hugh.radkins@LIGO.ORG - posted 10:44, Friday 24 February 2017 - last comment - 10:55, Monday 27 February 2017(34380)
EndY PEM T240 Mass Center checked--Okay, not centered
Checked the mass centering on the T240 Deployed Wednesday, but I did not center them.
Day U V W
Wednesday 0.12 0.09 0.02V
Friday -.11 -.22 -.32
So the warm up of the springs is evident on the mass positions but it is still within comfortable range.
It will need re-centering when we put the T240 into the BRS enclosure (Tuesday.)
Here is spectra for the T240 (current ADC_0_ traces) compared to the ISI gnd STS (insulated) and from the PEM STS inside the BRS enclosure (Reference ADC channels.) I'll attribute the difference at low frequency to the un-insulated state of the T240 and when inside the BRS (maybe it will get some extra insulation then) it will compare better at lower frequencies.
I'm a bit surprised they don't agree more at the microseism but there may be a scale factor mismatch between the two seismometers. It would be good to look at the coherence between the two.
But the T240 does look better at low frequencies and is more promising. One thing I thought was interesting was the difference at high frequencies between the on-floor seismometers and the BRS-platform seismometer. The BRS-platform has three swivel-feet with ~3 mm rubber shims under them, resulting in increased motion between 10-50 Hz and maybe reduced motion at higher frequencies. Perhaps the feet could be redesigned to reduce this motion.
Here is this morning's look at the PEM T240 located on the floor next to the BRS (opposite side of the BRS to the ISI_GND_STS.
The PEM ADC is a bit unknown to me so like before when I made the PEM STS equal to the ISI GND STS by using a gain proportional to the ratio of the ISI STS/PEM STS amplitude at the useism, I now multiplied that scale factor by 5/4 (the ratio of the STS/T240 sensitivity.) If you compare this ASD with that in aLog 34381, one might argue the traces are more similar at the useism. Edit--added Coherence.
Tomorrow, this T240 will be moved into the BRSY enclosure replacing the STS that has been giving me troubles for the past few weeks.