Subject: Re: (No subject) From: "rem11560@............ rem11560@netzero.com Date: Thu, 1 Jul 2004 01:40:59 GMT Hi Jason, I have some suggestions. Others please feel free to disagree. 1. Greatly reduce the mass of the pendulum. A mass of 5 pounds is probably too much for your superstructure. As the pendulum moves, it exerts a transverse moment on the support structure and baseplate, making it hard to achieve a stable long period. High mass also makes shunt resistance damping practically impossible. 2. Stiffen the superstructure laterally with cross bracing. 3. Having a magnet on the pendulum makes the sensor responsive to stray magnetic fields. Put the coil on the pendulum and the magnet on the base. While you are at it, place a second magnet on the opposite side of the coil, with poles reversed. You will get twice as much sensitivity, much better linearity of response, and half as much shunt conductance required for a given damping level. With the coil mounted on the pendulum, you might not need any extra mass, and that would make shunt damping easier as well. 4. Be sure to use a cover which shields the sensor from ambient temperature change and drafts. You may need a heater inside at the top to prevent convection of air upward from the baseplate. 5. Put a one microfarad capacitor across the input terminals of your amplifier. I have amplifiers of differing designs, and they all oscillate internally if there is no shunt capacitance across the input terminals when the source is inductive (i.e., a sensor coil). You cannot see this oscillation at the output terminals; it manifests itself as excess output noise, and in the case of my DC amplifiers, a large and fluctuating bias. If you want to see my sensors, visit John Lahr's web site at the pages he kindly provides for my amateur efforts: http://www.jclahr.com/science/psn/mcclure/ Regards, Bob McClure Locust Valley, NY ________________________________________________________________ The best thing to hit the Internet in years - NetZero HiSpeed! Surf the Web up to FIVE TIMES FASTER! Only $14.95/ month -visit www.netzero.com to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: (No subject) From: "Larry Cochrane" lcochrane@.............. Date: Wed, 30 Jun 2004 21:30:41 -0700 > 5. Put a one microfarad capacitor across the input terminals of your amplifier. I have amplifiers >of differing designs, and they all oscillate internally if there is no shunt capacitance across >the input terminals when the source is inductive (i.e., a sensor coil). You cannot see this >oscillation at the output terminals; it manifests itself as excess output noise, and in the >case of my DC amplifiers, a large and fluctuating bias. I question this one... I have never seen a need to place a cap on the input of an op-amp to stop internal oscillations. If you are getting some RF into the input you can place a .01 ceramic cap across the input to shunt out the RF before it gets into the op-amp. I have seen oscillation problems with op-amps driving large capacitance or inductive loads. -Larry Cochrane Redwood City, PSN __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Your seismometer From: Jason Brady jr_brady@........... Date: Thu, 01 Jul 2004 19:09:28 -0700 Hello Bob, Thanks for taking the time to provide feedback. Please see my responses/questions below. Jason At 06:47 PM 06/30/2004, you wrote: >Hi Jason, > > I have some suggestions. Others please feel free to disagree. > >1. Greatly reduce the mass of the pendulum. A mass of 5 pounds is probably >too much for your superstructure. As the pendulum moves, it exerts a >transverse moment on the support structure and baseplate, making it hard >to achieve a stable long period. High mass also makes shunt resistance >damping practically impossible. How much weight is preferable--is there a rule of thumb (or better yet, mathematical formulas) based on the boom size and/or other parameters? >2. Stiffen the superstructure laterally with cross bracing. It seems pretty sturdy but I can easily add another cross-brace. >3. Having a magnet on the pendulum makes the sensor responsive to stray >magnetic fields. Put the coil on the pendulum and the magnet on the base. >While you are at it, place a second magnet on the opposite side of the >coil, with poles reversed. You will get twice as much sensitivity, much >better linearity of response, and half as much shunt conductance required >for a given damping level. With the coil mounted on the pendulum, you >might not need any extra mass, and that would make shunt damping easier as >well. Easy enough, but where should I run the wires? Along the boom or up the suspension? >4. Be sure to use a cover which shields the sensor from ambient >temperature change and drafts. You may need a heater inside at the top to >prevent convection of air upward from the baseplate. Will make an enclosure of Celotex. How about a small appliance lamp instead? >5. Put a one microfarad capacitor across the input terminals of your >amplifier. I have amplifiers of differing designs, and they all oscillate >internally if there is no shunt capacitance across the input terminals >when the source is inductive (i.e., a sensor coil). You cannot see this >oscillation at the output terminals; it manifests itself as excess output >noise, and in the case of my DC amplifiers, a large and fluctuating bias. In parallel with the damping resistor? > If you want to see my sensors, visit John Lahr's web site at the pages > he kindly provides for my amateur efforts: > > http://www.jclahr.com/science/psn/mcclure/ > >Regards, >Bob McClure >Locust Valley, NY Hello Bob,

Thanks for taking the time to provide feedback.  Please see my responses/questions below.

Jason

At 06:47 PM 06/30/2004, you wrote:
Hi Jason,

  I have some suggestions. Others please feel free to disagree.

1. Greatly reduce the mass of the pendulum. A mass of 5 pounds is probably too much for your superstructure. As the pendulum moves, it exerts a transverse moment on the support structure and baseplate, making it hard to achieve a stable long period. High mass also makes shunt resistance damping practically impossible.

How much weight is preferable--is there a rule of thumb (or better yet, mathematical formulas) based on the boom size and/or other parameters? 

2. Stiffen the superstructure laterally with cross bracing.

It seems pretty sturdy but I can easily add another cross-brace.

3. Having a magnet on the pendulum makes the sensor responsive to stray magnetic fields. Put the coil on the pendulum and the magnet on the base. While you are at it, place a second magnet on the opposite side of the coil, with poles reversed. You will get twice as much sensitivity, much better linearity of response, and half as much shunt conductance required for a given damping level. With the coil mounted on the pendulum, you might not need any extra mass, and that would make shunt damping easier as well.

Easy enough, but where should I run the wires?  Along the boom or up the suspension?

4. Be sure to use a cover which shields the sensor from ambient temperature change and drafts. You may need a heater inside at the top to prevent convection of air upward from the baseplate.

Will make an enclosure of Celotex.  How about a small appliance lamp instead?

5. Put a one microfarad capacitor across the input terminals of your amplifier. I have amplifiers of differing designs, and they all oscillate internally if there is no shunt capacitance across the input terminals when the source is inductive (i.e., a sensor coil). You cannot see this oscillation at the output terminals; it manifests itself as excess output noise, and in the case of my DC amplifiers, a large and fluctuating bias.

In parallel with the damping resistor?

  If you want to see my sensors, visit John Lahr's web site at the pages he kindly provides for my amateur efforts:

     http://www.jclahr.com/science/psn/mcclure/

Regards,
Bob McClure
Locust Valley, NY
Subject: Re: Your Seismometer From: "rem11560@............ rem11560@netzero.com Date: Sat, 3 Jul 2004 01:50:21 GMT Hi Jason, Here are my answers to your questions, to the best of my ability to answer them >>1. Greatly reduce the mass of the pendulum. >How much weight is preferable--is there a rule of thumb (or better yet, mathematical formulas) based on the boom size and/or other parameters? Answer: There is no theoretical lower limit on mass, except a quantum one. You could't reduce the mass enough for that to have any effect. The practical limits are susceptibility to air currents, friction in the upper and lower pivots, and over damping caused by the input impedance of the amplifier. Sensors do not have to drive styluses over smoked paper any more. >>2. Stiffen the superstructure laterally with cross bracing. >It seems pretty sturdy but I can easily add another cross-brace. Answer: Just make sure that you have at least one diagonal member. >>3. Having a magnet on the pendulum makes the sensor responsive to stray magnetic fields. Put the coil on the pendulum and the magnet on the base. >Easy enough, but where should I run the wires? Along the boom or up the suspension? Answer: I run my wires down the boom, and let them dangle in a loose coil on the way to a terminal block. >>4. Be sure to use a cover which shields the sensor from ambient temperature change and drafts. You may need a heater inside at the top to prevent convection of air upward from the baseplate. >Will make an enclosure of Celotex. How about a small appliance lamp instead? Answer: Others with experience with large Lehman sensors could answer this with more authority. I would think a small appliance lamp would be OK. >>5. Put a one microfarad capacitor across the input terminals of your amplifier. >In parallel with the damping resistor? Answer: Yes, at the amplifier terminals. Larry Cochrane doubts the necessity of this, but I am using one of his amplifiers, and it was certainly necessary for me. Regards, Bob ________________________________________________________________ The best thing to hit the Internet in years - NetZero HiSpeed! Surf the Web up to FIVE TIMES FASTER! Only $14.95/ month -visit www.netzero.com to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Emon7.2 From: "Alby Judge" martinobs@.............. Date: Sat, 3 Jul 2004 21:31:48 +0800 Does anyone have a copy of Emon 7.2 with support for the Axiom AX-5210 = A/D board that they could send me please. Thanks, Alby, Martin Observatory, Western Australia.
Does anyone have a copy of Emon 7.2 = with support=20 for the Axiom AX-5210 A/D board that they could send me = please.
Thanks,
Alby,
Martin Observatory, Western=20 Australia.
Subject: RE: Emon7.2 From: "Bob Shannon" earth@........... Date: Sat, 3 Jul 2004 07:19:27 -0700 Sorry I do not.but I am sure others will have..Your message gave me pause for thought. Does anyone have a DOS version of Seismic? Alan no longer supports it and did send me a Copy snail mail about 9 years ago..but I hesitate to bother him for a third time. I am setting up a 486 with DOS 6.11 the unbugged version, in order to use as a fast machine for My own Point EQ locator program.the one I wrote in BASIC and compiled back in 1992.Thanks Bob Shannon Pinpoint -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Alby Judge Sent: Saturday, July 03, 2004 6:32 AM To: PSN-L@.............. Subject: Emon7.2 Does anyone have a copy of Emon 7.2 with support for the Axiom AX-5210 A/D board that they could send me please. Thanks, Alby, Martin Observatory, Western Australia.

