Whenever the NIRC2 #2 cold head temperature goes above its set point by approximately 5 degrees (i.e., increases from 50K to 55K), the auto-pump system will kick on. As of this writing, this event has occurred only on those occasions when the CCR system becomes unavailable for approximately two hours or more (typically due to difficulties with the facility glycol system).

The following procedure should be followed once temperatures have returned to their nominal values (in particular, thead2hi is again 50K and controlling close to that level). Note that there is no particular rush to return the system to its nominal (i.e., solenoid valve closed and turbo-pump off) state, however, ideally, it should be followed within a few hours after the cryo system is stable for at least two reasons:

  1. avoid pump vibration for adaptive optics observations, and
  2. close off the solenoid-controlled valve that, in the worst case, might expose NIRC2 to atmospheric pressure.

Procedure:

  1. Confirm that the lakeshore alarm was indeed triggered by typing ad 5 "ALARMST?_B". The value will read 1,0 (see caveat below) if the system is in the over-temp (pump-on) state.
  2. Use snaptemps to record the state of the cryo system and save the file in your records for later.
  3. Arrange for a person on the summit to be in the AO enclosure.
  4. Have that person confirm that the pump is on (it is loud), that the pump is not escessively hot (should be only warm to the touch), and that the solenoid valve is open (black plunger extended).
  5. After preparing the person in the enclosure to listen for the relay and watch NIRC2 from the telephone handset position, at the nirc2eng at waikoko prompt type td 5 "ALMRST".
  6. The expected behavior (witnessed for example following the July 9, 2010 failure) is: the sound from the relay is clearly audible, the pump goes off, and the solenoid valve closes (indicated by the back plunger returning to its flush position in the yellow-cylinder valve housing).
  7. Record cryo state with snaptemps again, and save the file.
  8. Monitor the sytem for the next approximately 4 hours, taking occasional snaptemp measurements.

Caveat regarding NIRC2 cryo alarm status

There has been much confusion about the meaning of the return from the ad 5 "ALARMST?_B". As of this writing (August 22, 2010), we are fairly certain that: 

0,0 => No alarms on 
1,0 => High temp alarm (pump on until reset) 
0,1 => Low temp alarm (no action required)
1,1 => Both alarms on

In particular, on August 22, 2010 the returned value was 0,1 and:

  1. Visual inspection confirmed pump off
  2. Temperature never reached 55K
  3. nirc2dewar.watch returned "OK"