jenne.driggers@LIGO.ORG - posted 11:04, Wednesday 07 December 2022 - last comment - 15:34, Wednesday 07 December 2022(66230)
omc lsc has temp minus sign
Brief alog as I run to a meeting, but the omcparams has a minus sign for now for the OMC LSC, to allow the omc to lock.
Also, I've loaded in my new guardian state that will prevent us from powering up when the violin modes are too high. We may want to change how it's in the path (i.e. maybe it shouldn't *prevent* us from going forward), but for now it'll keep us from saturating our DCPDs.
After carefully comparing old and new models, the currenmt configuration has the PZT1/2 drives swapped in the lsc model and on the cables out on the floor. So, this should work. The lsc model has been fixed. If it gets loaded, the cables need to swap back.
One thing to be aware is that the PZT dither signal is also delayed by 1 cycle (at 16384Hz). This is significant because the dither frequency is 4100Hz. This corresponds to an almost exact 90 degree phase shift!
Sheila pointed out that the last time our template for phasing the OMC LSC was saved was early 2019, so perhaps our phase hasn't been so excellent, and that's why my new phase isn't 90 deg from the old phase. But, I measured the OMC LSC OLG (TLAs anyone? ;) while changing the demod phase and I found that in total I needed +220 degrees (or, -140 deg) from our previous (before Tuesday) situation. I'm leaving in my 'temporary' minus sign in omcparams, so that's 180 deg, and then I get the highest UGF when the digital demod phase is +40 from where it started today. This puts our UGF just a hair lower than the reference from 2019, but all these measurements were within a few dB of each other, and the loop is super duper stable, so I don't think it matters too much.
Attached is the DTT of these quick measurements.