long section than you are currently getting with your symmetrical arrangement. Balancing is a little more tricky because of the asymmetry. Given that this is probably working as a tilt meter, getting a long period may not be too important. Ian Brett Nordgren wrote: > Geoff, > > I believe that the only problem is that the amplitude of tilt > oscillations from quakes would be rather small, and they are only > associated with some of the phases. But it should definitely be worth > a try. > > Regards, > Brett > > At 01:21 PM 2/24/2008 -0700, you wrote: >> WHAT WOULD be wrong with building a >> device that is fixed in a level >> fashion and measure only tilt since >> distortions stress and strain in the earth >> will manifest itself as a tilt ? >> >> It may be easier and cheaper to do this ? >> >> regards; >> geoff > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: NEIC Link Address From: Larry Cochrane lcochrane@.............. Date: Mon, 25 Feb 2008 00:10:37 -0800 Hi Steve, The current WinQuake report files can be downloaded here: http://www.seismicnet.com/software/wqreport.zip Regards, Larry Cochrane Redwood City, PSN Steve Hammond wrote: > Would somebody please post the NEIC links that work with Winquake. The one I > have stopped working. > Thanks, Steve Hammond __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: tchannel1@............ Date: Mon, 25 Feb 2008 06:03:28 -0700 Hi Ian, That was my next test, I want to try this just as you indicated. What did you find? Did it change the maximum period possible? Did you find that your experiments, where the pendulum wanted to favor the 2: o'clock vs vertical, as you approached longer periods? Thanks, Ted ----- Original Message ----- From: "ian" To: Sent: Monday, February 25, 2008 12:49 AM Subject: Re: Fw: Long Period Pendulum >I was playing with something like this but with the pivot near the top end >of the rod. The top weight was much bigger than the lower weight in >proportion to the lengths of the sections above and below the pivot. That >way, you'll get more movement at the bottom end of the long section than >you are currently getting with your symmetrical arrangement. Balancing is >a little more tricky because of the asymmetry. > > Given that this is probably working as a tilt meter, getting a long period > may not be too important. > > Ian > > > Brett Nordgren wrote: >> Geoff, >> >> I believe that the only problem is that the amplitude of tilt >> oscillations from quakes would be rather small, and they are only >> associated with some of the phases. But it should definitely be worth a >> try. >> >> Regards, >> Brett >> >> At 01:21 PM 2/24/2008 -0700, you wrote: >>> WHAT WOULD be wrong with building a >>> device that is fixed in a level >>> fashion and measure only tilt since >>> distortions stress and strain in the earth >>> will manifest itself as a tilt ? >>> >>> It may be easier and cheaper to do this ? >>> >>> regards; >>> geoff >> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body of >> the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> >> > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: ian ian@........... Date: Mon, 25 Feb 2008 13:33:35 +0000 Hi, I didn't get very far, due to lack of time. I used a threaded rod which screws through a threaded hole in the body of the pivot. The rod was only 5mm in diameter and wasn't very strong, so when the pendulum was heading towards each extreme it would bend and the pendulum's motion was very complicated. My next step would be to try it with a larger diameter rod, one day... With the limitations mentioned above, I only got 5 seconds out of it and it wasn't stable enough to behave in the way it should, like resting at 2 o'clock. I think the main benefit of an asymmetrical arrangement will be that you get more movement at the bottom end (for a given length) which may make seismic excitations of the pendulum (as a tiltmeter) measurable! Good luck! Ian tchannel1@............ wrote: > Hi Ian, That was my next test, I want to try this just as you > indicated. What did you find? Did it change the maximum period possible? > Did you find that your experiments, where the pendulum wanted to favor > the 2: o'clock vs vertical, as you approached longer periods? > Thanks, Ted > > ----- Original Message ----- From: "ian" > To: > Sent: Monday, February 25, 2008 12:49 AM > Subject: Re: Fw: Long Period Pendulum > > >> I was playing with something like this but with the pivot near the >> top end of the rod. The top weight was much bigger than the lower >> weight in proportion to the lengths of the sections above and below >> the pivot. That way, you'll get more movement at the bottom end of >> the long section than you are currently getting with your symmetrical >> arrangement. Balancing is a little more tricky because of the >> asymmetry. >> >> Given that