PSN-L Email List Message

Subject: Re: compound vertical seismometer
From: "Ted Channel" tchannel@............
Date: Sun, 20 Dec 2009 07:31:43 -0700

Dear Dr. Peters,   Thank you for taking the time to respond.   I am not much 
of a scientist, more of a builder.  I get a big kick from trying different 
approaches to seismometers.  My web site is 
primitive, but there you can see pictures of some of the sensors I have 

Not shown are my torsion springs sensors.   I have done several, and they 
have worked out well.    Your idea is amassing to me.   I would like to give 
it a try, but before I begin, and if you have time could you explain the 

In the pdf file,  fig. 4,  axis offset (r/R).....on the left side if we 
point to
11,  is this   11x R= arm length, cm?   and R being the alum. tube radius.

  Could you give me an example for the
dimensions,   r, R, and arm length,  assuming the cylinder is 3.8cm id? 
Basically, what I am after, is a starting point.......and if you could 
state, r, R and the arm length then I could understand the ratios.


----- 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, 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
    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 Chapman responded
    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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