elenna.capote@LIGO.ORG - posted 09:04, Friday 24 October 2025 - last comment - 12:47, Friday 24 October 2025(87713)
ETMY reaction chain length tracking causing saturations
We have been getting saturation warnings on EY after going through the lownoise coil drivers state. We finally tracked it down to the R0 F2 and F3 drivers. The reaction chain length drive (aka reaction chain tracking) is causing these saturations. This servo is run using the L2 OSEMs as a witness to then drive the R0 chain to follow the main chain. I turned off the length drive and the saturations stopped. When I turn it back on it continues to saturate.
The only recent change I can think of is the L2 satamp swap on all the test masses.
Adding a comment: We've only had these saturations intermittently the last few days, in this lock it is now contiuous if the R0 tracking is on. The sat amp swap happened Oct 14th, so perhaps this is some delayed consequence of the swap.
I was also reminded that the EY tiltmeter is possibly not performing as well as it can either as of Tuesday this week.
After the ETMY L2 satamp was swapped back, we no longer get saturations on EY with R0 tracking on!