PSN-L Email List Message

Subject: Re: Vertical Sensor
From: "tchannel" tchannel@..............
Date: Sun, 10 Dec 2006 18:51:39 -0700


Chris,  Thanks, these are great sites, and just what I needed.  Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Sunday, December 10, 2006 6:03 PM
  Subject: Re: Vertical Sensor


  In a message dated 2006/12/10, tchannel@.............. writes:


    I am thinking I would like to build a vertical sensor.  I have read =
that the AS1 has a period of 1.5 seconds, but is extended =
electronically.

    Q 1  Is there a program which does this? Maybe an article which =
explains it.


  Hi Ted,

         In thinking that, remember that vertical seismometers are more =
difficult to build and to set up than horizontal ones. Having access to =
a small metal turning lathe and a drilling / milling machine are very =
helpful. Quite a lot of 'practical machanics' are involved and also =
various sources of constructional materials.=20

         Some drawings for the AS-1 are on John Lahr's website. See =
http://jclahr.com/science/psn/as1/index.html=20

         An electromagnetic damper to replace the messy oil damper is =
described at =
http://jclahr.com/science/psn/chapman/as1%20damping/index.html
        =20
         The period can be extended with the Robert' circuit or an =
adaption of it. See http://jclahr.com/science/psn/roberts/index.html=20

         You can get stable periods out to about 4.5 secs with steel =
springs, but any further extension needs springs wound with / made of =
Ni-SpanC alloy to control the stiffness / temperature variations. A =
'fairly happy' compromise might be to set up the seismometer with a =
steel spring for ~3 secs period and to then extend this to 30 secs, =
electronically or in software. If you do it in software, you really need =
a 16 bit ADC, since your dynamic range is reduced by maybe x100. Plan to =
cover the periods around 20 secs fairly typical of Rayleigh waves.


    Q 2  I have articles on the AS1 which shows its basic design. Is =
there an article showing "how to" build your own Vertical?
    My basic questions would be over all dimensions, and locating the =
proper spring.


         There is a drawing of a similar device built by Dewayne Hill =
See http://jclahr.com/science/psn/hill/index.html

  and a prototype of a rather better construction at =
http://quake.eas.gatech.edu/Instruments/LPVERT0.htm

      It might be possible to build one like this inside a glass vessel =
or a tubular enclosure. Allan Coleman used an Al damper casing from a =
scrap yard. A serious problem with vertical sensors is that they are =
sensitive to air density changes / wind noise. These noise levels can be =
100 times that of a horizontal seismometer.

      Also have a look at the EAS vertical and the drawings in the EAS =
Manual at http://www.eaiinfo.com/EAI2004/Index.htm This uses the ready =
made 60 deg agate bearings produced for chemical balances. However, =
there is no reason why you should not use a crossed rod Carbide =
suspension, or the dual foil one of the LPVERTO. The LP construction =
would enable you to add an air flotation chamber on the opposite side of =
the arm to the mass to greatly reduce atmospheric noise. Something like =
a miniature Al drinks can, drilled, emptied, rinsed out and then =
resealed? =20

      Have a look at the STM-8 designed by Sean Morrissey at =
http://www.eas.slu.edu/People/STMorrissey/index.html and read his notes =
at http://psn.quake.net/info/stm-mail.zip
  Keith has a working seisometer of this type with photos at =
http://www.bryantlabs.net/seismo.html =20


    Q 3  On a different subject.  I am in Idaho and sure would like to =
find someone in Idaho to share .PSN files and notes with. When I record =
an event I would love to compare my signal with other local stations.  =
Please if you are in the area or know of a station, near Boise, let me =
know.


         Look up all registered American stations? See links on the =
World Map at http://www.sydneystormcity.com/map.htm There is Don Sieber =
in Boise and Jan Marshall in Nampa, both close to you. There is also an =
associated contact and equipment list. There are also several =
educational groups operating across the USA.

         Since P waves travel at maybe 8 km  / sec you might also =
consider anyone 100 to 300 km distant?

         Can you set up a website with photos of your seismometer / =
alternatively send photos to John Lahr to display?

