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Detector Characterisation (Glitches)
mwas - 11:55 Tuesday 25 July 2017 (38815) Print this report
Some low frequency glitches last night were SDB2 scattered light arches
I have looked at last nights data that had lots of low frequency glitches (figure 1) that Nicolas mentioned today to be due to high microseismic.

Figure 2, if I look at random time some of the glitches are due to large motion of SDB2 wrt to SDB1 (black line projection). But there are also some other glitches in the same minute due to something else (I checked it is not ACL elapsed time glitches). These glitches are coincident with the same glitches on B4_DC (figure 4), so maybe these glitches come from MICH, but they don't seem to be scattered light on SPRB.

Figure 3, if I look at time with a large SDB2 position fluctuation there is clearly a large glitch at the same time.

Looking in the trend data, the SDB2 vs SDB1 translation control loop was not enabled last night. It would have been a good time to test that loop...
I have turned it on this morning during the maintenance, and added checks in DMS for SNEB, SWEB and SDB2 that the loop is closed so that it doesn't get forgotten in the future.

Figure 5, looking in time domain at the glitches that are not due to SDB2 scattered light. They seem clearly to have their origin on B4. It could be either scattered light (but doesn't correlate well with SPRB motion) or MICH loop gain peaking (but the frequency is not always the same) as the oscillation also shows up in the MICH error signal not only in the B4_DC/Audio light.
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travasso, swinkels, fiori - 19:10 Tuesday 25 July 2017 (38830) Print this report
Triggered by Excavator data (https://scientists.virgo-gw.eu/DataAnalysis/Excavator/logbook/2017-07-25_useism/) we searched for a correlation between Hrec_hoft channel vs NI_MIR_Z_50Hz channel (plot 1) and Hrec_hoft vs SDB2_LC_Z_err_ground_corrected_50Hz channel (plot 2) using a matlab-code produced by Bas: the two results are complementary. As noted by Paolo, the NI local control sensor does not see a movement of the mirror, but a movement of the ground: the scattered light path is not yet understood.

In order to match better the spectrogram, we multiplied NI_MIR channel for a factor 2 and SDB2 for a factor 1.5
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