Evan, Alexa, Dan, Sheila
Tonight we made some more measurements of the plants for DHARD WFS, this time with no watchdogs tripped. The screens shots attached show both the open loop gains and the plant measurements for pitch and yaw. We plan to fit these and make a better loop for on resonance during maintence day today.
All of these measurements were made with the oplev damping on the ETMs off. The plant inversion used for the measurements at 50 pm was a little different than what we used on resonance.
In full lock, we had the following loops closed:
- ASA45Q → diff ETM pitch: FM3, FM4, FM7, FM8, FM9, FM10, gain 8 ct/ct [in the DHARD pitch filter module]
- ASA45Q → diff ETM yaw: FM3, FM4, FM7, FM8, FM9, FM10, gain 20 ct/ct (down from 80 ct/ct earlier in the locking sequence) [in the DHARD yaw filter module]
- REFLB9I → IM4 pitch: FM2, FM3, gain −0.3 ct/ct [in the INP1 pitch filter module]
- REFLB9I → IM4 yaw: FM2, FM3, gain 0.03 ct/ct [in the INP1 pitch filter module]
- ASB36Q → BS yaw: FM2, FM3, gain 0.03 ct/ct [in the MICH yaw filter module]
After engaging ASB36Q, we ramped down the yaw oplev damping on the BS. After a few seconds, ASB36Q began ringing at 1 Hz or so and the lock broke. Unclear whether this was a WFS loop instability or unsuppressed motion of the BS.
I altered the plant inversion for the diff ETM loops so that we are not applying so much drive above 10 Hz. Instead of five poles at 100 Hz and an ELP at 30 Hz, there are now three poles at 20 Hz, two poles at 100 Hz, and an ELP at 10 Hz. We lose some phase though, so we might not be able to get 1 Hz bandwidth out of these loops.