While at 10W input to JAC and commissioners working on IFO alignment this afternoon, we noticed the output power of JAC and the IMC start to gradually drop until finally JAC unlocked. Anecdotally, some of us have seen this happen at random times before, and JAC has always relocked easily pretty much immediately afterwords, so we haven't given it much thought, but it would be great if JAC didn't do this. I trended several things and can't tell what exactly happened first to cause this, but clearly the length servo and ASC outputs started changing dramatically over about 15 seconds until the cavity unlocked. I've attached short-term and long-term trends leading up to this unlock. I don't have a proposed solution, but mostly wanted to document this happening.
The PZT was railed at that moment. Temperature is changing more from 2days ago, after EOM was swapped. Anything changed in the heater servo?
No I haven't changed it since before the EOM swap. I had a look at the JAC heater guardian and there is not hard coded limits in there so it might be happening just due to there being less light power (alog #91943) through the JAC heating it up. Not sure why the servo is not holding the temperature as steady. Tomorrow evening I might try a higher gain and some filter changes.