Tamper injections showed some upconversion from the tens of Hz region into the region above 60 Hz. The HVAC makes noise in this region so I did the test I had done in iLIGO, I shut down all turbines and chiller pad equipment on the entire site. This increased the range by almost 5 Mpc (see figure - the 3 range peaks are during the shutoff periods below).
Checks:
1) make sure all VFDs are running at 45 or less
2) if possible use only 2 turbines for the LVEA
We did not drop out of science mode but here are the times of the changes (Oct. 15 UTC):
2:05:00 shutdown started, 2:08:00 shutdown complete
2:18:00 startup started, 2:21:30 startup complete
2:31:00 shutdown started, 2:37:00 shutdown complete
2:47:00 startup started, 2:51:00 startup completed
3:01:00 shutdown started, 3:03:30 shutdown complete
3:13:30 startup started, 3:17:00 startup complete
Here is a comparison of the calibrated DARM spectrum from times when the HVAC was ON and OFF, in the frequency band that was affected.
I plotted glitchgrams and trigger rates during this time. Doesn't seem to have made a noticable change.
https://ldas-jobs.ligo-wa.caltech.edu/~jordan.palamos/detchar/HVAC/glitchgram_HVAC_1128909617.png
https://ldas-jobs.ligo-wa.caltech.edu/~jordan.palamos/detchar/HVAC/rate_HVAC_1128909617.png
Attached are ASDs of DARM and one of the PEM seismometer channels (corner station Z axis) for all of the times when the HVAC was turned on and off (not including the times of transition). In general, the noise level between 40-100 Hz is lower during the times when HVAC was off. The peak around 75 Hz was better during the second two off times, but not in the first segment. (1128910297 to 1128910697)
More PEM seismometer channels are here: https://ldas-jobs.ligo-wa.caltech.edu/~marissa.walker/O1/Oct15HVACtest/
(note: the seismometer calibration from pem.ligo.org is only valid from 0-20 hz)
