PSN-L Email List Message

Subject: Seismograph noise problem
From: Larry Conklin lconklin@............
Date: Sat, 09 Feb 2008 11:24:17 -0500

Hi all,

I think I must have a haunted system.  I have been running a SG 
seismometer for about seven years.  The mechanical design is very 
similar to the one described on the PSN web site, and I am Using Larry's 
electronics board.  Over nearly the entire time I have been running this 
system I have had repeated episodes of extreme noise or some sort of 
spurious signal.  When It occurs, the problem persists with little 
change for anywhere from a few days to several months, and then seems to 
fade away over the course of several days.  The problem reoccurred a 
couple of weeks ago.  It was apparently precipitated by the disturbance 
I caused by adjusting the leveling screw to recenter the pendulum 
(something I do frequently, with no problem).  Before making the 
adjustment, I was getting about +/- 30 counts of signal excursion from 
the low frequency channel.  Immediately after, I got around +/- 350 
counts, rendering the system essentially worthless.

I have put a lot of effort into trying to figure out what is going on, 
to no avail.  In one of the previous episodes, I disconnected the power 
to the oscillator that drives the antenna plate, and opened the loop for 
the feedback damping.  There was no significant change in the output, 
which led me at the time to conclude that there must either be something 
wrong with the electronics board,
or some sort of electrical/magnetic pick-up.  Despite a lot of diddling 
around, I couldn't determine a cause, and eventually, the system settled 
down without my having done anything specific to fixing it.  And, 
neither theory fits well with this current episode, which started when I 
mechanically disurbed the sensor a little by adjusting the leveling.

So, do I have a poltergeist detector when I thought I had a seismometer? 
  I threw together a web page that shows the onset of the problem, as 
well as short time intervals  before and after the problem started this 
time.  If anyone cares to take a look at it and offer their thoughts (or 
condolences), I'd like to hear them.

Larry Conklin
Liverpool, NY

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