I started to have a quick look at the lockloss last night where the apparent range was elevated. It looks like we had some high frequency peaks above 20 kHz come up. So, perhaps this combination of ring heaters and circulating arm power rings up some mode(s) there that we'll need to damp.
Both attachments are the same times, just different x-axis zooms.
- All 10 avg, BW=1.499
- Ref0: 1364208299. Before range or PI BLRMS elevated.
- Ref1: 1364208699. Range still 'normal', PI BLRMS band 2 elevated.
- Ref2: 1364208950. Range elevated, overall spectrum looks like something must have been saturating, but no one clear peak causing it. Forest around 20 kHz elevated.
- Ref3: 1364209050. Range elevated, saturations much more egregious, some peaks at 20 kHz further elevated.
- Further times don't really add any more info, some glitch-like spectra and then lockloss.
In this next lock, we are now well past the ~4 hours 10 min that it took to ring up that 20 kHz forest. So, perhaps with the additional thermalization of the ring heaters over the subsequent hours, we're going to be okay? We'll just have to see.
It appears that we have a PI ringing up right before the lock loss at 20.862 kHz, this coincides with the arm 4th order mode.
Yikes. There's perhaps a lack of AMD coverage at these frequencies [slide 5, presentation]. There's a gat least one of Pitch and Yaw orientated mechanical modes that could easily have good overlap in that region, that I had a glance at. This raises worries over at LLO side; I guess I should re-jig the monitoring frequencies.