[Halld-online] what tripped the TAGH hv yesterday?

[Richard Jones]

Hello all,

I had a quick look at the EPICS history related to the unexpected loss of
hv on a the low-energy portion of the TAGH yesterday. Here is what I found.

   1. It happened at 12:43:13 local time, while run 40858 was still in
   progress. Sasha noticed it after the next run 40859 had started but it took
   place while 40858 was still going. Run 40858 ended at 14:05:44, so only the
   last 20 minutes of run 40858 is affected.
   2. It did not happen in response to someone pressing the ON/OFF button
   on the GUI. The last time anyone turned the power on and off in the usual
   way prior to the dropout was at 13:24:58 on 1/11/2018 several days before.
   3. It was not accompanied by a trip event being logged by EPICS
   4. It was not accompanied by a ramp-down, which would be logged by EPICS
   5. The voltages dropped from ~850V down to zero in less than 1s.
   6. At the moment it happened, I was still at church (the perfect alibi)
   7. In spite of that, I doubt it was a miracle :)

Sorry about that last point, but if I hadn't said it, someone would have
asked.

-Richard
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