PSN-L Email List Message

Subject: Re: C-Spring Sensor - 5/6 Second Period
From: Geoffrey gmvoeth@...........
Date: Thu, 20 Jan 2011 00:37:50 +0000

Me Thinks, the seismometer graph
to be wrong for the electrical velocity characteristics
which will show at the output terminals.

Me thinks, the that given the very same
amplitude but increasing frequency that the
voltage should be increasing like N=1
above resonance since voltage and
velocity are related.

Me thinks, You will end up with a dead spot at resonance using
this seismometer response to design your circuit.
not really a dead spot but you will see
a reduction at the noise level there
instead of being steady across resonance.
It is my opinion (I don’t really have to say that)
you would like to see a steady noise level at all frequencies.
if possible.

Or so, me thinks.


-----Original Message----- 
From: Kay Wyatt
Sent: Wednesday, January 19, 2011 7:10 PM
To: psnlist@..............
Subject: Re: C-Spring Sensor - 5/6 Second Period

Hi Chris,
Thanks for sending information on imnproving the C-Spring Sensor.  Just a quick correction on the link to Robert's circuit for 
extending the period of geophones.  Leave out the "epics" part of your link.

How would you compare the C-Spring sensor to an AS-1 type vertical seismometer modified with either a "piano wire hinge" or a razer 
blade hinge clamped at both ends?


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

From: Christopher Chapman
To: psnlist@..............
Sent: Wednesday, January 19, 2011 7:31 AM
Subject: Re: C-Spring Sensor - 5/6 Second Period

Subject: C-Spring Sensor - 5/6 Second Period

Has anyone tried this one? A vertical with a 5 to 6 second period using two hacksaw blades. Would like to hear opinions as to 
whether this is a worth-while build.

Hi Richard,

    This is an old design. Never use oil damping. It is non linear both with period and with amplitude. It is hideously temperature 
sensitive and it is not easy to adjust..

    There is a design for a magnetic damper for a vertical seismometer at Mount the 1/16" thick copper damping blade on the arm and put the quad 
damping magnet block on the base. You can use soft Aluminum sheet for the blade - if you can buy it - NOT hard or alloy sheet - but 
copper is better, since it is not significantly diamagnetic.

    Buy fully hardened hacksaw blades.The ordinary ones have a hardened edge, but with a softer blade. Grind off both the teeth and 
the wavy bends on the base, otherwise you get cracks developing quite rapidly when the blade is stressed.

     DON'T mount a magnet on a seismometer arm. It picks up noise from the Earth's magnetic  field, current surges in the house 
wiring, the movement of large vehicles, etc. Mount the pickup coil on the arm and use a shielded quad NdFeB magnet block, or use an 
optical position detector.

    The response can easily be extended to over 20 seconds using Robert's circuit for extending the period of geophones. You can get 
a x10 period extension before running into sensor / amplifier noise, but it does mean that you have to build your own specialised 
amplifier - not too difficult to do using stripboard? See

    Do look through the articles on the jclahr website.


    Chris Chapman


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