Sorry I do not…but I am sure = others will have….Your message gave me pause for thought.
Does anyone have a DOS version of Seismic? Alan no longer supports it = and did send me a

Copy snail mail about 9 years = ago….but I hesitate to bother him for a third time.

  I am setting up a 486 with DOS 6.11 the unbugged version, in order to use as a fast machine = for

My own Point EQ locator = program…the one I wrote in BASIC and compiled back in = 1992…Thanks

Bob = Shannon

Pinpoint

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Alby Judge
Sent: Saturday, July 03, = 2004 6:32 AM
To: = PSN-L@..............
Subject: = Emon7.2

 

Does anyone have a copy of = Emon 7.2 with support for the Axiom AX-5210 A/D board that they could send me = please.

Thanks,

Alby,

Martin Observatory, Western Australia.

Subject: RE: Emon7.2 From: "Steve Hammond" shammon1@............. Date: Sat, 3 Jul 2004 11:48:19 -0700 In a side note I sent EMON 7.0 that I had. I see it has EMON 6.2 opt file the supports the Axiom. Ted sent me a lot of his software to test. Caution. From time to time, there were a few bugs. Regards, Steve Hammond PSN San Jose. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Alby Judge Sent: Saturday, July 03, 2004 6:32 AM To: PSN-L@.............. Subject: Emon7.2 Does anyone have a copy of Emon 7.2 with support for the Axiom AX-5210 A/D board that they could send me please. Thanks, Alby, Martin Observatory, Western Australia.
In a=20 side note I sent EMON 7.0 that I had. I see it has EMON 6.2 opt file the = supports the Axiom. Ted sent me a lot of his software to test. Caution. = From=20 time to time, there were a few bugs.
Regards, Steve Hammond PSN San Jose.
-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Alby=20 Judge
Sent: Saturday, July 03, 2004 6:32 AM
To:=20 PSN-L@..............
Subject: Emon7.2

Does anyone have a copy of Emon 7.2 = with support=20 for the Axiom AX-5210 A/D board that they could send me = please.
Thanks,
Alby,
Martin Observatory, Western=20 Australia.
Subject: RE: Emon7.2 From: "Steve Hammond" shammon1@............. Date: Sat, 3 Jul 2004 11:48:19 -0700 In a side note I sent EMON 7.0 that I had. I see it has EMON 6.2 opt file the supports the Axiom. Ted sent me a lot of his software to test. Caution. From time to time, there were a few bugs. Regards, Steve Hammond PSN San Jose. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Alby Judge Sent: Saturday, July 03, 2004 6:32 AM To: PSN-L@.............. Subject: Emon7.2 Does anyone have a copy of Emon 7.2 with support for the Axiom AX-5210 A/D board that they could send me please. Thanks, Alby, Martin Observatory, Western Australia.
In a=20 side note I sent EMON 7.0 that I had. I see it has EMON 6.2 opt file the = supports the Axiom. Ted sent me a lot of his software to test. Caution. = From=20 time to time, there were a few bugs.
Regards, Steve Hammond PSN San Jose.
-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Alby=20 Judge
Sent: Saturday, July 03, 2004 6:32 AM
To:=20 PSN-L@..............
Subject: Emon7.2

Does anyone have a copy of Emon 7.2 = with support=20 for the Axiom AX-5210 A/D board that they could send me = please.
Thanks,
Alby,
Martin Observatory, Western=20 Australia.
Subject: RE: Emon7.2 From: "Steve Hammond" shammon1@............. Date: Sat, 3 Jul 2004 11:57:50 -0700 Hi Bob, in a side note I have sent you the Seismic II zip you requested. My version is from 1993... I tested it and it still works. Regards, Steve Hammond PSN San Jose, Aptos CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Bob Shannon Sent: Saturday, July 03, 2004 7:19 AM To: psn-l@.............. Subject: RE: Emon7.2 Sorry I do not.but I am sure others will have..Your message gave me pause for thought. Does anyone have a DOS version of Seismic? Alan no longer supports it and did send me a Copy snail mail about 9 years ago..but I hesitate to bother him for a third time. I am setting up a 486 with DOS 6.11 the unbugged version, in order to use as a fast machine for My own Point EQ locator program.the one I wrote in BASIC and compiled back in 1992.Thanks Bob Shannon Pinpoint -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Alby Judge Sent: Saturday, July 03, 2004 6:32 AM To: PSN-L@.............. Subject: Emon7.2 Does anyone have a copy of Emon 7.2 with support for the Axiom AX-5210 A/D board that they could send me please. Thanks, Alby, Martin Observatory, Western Australia.
Hi=20 Bob, in a side note I have sent you the Seismic II zip you requested. My = version=20 is from 1993... I tested it and it still works.
Regards, Steve Hammond
PSN=20 San Jose, Aptos CA
-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Bob=20 Shannon
Sent: Saturday, July 03, 2004 7:19 AM
To:=20 psn-l@..............
Subject: RE: = Emon7.2

Sorry I do = not…but I=20 am sure others will have….Your message gave me pause for = thought.
Does=20 anyone have a DOS version of Seismic? Alan no longer supports it and = did send=20 me a

Copy snail = mail about=20 9 years ago….but I hesitate to bother him for a third=20 time.

  I am setting up a 486 with = DOS 6.11=20 the unbugged version, in order to use as a = fast=20 machine for

My own = Point EQ=20 locator program…the one I wrote in BASIC and compiled back in=20 1992…Thanks

Bob=20 Shannon

Pinpoint

 

-----Original=20 Message-----
From:=20 psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Alby = Judge
Sent: Saturday, July 03, 2004 = 6:32=20 AM
To:=20 PSN-L@..............
Subject:=20 Emon7.2

 

Does anyone have a copy = of Emon=20 7.2 with support for the Axiom AX-5210 A/D board that they could send = me=20 please.

Thanks,

Alby,

Martin Observatory, = Western=20 = Australia.

Subject: RE: Emon7.2 From: "Bob Shannon" earth@........... Date: Sat, 3 Jul 2004 14:45:02 -0700 Danke Mucho! It was originally a fine program that developed into a great program. Alan is so humble about his work.and to anyone still using DOS.(r there such people?). it is pretty darn nice for an older machine. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Saturday, July 03, 2004 11:58 AM To: psn-l@.............. Subject: RE: Emon7.2 Hi Bob, in a side note I have sent you the Seismic II zip you requested. My version is from 1993... I tested it and it still works. Regards, Steve Hammond PSN San Jose, Aptos CA

Danke Mucho! It was originally a fine program that developed into = a great program. Alan is so humble about his work…and to anyone = still using DOS…(r there such people?)… it is = pretty darn nice for an older machine.

 

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond
Sent: = Saturday, July 03, = 2004 11:58 AM
To: = psn-l@..............
Subject: RE: = Emon7.2

 

Hi Bob, in a = side note I have sent you the Seismic II zip you requested. My version is from = 1993... I tested it and it still works.

Regards, Steve = Hammond

PSN = San Jose, Aptos CA<= /st1:State>

 

