PSN-L Email List Message

Subject: Re: Seismograph noise problem
From: Roger Sparks rsparks@..........
Date: Sat, 09 Feb 2008 22:20:31 -0800

Hi Larry,

Sorry that you are having the noise problem after adjusting your

I had a similar problem for a while that was caused by poor contact to
the solid surface.  In my case, I was going through a rug to a concrete
surface.  For a while, one leg did not properly contact the hard
surface.  The microsiems caused a rocking that displayed as noise.

I did not know I had a problem until an FFT of the noisy signal showed a
higher frequency spectra that was not present in the older traces.  The
fix was simply to beef up my penetrations through the rug.

Are you using a three leg mount?  Are the contacts to the hard surface
made with points?  Do you have a locking nut or other mechanism to fix
the adjusting screws after adjustment?  Do you have any loose parts that
could "rock" due to the microsiems?  Do you "set" your seismometer after
adjustment by putting extra pressure to help reset the contact points?

Good luck on the repairs,


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> Subject: Seismograph noise problem
> From:    Larry Conklin 
> 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
> lconklin@............


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