John Tacinelli wrote:
>  My problem is that at 8:45 PM every night I get a sudden increase (or decrease) in voltage through my amplifier that causes 
the trace to move off to the right hand side of the screen.  It stays there until 5:45 every morning.  Then it goes right back.
  The seismograph itself doesnt seem to move.  I have run it on an uninterruptible power supply and it still does it.  I watche
d it happen tonight and I could detect no environmental change in the area of the seismograph.
> The seismograph is set up at the school where I teach.  Maintenance thought it might be the outside lights turning on but tha
t happens much earlier.  That timing happens to coincide with the setting and rising of the sun (pretty close) but I can't thin
k of anything solar that could affect a magnetic coil inside a building in a time span of about 2 seconds. 

If it's synchronized with sunrise & sunset, then it's probably related
to the streetlights that are turned on/off with photoelectric cells.  I
would look for noise on the power line though, I like the battery
operation experiment.

At Geometrics, we had a problem with a new magnetometer design that was
noisy until about 3 AM.  Turns out that BART, the Bay Area Rapid
Transit, generated a magnetic field running DC trains that we could see
50 miles away.  At 3 AM the trains stopped and the noise went away. Of
course that wasn't technically an instrument noise problem, it was a
real magnetic field we were measuring.

Doug Crice
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