Subject: Network event reports From: Arie Verveer greensky@............ Date: Wed, 07 Jul 2004 20:43:05 +0800 Hi, It's been a while since I used the "Network Event Reports" function in Winquake, and it appears my old, "recent worldwide quake" (finger) address appears to be changed. Anyone, got a working address to current worldwide quakes ? Path: Winquake -> event report -> network Report. Cheers Arie __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Network event reports From: John or Jan Lahr johnjan@........ Date: Wed, 07 Jul 2004 10:27:25 -0600 Hi Arie, Finger is dying or dead due to recently enhanced security provisions made at the USGS. One alternative is: ftp://ghtftp.cr.usgs.gov/pub/cnss/quake Another, with a listing of events for the past two weeks is: ftp://ghtftp.cr.usgs.gov/pub/cnss/cnss_14.fing Hope this helps! John At 06:43 AM 7/7/2004, you wrote: >Hi, It's been a while since I used the "Network Event Reports" function in >Winquake, >and it appears my old, "recent worldwide quake" (finger) address appears >to be >changed. Anyone, got a working address to current worldwide quakes ? >Path: Winquake -> event report -> network Report. > >Cheers > >Arie > > > >__________________________________________________________ > >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: Network event reports From: "Larry Cochrane" lcochrane@.............. Date: Wed, 7 Jul 2004 23:44:05 -0700 Hi Arie, If you add the following (without the quotes) to the network.dat file you should get a list similar to the old finger report. "ftp://ghtftp.cr.usgs.gov/pub/cnss/cnss_14.fing (All NEIC Events)" This file is located in the WinQuake root directory. Regards, Larry Cochrane Redwood City, PSN ----- Original Message ----- From: "Arie Verveer" To: < " > Sent: Wednesday, July 07, 2004 5:43 AM Subject: Network event reports > Hi, It's been a while since I used the "Network Event Reports" function > in Winquake, > and it appears my old, "recent worldwide quake" (finger) address > appears to be > changed. Anyone, got a working address to current worldwide quakes ? > > Path: Winquake -> event report -> network Report. > > Cheers > > Arie > > > > __________________________________________________________ > > 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: What is your advice? From: "rem11560@............ rem11560@netzero.com Date: Sun, 11 Jul 2004 16:53:26 GMT Hi Larry, I know that I am a fuss pot, but I would like to submit the following advice to the PSN List. I need your input before I do. I practice what I preach, and I think the files that I now regularly submit are as good or better than most that I see. I am especially annoyed that hardly anyone takes the trouble to calibrate their sensors. Maybe there should be a discussion among list members and a concensus reached on what advice to amateurs would be best to prominently and permanently post on your web site. I also don't like overly large over-sampled files. I would think that you would rather not have to archive such files. Regards, Bob McClure Locust Valley, NY >Re: What is your advice? >Hi Bob, >I don't have a problem with you sending out your request to the PSN list. >-Larry ~~~~~~~~~~~~~ HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA LOGGER: 1. Be sure that your STATION COORDINATES are correct. You can use Microsoft Streets and Trips, or online MapQuest for the purpose. Also align horizontal sensors to true North or East, or else give true direction in sensor comments box. 2. LOCK your timing to GPS or WWV or a crystal clock slaved to WWVB. 3. CALIBRATE YOUR SENSOR. You would not have much use for a voltmeter with no scale on it, would you?. For open loop sensors, I have two methods. One uses the raw sensor output of pendulum movement between fixed stops, the other measures the force exerted by the pendulum in response to a known current. I can tell you more if you ask. 4. DO NOT submit files with high sample rates on distant teleseisms. High frequencies are attenuated with distance, and files with excessive sample rate only take up bandwidth and archival storage space. Decimate before submitting. One to five samples per second should handle most teleseisms without loss of waveform detail. Also, do not cover an overly large time span after the L wave onset. 5. DO NOT use any more FILTERING than absolutely necessary. Let some microseisms come through. Leave it to the downloader of files do more filtering if they wish. 6. If possible, adjust your sensor's NATURAL PERIOD to least 16 seconds if you record and report teleseisms. If that is not practical, I have written an application program for WinQuake files which can digitally extend the effective period of your sensor by up to a factor of five. I use it routinely on my sensors which have natural periods of 5, 8, and 14 seconds to extend their response to 24 seconds. 7. Control your sensor DAMPING. The barest amount of overshoot on a displaced pendulum is about right. 8. Use as little AMPLIFIER GAIN as possible to avoid clipping on major events. Most of the files I see on the seismicnet site have been recorded at far more gain than necessary. You may have to make component value changes in your amplifier to accomplish this. ~~~~~~~~~~~~~~~ ________________________________________________________________ The best thing to hit the Internet in years - NetZero HiSpeed! Surf the Web up to FIVE TIMES FASTER! Only $14.95/ month -visit www.netzero.com to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: What is your advice? From: "Steve Hammond" shammon1@............. Date: Sun, 11 Jul 2004 11:16:01 -0700 Boy, this could become an ugly discussion. I'm sure there is a few people that don't agree with your comments and parts of them will be taken very personally. For example, if you are talking about the AT1 and AT2 sensors in Aptos, I will be the first to tell you that they are crap and I'm very unhappy with their operation. I was forced to cut the booms down in size because I didn’t have the physical space needed for 38-in. booms, which is what I had used in the San Jose location. Additionally, I only have one spot in my small yard for the seismic box and the cover box will only align off the N/S axis, which limits the boom direction to be off the N/S axis. Let me put it this way, getting the existing hardware to a period of greater than 12-14 seconds will require divine intervention. My point is this; I don’t care if the person submitting the data provides it from a magnet daggling from a string, if they wish to contribute to the dataset, they can. This is the “Public Seismic Network” and all are welcome to take part, regardless of how crappy their equipment is. Instead of stating hard fast rules, I think we should describe desired results as goals. I would like to discuses the goal of sample rates. I believe the teleseimic sample rate goal should be 25 SPS. While Ed Cranswick of the USGS is not here to defend himself, I base this goal on a discussion I had with him in 1991. Ed said, and this is not an exact quote, “any data sampled below 25 samples per second is worthless for future study. Most researchers prefer to extrapolate the needed research data themselves. They would also prefer the data be unfiltered so that they can apply the needed filters. Data that has been highly processed is suspect because the processing algorithms are unknown and not documented and therefore the data may not represent the actual event.” Regards, Steve Hammond PSN San Jose -- Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of rem11560@........... Sent: Sunday, July 11, 2004 9:53 AM To: psn-l@.............. Subject: What is your advice? Hi Larry, I know that I am a fuss pot, but I would like to submit the following advice to the PSN List. I need your input before I do. I practice what I preach, and I think the files that I now regularly submit are as good or better than most that I see. I am especially annoyed that hardly anyone takes the trouble to calibrate their sensors. Maybe there should be a discussion among list members and a concensus reached on what advice to amateurs would be best to prominently and permanently post on your web site. I also don't like overly large over-sampled files. I would think that you would rather not have to archive such files. Regards, Bob McClure Locust Valley, NY >Re: What is your advice? >Hi Bob, >I don't have a problem with you sending out your request to the PSN list. >-Larry ~~~~~~~~~~~~~ HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA LOGGER: 1. Be sure that your STATION COORDINATES are correct. You can use Microsoft Streets and Trips, or online MapQuest for the purpose. Also align horizontal sensors to true North or East, or else give true direction in sensor comments box. 2. LOCK your timing to GPS or WWV or a crystal clock slaved to WWVB. 3. CALIBRATE YOUR SENSOR. You would not have much use for a voltmeter with no scale on it, would you?. For open loop sensors, I have two methods. One uses the raw sensor output of pendulum movement between fixed stops, the other measures the force exerted by the pendulum in response to a known current. I can tell you more if you ask. 4. DO NOT submit files with high sample rates on distant teleseisms. High frequencies are attenuated with distance, and files with excessive sample rate only take up bandwidth and archival storage space. Decimate before submitting. One to five samples per second should handle most teleseisms without loss of waveform detail. Also, do not cover an overly large time span after the L wave onset. 5. DO NOT use any more FILTERING than absolutely necessary. Let some microseisms come through. Leave it to the downloader of files do more filtering if they wish. 6. If possible, adjust your sensor's NATURAL PERIOD to least 16 seconds if you record and report teleseisms. If that is not practical, I have written an application program for WinQuake files which can digitally extend the effective period of your sensor by up to a factor of five. I use it routinely on my sensors which have natural periods of 5, 8, and 14 seconds to extend their response to 24 seconds. 7. Control your sensor DAMPING. The barest amount of overshoot on a displaced pendulum is about right. 8. Use as little AMPLIFIER GAIN as possible to avoid clipping on major events. Most of the files I see on the seismicnet site have been recorded at far more gain than necessary. You may have to make component value changes in your amplifier to accomplish this. ~~~~~~~~~~~~~~~ ________________________________________________________________ The best thing to hit the Internet in years - NetZero HiSpeed! Surf the Web up to FIVE TIMES FASTER! Only $14.95/ month -visit www.netzero.com to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: "What is your advice?" From: Douglas Gavilanes gavilan1@............. Date: Mon, 12 Jul 2004 12:29:39 -0700 psn-l-digest-request@.............. wrote: > *SNIP* > >Instead of stating hard fast rules, I think we should describe desired >results as goals. I would like to discuses the goal of sample rates. I >believe the teleseimic sample rate goal should be 25 SPS. While Ed Cranswick >of the USGS is not here to defend himself, I base this goal on a discussion >I had with him in 1991. Ed said, and this is not an exact quote, “any data >sampled below 25 samples per second is worthless for future study. Most >researchers prefer to extrapolate the needed research data themselves. They >would also prefer the data be unfiltered so that they can apply the needed >filters. Data that has been highly processed is suspect because the >processing algorithms are unknown and not documented and therefore the data >may not represent the actual event.” > >Regards, Steve Hammond PSN San Jose -- Aptos, CA > > What he said. ;-) Best Regards, Doug Gavilanes Garden Grove, CA. