PSN-L Email List Message
Subject: Re: compound vertical seismometer
From: "Geoffrey" gmvoeth@...........
Date: Mon, 21 Dec 2009 18:48:03 -0700
A note on the complexity of your verbosity;
For us laymen (namely me) it would be nice if you talked
in terms of reducing the effects of gravity to
lengthen the free period of any system.
most of you seem to me to be pros instead of amatures
because your language suggests your education
level on par with engineers.
Are any of you able to "Talk Down"
like the military instructors are
taught to do to the troops working
on things who lack a university education.
You do not need to label things according to their inventors
just mention them at the end of whatever you say.
But like a pendulum where
P = 2Pi*SQR(l/g)
l = (P/2Pi)^2*g
just tell us how your device is lowering the g factor to
get a period of 5 or more seconds free period.
Springs are behaving very similar to a pendulum
they pretty much obey this formula too.
g is like 9.80665 meters/sec^2 or 9.80665E003/25.4 inches per second squared
you must whatever you are doing be lowering the g factor
to increase your periods.
Using this as your reference could greatly simplify all the
technical jargon you guys are using.
Show us an exploded diagram along with the details of every part
and leave out the hard to understand jargon for those
who lack the education.
Tell us how you are lowering the g constant factor.
A photo is very good but does not tell
the story like an exploded diagram with parts list
explaining each and every part.
Dont laugh at this idea, but, its a classic case of anti-gravity. :-)
There is nothing like a set of blueprints or formal mechanical drawings to build something by.
Amatures are lacking technical standards for building (cheaply) things (seismometers) that
give uniform results whoever builds whatever.
It seems the pros do not want the amatures to understand
their designs for fear of loosing money at the industrial
level of building things.
It is my great hope to see a velocity or displacement vertical with a free period
between 10 seconds and 5 seconds that I can build myself
for under $200, one I can bury in the ground without having
to dig a big hole like the mammoth cave in Virginia.
My aging back can not do that anymore.
Just a note of hopefulness for meaningful simplification of whatever;
----- Original Message -----
From: "Randall Peters"
Sent: Sunday, December 20, 2009 6:44 AM
Subject: compound vertical seismometer
The vertical seismometer that I showed at the broadband conference in 2004
http://www.iris.edu/stations/seisWorkshop04/seisWorkshop.htm, which you referenced by
operates on the principle of the archer's compound bow. I published a paper in 2000 concerned with the physics of the compound
bow, titled "Archer's compound bow, smart use of nonlinearity". It is online at http://physics.mercer.edu/petepag/combow.html.
Because of force reduction at full draw, due to the eccentrics (cams), the bow concept can be used to lengthen the period of a
similarly operating seismometer. John Nelson asked about this possibility in a mailing to the listserve in 2003, to which Chris
For additional pictures of the prototype that I built, you may go to my webpage at
The sensor employed in this prototype is one of my fully-differential capacitive forms, but other types (such as coil/magnet)
could be used. As Chris has frequently pointed out, if you were to use the Faraday law sensor, it is important that the coil (not
the magnet) be the moving part.
I never had time to pursue this concept the way I wanted to, but the data that was presented at the IRIS-sponsored conference
(first reference above) shows that it has promise--especially if you were to build one a lot bigger. I wanted to try this with an
elastic element using carbon epoxy elements in some arrangement, but never got around to it. Incidently, the first one of these
ever built was by one of my students when I was at Texas Tech University, around 1997. It was much larger and used a coil spring
(approximately LaCoste zero-length type) instead of the torsion wires of the prototype, but I never got around to seriously using
it, since I moved to Mercer University soon thereafter.
You may be interested to know that Erhard Wielandt, who was at the conference, encouraged me to try and get amateur
seismologists interested in using the ideas. A number of the folks there were very curious about the instrument, since it had been
setup on a table and made quasi-functional.
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