PSN-L Email List Message

Subject: Re: Volksmeter sensor and the AD774x CDC chip
From: "ratosha morgan" morganrat@.......
Date: Thu, 20 Apr 2006 14:00:36 -0400

I built a seismometer and I measured my data in currnt and time. I am trying to convert that into wavelength and oscillation. How can I do that?

From:  Larry Cochrane <lcochrane@..............>
Reply-To:  psn-l@..............
To:  psn-l@..............
Subject:  Re: Volksmeter sensor and the AD774x CDC chip
Date:  Wed, 19 Apr 2006 23:40:41 -0700
>Hi Chris,
>ChrisAtUpw@....... wrote:
>>In a message dated 18/04/2006, lcochrane@.............. writes:
>>     The discussion last week about the AD7745/6 chip was rather
>>     The event files that I have been posting on the event file
>>     system with the file extension of *.LCTST.PSN are from the new
>>     Volksmeter sensor. If you compare the LC8 channel of my S-G
>>     and the new Volksmeter sensor you will see they are similar
>>     they both use a short period pendulum and a displacement
>>Hi Larry,
>>      What period compensation are you claiming for this sensor?
>>     Do the plots show a compensated velocity / compensated
>>displacement / uncompensated signal, or what?
>>     How are you performing the velocity feedback / damping
>>necessary to stabilise the response?
>There is no period compensation in either the SG sensor or the
>Volksmeter (VM). Both use simple damping. The SG sensor has a
>feedback loop but it's just there to damp the pendulum. It might
>make the sensor more stable do to the feedback loop, but I'm not
>sure of that. The VM sensor uses eddy-current damping and has no
>feedback system. Randall will be sending a response to this shorty.
>The plots are from the raw data right out of the sensor, but with a
>60 second 2 pole high-pass and 2 Hz 2 pole low-pass filter applied
>to the data before making the GIF image. The event files are the raw
>data from the AD7746 chip.
>>      I note that in your SG EMail reference, you claim a flat
>>response from 50 sec to 3 Hz, but remarked that you had to
>>substantially increase the damping to get this. I note that in your
>>latest circuit diagram, you seem to have greatly reduced the
>>itegration time and wondered if the circuit values were correct?
>Like the VM channel (LCTST) my LC8 channel is pretty much the raw
>data from the pickup except there are two 60 second high-pass
>filters in the signal path. My LC3 channel, the integrated output,
>should have a velocity response from about 1 second, the period of
>the pendulum, to about 50 seconds. I have not made any changes to my
>SG sensor for many years so the value of the integrator parts should
>be the same.
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