Maybe this is known, but I didn't find an alog showing this feature of ITMY.
Plot 1: ITMY
- oplev sum - red
- oplev pitch - green
- M0 OSEM LF - brown
- M0 OSEM RT - cyan
OSEMs LF and RT have a peak at 0.55Hz throughout the long lock yesterday, T0 = 11/19, 16:00UTC, 750 averages
The peak in the LF and RT OSEMs seems to suggest the optic is swinging at 0.55Hz in pitch all the time, and that that swinging gets kicked up at lock loss.
Plot 2: ITMY, ITMX, ETMY, ETMX, OSEMs LF and RT, all optics
- ITMY - red, magenta
- ITMX - blue, cyan
- ETMY - green, orange
- ETMX - brown, black
The peak at 0.55Hz in OSEMs LF and RT is unique to ITMY.
It's not really helpful, because we don't yet have a solution, but here's the aLOG where this problem has been explored: LHO aLOG 31404. I have no suggestions as of yet on how to fix it, other than re-designing the loops to add more gain (read: *any* gain) at this frequency. Hugh is studying how far back in time this problem has persisted (it's been a problem since at *least* Oct 28), in hopes to find some sort of coincident hardware/electronics activity to blame. But so far, no dice.
Jeff K, Sheila, Jenne, Evan
While we were having an EQ, we took a quick look at what is wrong with ITMY.
Since Cheryl pointed out that this motion is seen in LF and RT, we became suspicous of a problem with top mass V and R damping. Indeed, there was a "bounce" filter engaged in ITMY top mass V damping which must have been a mistake. Once we turned this off the OLTF of the vertical damping looks verry similar between ITMX and ITMY. With this filter on ITMY damping was garbage.
I accepted the change in SDF. We also noticed while doing this that the top mass actuator state for ITMX was 1, while the rest of the quads were in state 2, so we switched that. The large peak at 0.55 Hz that Cheryl aloged is gone now, and hopefully we won't have the problem with long long ringdowns on ITMY.
