I wonder if the 80 kHz ETMX PI lockloss this morning was due to the HVAC testing; we haven't seen an 80 kHz PI lockloss in a while. This time, as the EX VEA temp increased by 0.5degC (w/EY temp constant), the 80 kHz ETMX PI rung up about 2.5 hours into the lock. Maybe the EX HVAC change served as sufficient thermal change to ring up the 80 kHz PI on ETMX? Is it possible we are this marginal on the TCS for ETMX? Elenna has looked at the HOM spacing, and it is noticeably different with the HVAC changes.
In any case, next time I'll try to send the ETMX ESD PI drive to damp the mode in Diff, with LL/UR = 1/-1 (specifically, LL = H1:SUS-ETMX_PI_UPCONV_OUT_MTRX_1_3 = 1, UR = H1:SUS-ETMX_PI_UPCONV_OUT_MTRX_2_3 = -1). I think LLO:64490 has seen that this 80kHz mode is asymmetric, so maybe driving in diff helps. The PI damping guardian tried to damp the 80 kHz PI for 4-5 minutes with a common ESD drive to ETMX (first guardianized late April), but it wasn't able to. I confirmed the PLL integrator was locked to the correct frequency when trying to damp. Not sure if we'll be more successful with differential ESD driving, but we'll try.
To clarify, there was no TCS tuning, just in case anyone is wondering why we were doing that (we weren't). There were thermal changes due to HVAC-off tests (which were done today, and have been done in the past, in Observing since they are guaranteed to only improve the data quality). But those thermal changes were not related to our Thermal Compensation System.
EDIT: This comment was in reply to a previous version of this log post that referred to the TCS. The top alog post has been corrected, so please disregard :)
When IFO was down from an earthquake, I changed it to differential ESD driving as stated above and saved the change to SDF.