Previously posted as comment to 17504.
Note that ISI Stage2 was a State3 trip meaning that the Damping Loops were still functional. It would be nice to know when/why the stage tripped. But I'd guess that the Guardian was set to fully isolated before the ~0700utc short lock and was untripped during the short lock, likely triggering during acquisition and then triggering again at the trip. That is what I first thought.
See attached--It looks like the stage2 when isolated survived the IFO lock loss but not the MICH reacquisition. This means, we can use the Guardian to transition the ISI between Isolated Damped and Fully Isolated with tripping nor requiring operator intervention.
This is a 50 minute stretch so the IFO lock Loss is only a couple minutes before the St2 WD trigger but there may be enough time to deisolate stage2. Looking at a zoomed in full data, looks like a full 70+ seconds after lock loss based on this CAL_DELTAL channel. The second lock loss had even more time so I don't think it is tied to the lock loss but more to the reacquisition.
Of course, we also need to show that turning Stage2 Isolation loops on is a positive thing.
When I look at the MASTER_(local-drive)DRIVE_DQ, there isn't actually a data point(full data) that exceeds the trigger threshold. These are the channels the watchdog plotting scripts display. However, when I look at the OUTF_SATURATION totalizers, I see that indeed H1 had 2 saturations (I've set this counter threshold to 31000cts.) All the other drives had no saturations at the lock loss. I wonder if there is a way we could ride this out? Of course if we hadn't shut off the Isolation, we probably would have a lot more.