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Message ID: 1090     Entry time: Fri Oct 24 22:30:38 2008
Author: Jenne,rana 
Type: Update 
Category: PEM 
Subject: Noise from Guralp Seismometer 
Attached is a Power Spectrum of the noise on the Vert1 channel of the Guralp seismometer. The noise is in the several hundreds of nV/rtHz up near 50Hz and higher, but is in the several microV/rtHz range at lower frequencies. Our high frequency noise is almost definitely below the noise of the ADC, but the lower frequencies, where we actually care, it's not as clear.

To Do list:
  • Measure the noise of the ADC - is the Guralp Box lower for all frequencies?
  • Use conversion factors to convert this measured noise into the minimum ground motion that we can measure. Is this at least a factor of 100 lower than our regular ground motion?

** UPDATE: This is actually the noise of the Guralp breakout box, not the Guralp itself. It is the noise measured on the output of the box
with the input shorted. The board is configured to have a gain of 20 (10 from the AD620 and 2x for differential drive). We also measured
directly at the AD620 output and all of this noise comes directly from that chip. If Jenne calculates that this noise is too high we would
have to find a replacement with a better low frequency floor (e.g. LT1012 or LT1007 depending on the Guralps source impedance).
Attachment 1: Vert1_Noise_24Oct2008.png  8 kB  | Hide | Hide all
Vert1_Noise_24Oct2008.png
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