yannick.lecoeuche@LIGO.ORG - posted 03:11, Tuesday 20 August 2019 - last comment - 07:26, Monday 26 August 2019(51400)
Range decrease correlating with SQZ channel
The range started decreasing around 08:30 UTC without any corresponding changes in ground motion or windspeed, so I started trending OSEMs/ other channels to look for corresponding changes. I found a candidate in H1:SQZ-DCPD_RATIO_2_DB_MON on the "optimize BLRMS" scopes (found on the SQZ overview medm) and plotted the trend next to the range, which has since come back up (see attached).
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J. Kissel, S. Dwyer We don't think this was a squeezer problem -- the BLRMS channel you found is a ratio of the SQZ output against the OMC DCPDs -- i.e. the source DARM error signal. Thus, this BLRMS can't distinguish between the squeezer loosing dB's and any ol' noise in the IFO. I attach a ASD of DARM comparing just before the noise kicked in -- 2019-08-20 08:00 UTC -- and at the worst of the noise an hour later -- 09:08 UTC. One can see that the noise is some broad-band problem between 80 and 400 Hz. We would expect squeezer problems to affect ~a few 100 Hz and above up to several kHz. Also -- I attach every trend that's canned from the squeezer team from their MEDM overview for the surrounding +/- 10000 seconds (+/-3 hrs or so), and I don't see anything that correlates with the increased noise start (~08:43 UTC) or stop (~10:53 UTC). Worth further investigation though!
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I was wondering if we know any more about this? The lasso tool on the detchar page has identified pretty strong correlations for the range drop with a couple of channels, although I don't know what exactly they measure (one of them is a H0 Vac).
https://ldas-jobs.ligo-wa.caltech.edu/~detchar/summary/day/20190820/detchar/lasso/