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: What is your advice? From: Jason Brady jr_brady@........... Date: Mon, 12 Jul 2004 13:22:31 -0700 All, I appreciate Bob's suggestions. Straightforward, succinct guidelines like this are invaluable for newcomers like me. If I understand correctly, he is striving for quality and uniformity of data. Ensuring that an instrument is calibrated and processing parameters correctly set/optimized is crucial to achieving that goal. On the other hand, it appears that amateur instruments and processing environments are unique--so how does one define and enforce a set of reasonable standards for data submission? I'm too new to even guess at this point. But perhaps Bob is on the right track with his suggestions. Regarding event data, what would really be helpful is a guidebook with examples to assist new people with understanding how to use their seismo equipment. Examples: how to recognize actual events vs. background noise and understand the intricacies of recording seismic events. Math and engineering aren't my strong suits (I've got precious few of them anyway) and need all the help I can get. Perhaps something like this already exists? Just my $.02. Thanks, Jason Brady __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: What is your advice? From: "Steve Hammond" shammon1@............. Date: Mon, 12 Jul 2004 15:45:49 -0700 Hi Jason (and others'), please don't misunderstand my comments. I'm a college professor and tend to make my concerns heard. This time I happened to make my comment heard during the middle off grading mid-terms when I took a little time to do my Email... I think the PSN should have guidelines for data. I just don't think they should be any specific requirements to submit data to Larry's site other than what Larry requires. Larry has rejected a few of my datasets recently when converting to his new serial data collection system using WinSDR because of data integrity issues. I didn't have the correct information in some of the required fields. I think that Larry acted correctly in doing so. My concern with the original suggestion was that we are an open group and all that wish to contribute should be allowed to do so. I think that every point that was made in the original note is a valid point and we should have a guideline for each point made. But, it should be in the form of goals and not rules / requirements for the data. This is armature seismology group and my first seismograph was built from a 3/8 brass rod with water filled toilet tank float for mass weight. The guys' from the USGS would ask me to keep the cover closed when there was a photographer around. However, that did not stop me from taking part or them from evaluating and reviewing my data. I think we should continue with the same tradition. I suggest we start working on the "Data Collection Goals" and that they be described in a FRQ. What do you think the SPS goal for a distant seismic event should be? I'm current running my AT1 and AT2 devices at 25 SPS based on Ed Cranswick suggestion. Do you feel this is too high or to low? Why? On item 3. CALIBRATE YOUR SENSOR, Bob, this sounds like you have put a lot of work into this. Could you send me the write-ups or are they posted some place? I would be happy to try your methods. I'm already certain the damping magnets on my LP's are not strong enough. I have them right up agents the brass bar and the WAWA test looks OK on one but the other is questionable. I have been using events to fine tune the settings in WinSDR for sensor correction values. A few event-mag values have been correct and a few have not. I'm about 50/50 right now. Regards, Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Jason Brady Sent: Monday, July 12, 2004 1:23 PM To: PSN-L@.............. Subject: What is your advice? All, I appreciate Bob's suggestions. Straightforward, succinct guidelines like this are invaluable for newcomers like me. If I understand correctly, he is striving for quality and uniformity of data. Ensuring that an instrument is calibrated and processing parameters correctly set/optimized is crucial to achieving that goal. On the other hand, it appears that amateur instruments and processing environments are unique--so how does one define and enforce a set of reasonable standards for data submission? I'm too new to even guess at this point. But perhaps Bob is on the right track with his suggestions. Regarding event data, what would really be helpful is a guidebook with examples to assist new people with understanding how to use their seismo equipment. Examples: how to recognize actual events vs. background noise and understand the intricacies of recording seismic events. Math and engineering aren't my strong suits (I've got precious few of them anyway) and need all the help I can get. Perhaps something like this already exists? Just my $.02. Thanks, Jason Brady __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: feasible maximum mass for a Lehman seismometer From: "tdick" dickthomas01@............. Date: Mon, 12 Jul 2004 20:09:38 -0500 At the risk of ruining a good discussion going on the last couple of = days -- I would like to have some input on what the best/maximum mass = for Lehman horizontal seismometer
At the risk of ruining a good = discussion going on=20 the last couple of days -- I would like to have some input on what the=20 best/maximum  mass for Lehman horizontal=20 seismometer
Subject: Dup messages From: "Kareem" kareem@............. Date: Mon, 12 Jul 2004 18:28:39 -0700 Hi PSN, Just to let you know... I've been receiving duplicate messages from the PSN list serv. Not sure why.. Is it me? Kareem __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: seismometer calibration From: BOB BARNS royb1@........... Date: Mon, 12 Jul 2004 21:37:46 -0400 Hi gang, There has been some recent discussion about calibrating seismometers. Several years ago, my article on a calibrator using a meter movement as a force transducer was put on our 'home' www.seismic.com. Go to "Build Your Own Seismographic Station" then to "Article by Bob Barns". Jack Ivey built one these and I asked him to describe his experience. His reply is below. It includes an interesting remark about differences in behavior between large and small motions. I have not seen this discussed before. We would benefit if others with experience with the calibrator were to report. Bob Barns =========== Bob, I used the calibrator extensively in determining the response of a couple of my Lehman derivatives. I found it very easy to set up and use and indispensable in determining the period and damping of the system, even if you aren't terribly interested in the absolute calibration of your seismometer. This is because the return force and damping of a practical Lehman system can be quite nonlinear, and if you adjust the period and damping by bumping the boom with your thumb and eyeballing it, the behavior is quite different than when you start measuring nanometer-scale movements (I found there was way less damping for small displacements than for large). The calibrator is one of the only practical ways I've seen to apply the tiny force needed. I also think the quakes people post would be considerably more interesting if they had an engineering units scale marked. I tried to use your arrangement to calibrate my force-feedback add-on to a 1-second vertical, however the force produced by the meter movement was too small to be useful. It would be nice to have an arrangement that produces 10x or 100x the force for that application (I sacrificed several types of meter in the attempt). You're welcome to use these comments as you wish, no need to credit me. Jack ============================== -----Original Message----- __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: feasible maximum mass for a Lehman seismometer From: "Connie and Jim Lehman" lehmancj@........... Date: Tue, 13 Jul 2004 10:12:39 -0400 T.Dick--thanks for your inquiry. I can only comment on the original = design and how we arrived at the mass. The first model had a boom of = 140 cm and a mass of 4kg or about 9 lbs.--empirical all the way. Those = early Jesuit "cantilever" systems used much heavier masses, as they were = friction linked to give a mechanical readout on smoked paper, but later = , a reflected beam of light on photographic paper reduced the need for = such a heavy mass. The mass is related to the natural period of swing somewhat--(even = though different masses of a bob on a free hanging pendulum makes little = difference in period). More important--the mass must be = supported...The support wire at the angle with horizontal suggested must = be strong. If you do the arithmetic, a 5 lb mass will tug a tension of = between 30 & 40 lbs on the upright hinge area when the angle is 30-40 = degrees. ((Now if you want a real puzzle. As that angle goes to zero, = the tension approaches infinity)) When we made the final design as published, a 5 lb mass was suggested = as 5 lb "bricks" of lead were available. We reduced the boom to fit = everything under a 1 meter box. The physical sensor worked so well with = set up procedure, stability and performance we haven't deviated from = those parameters. That is not saying other parameters won't work. With = care no doubt the physical size of the "Lehman" could be halved, but = instabilites no doubt would frustrate the user. On a bit of related technology. Several years ago we built a = portable Foucault pendulum on a 4-ft tripod, drove it magnetically from = below, and achieved 5% accuracy. We thought this was pretty neat, until = a gentleman from Michigan built a good working model about 12 inches = high. One never quite knows where the empirical approach in mechanical = devices take one!! Best Wishes--Jim Lehman ----- Original Message -----=20 From: tdick=20 To: psn-l@................. Sent: Monday, July 12, 2004 9:09 PM Subject: feasible maximum mass for a Lehman seismometer At the risk of ruining a good discussion going on the last couple of = days -- I would like to have some input on what the best/maximum mass = for Lehman horizontal seismometer
T.Dick--thanks for your inquiry.  = I can only=20 comment on the original design and how we arrived at the mass.  The = first=20 model had a boom of 140 cm and a mass of 4kg or about 9 lbs.--empirical = all the=20 way.  Those early Jesuit "cantilever" systems used much heavier = masses, as=20 they were friction linked to give a mechanical readout on smoked paper, = but=20 later , a reflected beam of light on photographic paper reduced the need = for=20 such a heavy mass.
    The mass is related = to the=20 natural period of swing somewhat--(even though different masses of a bob = on a=20 free hanging pendulum makes little  difference in period).  = More=20 important--the mass must be supported...The support wire at the angle = with=20 horizontal suggested must be strong.  If you do the arithmetic, a 5 = lb mass=20 will tug a tension of between 30 & 40 lbs  on the upright hinge = area=20 when the angle is 30-40 degrees.  ((Now if you want a real = puzzle.  As=20 that angle goes to zero, the tension approaches infinity))
   When we made the final = design as=20 published, a 5 lb mass was suggested as 5 lb "bricks" of lead were=20 available.  We reduced the boom to fit everything under a 1 meter=20 box.  The physical sensor worked so well with set up procedure, = stability=20 and performance we haven't deviated from those parameters.  That is = not=20 saying other parameters won't work.  With care no doubt the = physical size=20 of the "Lehman" could be halved, but instabilites no doubt would = frustrate the=20 user.
    On a bit of related=20 technology.  Several years ago we built a portable Foucault = pendulum on a=20 4-ft tripod, drove it magnetically from below, and achieved 5%=20 accuracy.  We thought this was pretty neat, until a gentleman from = Michigan=20 built a good working model  about 12 inches high.
   One never quite knows = where the=20 empirical approach in mechanical devices take one!!  Best = Wishes--Jim=20 Lehman
----- Original Message -----
From:=20 tdick
Sent: Monday, July 12, 2004 = 9:09 PM
Subject: feasible maximum mass = for a=20 Lehman seismometer

