The commissioners have been complaining about too much motion in Yaw on the BS (almost 2microns peak to peak at 10 mHz (!!)).
We know we have some pick up between Z and RZ (see the various SEI logs from the last 6 months), so I switched from a ~100mHz blend in Z to a 750mHz. Relaxing the actuation in Z reduced the pick up seen in RZ.
I was afraid to degrade pitch with this change, but we improved yaw by a factor of ~5 without changing the pitch integrated RMS (it introduced a peak around 1Hz though).
I've tried to implement a 250mHz blend, but no improvement...
Thus, the configuration that seems to satisfy the commissioners is:
- Tbetter: X, Y, RX, RY
-Tcrappy: RZ
- T750: Z
I'll check what is the status of this "pick up" on the other chambers ASAP.
Yes, this was certainly better for PRMI stability.
We now need to work some more on the angular stability of the other loops. Peeking over Kiwamu's shoulder, I see that the RMS of the other DRMI mirrors is ~0.1 urad (for 0.01 < f < 0.5 Hz). We should tailor the ISI and HEPI loops to move this RMS down to lower frequencies (0.01-0.1 Hz) so that the WFS loops can handle it.
I think that this is the configuration that we want for now, one comment is that it would be worth plotting the oplev signals only up to 19Hz (or 10Hz or whatever frequency it is that cuts off that ugly peak), the 29Hz peak is room fans, I'm guessing that the 19Hz peak is an oplev pier resonance, then we could get an RMS that better represents the optic motion.