PSN-L Email List Message

Subject: Re: seismograph calibration?
From: "Larry Conklin" lconklin@............
Date: Tue, 14 Nov 2000 17:22:13 -0500

By any chance are you the same Dave Saum that used to work for GE in
Syracuse about 15 years ago?  The one I knew migrated to somewhere in Va, I

Hope you get some good answers to your question.  I too have been trying to
get a handle on whether my typical background is just noisy or really really
noisy.  It would also be interesting to see some FFTs of "typical"

Larry Conklin

----- Original Message -----
From: "David Saum" 
Sent: Tuesday, November 14, 2000 5:07 PM
Subject: seismograph calibration?

> I read Bob Barns' 1996 article about seismograph calibration
> and I wonder if there is not a much simpler method that does
> not require any special equipment.
> Suppose you just take the damping off a Lehman pendulum and
> give it a little shove.  It will begin to oscillate and if you
> know the period and the amplitude then you can calculate
> the peak velocity in nm/s.  Then you read the peak value
> from your ADC and that allows you to compute the
> velocity sensitivity of your seismograph in nm/s per bit.
> By observing your backgraound noise level in bits during normal
> damped operation you can convert it to nm/s.
> Or am I making a stupid mistake?
> And what is a good value for sensitivity and background noise level?
> When I do the tests above, it looks like I have a sensitivity of
> about 120nm/s/bit and my noise level is about +/- 3.  I have
> a 16 bit ADC so should I crank up the analog gain a tad?
> The reason I am trying to calibrate my Lehman is that I just
> got it working and I can not figure why it detects some quakes
> well and others poorly.  I am comparing my results with those
> posted on seismicnet.  Especially the results from Herndon, VA
> which is just a few miles away from me at Bailey's Xroads, VA.
> I am trying to figure out whether I need more gain or is my location
> on a office building basement slab next to a busy street just too noisy?
> TIA for any help,
> Dave Saum
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Larry Cochrane <cochrane@..............>