nutsinee.kijbunchoo@LIGO.ORG - posted 08:04, Thursday 11 June 2015 - last comment - 19:34, Friday 12 June 2015(19067)
Owl Shift Summary
00:00 The ifo locked right before I came in. Wind speed is <20 mph. 90 mHz blend filter is used for BSC2.
I noticed the BS oplev sum is saturated (> 80000 counts). Is this alright? It's been around this value for 10+ days.
01:55 There's a big bump at ~30 Hz that caused a big dip in the BNS range. SUS Oplev plots didn't show anything suspicious. The bump at this frequency happened through out the night, just not as big.
02:00 A 4.7 MAG earthquake in Ecuador shook PR3 a little and BNS range dropped slightly (from 61 Mpc to 60 Mpc), but that's all it did. No WD tripped.
08:00 We've been locked for 8+ hours and still going strong at 61 Mpc! We had 5+ hours of coincidence with Livingston tonight. Handling the ifo to Jeff B.
Judging from the normalized spectrograms on the summary pages, the 30Hz noise looks like occasional scattering noise, likely from the alignment drives sent to the OMC suspension. Currently the Guardian sets the OMC alignment gain at 0.2 (for a UGF of around 0.1-0.5 Hz in the QPD alignment loops). This is probably too high from a scattering-noise perspective, it can be reduced by a factor of two without ill effects.
To follow up on this noise, here is a plot of one of the noise bursts around 20-30Hz, alongside the OMC alignment control signals. The noise has the classic scattering-arch shape, and it is correlated with the ANG_Y loop, which send a large signal to the OMC SUS. We've seen this kind of thing before. The start time for the plot is 09:27:10 UTC, June 11 (the time axes of the two plots are a little off, because apparently indexing for mlab PSDs is the hardest thing I've had to do in grad school.)
The second plot attached compares the OMC-DCPD_SUM and NULL channels at the time of the noise bursts in the first plot, to a quiet time one minute prior. The scattering noise is largely coherent between the two DCPDs.