PSN-L Email List Message
Subject: Volksmeter sensor and the AD774x CDC chip
From: Larry Cochrane lcochrane@..............
Date: Tue, 18 Apr 2006 01:37:26 -0700
The discussion last week about the AD7745/6 chip was rather timely. Below is an email
from Dr. Randall Peters regarding the new Analog Devices converter chip and it's use
in seismology. The event files that I have been posting on the event file archive
system with the file extension of *.LCTST.PSN are from the new Volksmeter sensor. If
you compare the LC8 channel of my S-G sensor and the new Volksmeter sensor you will
see they are similar since they both use a short period pendulum and a displacement
Redwood City, PSN
From Dr. Randall Peters:
With the considerable recent interest expressed on the list-serve concerning Analog
Devices new capacitance to digital converter chip, the AD774x; I figured it was time
for me to mention the following:
Two instruments using my patented (fully differential capacitive) sensor have already
been outfitted with this marvelous new technology. The first was the computerized
Cavendish balance sold by a physics instrument company in Michigan:
This instrument has been in alpha/beta test phase for about a month now, and the
results look very promising.
The second instrument involves my business partners Les Lazar of Zoltech Corp. (
http://zoltech.com/ ) and your own Larry Cochrane.
Let me give you a little background on this instrument before discussing the details
of its operation with the AD774x (x = 5 for the single channel chip and x = 6 for the
dual channel chip)..
This instrument, which is a conventional pendulum having a period of about 1 s, is
called the Volksmeter. The name was influenced by Spiegel in Germany after a Mercer
University news release following the great Andeman-Sumatra earthquake. Subsequent
articles included a piece in Popular Science (April 2005), which motivated Les to
contact me, expressing his wish to build the instrument.
Tested first with analog electronics (using the now-defunct NE5521 integrated circuit
that was developed for LVDT operation), the Volksmeter has demonstrated excellence
for the detection of body waves from local earthquakes.
For most, there is a surprise associated with this instrument, since the simple
pendulum as a seismometer lost favor with the professional seismologists about a
century ago. Based on my research activities with Jim Shirley of the Jet Propulsion
Laboratory (basis for the progenitor to the Volksmeter and which responded to the
tsunami-causing earthquake) I was confident that such a pendulum was useful for more
than just local events (see, for example http://arxiv.org/html/physics/0508028 ).
For neither Les nor myself, was our experience suited to the task of outfitting an
AD7746 to the Volksmeter. But after Les contacted Larry, it became clear that we had
found somebody whose experience was just of the right type. In a matter of less than
two days, Larry had a single-pendulum Volksmeter operating with an AD7746 evaluation
board—and even placed the instrument online, using one of his existing PIC chips..
(For those who might think the evaluation board could serve as the backbone for a
practical instrument, the answer is a definite NO. The company has no intention of
letting you do this, and the maximum duration of a recorded record is 8-h at the
slowest sample rate (2.3 per s) permitted by their LabView generated executable—which
has some bugs, as I discovered.)
For those interested in watching this instrument’s capabilities, I refer you to
Larry’s website at the following URL:
The helicord record is updated every five minutes, and I noticed that just this
morning (16 April) it had recorded an earthquake of magnitude 2.8 at a distance of
25.3 miles from Larry’s home where the instrument sits on a wood-over-concrete slab
floor. The instrument also responded last week to teleseismic surface waves of
period 16 s, from the Fiji Islands earthquake.
Schedule permitting, I will plan on giving more details about the Volksmeter and some
of my own research that spawned it in the weeks to come. Larry has graciously
consented to ‘serve as a buffer’ for me, since in all likelihood my ‘plate is too
full’ with university duties at this time to try and answer individual emails. Such
mail consumes a lot of my time already; but I would like to hear from you—if you
should not be offended in the event that I don’t respond quickly if at all.
Professor and Chairman
Department of Physics
1400 Coleman Ave.
Macon, Georgia 31207
Public Seismic Network Mailing List (PSN-L)
[ Top ]
[ Back ]
[ Home Page ]