jeffrey.kissel@LIGO.ORG - posted 09:36, Thursday 11 May 2023 - last comment - 10:42, Thursday 11 May 2023(69499)
POP A RF 45 Gain Needs to Stay at +21 dB for Initial Alignment (As opposed to +15 dB, 6 dB lower, to allow for large SRCL Offset)
J. Kissel, T. Shaffer I came in this morning and TJ was having trouble with initial alignment, and having trouble in the same steps -- ALIGN_IFO guardian's XARM IR LOCKED state -- that he says operators have been struggling with "all week." Namely, the ALIGN_IFO / INIT_ALIGN guardians would suggest that the XARM was locked, but it was not -- it would trigger but not hold. The practice in that past week was to "just skip" ALIGN_IFO guardian's XARM IR LOCKED state, where we use POP_A_45 to lock the XARM. I connected the dots between "trouble with POP" and us needing to decrease the POP_A_45 analog gain to allow for an increased SRCL offset during normal, nominal low noise last week LHO:69350. As such, TJ and I tried reverting the analog gain, H1:LSC-POP_A_RF45_WHITEN_GAIN, to +21 dB, and then compensated the analog gain increase with the corresponding digital gain compensation -- switching back to FM4 in the H1:LSC-POP_A_RF45_I and H1:LSC-POP_A_RF45_Q banks. Reverting to higher gain immediately restored the functionality of the XARM IR LOCKED. FIXED IT. So, we'll code this adjustment up in the initial alignment guardian sequence.
This is now loaded into the ALIGN_IFO node to change it to 21 and the ISC_LOCK guardian to change it back. SDF_Revert should cover the FM change back, but not the gain change. With an over amount of caution we put both in ISC_LOCK. We will need to test this with initial alignment soon.