this is probably working as a tilt meter, getting a long >> period may not be too important. >> >> Ian >> >> >> Brett Nordgren wrote: >>> Geoff, >>> >>> I believe that the only problem is that the amplitude of tilt >>> oscillations from quakes would be rather small, and they are only >>> associated with some of the phases. But it should definitely be >>> worth a try. >>> >>> Regards, >>> Brett >>> >>> At 01:21 PM 2/24/2008 -0700, you wrote: >>>> WHAT WOULD be wrong with building a >>>> device that is fixed in a level >>>> fashion and measure only tilt since >>>> distortions stress and strain in the earth >>>> will manifest itself as a tilt ? >>>> >>>> It may be easier and cheaper to do this ? >>>> >>>> regards; >>>> geoff >>> >>> >>> __________________________________________________________ >>> >>> Public Seismic Network Mailing List (PSN-L) >>> >>> To leave this list email PSN-L-REQUEST@.............. with the body >>> of the message (first line only): unsubscribe >>> See http://www.seismicnet.com/maillist.html for more information. >>> >>> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body >> of the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of > the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: tchannel1@............ Date: Mon, 25 Feb 2008 09:00:19 -0700 Ian, Thanks again for this info.......Yes I think you are correct on all this, and the results would simply act (a bit) like a Tilt meter. I am now testing a simple 2 second Tilt meter,(for lack of a better name). I am please with the recordings, I am posting them at PSN, under the name TCIDTM. Very happy with it so far. Any advise on this subject is appreciated. Ted ----- Original Message ----- From: "ian" To: Sent: Monday, February 25, 2008 6:33 AM Subject: Re: Fw: Long Period Pendulum > Hi, > > I didn't get very far, due to lack of time. I used a threaded rod which > screws through a threaded hole in the body of the pivot. The rod was only > 5mm in diameter and wasn't very strong, so when the pendulum was heading > towards each extreme it would bend and the pendulum's motion was very > complicated. My next step would be to try it with a larger diameter rod, > one day... > > With the limitations mentioned above, I only got 5 seconds out of it and > it wasn't stable enough to behave in the way it should, like resting at 2 > o'clock. I think the main benefit of an asymmetrical arrangement will be > that you get more movement at the bottom end (for a given length) which > may make seismic excitations of the pendulum (as a tiltmeter) measurable! > > Good luck! > > Ian > > tchannel1@............ wrote: >> Hi Ian, That was my next test, I want to try this just as you >> indicated. What did you find? Did it change the maximum period possible? >> Did you find that your experiments, where the pendulum wanted to favor >> the 2: o'clock vs vertical, as you approached longer periods? >> Thanks, Ted >> >> ----- Original Message ----- From: "ian" >> To: >> Sent: Monday, February 25, 2008 12:49 AM >> Subject: Re: Fw: Long Period Pendulum >> >> >>> I was playing with something like this but with the pivot near the top >>> end of the rod. The top weight was much bigger than the lower weight in >>> proportion to the lengths of the sections above and below the pivot. >>> That way, you'll get more movement at the bottom end of the long section >>> than you are currently getting with your symmetrical arrangement. >>> Balancing is a little more tricky because of the asymmetry. >>> >>> Given that this is probably working as a tilt meter, getting a long >>> period may not be too important. >>> >>> Ian >>> >>> >>> Brett Nordgren wrote: >>>> Geoff, >>>> >>>> I believe that the only problem is that the amplitude of tilt >>>> oscillations from quakes would be rather small, and they are only >>>> associated with some of the phases. But it should definitely be worth >>>> a try. >>>> >>>> Regards, >>>> Brett >>>> >>>> At 01:21 PM 2/24/2008 -0700, you wrote: >>>>> WHAT WOULD be wrong with building a >>>>> device that is fixed in a level >>>>> fashion and measure only tilt since >>>>> distortions stress and strain in the earth >>>>> will manifest itself as a tilt ? >>>>> >>>>> It may be easier and cheaper to do this ? >>>>> >>>>> regards; >>>>> geoff >>>> >>>> >>>> __________________________________________________________ >>>> >>>> Public Seismic Network Mailing List (PSN-L) >>>> >>>> To leave this list email PSN-L-REQUEST@.............. with the body of >>>> the message (first line only): unsubscribe >>>> See http://www.seismicnet.com/maillist.html for more information. >>>> >>>> >>> __________________________________________________________ >>> >>> Public Seismic Network Mailing List (PSN-L) >>> >>> To leave this list email PSN-L-REQUEST@.............. with the body of >>> the message (first line only): unsubscribe >>> See http://www.seismicnet.com/maillist.html for more information. >>> >> >> __________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email PSN-L-REQUEST@.............. with the body of >> the message (first line only): unsubscribe >> See http://www.seismicnet.com/maillist.html for more information. >> >> > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the > message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: NEIC Link Address From: "Thomas Dick" dickthomas01@............. Date: Mon, 25 Feb 2008 10:22:04 -0600 Larry, I am having trouble getting into the file you referred to...when unzipped it brings up an audio file format......??? ----- Original Message ----- From: "Larry Cochrane" To: Sent: Monday, February 25, 2008 2:10 AM Subject: Re: NEIC Link Address > Hi Steve, > > The current WinQuake report files can be downloaded here: > http://www.seismicnet.com/software/wqreport.zip > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Fw: Long Period Pendulum From: Brett Nordgren Brett3mr@............. Date: Mon, 25 Feb 2008 11:23:33 -0500 Ian, If you are just wanting to measure tilt (rotational oscillation), as Randall Peters has pointed out elsewhere, the natural period doesn't enter into the calculation. Natural period does get involved with a second-order effect related to moments generated by an imperfect hinge or by intentional damping, but those could likely be reducedd or ignored. I think, In general, for measuring rotational motion you would prefer a pendulum which maintains a stable position rather than a less stable long-period setup. Brett At 01:33 PM 2/25/2008 +0000, you wrote: >Hi, > >I didn't get very far, due to lack of time. I used a threaded rod which >screws through a threaded hole in the body of the pivot. The rod was only >5mm in diameter and wasn't very strong, so when the pendulum was heading >towards each extreme it would bend and the pendulum's motion was very >complicated. My next step would be to try it with a larger diameter rod, >one day... > >With the limitations mentioned above, I only got 5 seconds out of it and >it wasn't stable enough to behave in the way it should, like resting at 2 >o'clock. I think the main benefit of an asymmetrical arrangement will be >that you get more movement at the bottom end (for a given length) which >may make seismic excitations of the pendulum (as a tiltmeter) measurable! > >Good luck! > >Ian __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: pendulum types From: Randall Peters PETERS_RD@.......... Date: Mon, 25 Feb 2008 14:15:10 -0500 With all the attention to non-simple pendulums of late, perhaps some readers will be interested in the following old one of my webpages: http://physics.mercer.edu/petepag/pend.htm#torsion The 'pendulum' titled 'tiltmeter' is an example of a system for which the influence of earth tilt can be greatly 'magnified'.as the operator changes the orientation of the torsion wire, causing approach toward a critical value. A system similar to it was used by one of my students in the early 1990's to study chemisorbed gases on metals. With it he was the frist person to observe (accidently) earth hum having frequencies below a few milliHertz. There was much, much geoscience interest in later, similar earth oscillations at mainly higher frequency, starting about 1998. Randall Subject: Re: pendulum types From: tchannel1@............ Date: Mon, 25 Feb 2008 13:19:27 -0700 Hi Randall, Thanks for this great artical. Ted ----- Original Message ----- From: "Randall Peters" To: Sent: Monday, February 25, 2008 12:15 PM Subject: pendulum types > With all the attention to non-simple pendulums of late, perhaps some > readers will be > interested > in the following old one of my webpages: > http://physics.mercer.edu/petepag/pend.htm#torsion > The 'pendulum' titled 'tiltmeter' is an example of a system for which the > influence of > earth tilt can be greatly 'magnified'.as the operator changes the > orientation of the torsion > wire, causing approach toward a critical value. > A system similar to it was used by one of my students in the early 1990's > to study > chemisorbed > gases on metals. With it he was the frist person to observe (accidently) > earth hum having > frequencies below a few milliHertz. There was much, much geoscience > interest in later, > similar earth oscillations at mainly higher frequency, starting about > 1998. > Randall > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: NEIC Link Address From: Mark Robinson mark.robinson@............... Date: Tue, 26 Feb 2008 09:57:48 +1300 Thomas, you may wish to adjust the file type associations in your operating system. Thomas Dick wrote: > Larry, I am having trouble getting into the file you referred to...when > unzipped it brings up an audio file format......??? > ----- Original Message ----- From: "Larry Cochrane" > >> Hi Steve, >> >> The current WinQuake report files can be downloaded here: >> http://www.seismicnet.com/software/wqreport.zip -- cheers Mark Robinson __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: NEIC Link Address From: John Lahr johnjan@........ Date: Mon, 25 Feb 2008 14:28:13 -0800 Thomas, Unzip the file wqreport-1.zip to get these two files -- network.dat and report.dat. Put these two files into the WinQuake folder. Cheers, John At 12:57 PM 2/25/2008, you wrote: >Thomas, you may wish to adjust the file type associations in your >operating system. > >Thomas Dick wrote: > > Larry, I am having trouble getting into the file you referred to...when > > unzipped it brings up an audio file format......??? > > ----- Original Message ----- From: "Larry Cochrane" > > > >> Hi Steve, > >> > >> The current WinQuake report files can be downloaded here: > >> http://www.seismicnet.com/software/wqreport.zip >-- >cheers >Mark Robinson > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with >the body of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Long Period Pendulums From: ChrisAtUpw@....... Date: Mon, 25 Feb 2008 23:20:34 EST In a message dated 2008/02/23, tchannel1@............ writes: > Hi Folks, http://www.phy.mtu.edu/~suits/PH3110/pendulums.html This is a > description of different long period pendulums. My goal in building sensors > is to obtain the long period, like 20 seconds, In most cases I have found > this hard to do. I know it can be done, but even with the Lehman the setup to > get to 20 second is, for me difficult. I usually give up at about 15 > seconds. Hi Ted, You WON'T get long periods unless you use a good suspension system and magnetic damping. Knife edge and point in a cup suspensions will PREVENT you from getting long periods. > After thinking about the "Rocking Chair Pendulum" recently discussed, I > saw a similarity between it and one of these Long period pendulums, so I went > back to the shop and made another mock up of the "Nearly Balanced Pendulum" > This time I took a little more time. Using a 48" dowel, I drilled a pivot > hole in the center, inserted a finishing nail into the pivot hole, attached > the nail to a table top, so the dowel would spin like a propeller. Next I > threaded a 1/2" machine bolt, nut onto one end of the dowel. I timed the > period at 2.5 seconds. I threaded another nut on to the opposite end of the > dowel, this time one half the distance, from the end to the pivot. I timed the > period at about 3.5 seconds. I keep moving the second nut closer to the > end of dowel, to match the first nut which remained at the opposite end of the > dowel. As I move the nut the period got longer and longer. When I reached > the end of the dowel, I got a 20 second period, with very little effort. > > All this may be old news to some of you, but I found it to be amassing. > Now I need to build another sensor, using this approach. What do you want to achieve? You can get long periods this way, but it is near useless as a seismic sensor. If you drill the dowel and fit a horizontal round rod at right angles rolling on two horizontal round rods, you can get very long periods with very low hysteresis / offset. Regards, Chris Chapman In a me= ssage dated 2008/02/23, tchannel1@............ writes:

Hi Folks,  http://www.phy.mtu.edu/~sui= ts/PH3110/pendulums.html  This is a description of different long p= eriod pendulums.   My goal in building sensors is to obtain the lo= ng period, like 20 seconds,  In most cases I have found this hard to do= ..   I know it can be done, but even with the Lehman the setup to g= et to 20 second is, for me difficult.   I usually give up at about= 15 seconds.


Hi Ted,

       You WON'T get long periods unless you u= se a good suspension system and magnetic damping. Knife edge and point in a=20= cup suspensions will PREVENT you from getting long periods.

After thinking about the "Roc= king Chair Pendulum" recently discussed, I saw a similarity between it and o= ne of these Long period pendulums, so I went back to the shop and made anoth= er mock up of the "Nearly Balanced Pendulum"    This time I t= ook a little more time.  Using a 48" dowel, I drilled a pivot hole in t= he center, inserted a finishing nail into the pivot hole, attached the nail=20= to a table top, so the dowel would spin like a propeller.   Next I= threaded a 1/2" machine bolt, nut onto one end of the dowel.   I=20= timed the period at 2.5 seconds.   I threaded another nut on to th= e opposite end of the dowel, this time  one half the distance, from the= end to the pivot.   I timed the period at about 3.5 seconds. = ;  I keep moving the second nut closer to the end of dowel, to match th= e first nut which remained at the opposite end of the  dowel. &nbs= p; As I move the nut the period got longer and longer.  When I