andrew.lundgren@LIGO.ORG - posted 06:11, Wednesday 19 August 2015 - last comment - 09:43, Wednesday 19 August 2015(20675)
Checking for lines in OSEM channels
Matt asked if Detchar could check other OSEMs for problems like the ones seen in this alog. We're working on an automated solution, but for now Josh has suggested just plotting all the spectra. There are 270 channels in the attached PDF, with spectra taken in the middle of the most recent observation intent time (Aug 19 11:20 UTC). These are 60 seconds of data, 4 second FFTs, 75% overlap. We can easily make plots at other times, repeat this for L1, etc. I'll clean up the script and make it available. Here's a quick list of channels with lines or other bad features in them. You can search the PDF to see the plots. The first two groups are the ones to be most concerned about. Detchar should follow these up, especially the 'bouncy' spectra (which may be time-domain glitching). These channels have a distinct line, that may be aliased down like the 1821 Hz from the TMSX was: All OM1_M1 - just below 120 Hz All OM3_M1 - just above 90 Hz SR3_M1 T1 - about 65 Hz SR3_M2 LR - about 65 Hz SRM_M1 LF, RT, and SD - about 70 Hz, and something weird at high frequencies SRM_M2 UL - about 65 Hz SRM_M3 UR - about 65 Hz The following have 'bouncy' spectra, which usually means repeated glitches that are better seen in the time domain: MC2_M1 SD PR2_M1 T2 PR2_M3 LL and UL SR2_M1 T1 The following all have a big 60 Hz line and the spectra above 60 Hz is not smooth. Maybe there's a forest of lines or wandering lines. ITMX_M0 LF and RT ITMX_R0 LF and RT ITMY_L1 UR ITMY_L2 UR ITMY_R0 RT PRM_M1 RT and SD PR3_M1 T1 and T2 All PR3_M3 PR2_M3 UR MC2_M1 RT All SR2 M1 and M2 ETMY_M0 F1, F2, and SD All IM2_M1
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Josh, Andy, TJ
We had a look into the channels in the "bouncy" spectra category above. These are strong glitches that come in pairs, one pair every two seconds. Even more strangely, the glitches are in sync in all of the mentioned channels, even though they are different suspension stage OSEMs and different suspensions! Attached is a four-page PDF with normalized spectrograms and timeseries of the glitches on the OSEMS for PR2 (M1 T2,M3 UL), MC2 (M1 SD), and SR2 (M1 T1), showing that they are synchronous.
Notes:
- Only some OSEM channels are glitchy, on SR2 M1 T1, T2, and T3 are glitchy, but others are fine.
- We checked that these glitches exist both in the lock Andy used above, and in the current lock at 2015-08-19 15:00 UTC.
- We see the glitches in MASTER OUT channels too (pages 3,4 of PDF) and note that these see the glitches with better SNR all the way up to 200Hz.
- We did find any obvious DAC major carry transition associated with these.
- We did not see an obvious glitch correlation with PRCL or DARM (but there is a lot of nonstationary noise in those channels at these frequencies that might mask weak coupling).
- We checked SR2 ISIWIT channels, where ISI transitions to SUS and didn't see these glitches.
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