PSN-L Email List Message

Subject: Re: Mass deflection weight test
From: "Geoff" gmvoeth@...........
Date: Thu, 1 Nov 2007 23:03:18 -0700

Hello Cruel World;

My geophone here at GVA is buried underground
so I can do no direct testing. It seems that Chris's
Capacitor test may very well one of the best.
But i would not use any resistors I would simply
short it across the geophone as it sits attached
to the amplifier, let the circuit do whatever so
you can see its normal response to the stimulus.

Here I am plagued by static electricity so I would
be careful there. You might damage the amplifier
or geophone insulation if you present somehow
100,000V static charge instead of only the
1 or so volts desired depending upon the value
of the capacitor.

I used to work in FAT on DEC ( Digital Equipment Corp now owned by HP )
Digital Data comm boards (1980s  :-(  ) and would see field service people get returns
that had a dendrite of chips fail due to static discharges
like lightning.
Not just the input chip but fanning out several chips deep.

I see these computers with big plexiglass holes in the
sides. It seems to me any kind of EMP like lightning
can get in there and do some damage. You really
need a faraday shield to protect anything today.


----- Original Message ----- 
From: "Mark Robinson" 
Sent: Thursday, November 01, 2007 5:34 PM
Subject: Re: Mass deflection weight test

> ChrisAtUpw@....... wrote:
>> In a message dated 01/11/2007, johnjan@........ writes:
>>     There are two issues involved.  One is the absolute deflection due to
>>     adding a weight and the other is the electronic response, once some
>>     motion sensor has been applied.
>> I find it easier to cut a measured length of Copper wire and bend it 
>> so that it gives a three point contact - a small U loop and a larger U 
>> loop at right angles to it. You can look up the weight either in wire 
>> tables or by the diameter for that gauge and the density of Copper.
> Pharmacists usually have a good accurate scale and will weigh things for me if 
> I provide them with some conversation which goes beyond their daily fare of 
> pills and potions.
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