J. Warner, J. Kissel, K. Venkateswara
After improved modelling of sensor correction (SC), thanks to Rich M. (615, 623), we re-attempted SC along X (and along Z). X sensor correction was to stage 1 ISI, while Z was on HEPI. Unlike our previous attempt (14896), we used Rich's SC_filter described previously in 14570.
The first pdf shows the ASD from before SC for X and Z. Stage 1 T240, CPS and ground motion is shown and the coherence between them. The second shows the platform motions after SC. The third pdf shows a comparison between the configurations as measured by the T240 showing the expected 2-5 factor improvement between 0.1 to 0.5 Hz. It also shows an improvement below that which is more surprising (maybe from Z SC?). There is no visible re-injection of noise (factor of ~2 is epxected between 20-40 mHz), because we are probably dominated by pre-existing noise which is larger. More testing will be done tomorrow. The OpLevs are currently mis-aligned so I can't see the effect of SC on them.
Note that the we did not use tilt-subtraction at the moment because wind-speeds were practically zero. We will test the tilt-subtraction when winds pick up a bit.
Once again, if this appears to be adding noise instead of helping, the comissioners can turn it off from the ETMX ISI medm screen as before.
Looks like the X arm is better behaved this time. I've attached ASD of the ALS-X control signal and the Stage 1 CPSs for ETMX and ITMX from tonight's locking.
This morning, I tried using the tilt-subtracted ground super-sensor for sensor correction along X, rather than the plain ground sensor. The attached pdf shows the Ground Sensor (T240), the super-sensor, Stage 1 T240 X, BRS RY OUT * g/w^2 and the Stage 1 CPS. Please note that the CPS data is after the sensor correction (it is input to the blend filters), hence it is should be less than the ground motion above ~100 mHz.
The plot shows that in non-windy periods, the super-sensor is not much noisier than the regular ground sensor and tilt-subtracted sensor correction is therefore about the same as regular sensor correction.