Yesterday we changed ITMY lens by -5uD with the ring heater. We've now undone that change. We have got the ITMY HWS leveled off to value we were going into DRMI locking with before the RH change yesterday (~30uD). DRMI has locked the last several times in a minute or less.
Alignment still doesn't look great, We are currently losing locks around DRMI_LOCK_CHECK_ASC and OFFLOAD_DRMI_ASC. Adjusting alignment to get the error signals zeroed better before going up.
craig.cahillane@LIGO.ORG - 18:47, Sunday 16 December 2018 (45998)
DRMI_LOCKED_CHECK_ASC Locklosses:
Caused by turning on the ISS second loop, the only thing of import that happens in that stage (pic 1). I noticed ISS turn-on DRMI locklosses several times over the last couple of weeks appearing in ASC-MICH control, but didn't know the cause until now.
EDIT: Pic 3 shows a DMRI lock, then a DRMI-only lockloss from the ISS turning on, then a DRMI reacquistion.
OFFLOAD_DRMI_ASC Locklosses:
When switching MICH control from AS_B_RF45_Q to AS_A_RF36_Q. Could be because of the smooth limiter limiting the oscillatory error signal too much (pic 2). I disengaged the smooth limiter in this state for now, we'll see if this helps.
EDIT: This seem to have worked once at least.
--------------------------------------------------------------------------------------------------------------------------------
EDIT2: I turned off the ISS second loop in guardian after it caused two DRMI locklosses in a row.
IMC_LOCK.py Line 513: ezca['PSL-ISS_SECONDLOOP_ENABLE'] = 0
Images attached to this comment
sheila.dwyer@LIGO.ORG - 10:25, Monday 17 December 2018 (46007)Lockloss
The other thing that is happening during these guardian states is that DRMI length control is being switched over to the 3F sensors.
The attached plot shows the LSC signals for the lockloss that Craig is plotting. In this case it looks ambiguous to me which thing causes the lockloss. (The ISS is enabled after the MICH ASC control signal gets large and the LSC error signal has a large excursion.)
The second attachment shows a very similar lockloss to the one that Craig plotted last night where we waited in the DRMI states (and the ISS was commented out of the guardian). At around -25 seconds, the DRMI control is switched to 3F and all the LSC signals become noisier. Immediately after the transition to 3F, there is a large glitch in the LSC signals when the coil driver state switches at -23 seconds (see 4th plot in top row). After this, the M2 gain (which is really just an input gain on the signal going to M1 since we don't send the length control to M2) is increased on PRM and SRM, with a 10 second ramp. The large distubance in MICH seems to start 10 seconds after the M2 gain ramp should be finished, so I am not sure what caused it.
For now I have done 2 things, neither of which I expect to solve the problem: I added the ISS second loop back into the guardian because we don't think it's the problem. I also edited the wait in the DRMI guardian that was intended to wait for the gain ramping to finish, but was shorter than the ramp time.
Yesterday we changed ITMY lens by -5uD with the ring heater. We've now undone that change. We have got the ITMY HWS leveled off to value we were going into DRMI locking with before the RH change yesterday (~30uD). DRMI has locked the last several times in a minute or less.
Alignment still doesn't look great, We are currently losing locks around DRMI_LOCK_CHECK_ASC and OFFLOAD_DRMI_ASC. Adjusting alignment to get the error signals zeroed better before going up.
The other thing that is happening during these guardian states is that DRMI length control is being switched over to the 3F sensors.
The attached plot shows the LSC signals for the lockloss that Craig is plotting. In this case it looks ambiguous to me which thing causes the lockloss. (The ISS is enabled after the MICH ASC control signal gets large and the LSC error signal has a large excursion.)
The second attachment shows a very similar lockloss to the one that Craig plotted last night where we waited in the DRMI states (and the ISS was commented out of the guardian). At around -25 seconds, the DRMI control is switched to 3F and all the LSC signals become noisier. Immediately after the transition to 3F, there is a large glitch in the LSC signals when the coil driver state switches at -23 seconds (see 4th plot in top row). After this, the M2 gain (which is really just an input gain on the signal going to M1 since we don't send the length control to M2) is increased on PRM and SRM, with a 10 second ramp. The large distubance in MICH seems to start 10 seconds after the M2 gain ramp should be finished, so I am not sure what caused it.
For now I have done 2 things, neither of which I expect to solve the problem: I added the ISS second loop back into the guardian because we don't think it's the problem. I also edited the wait in the DRMI guardian that was intended to wait for the gain ramping to finish, but was shorter than the ramp time.