Jennie W, Ryan S, Keita K
Summary: MC suspensions back to good time from 10th of Feb, we should only lock the IMC length loop manually during this installation period to avoid the WFS engaging.
Today Ryan and I had the task of figuring out why the IMC suspensions seemed to be badly aligned on Friday.
We found a good reference time 16:48:29 UTC on Tuesday 10th Feb at the end of the period where Olli, Jenne and I set the IMC axis back to its nominal state before the vent using ASC loops for DOF 1 and 2 of the IMC plus manual moves of the JM3 mirror in chamber as this cannot be moved by an ASC loop as it is not a tip-tilt currently. See photo of the WFS and MC mirror top mass OSEMS here. Note it is important to choose a time when IMC is in the locked state as the MC2 mirror gets mis-aligned when the IMC guardian is offline.
We figured out that the alignment was changed about 19:33:17 UTC on 13th Feb probably by the IMC guardian as Elenna used it to lock the IMC for phase check measurements. See photo, where the vertical cursors are set at the good reference time and today.
After some investigation of the guardian we reminded ourselves that DOFs 3-5 are turned off in the IMC WFS MASTER filter banks. DOF4 and 5 are normally off and DOF3 is intentionally left off because of the replacement of PSL PZT actuator by JM3.
When the IMC guardian is used to lock it automatically triggers the WFS through some logic from the simulink model, and so when Elenna used the guardian to lock it turned on the feedback to DOFs 1 and 2.
Until we install the JM3 tip-tilt and are finsihed most commissioning of the HAM1 hardware we should only lock the IMC manually by engaging the MC-L servo using the common mode servo board controls.
Keita and I zeroed the M1 LOCK fiters for all 3 MC mirrors and I changed the alignment sliders so the M1 osems were back to their values from the reference time on the 10th. See photo of ndscope.
To ensure the IMC WFS loops don't cause the MC mirrors or the PZT upstream of JAC to move on us like they did last week, we've turned the outputs of the IMC-DOF_{1,2,3}_{P,Y} filters OFF. Since these outputs are not touched by the IMC_LOCK Guardian, we can now safely use the Guardian to lock the IMC without the concern of WFS turning on and changing alignments.
At some point, the h1ascimc model will need to be updated to send the output of the DOF_3 loop to JM3 instead of the PZT (and medm screens updated too), as that's what's immediately upstream of the IMC now.