PSN-L Email List Message

Subject: Re: Amplifier noise?
From: Mark Robinson other@...............
Date: Sun, 24 Dec 2000 10:55:04 +1300

Hi Mark,

without referring to the specifics of Larry's amplifier or A-D I would
suggest a small rearrangement of your earthing arrangement.

In general it is good practise to keep all the sheilding and casework
bonded together and kept insulated from the electronics at all but one
point. This keeps all the metalwork electrically safe, reduces the
possibility of any of it acting as an antenna, and stops any voltage
gradient (read earth loop) present bewteen the computer and the
amplifier or sensor from adding to the signal as an error. The main
system earth is usually a low impedance balanced point in the middle of
the power supply.



Mark Andrews wrote:
> Hello Everyone,
> Recently I finished construction on my first seismometer.  I used
> schematics off of Larry Cochrane's web site to wire wrap the amplifier:
> and
> I housed the amplifier in a steel box, grounded to analog ground on the
> amplifier board.
> I have the output of the amplifier connected to Larry's 16 bit A to D board
> with about 16 feet of shielded wire.  The shield, around the wire, is
> grounded to the case of my computer.  When viewing the output with SDR I am
> getting about 80 to 100 counts of continuous noise.  I don't know what the
> frequency of the noise is but the period is too short to see on SDR.
> Is this noise level abnormally high and does anyone have any suggestions on
> how to reduce the noise.
> Thanks for your time!
> Mark
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