[Sheila Arnaud]
EY oplev signal got somehow really noisy during the afternoon. It doesn't seem to be seimic noise. It is not clear why, but we should check this when possible.
Attached is a comparison spectra of EY oplev pitch at two different times this afternoon, with ISI isolated. Pink curve is the most recent one.
We started looking at this OpLev because we saw 1urad pp in pitch, which may have been one reason the arm cavity wasn't locking stably. We tried a few configurations with different blends.
With Tbetter everywhere except RZ, we see almost 1urad pit pp (over 16 seconds) and 0.4urad yaw.
With Tcrappy on Stage 2 and Tbetter on stage except for RZ we see 0.25pp PIT, which is now dominated by motion around the suspension resonances instead of the low frqeuency motion we saw with Tbetter.
Turning on and off sensor correction didn't seem to change the situation much, it is off right now.