PSN-L Email List Message

Subject: Re: Comparison of available seismometers
From: "Les LaZar" llazar@..................
Date: Thu, 31 Jan 2008 13:40:28 -0800

Hi Brett,

I believe that the VolksMeter User's Manual, Appendix A - Theory Of 
Operation, addresses the frequency response issue.  The User's Manual is 
available on-line at our website,  Section 7 (which 
starts on page 7 of the appendix document) is relevant to your question:

In short, the frequency response is flat from DC to the natural frequency of 
the pendulum (~0.9 sec) and then falls off exponentially (linearly on a log 
scale) at higher frequencies.  The practical high frequency limit is 40Hz, 
which is set by the maximum sampling rate of 80 samples per second (of the 
electronics).  Further, there is a drop off in usable sensor resolution at 
higher sample rates, so 16 bits is the highest resolution that is usable at 
80 sps due to sensor/electronics noise issues.  Resolution of 20-24 bits is 
practical at sample rates in the 20 to 10 sps range (10Hz - 5Hz maximum 
frequency).  For lower frequencies, digital filtering (signal averaging) 
that is available in the software package can reduce noise still further.

The VolksMeter sensor responds to acceleration and/or tilt.  Velocity 
information is derived from the raw data through signal processing 
(integration in this case) which is part of the included WinSDR/WinQuake 
software package.

I hope this answers your questions.  If not, please let me know.


Les LaZar
RLL Instruments / a division of Zoltech Corporation

----- Original Message ----- 
From: "Brett Nordgren" 
Sent: Thursday, January 31, 2008 8:06 AM
Subject: Re: Comparison of available seismometers

> Les,
> Yes, I do have one question.  I may just have missed it, but it wasn't 
> clear to me from the literature, exactly what the frequency response of 
> the VolksMeter was.  Is it flat to velocity between two frequencies and 
> what are its sensitivity and corner frequencies?  Also how fast does the 
> velocity response fall as you approach zero?
> If it's easier to express these in terms of displacement or acceleration 
> response, that's fine, too.  Poles and zeros would be OK also.
> Thanks for your help,
> Brett
> At 11:01 PM 1/30/2008 -0800, you wrote:
>>Hello Benoit,
>>I am the project engineer for the VolksMeter.  I would be happy to answer 
>>any questions you have on the VolksMeter.
>>Les LaZar
> You can always use my mail form at:
>                            using your Web browser.
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