Before the vent, we had lowered the DARM offset used at the end of the DARM_OFFSET state for locking the OMC since we had seen the PRG fall off and cause a lockloss with the nominal offset of 9e-05 (see alog79082 for details). When locking this afternoon, I raised the offset from 6e-05 back to 9e-05 after running through DARM_OFFSET, and seeing that the PRG didn't plummet and cause a lockloss, we continued locking. The OMC locked on the first try, something that hasn't been the case recently, so having more carrier light there seems to help. I compared OMC scans from this lock against the last lock, which used the lower DARM offset; attachment 1 shows the scan with the higher offset and attachment 2 with the lower offset. According to the OMC-DCPD_SUM channel, we get ~10mW more carrier light on the OMC when locking with this higher DARM offset.
I've put this DARM offset of 9e-05 back into ISC_LOCK and loaded it. We can watch over the next couple of lock acquisitions to see if the problem wth the PRG dropping off resurfaces.
Tagging OpsInfo
If you see the power recycling gain start falling soon after DARM_OFFSET, you can turn off the LSC-DARM1 filter module offset, lower it, and turn it back on until the PRG stays steady, then proceed with OMC locking.
Now that we've locked several times successfully since yesterday with this higher DARM offset, I've also rearranged the state order in ISC_LOCK so that the DARM offset is applied before any ASC so that the OMC can work on locking while ASC converges (this is how the order used to be before the DARM offset issues started).
See attached for the new state progression around this point in locking.
