austin.jennings@LIGO.ORG - posted 22:23, Sunday 11 June 2023 - last comment - 11:06, Monday 12 June 2023(70352)
Mid Shift Eve Report
H1 is down and in corrective maintanence to troubleshoot an issue with the PMC. Currently working with team PSL to diagnose the cause.
J. Oberling, R. Savage, A. Jennings
Logged in from home, all signals looked OK, we had RF and high voltage to the PZT, signal on the locking PD, and the ramp worked. Tried locking and got nothing. There was no obvious reason why it wouldn't lock (same as Ryan and Jenne saw when Austin called them). Since I couldn't tell what the issue was from home, I drove to the site to take a look; Rick joined in case we needed to swap something out. Austin took a look at the electronics (PSL rack and CER), and I confirmed, all electronics visibly OK, nothing seemed out of place. Decided to watch the signal on the locking PD and turned on the PZT ramp. Flashes could be seen, but nothing down around the trigger threshold level, so I increased it from 0.1 V to 0.2V (where I had seen the threshold drop to a couple times), and the PMC locked right up without issue. First attachment shows when I changed the locking threshold and the resulting relock. Not sure why the threshold needed to be changed, but it's locked now. Unlocked and locked it several times, and it locked every time without issue. For some reason I currently do not know, the PMC would consistently not lock with a threshold of 0.1V, even if the locking PD voltage dropped below 0.1V; the 2nd attachment shows several instances when the PD voltage dropped below 0.1V, but the PMC did not lock (if the PMC locked then the PD voltage would have dropped to its usual locked value of ~20mV). This threshold value has been in place since at least the end of the 2021 PSL laser upgrade (likely back during O3 as well), so I'm not sure why the sudden change (and why I didn't think to try this first; lesson learned). I tried with the locking threshold at 0.15V, and this also locked without issue (3rd attachment), so I left the threshold here. I accepted the change in SDF; I didn't get a screenshot but did get a picture with my phone, will add that as a comment to this alog. At the time of this writing Austin has gone through an initial alignment and is now trying to lock the IFO; PMC so far has been stable, will monitor through this locking process.
FRS ticket 28260 has been created to track this issue.