At the risk of ruining a good = discussion going on=20 the last couple of days -- I would like to have some input on what the = best/maximum  mass for Lehman horizontal=20 seismometer
Subject: Sensor calibration From: "rem11560@............ rem11560@netzero.com Date: Tue, 13 Jul 2004 19:33:44 GMT Hi all, Sensor calibration seems to be the topic du jour. Calibration is a tedious but recommended procedure for the serious amateur. I wrote the following note on my calibration method to the PSN List on 07/19/2003, a year ago. At this time, I am adding a dissertation on how to use current applied to the sensor coil and measurement of the resulting force exerted by the coil to achieve calibration. Be reminded of the fact that these calibration methods only determine the sentivity of the sensor for frequencies greater than the natural resonant frequency of the sensor. Sensor response falls very rapidly at frequencies less than the natural frequency. Bob McClure Locust Valley, NY Web page: http://www.jclahr.com/science/psn/mcclure/ ----------------------- APPLIED MOTION METHOD: ----------------------- 1. Set up limit stops on the pendulum so that it can be displaced over a known and fixed number of millimeters at its radius of gyration. 2. Connect the sensor directly to the A/D, and log data as you move the pendulum gently back-and forth a few times between the stops. Record at a rate that gives a reasonable number of samples for the time taken to move between stops. Do not move so fast that you exceed the voltage range of the A/D, otherwise you won't get valid data, and you might even blow out the A/D. Also, verify that the resistance of the sensor coil is low compared to the input impedance of the A/D. 3. Make a WinQuake event file out of the data. 4. Use WinQuake to integrate the data. You should see the actual displacement versus time, measured in counts. Measure the peak-to-peak displacement in counts, using the mouse readout when it is positioned on successive peaks. 5. Scale the count measurement to what you would have obtained for one centimeter of motion. If you used 5mm of displacement, for example, you would multiply your count estimate by two. 6. Multiply the scaled counts by the voltage gain setting of the amplifier you normally use. 7. Take the inverse of the number obtained in step 6. This is the number you should enter for "Sensitivity:" in the Sensor Information Dialog box. ------------ ------------------------ APPLIED CURRENT METHOD: ------------------------ Recall the following from your physics textbook: Generator Law: Volts= B*L*(dx/dt), where B= magnetic field in Teslas, L= total length of wire in meters cutting flux lines, (dx/dt)= velocity of coil motion in meters per second. Motor Law: Force=B*L*I where F= force in newtons, B in Teslas, L in meters. Combining the two laws, we obtain V/(dx/dt) = F/I so, if we measure F/I we know V/(dx/dt), the sensor output in volt-seconds per meter. We don't need to know anything about magnetic field strength or coil configuration. One newton is the force required to accelerate one kilogram mass at one meter per second. In grams, it is 1000/9.8 = 102.04. Suppose we apply a current of 5 milliamperes to the coil and measure a force of 40 grams. I=.005 amperes, F= 40/102.04= .392, F/I= 78.4 volt-seconds per meter. ~~~~~~~~~~~~~ The equation is simple, but execution of the measurement is not. If you use a countertop digital scale, you have to figure out how to transmit the force from the sensor to the scale. This ususually would require rigging up levers and pushrods. I did this measurement, but using only the component parts -- the magnet and the coil. My coil is a flat pancake, positioned in a 4-pole Nd magnet assembly. What I did was to place the magnet on edge on the scale, and make up a rig to hold the coil in place from the counter top. I then measured the apparent change in the weight of the magnet as current was applied in either direction to the coil. If you use a heavy magnet, you will probably have to secure the coil to the scale, and the magnet to the counter top. Estimate coil current by dividing the applied DC voltage by the coil resistance in ohms. If you have a sensitive spring scale, that's great. You can probably use it on an assembled sensor. Just be sure that you pull the boom back to its normal rest position when the scale is being pulled upon by the current being applied to the coil. Measure how far from the boom pivot you took the force reading, and estimate the radius of gyration of the pendulum. By whatever means you measure force, you will have to figure out what the force actually would be at the radiu of gyration, which is not usually at the center of the coil. You will have to make lever arm corrections to convert the measured force at the point of measurement to the force at the radius of gyration, which in most cases is very near the center of the extra mass added to the boom. After you have made the F/I measurement, make the lever arm correction to find the equivalent value at the center of gyration. Divide this F/I by 100 to get volt-seconds per centimeter, and multiply that result by your amplifier's voltage gain. Next, divide your A/D's full scale volts by the full scale digital word value. Usually, you will be dividing 10 by 32,768, yielding 0.000305176 volts per bit. Divide the result by the amplified F/I to get the number to be entered for sensitivity in WinQuake. You also have the option of letting WinQuake do the calculations for you. Just enter the sensor output (volt-seconds per centimeter) in the "Output Voltage:" box, the amplifier voltage gain in the "Amp Gain:" box, the A/D full scale voltage in the "A/D Voltage:" box, and the A/D bit number in the "A/D Bits:" box, and then click on the "Calc Sens" box. (Note to Dataq users: Always enter 16 for A/D bits, even though the actual number is less. Dataq always scales 10 volts to digital value 32,768, regardless of the number of active bits in the device.) ~~~~~~~~~~~~~~~~~~~~~~ Afterthoughts: If you use shunt resistance across the coil to provide damping, you may have to reduce your measured sensor output calibration value. The reduction factor is (Rshunt/(Rshunt + Rcoil). The value of Rshunt must also include the contribution of the amplifier input impedance: 1/Rshunt = 1/Rexternal + 1/Ramplifier. I recommend the use of shunt damping whenever possible because it permits easy measurement of natural period (with the shunt removed) and precise control of the degree of damping (amount of shunt conductance applied). It is easiest to use if your sensor has high output combined with low pendulum mass and low coil resistance. The conventional massive Lehman design may not have such properties, however. My own horizontal sensors are at the other extreme. They have a coil resistance of only 340 ohms, a pendulum mass of around 70 grams, and an output of 0.8 volt-sec/cm. Critical damping requires only 30K of shunt resistance. My amplifier input impedance is 100K, and so I add another 90K across that to get proper damping. My vertical sensor is more like a Lehman, with much more mass and much more coil resistance. Even so, I use shunt damping on it, at the loss of some sensitivity. If you are building a sensor, consider the use of multiple magnets. If you place a horseshoe magnet on one side of the coil, place another with poles reversed on the opposite side. You will get twice the output, and much better linearity. My own preference is a 4-pole magnet assembly using powerful Nd block magnets, a narrow gap, and a pancake coil. ________________________________________________________________ The best thing to hit the Internet in years - NetZero HiSpeed! Surf the Web up to FIVE TIMES FASTER! Only $14.95/ month -visit www.netzero.com to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: feasible maximum mass for a Lehman seismometer From: "tdick" dickthomas01@............. Date: Tue, 13 Jul 2004 16:27:43 -0500 I have two running now and am preparing to make changes. I used = speaker magnets plus a five lb piece of lead on the boom which is over = 30 inches long and 5/8 thick. I am thinking of imbedding a ball bearing = in the end of the shaft, adding another 5 lbs of lead and putting the = coil of wire on the boom instead of on the base, making the magnet = stationary.
 
