PSN-L Email List Message

Subject: Re: tiltmeter sensitivity
From: ian ian@...........
Date: Wed, 07 Feb 2001 16:50:03 -1000


thanks for that exhaustive analyses, I appreciate your efforts.  The tilt meter is
called an Electrolevel and is a "..closed tube containing a bubble of gas, an
electrically conducting liquid and electrodes...".  It is a metal cylinder about 3
inches long and 3/4 of an inch in diameter.  It's made in the UK, vintage 1990, and
has a range of +/- 0.5 degrees.

The box that drives it produces a voltage of about 0.5 mV per arc second.  I'll be
connecting this signal to a Krohn-Hite 3322 filter and setting the band pass to 20
seconds to 10 seconds (arbitrary choice).  I can switch in a gain of 1, 100 or
10000 to this, though it will depend on how much noise is produced by the drive
box.  My A/D is 12 bits and is set to +/- 20 mV.  So my estimate of 5 urad is a bit
of a guess.  I'll know better when I get the filter (hopefully this weekend).

I wouldn't be surprised if a lot of teleseismic events pass me by un-noticed as
your analyses suggests.  I think it may well depend on the integrety of the signal
produced by the drive box.


Ian Smith


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Larry Cochrane <cochrane@..............>