I spent today trying to sort out more sensor correction issues. Over the weekend I realized that sensor correction not working could be explained by bad blends. I looked at ETMY and sure enough, there are 2 T750 blends, one of which is an old version, not to be used. Additionally I found that the calibration filters for the STS weren't turned on. I also noticed that the 8hz peak that comes from HEPI looks a bit bigger than the same peak at ETMX, something Hugh had noticed in August(?) and we thought had been addressed. I tried a number of configurations, shown in the attached pictures. The first is how I found the chamber this morning, with bad blends, HEPI running and basically no sensor correction (there was a gain of .5, with the cal filter off that becomes ~.05). The second is how I'm leaving it tonight, with the right blends, STS cal filters engaged and sensor correction on. I wouldn't really call it better. The sensor correction seems to be re-injecting noise at ~1 hz, but cutting some at .1-.2 hz. This is not what I've found on E/ITMX, where sensor correction seems to cut more noise between .1-1hz and reinjects some below. Not sure what is going on there.
Since I mentioned ETMX, I'll put up some plots. JeffK suggested I project the ISI's motion to the optic, so Friday tried to do that. These are the results for ETMX, showing that most of the optic's longitudinal motion (the black trace) is mostly explained by the ISI's X (blue) motion (makes sense) down to about .1hz, where the ISI RY becomes a significant contributor. Below that X takes over again, but that's probably actually still tilt.