I have two = running now=20 and am preparing to make changes. I used speaker magnets plus a five = lb piece=20 of lead on the boom which is over 30 inches long and 5/8 thick. I am = thinking=20 of imbedding a ball bearing in the end of the shaft, adding another 5 = lbs of=20 lead and putting the coil of wire on the boom instead of on the base, = making=20 the magnet stationary.
Subject: infrasounds From: "jse" jse@............ Date: Sat, 17 Jul 2004 12:12:32 +0430 Hi all, I am thinking to build a easy seismometre. Is possible to detect infrasouns in the atmosphera with this seismometre? which seismometre would be the adequate for this objective? Best Regards =20
Hi all,
 
I am thinking to build a easy = seismometre.
Is=20 possible to  detect infrasouns in the atmosphera
with this=20 seismometre?
which seismometre would be the adequate for this=20 objective?
 
Best Regards

 
Subject: Re: infrasounds From: Arie Verveer greensky@............ Date: Sun, 18 Jul 2004 11:17:44 +0800 Well sort off. I have detected Infra-sound from major fireball reentry's but these are major regional events. The infra-sound impinges on the ground and your seismograph detects the vibration. This vibration is in the upper portion of the seismic spectra , say 0.5 hertz and above. By the way, sound is refracted in the atmosphere just like seismic waves are refracted in the earth. Also, infra-sound will refract up in the atmosphere and eventually refract back to to the earth then reflect off the earth surface, and so on. The wave pattern becomes very complex very quickly. So any possible detection within a few hundred kilometers will soon just look like the seismic background. Infra-sound from meteors can radiate down and cause the infra-sound to seismic signature. To detect infrasound you really need a specific detector. Actually, I just have started the third generation of this type of detector. When It's working I'll drop an email to this site with construction details. Arie jse wrote: > Hi all, > > I am thinking to build a easy seismometre. > Is possible to detect infrasouns in the atmosphera > with this seismometre? > which seismometre would be the adequate for this objective? > > Best Regards > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: FW: Re: what is your advice? From: "Meredith Lamb" meredithlamb@............. Date: Tue, 20 Jul 2004 23:16:13 -0600 The following msg is being forwarded and was reply written by Chris Chapman: Hi All, A few more comments on seismometers.... HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA LOGGER: 1. Be sure that your STATION CO-ORDINATES are correct. You can use Microsoft Streets and Trips, or online MapQuest for the purpose. Also align horizontal sensors to true North or East, or else give true direction in sensor comments box. OK on the alignment and reporting. Full details would often be most helpful. As far as I can see, the Lat/Long search option has now been removed from Mapquest. The Microsoft Streets and Trips CD only gives information for the USA and parts of Canada. Has anyone got a reference for a world wide map programme which you can use with Lat + Long? 2. LOCK your timing to GPS or WWV or a crystal clock slaved to WWVB. Fine, but it would be helpful if Larry included a programme which DECODED the WWVB minute long signals directly and could also update the clock at user defined intervals. WWVB modules are available. The receive limit is set by local radio interference / noise, but can be expected to be >2,000 miles at night. Keep the receiver well away (10 ft +) from a CRT display. The effective signal coverage is shown at http://www.boulder.nist.gov/timefreq/stations/wwvbcoverage.htm 3. CALIBRATE YOUR SENSOR. You would not have much use for a voltmeter with no scale on it, would you? For open loop sensors, I have two methods. One uses the raw sensor output of pendulum movement between fixed stops, the other measures the force exerted by the pendulum in response to a known current. I can tell you more if you ask. Remembering that seismometers are used which measure displacement, or velocity or acceleration, so we need several calibration methods. Remember also that the signal which you actually see can depend quite strongly on the local sub surface geological structures. If you are sitting on a thick layer of water saturated alluvial soil, it can shake much like a jelly. If your seismometer is calibrated in say volts / metre / sec, you may see some variation in signal with the reception angle and there may be large errors in the calculated amplitude / distance measurement. An alternative method is to measure the recorded amplitude of a series of 'known' quakes and then make up a rough correlation table. 4. DO NOT submit files with high sample rates on distant teleseisms. High frequencies are attenuated with distance, and files with excessive sample rate only take up bandwidth and archival storage space. Decimate before submitting. One to five samples per second should handle most teleseisms without loss of waveform detail. Also, do not cover an overly large time span after the L wave onset. You will have difficulty in separating out the P and S waves if your system cannot reproduce 0.5 to 1 Hz quite accurately. I would suggest that 10 sps is a more reasonable compromise. Local quakes also have P & S components of higher frequency. Some locations have relatively high damping down to below about 1/2 Hz. If you also have high environmental noise, you may have difficulty in resolving quake arrival times. 5. DO NOT use any more FILTERING than absolutely necessary. Let some microseisms come through. Leave it to the downloader of files do more filtering if they wish. Sure, but it is helpful if you can at least recognise the outline of the earthquake signal. I don't find a seismic signal which completely masked in either high frequency environmental or in instrument noise, very helpful. 6. If possible, adjust your sensor's NATURAL PERIOD to least 16 seconds if you record and report teleseisms. If that is not practical, I have written an application program for WinQuake files which can digitally extend the effective period of your sensor by up to a factor of five. I use it routinely on my sensors which have natural periods of 5, 8, and 14 seconds to extend their response to 24 seconds. This does depend on what sort of seismometer you use and on it's natural period. Local environmental noise may become serious by 10 Hz. The Ocean background will give quite large signals somewhere between 2 and 10 seconds, which need to be filtered out. Twin Tee rejection filters have been used successfully and can give over 50 dB peak rejection. The frequency and the amplitude may change with time. Using beam type seismometers, it is desirable to have the period between 20 and 30 seconds. A 10 second to 30 second range allows good detection of L & R waves. Simple damped pendulum seismometers with a 1.4 sec period are popular in Europe and pickup P & S waves quite nicely. 7. Control your sensor DAMPING. The barest amount of overshoot on a displaced pendulum is about right. I agree, but this is the ONE FACTOR in seismometer construction which is likely to give MOST PROBLEMS. I found it DIFFICULT to set up an oil damped system to about 0.8 x critical. I found it NEAR IMPOSSIBLE to keep it that way without oil temperature control, or frequent measurement / re-setup. Oil is messy, attracts dust, creeps over all surfaces, drowns insects (which then give 'bug quakes') and the viscosity is strongly temperature dependant. The surface tension also varies, which can give beam drift. For oil systems, you need to measure the damping for very small displacements - use your SDR recording programme to monitor and display this. If you pull the mass 1/2" to one side and then release it, you may observe a significantly higher damping due to swirl in the oil and the system may still be under-damped for normal seismic signals. I honestly don't know why anyone would try to use oil damping these days. EM damping using NdFeB magnets is simple, cheap, clean, easy to set up and to adjust. For a Lehman, the damping required is also strongly dependant on the period you choose and hence on the suspension adjustment. You need a fair range of damping adjustment available. There are two ways of providing electromagnetic damping. You can either use a flat Al or Cu plate in a pole gap with a strong magnetic field, or you can use a coil of wire half in the field and put a loading resistor across it. After having set up the period, you choose a load resistor (by experiment) which gives near critical damping. This was done with the cylindrical coils and magnets in the Sprengnether seismometers. However, the sensitivity then depends on the value of the damping resistor, which complicates matters. I prefer to keep the damping and sensor coil functions separate. With two N+S pairs of opposing flat magnets 1" x 1/2" x 1/4" on 1/4" baseplates, you just move the high central field over a 1/16" to 1/8" thick Al or copper tongue till you get the desired damping. Electro magnetic damping is far easier to adjust than oil damping and with the ready availability of strong NdFeB magnets, it is cheap and simple to implement. Suppliers are Sedona2 on Ebay, Amazing Magnets (occasional E-Bay), "Emovendo" on ebay only (perhaps the cheapest N48 supplier), K&J magnetics ( wide range) www.kjmagnetics.com and www.wondermagnet.com 8. Use as little AMPLIFIER GAIN as possible to avoid clipping on major events. Most of the files I see on the seismicnet site have been recorded at far more gain than necessary. You may have to make component value changes in your amplifier to accomplish this. Agreed, but the practical choice is likely to depend on the local environmental noise and on the Ocean background. You want to be able to resolve the background signals at times of "low noise", but you don't want strong quakes to saturate the sensor. Most amateurs do not have the option of siting their seismometer in quiet rural area. If you use 'period extending' software, you will need more amplification to cope with the lower amplitude of the longer period waves. You are likely to get uncertain readings if you are amplifying noise. 16 bit A/D converters, with three bits of converter noise, are not too helpful in this respect. Perhaps we could agree on a rough amplitude for the ocean background signals? The gain you can use also depends on the noise and resolution in your A/D Converter. A/D Converter boards with +/-1/2 LSB resolved internal noise are available. >> Subject: feasible maximum mass for a Lehman seismometer At the risk of ruining a good discussion going on the last couple of days -- I would like to have some input on what the best / maximum mass for Lehman horizontal seismometer. The best mass is the lowest which gives you clear low noise signals. This advice 'begs the question'. The 'kt' thermal excitation noise sets the minimum seismic mass at about an ounce, so you are better with 1/2 lb, minimum. If you use a solid metal beam, as opposed to a tube or a U channel, the moment of inertia of the beam can actually reduce the 'radius of gyration k' of the combined beam + seismic mass, giving a shorter period than you would get from the seismic mass at the end of a weightless arm. The beam needs to be light but rigid (aim for a tube weight less end fittings 1/4 the weight of the seismic mass or less). I have found the light 1/2" nominal welded stainless steel water pipe to be very satisfactory. The thermal expansion coefficient matches that of a piano wire suspension quite well. It is also cheap and you can buy brass compression fittings on which to mount the suspension, the seismic mass and the damping components. This makes the construction quite easy. This said, the period of a simple pendulum is independent of the mass. It is advisable to keep the boom length between 70 cm and 100 cm. This is because you are using the garden gate type of suspension and shorter lengths require you to set up the side to side level position with rapidly increasing precision. This can make a 12" beam not only exceptionally difficult to adjust, but very sensitive to tilt drift, either from the suspension system or from natural earth movements. Using a 30/60/90 degree triangle suspension is fine. Try to keep the boom / wire angle above 20 deg, or the suspension loading will be large. You can buy nickel coated 8 thou steel wire from a music shop, for stringing mandolins. To clamp wire, I drill a 1/16" hole just under the head of a bolt. Then I 'dish' a couple of washers by putting them on a wood block and hitting the centre hole with a large centre punch + hammer. You put the two washers on the bolt with the outer cup edges touching and feed the wire between these edges and through the hole in the bolt. This gives a good 'edge clamp' on the wire. For adjustment screws, I use stainless steel nuts and bolts bought from a marine / boat-builder supplier. I drill out the threaded end of the bolt with a centre drill and stick a stainless ball bearing in the conical hole. I drill a plain hole in the baseplate and stick a nut onto the lower side with methacrylate or epoxy cement. It is essential that the bolt and the nut are made of the same material, or the adjustment will drift with change in temperature. I usually use a second nut + a spring washer on the lower side of the mounting nut to provide tensioning / alignment in the thread. I stick stainless steel mounting plates onto the concrete floor, either with the special concrete 'pool adhesive' or with epoxy. If you use epoxy, it is a good idea to dry out the top of the cement thoroughly with a warm air blower. Lastly: >> Hi gang, There has been some recent discussion about calibrating seismometers. Several years ago, my article on a calibrator using a meter movement as a force transducer was put on our 'home' www.seismic.com. Go to "Build Your Own Seismographic Station" then to "Article by Bob Barns". ?? Can anyone help me find this article, please? www seismic.com seems like a huge website with lots of advertising, but only a very old article on seismology. 'Earth Science' seems to be just advertising vitamins... If you want a force calibration system with much higher forces than a meter movement, you can use a small NdFeB cube magnet with a Maxwell coil. These look similar to a Helmholtz coil, but with double the winding spacing and the windings connected in opposition. This gives a constant field gradient. You can calibrate it using a pendulum of a known length and mass, by measuring the deflection / coil current. Regards, Chris Chapman
 
The following msg is being forwarded and was reply written by Chris Chapman:
 
Hi All,
 
    A few more comments on seismometers....
 
HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA LOGGER:
1. Be sure that your STATION CO-ORDINATES are correct. You can use Microsoft Streets and Trips, or online MapQuest for the purpose. Also align horizontal sensors to true North or East, or else give true direction in sensor comments box.
    OK on the alignment and reporting. Full details would often be most helpful.
 
     As far as I can see, the Lat/Long search option has now been removed from Mapquest. 
 
    The Microsoft Streets and Trips CD only gives information for the USA and parts of Canada.
 
    Has anyone got a reference for a world wide map programme which you can use with Lat + Long?
2. LOCK your timing to GPS or WWV or a crystal clock slaved to WWVB.
    Fine, but it would be helpful if Larry included a programme which DECODED the WWVB minute long signals directly and could also update the clock at user defined intervals. WWVB modules are available. The receive limit is set by local radio interference / noise, but can be expected to be >2,000 miles at night. Keep the receiver well away (10 ft +) from a CRT display. The effective signal coverage is shown at http://www.boulder.nist.gov/timefreq/stations/wwvbcoverage.htm  
3. CALIBRATE YOUR SENSOR. You would not have much use for a voltmeter with no scale on it, would you? For open loop sensors, I have two methods. One uses the raw sensor output of pendulum movement between fixed stops, the other measures the force exerted by the pendulum in response to a known current. I can tell you more if you ask.
    Remembering that seismometers are used which measure displacement, or velocity or acceleration, so we need several calibration methods.
    Remember also that the signal which you actually see can depend quite strongly on the local sub surface geological structures. If you are sitting on a thick layer of water saturated alluvial soil, it can shake much like a jelly. If your seismometer is calibrated in say volts / metre / sec, you may see some variation in signal with the reception angle and there may be large errors in the calculated amplitude / distance measurement. An alternative method is to measure the recorded amplitude of a series of 'known' quakes and then make up a rough correlation table. 
4. DO NOT submit files with high sample rates on distant teleseisms. High frequencies are attenuated with distance, and files with excessive sample rate only take up bandwidth and archival storage space. Decimate before submitting. One to five samples per second should handle most teleseisms without loss of waveform detail. Also, do not cover an overly large time span after the L wave onset.
      You will have difficulty in separating out the P and S waves if your system cannot reproduce 0.5 to 1 Hz quite accurately.
    I would suggest that 10 sps is a more reasonable compromise. Local quakes also have P & S components of higher frequency.
    Some locations have relatively high damping down to below about 1/2 Hz. If you also have high environmental noise, you may have difficulty in resolving quake arrival times.
    
