sheila.dwyer@LIGO.ORG - posted 01:28, Wednesday 20 July 2016 - last comment - 21:03, Wednesday 20 July 2016(28510)
MC3 saturation
At 8:09 UTC (on July 20th) we had a large glitch in interferometer signals and MC3 saturated. This seems like a suspect for some kind of a suspension glitch that would be worth following up on.
Comments related to this report
andrew.lundgren@LIGO.ORG - 07:35, Wednesday 20 July 2016 (28513)DetChar, SUS
The glitch is at 8:08:24.5 UTC, and it seems to have originated from the MC3 M1 LF OSEM. The glitch there is 500 counts peak-to-peak, while it's about 40 in the RT OSEM. It looks like one short glitch that caused some ringing for three seconds, which was visible in T2 and T3 as well, but not nearly as large as LF and RT.
betsy.weaver@LIGO.ORG - 09:57, Wednesday 20 July 2016 (28522)
We had a similarly huge glitch a few seconds before 23:30:30 UTC (also July 20th). It doesn't seem to be the same MC3 LF problem that Andy found. In the first attachment you can see the glitch from last night showing up clearly in MC3 M1 LF, in the second attachment you can see the very similar glitch from this afternoon without anything happening in MC3. For this afternoon's glitch I also looked at top mass osems for all the other optics and don't see much happening.
Also, all 3 MC mirrors react to the 8:08 glitch, this is because we don't have much of a cut off on our MC WFS loops. Adding more cut offs might be a good idea.
We've had several unexplained and sudden locklosses lately, and I wonder if whatever causes these huge glitches also causes some locklosses.
For what it's worth - the overall trend of these signals did not change from before the little glitch event. OSEM signals look healthy.
We had a similarly huge glitch a few seconds before 23:30:30 UTC (also July 20th). It doesn't seem to be the same MC3 LF problem that Andy found. In the first attachment you can see the glitch from last night showing up clearly in MC3 M1 LF, in the second attachment you can see the very similar glitch from this afternoon without anything happening in MC3. For this afternoon's glitch I also looked at top mass osems for all the other optics and don't see much happening.
Also, all 3 MC mirrors react to the 8:08 glitch, this is because we don't have much of a cut off on our MC WFS loops. Adding more cut offs might be a good idea.
We've had several unexplained and sudden locklosses lately, and I wonder if whatever causes these huge glitches also causes some locklosses.