There was again coherence between DARM and SRCL in last night's lock, so I ran a SRCL injection and adjusted the gain of the FF. (FF attached)
I changed the gain from 1.15 to 1.12. 77570 and 77492 are other times this gain has been adjusted in the last few weeks.
The coherence of SRCL to DARM is low at the frequencies that we care most about for this injection (20-50Hz), but the noise in DARM is well above the ambient DARM noise.
Attaching SDF screenshot for both the SRCL and PRCL changes here.
Edit: the SRCL excitation was on from 18:18:57-18:22:00 UTC May 6 2024.
SRCL coupling is indeed non stationary, as shown by the spectrogram attached, where DARM is shown before, during and after the noise injection. During the 3 minutes when the injection was constant, DARM shows non-stationary noise levels at low frequencies.
Computing a BLRMS of DARM between 20 and 50 Hz makes the non-stationary noise level evident. Comaparison of the BLRMS time series with ASC and LSC signals doesn't give much insight.
However, a scatter plot of the BLRMS vs all the ASC and LSC signals gives some hints that the noise is higher when DHARD_P is positive.
Plotting the BLRMS time series together with DHARD_P seems to confirm, although it's not a very strong correlation.
