Jenne, SHeila, Patrick, Ketia
We are still not able to lock ALS for very long. We tried locking only ALS COMM, and were able to stay locked for more than 10 minutes. We have been sitting here watching signals from the green arms, and we see the same ALS glitches (in the Yarm) that are described in many old alogs: 31053 lists som.
Keita Patrick and I followed Jenne's instructions in alog 30519 to lock the green laser to the arm directly by passing the PLL. In this configuration we did not see the glitches, but now that we have swapped the cables back to the original configuration the glitches are bac. So it seems likely that the PLL is somehow involved in these glitches. I am not sure if these glitches are the reason we cannot lock, but in the past they have prevented locking.
Edited attachment with annotations to make it more clear. (ignore the grey smudge) We had the green arm locked bypassing the PLL from about 6-2-2017 1:38 UTC to 1:44 UTC
The second screenshot shows a repeat of this test using a gain of 6dB instead of 10dB. I think that the loop was oscillating with the 10dB setting, so this setting is better.
Not sure if this is helpful, but attached are screenshots of coherences of various ALS channels with H1:ALS-Y_REFL_CTRL_OUT_DQ for a time around a glitch and a time without a glitch.
Here are 5 examples of 25 minuites of second trends of the Y arm transmission over the last 5 days, you can see that the situation has been getting worse although we have had glitches the entire time. (4 examples in first attachment, second attachment is the last 25 minutes, the problem is still pretty bad.)
