Alexa, Evan
The ETMY oplev damping was off. We have turned both picth and yaw damping back on.
Additionally, I have tweaked the filters and the gain slightly in order to reduce gain peaking:
- Pitch now has an elliptic low-pass at 15 Hz rather than a Chebyshev at 10 Hz. The gain is now -0.3 ct/ct.
- For yaw, the filters are a 0:0.1 z:p pair, a broad notch at 0.6 Hz, a 15 Hz elliptic low-pass, and a notch at 1.33 Hz (this peak shows up in the yaw spectrum and I assume it is the PUM pitch mode of the suspension).
According to conlog, the loop gains appear to have been randomly adjusted several times over the last week.
We hope that this might improve the robustness of the ALS locking. If not, we might try a similar recommissioning of the ETMX oplev damping (since this are also off).
Nic, Evan
Last night, we were playing around a bit with the loop shape of the ETMY pitch oplev damping. We returned to the original shape, but found we could not reengage the loop without causing the optic to oscillate. It is currently locked with a factor of 10 less gain (0.3 → 0.03), which is stable but is probably not suppressing the optic motion at all.