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Entry  Thu Jun 11 11:48:43 2020, gautam, Update, VAC, Vac failure vacFailure.png
    Reply  Thu Jun 11 16:14:03 2020, gautam, Update, VAC, Vac failure - probable cause is serial comm glitch TP2_tempGlitch.pngPSL_shutterClosed.pngTP2tempGlitches.pdf
       Reply  Thu Jun 11 17:35:34 2020, gautam, Update, VAC, Pumpspool UPS needs battery replacement 
          Reply  Fri Jun 12 01:23:32 2020, Koji, Update, VAC, Pumpspool UPS needs battery replacement 
             Reply  Fri Jun 12 17:32:40 2020, Koji, Update, VAC, Pumpspool UPS needs battery replacement Screen_Shot_2020-06-12_at_17.22.23.png
                Reply  Fri Jun 12 19:02:52 2020, gautam, Update, VAC, Pumpspool UPS needs battery replacement 
                   Reply  Fri Jun 12 19:23:56 2020, Koji, Update, VAC, Pumpspool UPS needs battery replacement 
                      Reply  Fri Jun 12 19:33:31 2020, gautam, Update, VAC, Pumpspool UPS needs battery replacement 
                         Reply  Tue Jun 16 13:35:03 2020, Jon, Update, VAC, Temporary vac fix / IFO usable again Pumpdown.png
                            Reply  Wed Jun 17 16:27:51 2020, gautam, Update, VAC, Questions/comments on vacuum 
                               Reply  Thu Jun 18 11:00:24 2020, Jon, Update, VAC, Questions/comments on vacuum 
                                  Reply  Thu Jun 18 12:00:36 2020, gautam, Update, VAC, Questions/comments on vacuum 
                                     Reply  Thu Jun 18 14:13:03 2020, Jon, Update, VAC, Questions/comments on vacuum 
                                        Reply  Thu Jun 18 15:46:34 2020, gautam, Update, VAC, Questions/comments on vacuum 
                                           Reply  Fri Jun 19 07:40:49 2020, Jon, Update, VAC, Questions/comments on vacuum 
                                              Reply  Fri Jun 19 09:57:35 2020, gautam, Update, VAC, Questions/comments on vacuum 
Message ID: 15408     Entry time: Thu Jun 18 14:13:03 2020     In reply to: 15407     Reply to this: 15410
Author: Jon 
Type: Update 
Category: VAC 
Subject: Questions/comments on vacuum 
I agree there were MEDM fields, but I can't find any record of these channels being recorded till 2018 December, so I don't agree that they were being digitally monitored. You can also look back in the elog (e.g. here and here) and see that the display fields are just blank. I would then assume that no interlocks were dependent on these channels, because otherwise the vacuum interlocks would be perpetually tripped.

Right, I doubt they were ever recorded or used for interlocks. But the readbacks did work at one point in the past. There's a photo of the old vac monitor screen on p. 19 of E1500239 (last updated 2017) which shows the fields once alive.

Sorry but I'm having trouble imagining a scenario how the pressure gauges wouldn't register this before the IFO volume is compromised. Is there some back of the envelope calculations I can do to understand this? Since both the pressure gauges and the TP diagnostic channels are being monitored via EPICS, the refresh rate is similar, so I don't see how we can have a pump temperature / speed / current threshold tripped but NOT have this be registered on all the pressure gauges, seems like a bit of a contrived scenario to me. Our thresholds currently seem to be arbitrary numbers anyway, or are they based on some expected backstreaming rate? Isn't this scenario degenerate with a leak elsewhere in the vacuum envelope that would be caught by the differential pressure interlocks?​

I don't disagree that the pressure gauges would register the change. What I'm not sure about is whether the change would violate any of the existing interlock conditions, triggering a shutdown. Looking at what we have now, the only non-pump-related conditions I see that might catch it are the diffpres conditions:

  • abs(P2 - PTP2) > 1 torr (for a TP2 failure)

  • abs(P3 - PTP3) > 1 torr (for a TP3 failure)

  • abs(P1a - P2) > 1 torr (for either a TP2 or TP3 failure)

For the P1a-P2 differential, the threshold of 1 torr is the smallest value that in practice still allows us to pump down the IFO without having to disable the interlocks (P1a-P2 is the TP1 intake/exhaust differential). The purpose of the P2-PTP2/P3-PTP3 differentials is to prevent V4/5 from opening and suddenly exposing the spinning turbo to high pressure. I'm not aware of a real damage threshold calculation that any one has done; I think < 1 torr is lore passed down by Steve.

If a turbo pump fails, the rate it would backstream is unknown (to me, at least) and likely depends on the failure mode. The scenario I'm concerned about is if the backstream rate is slower than the conduction time through the pumspool and into the main volume. In that case, the pressure gauges will rise more or less together all the way up to atmosphere, likely never crossing the 1 torr differential pressure thresholds.

For the email alert, can you expose a soft channel that is a flag - if this flag is not 1, then the service will send out an email.

There's already a channel C1:Vac-error_status, where if the value is anything other than an empty string, there is an interlock tripped. Does that work?

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