Reports 1-1 of 1

MIF (ASC)

takafumi.ushiba - 9:32 Monday 02 June 2025 (34016)

Long-term drift of Y arm alignment

I checked the alignment during the longest lock last night and found that large drift can be seen in Y arm (fig1).
Since there seems no effect on X arm, the reason of the drift is very likely to be ETMY BPC, which controls Y arm SOFT mode.

According to the error signals of ETMY BPC (bottom two signals in fig2), following two things might be a problem:

1. ETMY PIT BPC doesn't seem to go zero. The sig of the loop might be wrong.
2. Large offset happened in ETMY YAW BPC error signas, which was reported in klog33989.

First, I will start from flipping the sign of ETMY PIT BPC.

Images attached to this report

34016_1748822045_Screenshot from 2025-06-02 08-53-02.png

34016_1748824315_Screenshot from 2025-06-02 09-28-06.png

Comments to this report:

takafumi.ushiba - 11:34 Monday 02 June 2025 (34021)

To solve the issue, I made following changes in OBSERVATION state.

1. Set offset of 0.097 at K1:BPC-YAW_ETMY_INF_OFFSET.
2. Increase gain of BPC by a factor of 10 by changing the gain at K1:BPC-{PIT,YAW}_ETMY_INF_GAIN from 1 to 10.
3. Change demod phase of ETMY YAW BPC for swapping the sign of the signals.

To achieve above modification without affecting the other states, I modified several states in the ASC_LOCK guardian as follows:

DOWN state:

Turn off OFFSET switch of K1:BPC-PIT_ETMY_INF filter bank.
Also, set the gain of 1 at K1:BPC-{PIT,YAW}_ETMY_INF_GAIN.

SET_BPC_FREQ_FOR_OBSERVATION state:

Change setting demod phase at K1:BPC-PIT_ETMY_DEMOD_PHASE from 47 to -133.
Turn on offset switch of K1:BPC-YAW_ETMY_INF filter bank.
Change gains at BPC-{PIT,YAW}_ETMY_INF_GAIN from 1 to 10.