Within a min afer a lockloss, the ISI ETMY ST1/2 WDs tripped. The medm said that it was ST1 T240 and the plots showed a slow drift to the WD trip level (plot attached). HEPI moved 170 um after lockloss before tidal began to bleed down. A further investigation is ongoing by the SEI team.
Looks like this is a trip we will suffer whenever the drive to the HEPI is large enough at the time of lockloss. That doesn't necessarily mean the length of lock but it is certainly related. If the tide turns around and the offset given to HEPI heads back to zero, we could be fine after a long lock stretch.
The attached 30 min second trend plots are around the three most recent locklosses from some low noise state. In each case you can see the T240 tilting towards trip level but only the most recent trip was the tidal offset large enough to 'tilt' the T240 long enough to hit the trigger. The HEPI output from ISC is in nm.
Is the problem the bleed off too fast? It seems this is 2um/sec. Is there horizontal to tilt coupling that needs to be addressed? Is it a problem anyway? The T240 will likely take a couple minutes at worse to settle and another minute for the ISI to reisolate.
