jeffrey.kissel@LIGO.ORG - posted 17:24, Friday 23 August 2019 - last comment - 18:02, Friday 23 August 2019(51479)
Unknown Time Dependent Broadband Noise in DARM
J. Kissel, R. Schofield, K. Merfeld, M. Ball, A. Helmling-Cornell After Robert completed his studies, I glanced up and saw the spectrum had some terrible broadband noise, killing our range. And then it changed. Trends seem to show that it's been a part of this lock-stretch (including observation time) all along. Attached are DELTAL_EXTERNAL ASDs of the few times I looked up. Needs further investigation! All of Robert's test equipment is OFF. Looked at ETMX driver low pass state, it's ON, in the correct configuration. Now SDF differences with settings (or else we wouldn't have been able to go in to observation ready). No glitching in the BRS (wouldn't cause this kind of broadband noise anyways). The last lock loss from observation ready was sudden, with unknown cause... maybe something broke? Investigtion continues. We've launched a BRUCO, results soon to come...
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It glitched again in the same manner at 00:32:12 UTC,
Since this looks like a force noise, and my spider-sense thinks this is some sort of electronics failure, I trended the coil current for the ETMX PUM and ETMX TST (i.e. the primary stages of the DARM actuator), and found nothing that didn't look the same is it did in the previous lock stretch. See attached.
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Here are some dtt's of the broadband moise in the darm spectrum. I had a look at the spectrum during the unexplained range drop from Niko's alog 51400. These ones we're having now seem to be at a lower frequency.
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Sheila to the rescue -- the ALS X shutter was open. (And the clue came from ALS X trying to lock, which changed the ALS X SERVO GAIN and knocked us out of observation intent...) Shutter is now closed and DELTAL_EXTERNAL is back to normal. Now investigating why the shutter didn't get closed during these sets of lock acquisitions............