PSN-L Email List Message

Subject: Orientation of magnet with Lehman setup?
From: "Michael Kimzey" mckimzey@...........
Date: Thu, 01 Feb 2007 22:59:19 -0500

I have continued to modify my initial Lehman prototype.  I had been getting 
noise so I tried several things... 1) boom now made of aluminum, lead and 
stainless steel.  No iron present.  2) Magnet on ground and coil on boom.  
3) Aluminum dampening.

     These seem to have removed some noise but some still remained, 
especially when little feet were jumping above the crawl space.  Looking at 
a design by Chris Chapman, he oriented the poles of the magnet up and down, 
as opposed to sideways.  I was wondering: is the up-down orientation better, 
as any up-down motion of the ground (probably noise) would _not_ induce a 
current because movement of the coil would then be parallel to the field 
lines, while side-to-side movement (in the axis of the pendulum) would still 
be perpendicular to the field lines and induce a current.  Any thoughts?

A second question - some have reported that the SG has some limitation 
because of electronics.  With some other seismometer designs using 
capacitance displacement (Allan Coleman's designs, volksmeter), has anyone 
thought about changing the design of the SG to using capacitance 
displacement, or would that be unfeasible?

- Mike


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