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Detector Characterisation (DetChar shifts)
vicere - 1:26 Sunday 14 July 2019 (46355) Print this report
Noise increase issue, starting 21:54 UTC, July 13th

Around 21:54 UTC, July 13th, the BNS range dropped to zero and the sensitivity update in vim-online stopped. However, the ITF stayed on lock, even though the spectra of hRec and DARM displayed a marked, stable increase in the broadband noise, as shown in Fig. 1. This drop was therefore different from previous sensitivity drops, which were temporary, lasting only a few tens of seconds.

The operator on phone confirmed that indeed the detector had not lost lock, and that upon a reset of the power stabilization loop the sensitivity had gone back to normal.

An inspection of the INJ signals shows that shortly before the sensitivity drop glitches are present in the PSTAB_PD1 signal (Fig. 2); one glitch is large enough to be seen as a glitch also in the PSTAB correction signal. Seconds later (Fig. 3) other glitches occur and apparently cause an unlock of the PSTAB loop, since the power stabilization signals saturate, shortly before 21:54:21 UTC.

In light of this episode, it is plausible that most of the sensitivity losses occurring today are due to similar issues with PSTAB. To be confirmed, by inspecting individual sensitivity loss events. 

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narnaud - 9:05 Sunday 14 July 2019 (46358) Print this report

Starting at 21:54 UTC, the BNS range went down to ~0.2 Mpc in ~20 seconds. It stayed around that value until 21:57:30 UTC when it went down to exactly 0 when the Hrec quality flags became active: Hrec_Flag_Quality went from 1 to -32 and then a few seconds later to -96 (= -32 -64 meaning that some bits were set). In parallel the state vector bits 0, 3, 4 and 10 became inactive, as shown in https://vim-online.virgo-gw.eu/resources/2019-07-13/resources/20190713_sum_statevector2d.png. From that time onwards the data were tagged as unusable for online analysis (bits 0 and 10 at 0). At the end of the bad period around 22:33:34 UTC the data quality flag went up to -64 and then to -1.The BNS range went back up at 22:33:46 UTC while state vector went finally back to its nominal state at 22:33:55 UTC (bits 1 and 2 had been inactive for a few seconds during the transition).

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