robert.lane@LIGO.ORG - posted 12:34, Thursday 16 June 2011 - last comment - 12:51, Thursday 16 June 2011(931)
X1 SUS Test Stand Test Channel DAQ Noise
J. Kissel, R. Lane After the recent upgrades to the test stand, we were doing some further 'checkout' testing of the test stand. We were driving small signals and observing for a reaction of the suspension in dataviewer. When we disabled the test signal we observed some noise in a couple of the stored frame builder channels (X1:SUS-BSFM-M1-TEST-L-OUT-DQ, X1:SUS-BSFM-M1-TEST-Y-OUT-DQ), that does not appear in the test points of the same channels. These particular channels receive no input from live sensors, so with out excitation, they should read identically zero. The noise is ridiculously small (~ 1e-21 cts / rtHz), and we only noticed it because dataviewer had auto-scaled it to *look* large. However, other channels appeared to not have this noise, and we just upgraded trying to get rid of other harmonics, so we bring it CDS's attention. Spectra show the noise is composed of ~89 Hz harmonics. Curiously, the 7th harmonic (712.125 -- exact frequency limited by the resolution of the quick spectra) appears the loudest at ~2e-19 cts. Attached are a amplitude spectra (pg 1) and time series of the noise (pg 2).
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Other interesting notes: - Clearing test points does not alleviate the problem. - Making the same drive-then-turn-off test on the R0 model (with the watchdog tripped so we didn't run into the two-models-using-the-same-DAC problem), we so no such noise.