With the AC off in the PSL, and the laser restored, we are back to locking. Tonight we started to implement the high bandwidth hard loops that we made filters for over the weekend. The idea here to to make some ASC loops that will be high bandwidth and introduce noise into darm, but be relatively simple to keep stable as we power up. Then we can worry about a low noise loop only at our final power. The loop designs using Jenne's model are attached, they are the same filt ers for CHARD and DHARD so only CHARD is attached. Since the top mass damping was made more uniform today, 27464
the damping is probably not acurate in the model anymore. We were able to turn the CHARD yaw loop up to 10 Hz, (gain of -250) and turn the pit loop up to about 5 Hz, but there is something that is unstable when they are both high bandwidth. We checked that the gain of the MICH loop is not changing as we increase the gain in CHARD.
- We have some badly rung up violin modes on ETMX, possibly because the guardian was paused when there was still actuation going to the test masses. Evan worked on some filter settings that will damp single modes for a few of these, the settings that are currently damping them are shown in the 3rd attachment. I'm hoping to leave the IFO locked with these damping settings, it would be great if we could continue damping in the morning.
- We reset the soft offsets tonight
- We changed the PUM coil drivers to the high range state
Driving an admixture of hard/soft is bad, as illustrated in these Bode plots. The left plot shows the PUM to UM TF in the optic basis, and the right one is in the hard/soft basis.
With different damping in the TOP stage, the actuation TF is different for each suspension and so we end up with some of these zeros that we see in the left plot. Matching the actuators should make the loop shapes more like the ones on the right, avoiding some of the multiple UGFs we see in measurements.
But what's a good way to make sure that we have pure hard/soft actuators? We don't have pure sensors.
Unfortunately the current RMS watchdog on the L2 stage of ETMX tripped at around 3:00 AM local this morning. This seems to have shut the drive signal of all four colis and therefore the ETMX mode was not damping at a good rate.
By the way, we were unable to untrip the watchdog from the control room using the SUS-ETMX_BIO_L2_RMSRESET channel. This seems to be a known issue (alog 20282). I drove to EX and power-cycled the PUM coil driver.
Travis opened an FRS for this issue of being unable to reset the watchdog of the current rms on the ETMX PUM (aka L2) driver.