PSN-L Email List Message

Subject: Re: Orientation of magnet with Lehman setup?
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sat, 3 Feb 2007 15:53:08 -0500

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

From: "Michael Kimzey" 
Sent: Thursday, February 01, 2007 10:59 PM
Subject: Orientation of magnet with Lehman setup?

MIKE  --I read your note with interest.  Seeing traces of "little feet"
above means your system is working.  A long period horizontal system setup
in a home is often fraught with undesired traces due to normal activities of
people, appliances turning off & on, wind in and around the house blowing
trees or bushes within a few feet of the sensor, changes of temperature at
the sensor area--insects/spiders doing their thing walking the boom or using
it as an anchor.  That shouldn't discourage one from running a system in a
remote ground level --home location .
   You mention your design has the coil on the boom, and magnet on the
ground.  That is quite ok I guess, but I have never understood the advantage
over the coil on the ground--with the coil on the ground, the boom is free
is any attachments.....Maybe I am missing something---
   Of course the ideal location is an institutional building of some size,
at ground level in a small room/closet.  The coil of course responds to 60
hz residual radiation around, and 40-50 hz mechanical noise from a nearby
mechanical HVAC room must be filtered out by a passive or active filter..
That is about as quiet as you can get short of a outdoor "bunker".
    The trick is to minimize external noise wherever you are--  Chris
suggests checking the alignment of your damping with the boom axis--offset
could provide an unnecessary torque.  I assume your damping ratio is ok--you
could change it a bit  to see if that helps  lessen the mechanical noise .
If your system is recording events as it should--regional and worldwide, you
will learn to live with the noise---no doubt the little feet above are happy
    Best wishes,   Jim Lehman >
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