As reported before, ITMY OL is making a huge fake triangular wave motion of 10 minutes period mainly in YAW (CH1).

We know that the optic itself is not moving because we cannot see this anywhere else, e.g. look at CH7 (AS_C QPD) and CH8 (L2 stage OSEM of ITMY).

We know that this is not the intensity noise. The RIN of OL SUM (CH6) for this 10min thing is about 0.3% pk-pk while each quadrant (CH2-CH5) sees two orders of magnitude larger signal. In addition, the phase of SEG1 and SEG4 are the opposite of SEG2 and SEG3.

It appears that  either the OL laser or the receiver or both are moving in YAW (unless the electronics of all four channels are conspiring together, which is very unlikely).

We could not find any apparent correlation between this fake OL motion and various FMCS and PEM channels. AOS people, please investigate.