The commissioners are aware of this now and some people are looking into it, but it seems that the new DARM offloading scheme has been sending big kicks (a few 10s to 200 microns) to the ETMX HEPI at almost every lockloss from NLN. This doesn't seem to be happening with ETMY. On attached trends, top blue trace is the ISC tidal signal sent to ETMX HEPI, yellow is the ISI watchdog state, bottom is the ISC LOCK state number. The ISI doesn't trip every time, but it's happend 5 times just over the last week. This isn't normal behavior, but it seems like we've just been ignoring this for a while. I recall having this happen a bit before the end of O4a, and we added a filter to the input to the HEPI model, but that just seems to slow the kick a bit.
Louis and I modified the aL1L3 filter (FM6) in ETMX_L1_LOCK_L by replacing the single pole at 50 Hz with a complex pair at 30 Hz, so that this offloading filter rolls off like 1/f above 30 Hz. Since the output of L1_LOCK_L is offloaded to HEPI, we suspect that this is what was causing the kick at EX. No DARM control is directly applied to EY, so that would explain why EY does not trip. The most recent lockloss did not trip anything.
It didn't trip the ISI, but we still are spiked up to about a third of the actuators drive range on the last lockloss. I'm less worried about tripping the ISI than I am about damaging something on the suspension or HEPI. attached trend shows the ISC signal to ETMX HEPI and the drives on the horizontal actuators at the last lockloss.
Evan added a 0.1Hz low pass filter into FM3 of H1:LSC-X_ERR_TIDAL_ERR, and for symmetry into H1:LSC-Y_ERR_TIDAL_ERR. Turned on filters and sdfs. We expect this to stop the kicks and not effect the slower tidal offloading: titdal to UIM is ~0.03Hz, to HEPI would be even slower 68749.
Since the 0.1Hz LP has been added, the two locklosses have not kicked the HEPI. See attached zoomed out and zoomed in plots.
