The Xarm ITM green camera only updates about 1/second, while the Yarm is updating at more like 16Hz. I'm not sure how long this has been happening, it's been at least a few days that the green X camera has been slow, but I didn't really realize that it wasn't right until I just now looked at both green ITM camera values at the same time.
Since we use these cameras for initial alignment of the arms to the green beams, this is slowing down the preparation for starting the lock acquisition sequence. The loops are slow enough that it seems to be working as-is, but it's clear that the Yarm was ready long before the X.
I recall seeing the Xarm be slow for at least a little while now, and we've been able to lock and get the full IFO ASC going, so this isn't a show stopper, but it will certainly be helpful to have it fixed. Maybe it'll be better after next week's computer reboot fest? I'm almost done with initial alignment by now, so it's likely not worth rebooting anything for it today, unless there will be a lot of IFO work over the weekend.
Hmmm, maybe I'm changing my mind. I don't think I can trust the current camera position. It's been weird like this at least as far back as the on-disk data goes (~8 days), but clearly it has been working. But, when I let the alignment loops run, the COMM beatnote wouldn't get above -17dBm. When I open the camera loop and just use the other 2 loops and put ITMX where it was when we were last locking, the COMM beatnote is back to -5dBm where it should be.
Keita pointed out to me that the rate of update is related to the exposure rate, and the Xarm exposure is set much higher than the Yarm, so the slowness is expected (why the exposures are different I don't know yet if it's an accident or intentional). The camera setpoints were changed to reflect our latest good full IFO alignment. I had mistakenly thought that we had done an initial alignment since the camera setpoints were changed (in which case someone would have caught the poor COMM beatnote, and realigned ISCT1), but looking at the guardian states, that's not true. So, this first alignment with the latest camera setpoints is just telling us that we need to realign on ISCT1.
Team TCS has the IFO right now, but if they finish or take a break to do calculations, we'll touch up the ISCT1 ALS alignment.
It looks like the x arm camera position was updated on Wednesday morning, but the alignment onto ISCT1 was not corrected with the picomotors in HAM3. This explains the poor comm beat note level. Attached plot shows camera references, PR gain and picomotor position over the last 5 days.
We can fix this when we next do initial alignment.