ryan.short@LIGO.ORG - posted 08:13, Monday 30 September 2024 - last comment - 09:20, Monday 30 September 2024(80358)
Looking into Recent Locklosses with FSS_OSCILLATION Tags
I don't consider this a full investigative report into why we've been having these FSS_OSCILLATION tagged locklosses, but here are some of my quick initial findings:
- FSS_OSCILLATION tags are just glitches over the tag threshold in the lockloss tool that happen with high frequency at a lockloss; not actual oscillations
- When glitches happen, drive to the FSS EOM (H1:PSL-FSS_PC_MON_OUTPUT) rises. Frequent glitches cause the drive to keep rising (see 7min screenshot)
- Glitches are (probably) too fast to be responses of suspensions moving and changing cavity length
- SUS not seen moving during these times
- Glitches happen while locked, although usually with lower frequency (see screenshot)
- Sometimes after lockloss, glitches can persist and cause actual oscillations, delaying IMC (and IFO) relocking time as the FSS is not ready, see screenshot from last week
- Non FSS_OSCILLATION tagged lockloss example: see screenshot
Please feel free to add comments of anything else anyone finds.
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Two interesting additional notes:
- The fist lockloss with FSS_OSCLATION tag was on Tuesday September 17th, during the fire alarm test, we've since had 28 more locklosses (from all states) with this tag. Could either the Tuesday maintenance activities (ETMX DAC swapped) in alog 80153 or the fire alarm lockloss 1410638748 have started this?
- In the FSS_OSCALTION tagged locklosses (and some that aren't tagged), H1:ASC-AS_A_DC_NSUM_OUT_DQ and H1:IMC-TRANS_OUT_DQ are loosing lock at the same time, this is very rare in O4. Iain Morton checked in G2401576 (tagged locklosses "SAME") that we'd had < 3 of these locklosses in the whole of O4 before the emergency vent. In G2201762 O3a_O3b_summary.pdf, I called this a TOGETHER and FAST lockloss and we saw it exclusively in the second half of O3b. A normal lockloss as the AS_A losing lock > 100ms before IMC. See plot attached of the last 3 NLN locklosses, the left plot is normal and the right two are the strange type where the IMC looses lock at the same time.
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