5. DO NOT use any more FILTERING than absolutely necessary. Let some microseisms come through. Leave it to the downloader of files do more filtering if they wish.
    Sure, but it is helpful if you can at least recognise the outline of the earthquake signal. I don't find a seismic signal which completely masked in either high frequency environmental or in instrument noise, very helpful.
6. If possible, adjust your sensor's NATURAL PERIOD to least 16 seconds if you record and report teleseisms. If that is not practical, I have written an application program for WinQuake files which can digitally extend the effective period of your sensor by up to a factor of five. I use it routinely on my sensors which have natural periods of 5, 8, and 14 seconds to extend their response to 24 seconds.
   This does depend on what sort of seismometer you use and on it's natural period. Local environmental noise may become serious by 10 Hz. The Ocean background will give quite large signals somewhere between 2 and 10 seconds, which need to be filtered out. Twin Tee rejection filters have been used successfully and can give over 50 dB peak rejection. The frequency and the amplitude may change with time.
    Using beam type seismometers, it is desirable to have the period between 20 and 30 seconds. A 10 second to 30 second range allows good detection of L & R waves. 
    Simple damped pendulum seismometers with a 1.4 sec period are popular in Europe and pickup P & S waves quite nicely.
7. Control your sensor DAMPING. The barest amount of overshoot on a displaced pendulum is about right.
    I agree, but this is the ONE FACTOR in seismometer construction which is likely to give MOST PROBLEMS. I found it DIFFICULT to set up an oil damped system to about 0.8 x critical. I found it NEAR IMPOSSIBLE to keep it that way without oil temperature control, or frequent measurement / re-setup. Oil is messy, attracts dust, creeps over all surfaces, drowns insects (which then give 'bug quakes') and the viscosity is strongly temperature dependant. The surface tension also varies, which can give beam drift.
    For oil systems, you need to measure the damping for very small displacements - use your SDR recording programme to monitor and display this. If you pull the mass 1/2" to one side and then release it, you may observe a significantly higher damping due to swirl in the oil and the system may still be under-damped for normal seismic signals.
    I honestly don't know why anyone would try to use oil damping these days. EM damping using NdFeB magnets is simple, cheap, clean, easy to set up and to adjust.
    For a Lehman, the damping required is also strongly dependant on the period you choose and hence on the suspension adjustment. You need a fair range of damping adjustment available.
    There are two ways of providing electromagnetic damping. You can either use a flat Al or Cu plate in a pole gap with a strong magnetic field, or you can use a coil of wire half in the field and put a loading resistor across it. After having set up the period, you choose a load resistor (by experiment) which gives near critical damping. This was done with the cylindrical coils and magnets in the Sprengnether seismometers. However, the sensitivity then depends on the value of the damping resistor, which complicates matters.
    I prefer to keep the damping and sensor coil functions separate. With two N+S pairs of opposing flat magnets 1" x 1/2" x 1/4" on 1/4" baseplates, you just move the high central field over a 1/16" to 1/8" thick Al or copper tongue till you get the desired damping.
    Electro magnetic damping is far easier to adjust than oil damping and with the ready availability of strong NdFeB magnets, it is cheap and simple to implement. Suppliers are Sedona2 on Ebay, Amazing Magnets (occasional E-Bay), "Emovendo" on ebay only (perhaps the cheapest N48 supplier), K&J magnetics ( wide range) www.kjmagnetics.com  and www.wondermagnet.com
 
8. Use as little AMPLIFIER GAIN as possible to avoid clipping on major events. Most of the files I see on the seismicnet site have been recorded at far more gain than necessary. You may have to make component value changes in your amplifier to accomplish this.
 
     Agreed, but the practical choice is likely to depend on the local environmental noise and on the Ocean background. You want to be able to resolve the background signals at times of "low noise", but you don't want strong quakes to saturate the sensor. Most amateurs do not have the option of siting their seismometer in quiet rural area.
    If you use 'period extending' software, you will need more amplification to cope with the lower amplitude of the longer period waves. You are likely to get uncertain readings if you are amplifying noise. 16 bit A/D converters, with three bits of converter noise, are not too helpful in this respect.
    Perhaps we could agree on a rough amplitude for the ocean background signals?
    The gain you can use also depends on the noise and resolution in your A/D Converter. A/D Converter boards with +/-1/2 LSB resolved internal noise are available.
 
>>    Subject: feasible maximum mass for a Lehman seismometer
    At the risk of ruining a good discussion going on the last couple of days -- I would like to have some input on what the best / maximum mass for Lehman horizontal seismometer.

     The best mass is the lowest which gives you clear low noise signals. This advice 'begs the question'.
    The 'kt' thermal excitation noise sets the minimum seismic mass at about an ounce, so you are better with 1/2 lb, minimum. 
    If you use a solid metal beam, as opposed to a tube or a U channel, the moment of inertia of the beam can actually reduce the 'radius of gyration k' of the combined beam + seismic mass, giving a shorter period than you would get from the seismic mass at the end of a weightless arm. The beam needs to be light but rigid (aim for a tube weight less end fittings 1/4 the weight of the seismic mass or less). I have found the light 1/2" nominal welded stainless steel water pipe to be very satisfactory. The thermal expansion coefficient matches that of a piano wire suspension quite well. It is also cheap and you can buy brass compression fittings on which to mount the suspension, the seismic mass and the damping components. This makes the construction quite easy.
    This said, the period of a simple pendulum is independent of the mass.
    It is advisable to keep the boom length between 70 cm and 100 cm. This is because you are using the garden gate type of suspension and shorter lengths require you to set up the side to side level position with rapidly increasing precision. This can make a 12" beam not only exceptionally difficult to adjust, but very sensitive to tilt drift, either from the suspension system or from natural earth movements.  
     Using a 30/60/90 degree triangle suspension is fine. Try to keep the boom / wire angle above 20 deg, or the suspension loading will be large. You can buy nickel coated 8 thou steel wire from a music shop, for stringing mandolins. To clamp wire, I drill a 1/16" hole just under the head of a bolt. Then I 'dish' a couple of washers by putting them on a wood block and hitting the centre hole with a large centre punch + hammer. You put the two washers on the bolt with the outer cup edges touching and feed the wire between these edges and through the hole in the bolt. This gives a good 'edge clamp' on the wire.
    For adjustment screws, I use stainless steel nuts and bolts bought from a marine / boat-builder supplier. I drill out the threaded end of the bolt with a centre drill and stick a stainless ball bearing in the conical hole. I drill a plain hole in the baseplate and stick a nut onto the lower side with methacrylate or epoxy cement. It is essential that the bolt and the nut are made of the same material, or the adjustment will drift with change in temperature. I usually use a second nut + a spring washer on the lower side of the mounting nut to provide tensioning / alignment in the thread. I stick stainless steel mounting plates onto the concrete floor, either with the special concrete 'pool adhesive' or with epoxy. If you use epoxy, it is a good idea to dry out the top of the cement thoroughly with a warm air blower.
 
Lastly:
>> Hi gang,
  There has been some recent discussion about calibrating seismometers.    Several years ago, my article on a calibrator using a meter movement as a force transducer was put on our 'home'  www.seismic.com.  Go to "Build Your Own Seismographic Station" then to "Article by Bob Barns".
 
    ?? Can anyone help me find this article, please? www seismic.com seems like a huge website with lots of advertising, but only a very old article on seismology. 'Earth Science' seems to be just advertising vitamins...
 
    If you want a force calibration system with much higher forces than a meter movement, you can use a small NdFeB cube magnet with a Maxwell coil. These look similar to a Helmholtz coil, but with double the winding spacing and the windings connected in opposition. This gives a constant field gradient. You can calibrate it using a pendulum of a known length and mass, by measuring the deflection / coil current.
 
