Gabriele refit the 11/15 LSC FF data 74220, allowing a higher magnitude at low frequency to give us a better fit, fit attached. I lowered the Q of the 17.7Hz feature and added this filter to MICHFF FM8 as "11-15-23B". We'll want to turn this FF slowly or before Tuesday Maintenance, as the excess low frequency could cause instability.
Plot attached, red is current MICHFF FM7, blue is new FM8 (double the strength of current FF <8Hz), green is Gabirele's original design before adjusting Q of 17.7Hz feature (all including the high pass filter in FM10).
I lowered the 17.7Hz Q's by a factor of 4 from the original design, to minimize effect on KAPPA_TST error 74259:
- Pole @ 17.8247Hz, Q = 194.416 -> reduced to Q = 48.604
- Zero @ 17.7598Hz, Q = 170.142 -> reduced to Q = 42.535
Turning this FM8 MICHFF on 2023/12/05 16:07:00 UTC to 2023/12/05 16:09:00 UTC, did not cause a lockloss. Comparing to 2 minutes before with current MICHFF FM7 16:02:00 UTC to 2023/12/05 16:04:00 UTC, DARM looks better with new FF but this was only a couple of minutes into NLN when the ADS lines were turning off, low frequency DARM shows no obvious change. As this new FF has higher gain at low frequency, you can see this as a factor of ~5 higher output on MICHFF_OUT, trend attached.
