PSN-L Email List Message

Subject: Re: Homade Geophone
From: "Charles R. Patton" charles.r.patton@........
Date: Thu, 04 Aug 2005 17:06:36 -0700

This has two problems.
1) Geometrically the difficulty is to have an output for any direction 
movement.   It would be easier to have two coils set for orthogonal 
output then do the vectorial addition in the PC (which would take two 
A/D channels also) . The PC could also give direction at the same time. 
   It can be done with analog multipliers also if you're a bit of a 
2) Having the magnet on the boom makes you very subject to variable 
magnetic fields all around, so then it becomes were you measuring a 
magnetic field variation or an earth movement.

So I would suggest you set up your Foucault pendulum with two orthogonal 
coils standing up, and put the single magnet pole on the floor pointing 
directly into the bottom of the bob.  

Charles Patton

Geoff wrote:

> Has Anyone ever made a horizontal Geophone
> using the pendulum idea with the magnet
> attached to as the weight of a pendulum
> and the coil fixed to the earth and
> free to move in all horizontal directions ?
> I would be interested in knowing what you
> used to dampen the mass and what overall
> gain you needed on the amplifier.
> The idea here is to get first time of arrival
> only and not worry about direction of ground motion.
> gmvoeth
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