andrew.lundgren@LIGO.ORG - posted 11:24, Tuesday 21 April 2015 - last comment - 03:53, Thursday 23 April 2015(17973)
Request to turn off HWS cameras in CS at a known time
Detchar would like to request that the HWS cameras in the center building be turned off for a few minutes at a known time. We're trying to track down some glitches in PEM and ISI sensors that happen every second, and Robert suspects the HWS. Just a few minutes with them off, and then on again, would be fine; we don't need the IFO to be in any particular state, as long as the ISIs are running fine. We would need the precise times (UTC or GPS preferred), as the channels that record the camera state don't seem trustworthy (alog).
This afternoon I tunred all HWS off and I will leave them off all night (both of the corner station HWS were on prior to this).
Here are three better spectrograms showing the transitioning off of the HWS and the loud once per second glitches going away in the ISI-*_ST2_BLND_Z_GS13_CUT_IN1 channels. These plots are made with https://ldvw.ligo.caltech.edu using 0.25 seconds per FFT and normalization turned on. Conclusions same as Andy's post above.
David Shoemaker asked the good question, do these glitches even show up in DARM? Well, that's hard to say. There are once per second glitches that show up in the ISI channels, and once per second glitches that show up in DARM. We don't know if they have the same cause. Figures are: 1. DARM once per second glitches, 2,3, BS and ITMX, 4. overlay of all showing that the glitches in DARM are just slightly ahead in time (in this 0.25 sec/fft view, unless there is some sample-rate timing bias).
In order to test whether they are both caused by the HWS it would be really useful if folks on site could turn the HWS on, then off, for a minute or so in each configuration during a low-noise lock and record the UTC times of those states.
We got to a low noise state which is not at as low noise as our best, with the spectrum about a factor of 10 worse at around 90 Hz than our best reference. We were in low noise, HWS off from 10:42:30 UTC to 10:47:30 UTC, i turned the cameras on according to Elli's instructions and we left the cameras on from 10:48:20 UTC to 10:53:40.