I understand this design to be sensitive to tilt as well as vertical displacement
but it seems to me if you can build two identical versions
in a differential input design they may be able to cancel
tilt motion while displaying only vertical motions.
Above resonance Hz that is.
not sure tho, never played with it b4.


geoff

-----Original Message----- 
From: Christopher Chapman
Sent: Wednesday, January 19, 2011 3:31 PM
To: psnlist@..............
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.

http://www.fairpoint.net/~sparksite/CSpring%20Printer.html

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 
www.jclahr.com/science/psn/chapman/as1%20damping/index.html 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 www.jclahr.com/science/psn/epics/roberts/index.html

    Do look through the articles on the jclahr website.

    Regards,

    Chris Chapman



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