On Thursday we (Sheila, Daniel & I) increased the Thresholds on the TIDAL RED TRIGGER when the very low value kept the ISC driving the HEPI too long. It would appear there was only one long lock stretch with these settings before Sheila reported that the tidal was not coming on, in some locks. Beam diverters?... When Nutsinee reverted the values of the RED TRIGGER Thresholds, things seemed to start working properly again. I don't pretend to understand this and it is pretty clear that reverting the values solved the problem. See attached four days trend, when lowering the THRESH_ON value started the TIDAL running (I did not zoom in but it looks correlated.) But also seen is the REDTRIG_INMON has dropped to 153000 from the previous 165000. If this level (Power?) change was enough to disable the 8000 count THRESH_ON setting, clearly something else must be in play. I need to understand the triggering better to really understand this. We don't want the ISI to trip as it can be several minutes for the T240s to settle and be ready for complete ISI isolation but obviously we need the TIDAL relief to engage.
It might be that the threshold wasn't exceeded, when it tried to engage REDLOCK. The fundamental problem is that neither the arm power nor the trigger thresholds are getting scaled with the power up, so the threshold needs to be set low enough to catch the lock at low power. Once you power up, the arm powers will then be far above threshold. Too much it seems. Probably best to figure out how to scale the NSUM value with the inverse of the input power. Alternatively, one could rewrite the trigger so that it scales automatically.
Opened FRS Ticket 6787. This has happened a few more times this evening.