The ISC crew has been complaining of excessive yaw on different platforms, which some seismic people have suspicions of actuator/T240 interaction. rDr at Livingston attempted to deal with this by trading some stage 1 isi isolation (by using higher frequency blend filters) for some increased HEPI isolation using STS to HEPI sensor correction. I tried to duplicate this here, but didn't have much success, as my attached plots attempt to show. The first screen shows the T240 spectra, where red is the Ryan's (as I understand it) configuration with T750 blend on st1 Z and his senscor filter on HEPI, and probably isi stage 1 sensor correction turned off (I don't remember cause I did this Friday, and Sheila had a couple this she wanted me to try that didn't get into my notes). Blue is our current configuration with low frequency blends, level 3 isolation and isi senscor,  no HEPI senscor, with HEPI position loops on. Light green is the blue configuration with stage 1 RZ turned off. The dark green is the red configuration, but no HEPI senscor. Looking at the T240's, it looks like we don't really win with HEPI senscor.

Looking at the oplev (second picture, same color sheme (red =hepi senscor, blue = baseline, light green= RZ off)) doesn't really make this simpler, though. It looks like as far as the oplev is concerned, turning off RZ gets a little better at about .1hz (likely because we're not re-injecting actuator/T240 cross-talk?), and otherwise no big changes. Sebastien is here, so I'll get his help to see if I'm missing anything here.