PSN-L Email List Message

Subject: Another Seismometer Design
From: ACole65464@.......
Date: Wed, 20 Sep 2000 22:44:38 EDT

Hello PSN,

Here is something close to the core interests of this group, reviewing 
someone else's seismometer design.

Last January, I decided it was finally time to build a VBB velocity 
instrument. Because Sean-Thomas was kind enough to share with the PSN the 
design of the STM-8 Leaf Spring Seismometer, particularly his Mathcad 
worksheets for the closed loop response, I could not resist the idea any 
longer. To help understand the ins and outs of a VBB design, I used an old 
force-balance accelerometer I previously made a year or two ago as a test 
bed. Its displacement transducer and feedback coil were already in place, and 
intact. I was going to replace my instrument's displacement transducer with a 
VRDT per Sean-Thomas' design, because of the excellent resolution it has over 
mine. Yet, over time my original design worked well enough to detect 
teleseismic events, see links on my Web page for some sample seismograms it 
has made. I am the first one to say that this design is no rival to the 
STM-8. I wrote the paper to show others that building a VBB seismometer based 
on Sean-Thomas' design, is very achievable. I must thank Chris Chapman for 
reviewing the paper. He helped me to improve the performance of the 
displacement transducer, as well as finding other errors in the text and 
circuit design. Below is the Web page address.

I would like to hear your comments and opinions. 





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