J. Kissel

Executive Summary: The current, 2023-03-21, OMC DCPD electronics' compensation filters "NewV2A" and "NewAW" are still very accurately compensating for the frequency dependence of the analog electronics' response, so this is NOT a contributing factor to the complexity of the low frequency sensing function AND the response continues to be stable in time.

As a part of the continued investigation as to why the low-frequency sensing function is so complicated (see page 1 of H1_calibration_report_20230628T015112Z.pdf from LHO:70908 report of the measurement from LHO:70902), I wanted to rule out any possibility that the OMC DCPD electronics' analog response had changed (like we'd seen during the initial 2022 "burn in" period of the electronics -- see the 2022 data within 20230310_H1_DCPDTransimpedanceAmp_OMCA_timeratio.pdf from LHO:68167).

See the first and second attachments. These show a comparison of the remote excitations of the OMC DCPD electronics chain between the second set of "while in nominal low noise" measurements from 2023-04-03 (i.e. from LHO:68377) in BLUE and the ones taken this morning with no light on the DCPDs (the IMC was OFFLINE) in RED. 

This transfer function, driving through the electronics *and* the compensation for those electronics' response continues to behave as "flat below 500 Hz." Thus the compensation is still doing an excellent job at compensating for the low-frequency response of the electronics. In fact, with no light on the DCPDs, the data is cleaner below 100 Hz.

This puts 3 data points "on the board" where the response has not changed within the precision / accuracy that matters:
    - 2023-03-10
    - 2023-04-03
    - 2023-07-11
If we agree that three makes a pattern, then we shouldn't need to worry about this again until the electronics change. Since we're experimentalists, I'll probably measure again in a month or two just to confirm.

For future Jeff:
(1) You can do this in ~20 minutes on a Tuesday morning.
(2) Take IMC to OFFLINE, or if folks need the beam, make sure the fast shutter is closed.
(3) Open templates from 
    /ligo/svncommon/CalSVN/aligocalibration/trunk/Common/Electronics/H1/SensingFunction/OMCA/Data/
        20230711_H1_TIAxWC_OMCA_S2100832_S2300003_DCPDA_RemoteTestChainEXC.xml
        20230711_H1_TIAxWC_OMCA_S2100832_S2300003_DCPDB_RemoteTestChainEXC.xml
and update the references.
(4) One DCPD at a time, turn ON the analog relay to allow the H1:OMC-TEST_DCPD_EXC to head out through the DAC, the whitening chassis, and into the TEST input of the TIA. These relays, H1:OMC-DCPD_A_RELAYSET and H1:OMC-DCPD_B_RELAYSET can be found from the sitemap > OMC control > "sum "norm" "null" sub screen > Relays screen.
(5) Hit go on the measurement.
(6) Restore the relays to OFF.
Done!