No immediately obvious cause. We had an incoming EQ alert at the same time, so I thought an S-wave could've hit and caused the lockloss, but no noticable ground motion was seen at the time.
Comments related to this report
ryan.short@LIGO.ORG - 22:15, Tuesday 25 June 2024 (78660)
Lots of unexplained locklosses at random pre-DRMI states, making this reacquisition longer. Not sure what the issue was, but otherwise PRM needed adjustment to eventually lock DRMI.
I also twice had an issue with the ALS X PLL showing the "Beat note strength" error message, which prevented it from locking and would put the ALS_XARM into FAULT. The beatnote was around -11dBm and the lower limit was set to -10dBm, so I simply raised the threshold to -12 and the PLL locked just fine (I later reverted the SDF diff to start observing). Trending the ALSX PLL beatnote back, it does seem to sometimes get this low, but not very often (attached). It's already made its way back up to -5dBm about an hour later.
H1 back to observing at 05:00 UTC.
Lots of unexplained locklosses at random pre-DRMI states, making this reacquisition longer. Not sure what the issue was, but otherwise PRM needed adjustment to eventually lock DRMI.
I also twice had an issue with the ALS X PLL showing the "Beat note strength" error message, which prevented it from locking and would put the ALS_XARM into FAULT. The beatnote was around -11dBm and the lower limit was set to -10dBm, so I simply raised the threshold to -12 and the PLL locked just fine (I later reverted the SDF diff to start observing). Trending the ALSX PLL beatnote back, it does seem to sometimes get this low, but not very often (attached). It's already made its way back up to -5dBm about an hour later.