         Regards,








Chris,  Thanks, these are great = sites, and=20 just what I needed.  Ted
----- Original Message -----
From:=20 ChrisAtUpw@.......
To: psn-l@..............
Sent: Sunday, December 10, 2006 = 6:03=20 PM
Subject: Re: Vertical = Sensor

In a=20 message dated 2006/12/10, tchannel@..............=20 writes:

I am thinking I would like to build a vertical = sensor.  I=20 have read that the AS1 has a period of 1.5 seconds, but is extended=20 electronically.

Q 1  Is there a program which does this? = Maybe=20 an article which explains it.

Hi=20 Ted,

       In thinking that, = remember=20 that vertical seismometers are more difficult to build and to set up = than=20 horizontal ones. Having access to a small metal turning lathe and a = drilling /=20 milling machine are very helpful. Quite a lot of 'practical machanics' = are=20 involved and also various sources of constructional materials.=20

       Some drawings for the = AS-1 are on=20 John Lahr's website. See http://jclahr.com/science/psn/as1/index.html=20

       An electromagnetic damper = to=20 replace the messy oil damper is described at=20 = http://jclahr.com/science/psn/chapman/as1%20damping/index.html
 &= nbsp;    =20
       The period can be extended = with the=20 Robert' circuit or an adaption of it. See=20 http://jclahr.com/science/psn/roberts/index.html=20

       You can get stable = periods out to=20 about 4.5 secs with steel springs, but any further extension needs = springs=20 wound with / made of Ni-SpanC alloy to control the stiffness / = temperature=20 variations. A 'fairly happy' compromise might be to set up the = seismometer=20 with a steel spring for ~3 secs period and to then extend this to 30 = secs,=20 electronically or in software. If you do it in software, you really = need a 16=20 bit ADC, since your dynamic range is reduced by maybe x100. Plan to = cover the=20 periods around 20 secs fairly typical of Rayleigh waves.

Q 2  I have articles on the AS1 which shows its = basic=20 design. Is there an article showing "how to" build your own = Vertical?
My=20 basic questions would be over all dimensions, and locating the = proper=20 spring.

       There = is a=20 drawing of a similar device built by Dewayne Hill See=20 http://jclahr.com/science/psn/hill/index.html

and a prototype = of a=20 rather better construction at=20 = http://quake.eas.gatech.edu/Instruments/LPVERT0.htm

  &n= bsp;=20 It might be possible to build one like this inside a glass vessel or a = tubular=20 enclosure. Allan Coleman used an Al damper casing from a scrap yard. A = serious=20 problem with vertical sensors is that they are sensitive to air = density=20 changes / wind noise. These noise levels can be 100 times that of a = horizontal=20 seismometer.

    Also have a look at the EAS = vertical=20 and the drawings in the EAS Manual at = http://www.eaiinfo.com/EAI2004/Index.htm=20 This uses the ready made 60 deg agate bearings produced for chemical = balances.=20 However, there is no reason why you should not use a crossed rod = Carbide=20 suspension, or the dual foil one of the LPVERTO. The LP construction = would=20 enable you to add an air flotation chamber on the opposite side of the = arm to=20 the mass to greatly reduce atmospheric noise. Something like a = miniature Al=20 drinks can, drilled, emptied, rinsed out and then resealed? =20

    Have a look at the STM-8 designed by Sean = Morrissey=20 at http://www.eas.slu.edu/People/STMorrissey/index.html and read his = notes at=20 http://psn.quake.net/info/stm-mail.zip
Keith has a working = seisometer of=20 this type with photos at http://www.bryantlabs.net/seismo.html  =

Q 3  On a different subject.  I am in Idaho = and sure=20 would like to find someone in Idaho to share .PSN files and notes = with. When=20 I record an event I would love to compare my signal with other local = stations.  Please if you are in the area or know of a station, = near=20 Boise, let me = know.

      =20 Look up all registered American stations? See links on the World Map = at=20 http://www.sydneystormcity.com/map.htm There is Don Sieber in Boise = and Jan=20 Marshall in Nampa, both close to you. There is also an associated = contact and=20 equipment list. There are also several educational groups operating = across the=20 USA.

       Since P waves travel = at maybe=20 8 km  / sec you might also consider anyone 100 to 300 km=20 distant?

       Can you set up a = website=20 with photos of your seismometer / alternatively send photos to John = Lahr to=20 display?

      =20 Regards,

       Chris = Chapman
=20

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