Dave, Nutsinee
Today we did a little test to confirm that there's no way to aviod CO2 laser tripping when oaf computer and IO chasis are bering restarted by unplugging the chillers from the front end which we thought might have worked at one point. Turned out as soon as the chillers were unplugged from the cables the CO2 controller box tripped immediately and the drawn currents went down to 0.7 A for TCSX and 0.8 A for TCSY (from their nominal at ~22A). Funny thing is when I went back to restart the controller boxes after plugging the chillers back in there're no red lights indicating that they had been tripped. They simply stopped lasing. The laser status looks like it's never tripped. So if somebody unplug the chillers and the lasers don't work, there's currently no obvious way to know from the control room that the chiller(s) have been unplugged (except that TCS laser locking guardian might throw fist and unreasonable DAC outputs).
Before I went out to the mezzanine I paused TCS guardian so that they won't try to talk to the chillers when they're disconnected. As soon as the chillers were disconnected (10:52 AM local) DAC output 1(ITMX pzt), 4(ITMX chiller), 9(ITMY pzt), 12(ITMY chiller) freaked out and dropped/jumped far from nominal. They didn't come back to their nominal values until I restarted the TCS laser locking guardian nodes after bringing everything back to normal.
We need Alastair's magic box to prevent TCS from tripping everytime oaf/dac is powered down.
TCS CO2 system layout can be fround here
If by magic box you mean the summing chassis, that wont stop the lasers from shutting off when the OAF computer goes down. That is installed at LLO and it still goes down. The summing chassis was for a different problem
Also on the CO2 control boxes in the LVEA after the laser goes down, red lights dont show. It should be that not all the green lights are displaying. That is your warning something is wrong. Its not until you rehit the red "gate" button that all the lights will come back on illuminating green (my memory could be wrong though).
Also you can see if the laser is ON by looking at the TCS screens and seeing the power coming out of the laser. Or you can look at the flow of the chillers, etc on the main TCS MEDM screens to see if the chillers are working