From: "Larry Cochrane" <cochrane@..............> Subject: Re: Sensor Information - Sensitivity Date: Fri, 26 Apr 2002 17:32:26 -0700
Benji,
You will need to measure both the gain of the amplifier board and the motor
constant of the coil and magnet. Measuring the gain of the amp is fairly
simple but you will need a function generator that can output a sine-wave
and a oscilloscope. Connect the function generator to the input of the amp
board and set the frequency to around 3 hz and the amplitude to 8 or 9 volts
peak-to-peak at the output of the amp channel. Now with the scope measure
the input voltage. The gain is the output voltage / input voltage.
Measuring the motor constant is more difficult and I have never done it
before so I can't help you. If you look at the PSN-L archives
(http://www.seismicnet.com/maillist.html#archives) you should be able to
find a post from Sean-Thomas Morrissey, who recently passed away, that
explains how to measure the motor constant and then convert that number to
volts/cm. You may find the message in this zip file
http://www.seismicnet.com/info/stm-mail.zip.
You may want to ask how to do this on the PSN-L list. There are more people
on this list and maybe someone there can help you.
-Larry
----- Original Message -----
From: "Benji & Wendi Johnson" <wjohnson@........>
To: <winsdr@..............>
Sent: Thursday, April 25, 2002 10:08 PM
Subject: Sensor Information - Sensitivity
> Hello! I would like to determine what my detector's sensitivity is, but
> I'm not sure how to go about doing this.
> I've followed the link http://www.seismicnet.com/calcsens.html to the
> Sensor Sensitivity Calculator webpage, but I'm stumped on how to fill in
> a couple of the fields.
> 1) Amplifier Gain - I'm using Larry's Amp/Filter board with the jumper
> removed and the trim pot increased by "4 full turns", but how do I
> measure what this amount is?
> 2) Sensor Sensitivity (volts/cm) - How is this determined?
>
> I am using a Lehman style detector. In addition to Larry's Amp/Filter
> board I am also using his A/D board. In playing around with the
> "WinQuake MI & Ms Correction" field, 5e-005 usually gets me to within
> 0.3 of the declared magnitude.
> In reviewing several of the posted events on the PSN site I noticed that
> a few people have calculated their detector's sensitivity, but most have
> not.
> Thanks.
> - Benji Johnson
>
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