Reports until 17:15, Tuesday 02 December 2014
H1 SEI
sheila.dwyer@LIGO.ORG - posted 17:15, Tuesday 02 December 2014 - last comment - 18:37, Tuesday 02 December 2014(15391)
gain filters for BS ISI ST2 GS13s

Alexa, Dan, Sheila

We found the BS ISI ST2 watchdog was tripping when the DRMI was acquiring lock; big transients in the MICH control signal would show up in the ST2 GS13s and saturate the inputs.  After some dataviewer'ing, we found that these transients are always there, but today they were large enough to hit the watchdog threshold.  We suspected the GS13 gains had changed, and conlog said that yesterday the 'Gain' filter (FM4) on the BS ISI GS13INF filter banks was turned on.  (We suspect that someone turned these off during the SEI work today?)  We turned them back on; the problem seems to be fixed.

None of the other BSC chambers have these filters on, but it looks like we need them for the BS, for now.

Comments related to this report
alexan.staley@LIGO.ORG - 17:26, Tuesday 02 December 2014 (15394)
Link

We tripped the ISI even while DRMI was locking (and luckily did not break the lock). We compared the length signal to the BS between today and yesterday, and concluded the LSC signals were not very different and were not the culprit.

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jeffrey.kissel@LIGO.ORG - 18:37, Tuesday 02 December 2014 (15397)
Link 

Note that these GS13INF gain filters are compensating for an analog switchable gain. I agree that if the GS13s are in "high gain" mode, i.e. with FM4 OFF, then they will saturate more easily. But, if you want to change the gains to "low gain" mode (with FM4 ON), you shouldn't just turn off the compensation filter. You need to use the command scripts (the dark beige button on the lower 1/3rd on the left of the overview screen -- then hit "GS13 HI / LO" button as you like, again on bottom 1/3rd of screen, but on the left) such that both the analog gain and the digital compensation are switched simultaneously. 

Good luck and god speed.