All three times we tried to move the input beam (76534, 76607 and yesterday), we caused a lock loss when moving in the yaw direction.
Approximate lock loss times: 1394946678 1395096385 1395535842
All lock losses appear to show the same behavior:
- IMC transmission drops in a "small" step before anything else happens. IMC transmission then stays constant for 120 ms, then drops quickly
- This corresponds to a "glitch" in REFL_SERVO_ERR, the start of a "ramp" in REFL_SERVO_OUT, and a discrete step in LSC error signals (PRCL, MICH, SRCL)
- Shortly after that, all signals go crazy, but there is no evident oscillation
Those lock losses are indeed very fast, and this seems to point to a CARM problem.
Some smart person suggested t check the ISS loops as the cause of those lock loss. It looks like this is the culprit: the ISS second lop is the first one to go crazy before each of those three lock losses. The error and control signals both go away from their trend value when we see the first jump in IMC transmitted power.
So maybe the ISS second is very marginal now.
Agreed, here are some more plots, it looks like we are probably saturating the AOM when we unclip the beam going into the second loop ISS array.
Also, it is interesting that looking at these times the out of loop PD power seems to increase as we move the input pointing (shown in the last plot, but similar for all three of these).
Edit: Keita suggested looking at indivdual PDs on the ISS, indeed the indivdual PDs are moving in different directions.
