jeffrey.kissel@LIGO.ORG - posted 09:21, Tuesday 31 January 2023 - last comment - 13:36, Wednesday 01 February 2023(67110)
H1 OMC DCPD Analog Whitening Chassis Changed for Lower Noise Components; Much Less Output Voltage Offset
J. Kissel IIET 24198 WP 10951 S/N S2300003 This morning I replaced the OMC whitening chassis we installed last week (LHO:66980, S2300002) with the next serial number in the design run, S2300003 that we've modified to have - Improved output voltage bias (from ~2.5 V_diff to 0.02 V_diff) - Improved self-noise (from ~520 [nV/rtHz] @ 1 kHz to 300 [nV/rtHz] @ 1 kHz) All mods were performed on the whitening filter board itself, D2200044. I've installed the chassis in the same position as S2300002 was -- in rack ISC-R5, u-height U24. Some details of recovering functionality of the signal chain: (1) After allowing for ~20 minutes of circuit warm up, a sixty second average of the ADC input for the channels (with the input mode cleaner OFFLINE and output fast shutter CLOSED, so there's assuredly no light on the DCPDs) now confirms the lower output voltage bias: $ z avg 60 -s H1:OMC-DCPD_A0_INMON H1:OMC-DCPD_B0_INMON H1:OMC-DCPD_A0_INMON 168.91770833333334 15.123899710278394 H1:OMC-DCPD_B0_INMON 143.98645833333327 15.403723185931069 As such, I've changed the nullifying offset from Former offset (for S2300002) Current/New Offset (for S2300002) DCPD A -16600 [ct] = 2.50 [V DIFF] -168.917 [ct] = -0.026 [V DIFF] DCPD B -16424 [ct] = 2.53 [V DIFF] -143.986 [ct] = -0.022 [V DIFF] I've accepted these new offset values in both the SAFE and OBSERVE SDF snap files (see first two attachments). (2) I've taken new high-quality transfer functions, and Louis has re-fit them. He'll comment on this aLOG with the fits, but using a sneak peak at the results he gave me, I've updated the compensation for the new S2300003 chassis' frequency response, over-writing the "NewAW" FM2 banks for the A and B channels: OMC_DCPD_A0 FM2 "NewAW" zpk([9.9021],[0.99655],1,"n") OMC_DCPB_B0 FM2 "NewAW" zpk([9.88272],[0.99486],1,"n") I've loaded these coefficients. (3) For future dark noise investigations, the above new compensation has been in place since 2023-01-31 17:15 UTC, the IMC is offline, and fast shutter closed until at least 17:20 UTC, with the entire signal chain on and thermalizing (import for the inductors in the in-vac preamp) for ~45 minutes (and stable for ~30 minutes leading up to 17:15 UTC). More details to come in the comments below.
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Posting fit results here for completeness. The model of the OMC Whitening chassis that we fit for is shown in comparison to the measured TF in 2023-01-30_OMCDCPDWhitening_report.pdf. The fitted model agrees with the measured response to within ~0.1% up to 100kHz. The first four pages in the pdf show bode plots of the measured & fitted OMC Whitening chassis transfer function on the left and the residual (measured data / fit) on the right in the following order: ChanA:WhiteningON, ChanA:WhiteningOFF, ChanB:WhiteningON, ChanB:WhiteningOFF. The last page contains a Bode Plot of just the transfer function from the amplifier test box used for all measurements, which is accounted for. I also ran Ethan's script (LHO:67018) to verify that the response function systematic error remains low. The calculation follows G2200551. We see the same ~1deg drift due to the TIA systematic error. Script to fit OMC Whitening Chassis zeros and poles compensation: /ligo/gitcommon/Calibration/ifo/scripts/electronics/omcwhitening/fits/fit_H1_OMC_Whitening_D2200215_S2300003_20230130.py Script to review contribution to response function systematic error: /ligo/gitcommon/Calibration/ifo/scripts/electronics/omcwhitening/models/Jan2023_H1_OMC_Whitening.py
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I updated the latest pyDARM parameter model file to include the new(er) OMC Whitening Chassis compensation values posted above. /ligo/gitcommon/Calibration/ifo/pydarmparams/pydarm_modelparams_PostO3_H1_20230125.ini