PSN-L Email List Message

Subject: Re: (No subject header)
From: "Geoff" gmvoeth@...........
Date: Fri, 12 Aug 2005 20:46:25 -0700

> I am in the process of setting up a station. I have a set of Larry's geophones
> and his amplifier/ filter boards along with his A/D board. I am trying to decide
> the best place to place my  sensors. I live in northwest TN almost on top of the
> New Madrid Fault. I want to set the geophones  up first then I may experiment
> with some other sensors ( I am also collecting parts to build a S-G sensor ). I
> have a couple of choices from the reading  I have done.  I have several questions
> about trying to decide which would be the "best"  place to mount them. 

From My experience it is best to have a Geophone underground
even 18 inches is better then none but it has to be
away from power lines and possibly 15 feet away from any structures
You must ground insulate and bond everything and make the Geophone
water proof it is humidity and moisture that will be
your worst enemy it will corrode the Geophone.
Guard any exposed cables from sunlight and being a tripping hazard.
If you were really professional you need to know
how far to bedrock underground and make sure there  are no
roads within the same distance as depth to the bedrock....I don't
understand why distance to bedrock is so important
but I understand bedrock is more resistant to noise sources
if you can get your geophones there.
I have also found it good to use a shielded cable and run
the cable shield to your power supply ground through a
small 0.1uf 250V non-electrolytic capacitor.
You might also want to use the cap trick to 120V 60Hz ground.
I mean ground here and not the neutral wire you got to be
careful when playing around with 60Hz noise sources if there
is more than 1ma of current leakage it can be a killer
it only takes 20uA through the heart to stop it.
Be careful with those 60Hz noise sources but they can be
canceled out if you are careful.

Good luck and tell us what you decided on.
Placing the geophone is quite important.



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