jeffrey.kissel@LIGO.ORG - posted 09:51, Tuesday 23 April 2019 - last comment - 11:06, Tuesday 23 April 2019(48695)
H1 PCAL EY 7,93 Hz Calibration Line Turned OFF
J. Kissel
Given that
- We've recently identified that glitching around 60 Hz in certain event trigger generation metrics has been a result of the 7.93 Hz PCAL EY calibration line, (LHO aLOG 48418),
- The GDS pipeline's calculation of the time-dependent correction factors for the SRC detuned optical spring (f_s and Q_s) has stopped using the 7.93 Hz calibration line, and its results are consistent with the reference model,
- that the front-end code that duplicates this calculation has been busted since we've had a pro-spring,
there is no longer a use for this now detrimental calibration line.
Thus, today, this morning, during maintenance, I have turned off this calibration line, and it will remain so in all future observation segments.
Note, that this also reduces the RMS requested drive from 6163 DAC counts to 5043 cts.
All other lines requested from the PCAL EY remain -- 17.1 Hz, 410.3 Hz, and 1083.7 Hz.
Attached are the screenshots of the SDF capture (done in both safe and OBSERVE snaps), and an ASD of the DAC request.
Stay tuned for details from @DetChar about the reduction in glitch rates.
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J. Kissel Also -- of interest to the CW group, and those investigating non-linearities in ADCs and DACs (see, e.g. LHO aLOG 48357, and LHO aLOG 48666) -- turning off this line drastically reduces several combs of harmonics in the RX and TX PD displacement spectrum. Unclear if these non-linearities are real displacement on the test mass (i.e. driven in to the light via a non-linear DAC system and making it past the optical follower servo's suppression, and then past the 1/f^2 force-to-length transfer function of the pendula), or non-linearities in the ADC for each photo-diode's electronics chain, though... I look forward to deep searches of h(t) with long FFTs comparing before vs. after this change.
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Thanks for the update, Jeff. It will take some time to gather enough statistics, but it will be nice to look before and after this and other calibration line changes to see what effect they have on spectral artifacts in h(t).