PSN-L Email List Message

Subject: Re: "EPICS" seismo suggestion
From: "Charles R. Patton" charles.r.patton@........
Date: Mon, 16 Sep 2002 21:51:37 -0700

Aa a sensor solution for the SG seimo, it was proposed to use "=85a $1.83=

A3515LUA sensor=85"

So this brings up this thought:  Most standard IC frames are magnetic -
consisting of a Kovar frame.  And magnetic sensors in particular are
often constructed with "magnetic concentrators" to focus magnetic flux
on to the sensitive area of the chip.  Both make the chip physically
attracted to ambient fields.  If the chip is not mounted on the SG arm,
then the magnets must be, which would be even worse about ambient
sensitivity.  So if one goes for the higher sensitivity of the SG,
doesn't this create problems in terms of an actual physical sensitivity
to the surrounding changing magnetic fields?  I'm thinking back to some
experiments that Roger Baker did on magnetometers in which his
magnetometer is actually a magnet on a torsion balance.  He said he
could detect a small magnet many feet away and I know he could sense
geomagnetic changes.  It would seem to me that would turn the SG seismo
into a geomagnetic field detector.    Roger's detectors were based on
photodetectors and LED or Laser LED sources.

I think I'd vote for the original SG variable capacitance detector. =

Today you can buy ICs which do all the detection.  For one source see
"Universal Capacitive ReadoutTM IC (MS3110)" at:
I don't know how much it costs, but in volume this can't be that
expensive.  I also know there is at least a couple of European companies
that makes a similar IC. =

Just some idle musings.

Charles R. Patton

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