I was tasked by Sheila to find out which of the 1st violin mode harmonics are consistently rung up. We were hoping to see just a few modes that like to ring up so we can have the guardian damp them automatically. However, pretty much everything in 1kHz rings up over time (also true back in O1). Some of the lines seem to be ringing down on their own and some don't. Because we only have 2-3 free violin filter banks per test mass I chose to damp some of the lines that are high and don't ring down on their own. The lucky frequencies that will be damp automatically by the guardian are:
[ITMX]
992.42Hz -- MODE9: FM8(BP), FM2(-60deg), FM4(100dB), -10gain
994.27Hz -- MODE10: FM5(BP), FM2(-60deg), FM4(100dB), -10gain
[ITMY]
994.65Hz -- MODE9: FM8(BP), FM2(-60deg), FM4(100dB), +10gain
998.81Hz -- MODE10: FM8(BP), FM2(-60deg), FM4(100dB) -10gain
[ETMX]
1003.67, 1003.78, 1003.91 -- MODE10: FM1(BBP), FM2(-60deg), FM4(100dB), +30gain -- Luckily the phases work out such that I can make a broader bp filter that covers all three lines. I wish to make more of these for other test masses but they weren't as straight forward.
1004.54 -- MODE9: FM9(BP), FM2(-60deg), FM4(100dB), +10gain
[ETMY]
1009.44, 1009.49 -- MODE1: FM6(BBP), FM4(100dB) +15gain (these two lines are generally the highest of 1k violin amplitude. I don't want to crank up to the gain too much. Just let them damp slowly, safely, and surely)
With permission from Keita I took the IFO out of observing briefly to test all the settings (LLO was down), wrote them in the ISC_GEN_STATES.py, and accepted the differences in the SDFs. I haven't hit the load button yet. I hit load button after a lockloss.
Note: BBP = Broad Band Pass filter (not that broad, actually, just broader than usual)
All the settings were tested for 30+ minutes and will be monitored until the end of shift. I also updated the violin mode table.
Notice that the damping filter of the 1009Hz lines may have an effect on the 2kHz glitch line reported here.
7 hours later the 1009.44Hz and 1009.49Hz are continued to be damped (I gave them a very small gain given their amplitudes). Other modes seem to be done damping.
Borja: I hope the "effect" is a positive one!