Because we have the infrastructure in place, I wanted to try using the CPS differential control on the corner station BSC ISIs. To do this I set the gains in the CPS_DIFF_FILT_MTRX screen so that ITMX X follows BS X and ITMY Y is tied to BS Y. I can then use the LSC-CPSFF channel as a measure of the differential motion seen between the CPS of these chambers. Seems to work, below 100 mhz.
Attached screenshot, the red is with the differential control off, green is with the differential control engaged. Below 100 mhz green is about a factor of 2 below red, meaning that MICH displacement witnessed by the CPS is smaller with the differential control than without, so with the differential CPS control engaged, the chamber motion is more common. Above 100mhz the motion is dominated by the microseism, which the CPS see, but the T240s would be easier to understand. It would be best to test this with a cavity, but they just opened the arms.
Jim, do you filter the CPS diff signals before feeding back, like for ham23 ?
Arnaud - yes, Jim has some 50mHz-focused bandpasses on for these.
As we try to lock for the first time since the vent, and since we're having some trouble (perhaps because we don't have end station sensor correction on??), I've turned this system on and off, and so far none of the IFO cavities seem to care, in that they still acquire nicely, but the transmissions are wobbly both with and without this system on. I haven't done an actual spectral comparison yet though.