PSN-L Email List Message

Subject: Geotech Blastcorder Mod. 5050" is on ebay #499098344
From: Doug Crice dcrice@............
Date: Thu, 16 Nov 2000 09:33:41 -0800

Geotech Blastcorder

I don't recognize this specific instrument, but most likely it's
designed to record vibrations from dynamite blasts.  There is a standard
that says a particle velocity of 2-inches/second is the threshold for
creating damage to structures.

Whenever people use explosives for one reason or another, such occasions
are followed by damage claims from the neighbors, even for cracks full
of dirt and cobwebs that have obviously been there for years.  To try
and introduce some logic into the legal process, the blasters will set
out instruments to record the actual vibrations around the area of the
explosions (also works for pile driving or even big trucks).  The
vibration records are used in the lawsuits.

The instrument consists of a 3-axis set of geophones (seismometers to
you earthquake fans), some amplification, an automatic triggering
device, and a means to record the maximum velocity (such as a strip
chart recorder).

Judging by the knobs, this one looks like an antique.  Modern versions
of this instrument are fully solid state (using digital memory to store
the information) stand-alone devices that connect to a PC for much more
complete analysis of the data.

Normally, the systems contain a vertical and two horizontal 4.5-Hz
geophones, which one of the PSN group might like to salvage as a sensor
for local events. The strip chart might be usable if working and if you
can still get paper for it, as would the fiberglass carrying case.  In
other words, buy it for the parts but don't pay too much.

Doug Crice

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