PSN-L Email List Message

Subject: VBB-BB Tiltmeter info
From: sean@...........
Date: Sun, 6 May 2001 01:45:02 -0500 (CDT)

Meredith and co.,

Re. info on the Very Broadband Beam-Balance Tiltmeter: the VBB-BBT:

I'm glad you found the AGU/SSA abstract on my web site. The poster
was presented at the April SSA meeting by Mark Meremonte of the USGS
in Golden, since I was unable to attend the meeting. Unknown to
me, Mark assembled the poster in the lobby of the USGS building so
as to see what it looked like. Had I known about it, I would have
emailed you to go have a look.

Mark has scanned the poster pages, and I will find out if they can
be posted on my site. He is an avid digital photographer, and somehow
I would like to get him to document the details of the new instrument.

I completed a 70 page preliminary technical report last fall.
Unfortunately none of it is HTML compatible (the text is unix nroff, 
and the figures are from old versions of Mathcad and Autocad).

The compact coil/magnet system was designed for the feedback coils
of this beam balance tiltmeter; two are used, one at each end of the 
beam, to maintain an absolute symmetry of forces about the center of 

The abstract explains the principle of its operation. Since the VBB-BBT
is insensitive to horizontal acceleration, which a horizontal seis 
senses, its output will only be the tilt noise of the pier environment,
which a horizontal seis is also sensitive to, especially at long periods.
So with identical tilt sensitivities, the signal from the VBB-BBT can
be subtracted from that of the broadband horizontal seis, leaving only
the true seismic signal of interest. The VBB-BBT signal must be digitized
and processed identically to the broadband seismic signal.


I will review the info on the bought magnet and the coil construction
and post it tomorrow. I also have a box flexure design for the BBT that 
I also used to make a compact (10" long) horizontal broadband seis as a 
companion to a compact version of the the leaf spring vertical.

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