    Regards,
 
    Chris Chapman
Subject: Re: Re: what is your advice? From: "Larry Conklin" lconklin@............ Date: Wed, 21 Jul 2004 11:05:21 -0400 I think we all should petition Chris to write a book on seismometer = construction. I have learned more from reading his postings than just = about any other source. Larry Conklin lconklin@............ ----- Original Message -----=20 From: Meredith Lamb=20 To: psn-l=20 Sent: Wednesday, July 21, 2004 1:16 AM Subject: FW: Re: what is your advice? The following msg is being forwarded and was reply written by Chris = Chapman: Hi All,=20 A few more comments on seismometers.... HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA LOGGER: 1. Be sure that your STATION CO-ORDINATES are correct. You can use = Microsoft Streets and Trips, or online MapQuest for the purpose. Also = align horizontal sensors to true North or East, or else give true = direction in sensor comments box. OK on the alignment and reporting. Full details would often be = most helpful. As far as I can see, the Lat/Long search option has now been = removed from Mapquest.=20 The Microsoft Streets and Trips CD only gives information for = the USA and parts of Canada.=20 Has anyone got a reference for a world wide map programme which = you can use with Lat + Long? 2. LOCK your timing to GPS or WWV or a crystal clock slaved to = WWVB. Fine, but it would be helpful if Larry included a programme = which DECODED the WWVB minute long signals directly and could also = update the clock at user defined intervals. WWVB modules are available. = The receive limit is set by local radio interference / noise, but can be = expected to be >2,000 miles at night. Keep the receiver well away (10 ft = +) from a CRT display. The effective signal coverage is shown at = http://www.boulder.nist.gov/timefreq/stations/wwvbcoverage.htm =20 3. CALIBRATE YOUR SENSOR. You would not have much use for a = voltmeter with no scale on it, would you? For open loop sensors, I have = two methods. One uses the raw sensor output of pendulum movement between = fixed stops, the other measures the force exerted by the pendulum in = response to a known current. I can tell you more if you ask. Remembering that seismometers are used which measure = displacement, or velocity or acceleration, so we need several = calibration methods.=20 Remember also that the signal which you actually see can depend = quite strongly on the local sub surface geological structures. If you = are sitting on a thick layer of water saturated alluvial soil, it can = shake much like a jelly. If your seismometer is calibrated in say volts = / metre / sec, you may see some variation in signal with the reception = angle and there may be large errors in the calculated amplitude / = distance measurement. An alternative method is to measure the recorded = amplitude of a series of 'known' quakes and then make up a rough = correlation table.=20 4. DO NOT submit files with high sample rates on distant = teleseisms. High frequencies are attenuated with distance, and files = with excessive sample rate only take up bandwidth and archival storage = space. Decimate before submitting. One to five samples per second should = handle most teleseisms without loss of waveform detail. Also, do not = cover an overly large time span after the L wave onset. You will have difficulty in separating out the P and S waves = if your system cannot reproduce 0.5 to 1 Hz quite accurately.=20 I would suggest that 10 sps is a more reasonable compromise. = Local quakes also have P & S components of higher frequency. Some locations have relatively high damping down to below about = 1/2 Hz. If you also have high environmental noise, you may have = difficulty in resolving quake arrival times. =20 5. DO NOT use any more FILTERING than absolutely necessary. Let = some microseisms come through. Leave it to the downloader of files do = more filtering if they wish. Sure, but it is helpful if you can at least recognise the = outline of the earthquake signal. I don't find a seismic signal which = completely masked in either high frequency environmental or in = instrument noise, very helpful. 6. If possible, adjust your sensor's NATURAL PERIOD to least 16 = seconds if you record and report teleseisms. If that is not practical, I = have written an application program for WinQuake files which can = digitally extend the effective period of your sensor by up to a factor = of five. I use it routinely on my sensors which have natural periods of = 5, 8, and 14 seconds to extend their response to 24 seconds. This does depend on what sort of seismometer you use and on it's = natural period. Local environmental noise may become serious by 10 Hz. = The Ocean background will give quite large signals somewhere between 2 = and 10 seconds, which need to be filtered out. Twin Tee rejection = filters have been used successfully and can give over 50 dB peak = rejection. The frequency and the amplitude may change with time. Using beam type seismometers, it is desirable to have the period = between 20 and 30 seconds. A 10 second to 30 second range allows good = detection of L & R waves.=20 Simple damped pendulum seismometers with a 1.4 sec period are = popular in Europe and pickup P & S waves quite nicely. 7. Control your sensor DAMPING. The barest amount of overshoot on = a displaced pendulum is about right. I agree, but this is the ONE FACTOR in seismometer construction = which is likely to give MOST PROBLEMS. I found it DIFFICULT to set up an = oil damped system to about 0.8 x critical. I found it NEAR IMPOSSIBLE to = keep it that way without oil temperature control, or frequent = measurement / re-setup. Oil is messy, attracts dust, creeps over all = surfaces, drowns insects (which then give 'bug quakes') and the = viscosity is strongly temperature dependant. The surface tension also = varies, which can give beam drift.=20 For oil systems, you need to measure the damping for very small = displacements - use your SDR recording programme to monitor and display = this. If you pull the mass 1/2" to one side and then release it, you may = observe a significantly higher damping due to swirl in the oil and the = system may still be under-damped for normal seismic signals.=20 I honestly don't know why anyone would try to use oil damping = these days. EM damping using NdFeB magnets is simple, cheap, clean, easy = to set up and to adjust. For a Lehman, the damping required is also strongly dependant on = the period you choose and hence on the suspension adjustment. You need a = fair range of damping adjustment available. There are two ways of providing electromagnetic damping. You can = either use a flat Al or Cu plate in a pole gap with a strong magnetic = field, or you can use a coil of wire half in the field and put a loading = resistor across it. After having set up the period, you choose a load = resistor (by experiment) which gives near critical damping. This was = done with the cylindrical coils and magnets in the Sprengnether = seismometers. However, the sensitivity then depends on the value of the = damping resistor, which complicates matters.=20 I prefer to keep the damping and sensor coil functions separate. = With two N+S pairs of opposing flat magnets 1" x 1/2" x 1/4" on 1/4" = baseplates, you just move the high central field over a 1/16" to 1/8" = thick Al or copper tongue till you get the desired damping. Electro magnetic damping is far easier to adjust than oil = damping and with the ready availability of strong NdFeB magnets, it is = cheap and simple to implement. Suppliers are Sedona2 on Ebay, Amazing = Magnets (occasional E-Bay), "Emovendo" on ebay only (perhaps the = cheapest N48 supplier), K&J magnetics ( wide range) www.kjmagnetics.com = and www.wondermagnet.com 8. Use as little AMPLIFIER GAIN as possible to avoid clipping on = major events. Most of the files I see on the seismicnet site have been = recorded at far more gain than necessary. You may have to make component = value changes in your amplifier to accomplish this. Agreed, but the practical choice is likely to depend on the = local environmental noise and on the Ocean background. You want to be = able to resolve the background signals at times of "low noise", but you = don't want strong quakes to saturate the sensor. Most amateurs do not = have the option of siting their seismometer in quiet rural area. If you use 'period extending' software, you will need more = amplification to cope with the lower amplitude of the longer period = waves. You are likely to get uncertain readings if you are amplifying = noise. 16 bit A/D converters, with three bits of converter noise, are = not too helpful in this respect. Perhaps we could agree on a rough amplitude for the ocean = background signals?=20 The gain you can use also depends on the noise and resolution in = your A/D Converter. A/D Converter boards with +/-1/2 LSB resolved = internal noise are available. >> Subject: feasible maximum mass for a Lehman seismometer At the risk of ruining a good discussion going on the last = couple of days -- I would like to have some input on what the best / = maximum mass for Lehman horizontal seismometer. The best mass is the lowest which gives you clear low noise = signals. This advice 'begs the question'. The 'kt' thermal excitation noise sets the minimum seismic mass = at about an ounce, so you are better with 1/2 lb, minimum.=20 If you use a solid metal beam, as opposed to a tube or a U = channel, the moment of inertia of the beam can actually reduce the = 'radius of gyration k' of the combined beam + seismic mass, giving a = shorter period than you would get from the seismic mass at the end of a = weightless arm. The beam needs to be light but rigid (aim for a tube = weight less end fittings 1/4 the weight of the seismic mass or less). I = have found the light 1/2" nominal welded stainless steel water pipe to = be very satisfactory. The thermal expansion coefficient matches that of = a piano wire suspension quite well. It is also cheap and you can buy = brass compression fittings on which to mount the suspension, the seismic = mass and the damping components. This makes the construction quite easy. This said, the period of a simple pendulum is independent of the = mass.=20 It is advisable to keep the boom length between 70 cm and 100 = cm. This is because you are using the garden gate type of suspension and = shorter lengths require you to set up the side to side level position = with rapidly increasing precision. This can make a 12" beam not only = exceptionally difficult to adjust, but very sensitive to tilt drift, = either from the suspension system or from natural earth movements. =20 Using a 30/60/90 degree triangle suspension is fine. Try to = keep the boom / wire angle above 20 deg, or the suspension loading will = be large. You can buy nickel coated 8 thou steel wire from a music shop, = for stringing mandolins. To clamp wire, I drill a 1/16" hole just under = the head of a bolt. Then I 'dish' a couple of washers by putting them on = a wood block and hitting the centre hole with a large centre punch + = hammer. You put the two washers on the bolt with the outer cup edges = touching and feed the wire between these edges and through the hole in = the bolt. This gives a good 'edge clamp' on the wire. For adjustment screws, I use stainless steel nuts and bolts = bought from a marine / boat-builder supplier. I drill out the threaded = end of the bolt with a centre drill and stick a stainless ball bearing = in the conical hole. I drill a plain hole in the baseplate and stick a = nut onto the lower side with methacrylate or epoxy cement. It is = essential that the bolt and the nut are made of the same material, or = the adjustment will drift with change in temperature. I usually use a = second nut + a spring washer on the lower side of the mounting nut to = provide tensioning / alignment in the thread. I stick stainless steel = mounting plates onto the concrete floor, either with the special = concrete 'pool adhesive' or with epoxy. If you use epoxy, it is a good = idea to dry out the top of the cement thoroughly with a warm air blower. Lastly: >> Hi gang, There has been some recent discussion about calibrating = seismometers. Several years ago, my article on a calibrator using a = meter movement as a force transducer was put on our 'home' = www.seismic.com. Go to "Build Your Own Seismographic Station" then to = "Article by Bob Barns". ?? Can anyone help me find this article, please? www seismic.com = seems like a huge website with lots of advertising, but only a very old = article on seismology. 'Earth Science' seems to be just advertising = vitamins...=20 If you want a force calibration system with much higher forces = than a meter movement, you can use a small NdFeB cube magnet with a = Maxwell coil. These look similar to a Helmholtz coil, but with double = the winding spacing and the windings connected in opposition. This gives = a constant field gradient. You can calibrate it using a pendulum of a = known length and mass, by measuring the deflection / coil current. Regards, Chris Chapman
I think we all should petition Chris to write a book on seismometer = construction.  I have learned more from reading his postings than = just=20 about any other source.
 
Larry Conklin
 
 
----- Original Message -----
From:=20 Meredith Lamb
To: psn-l
Sent: Wednesday, July 21, 2004 = 1:16=20 AM
Subject: FW: Re: what is your=20 advice?

 
The following msg is being forwarded and was reply = written=20 by Chris Chapman:
 
Hi=20 All,
 
    A few more comments on = seismometers....
 
HELPFUL HINTS FROM A FUSSY ELDERLY SEISMIC DATA = LOGGER:
1. Be sure that your STATION CO-ORDINATES are correct. You = can use=20 Microsoft Streets and Trips, or online MapQuest for the purpose. = Also=20 align horizontal sensors to true North or East, or else give true=20 direction in sensor comments box.
    OK on the alignment and reporting. Full = details=20 would often be most helpful.
 
     As far as I can see, the Lat/Long = search=20 option has now been removed from = Mapquest. 
 
    The Microsoft Streets and Trips CD only = gives=20 information for the USA and parts of Canada.
 
   &