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Entry  Thu Mar 1 00:05:23 2012, Den, Update, PEM, seis box noise DSC_3959.JPGnoise.png
    Reply  Thu Mar 1 21:48:34 2012, Den, Update, PEM, seis box noise noise2.pngnoise.png
Message ID: 6345     Entry time: Thu Mar 1 21:48:34 2012     In reply to: 6343
Author: Den 
Type: Update 
Category: PEM 
Subject: seis box noise 

Quote:

The noise increased at 0.5 Hz and is pretty big. This might explain the loose of coherence at low frequencies.

 This is because spectrum analyzer did not plot the real noise spectrum at the first few points at low frequencies. I've remeasured the noise at 1mHz - 3Hz at "output -" (TP9) and compared it to the seismometer signal

noise2.png

The noise seems to be much less then the signal. I've measured the noise several times and once I got a huge amount of noise

noise.png

 

I made another measurement in some time and got the low noise again. A circuit might have a bad contact somewhere.

The plan is to change AD620 adjustable resistor (R2) from 5.49kOhm to 500Ohm to increase the gain from 20 up to 200.

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