Autofills

The 3.8-liter dewar inside of HIRES consumes about 5% of its liquid nitrogen per hour, yielding a hold-time of approximately 20 hours. (This hold-time will vary somewhat depending on the ambient temperature inside of HIRES.) The computer will automatically initiate a dewar fill operation when the LN2 level in the 3.8-liter dewar reaches 10%. Manual fill operations can be initiated at any time. However, frequent "topping off" of the dewar is wasteful of liquid nitrogen, as a considerable volume is consumed in cooling down the plumbing between the 3.8-liter dewar and the 50-liter tank from which it is refilled.

Keywords

The following keywords display the status of the HIRES CCD dewar system: NOTE:These keywords will not return valid results during CCD readout, since communication with the Leach utility board is blocked by the readout. During CCD readout, these keywords will take on obviously bogus value, specifically: An alias has been added to quickly read these keywords;
   nuu% ln2

Requested Fills

To initiate a computer-controlled dewar fill operation, use the command:
	nuu% modify -s hires utbn2fil=on    
which from the kics account on nuu can be abbreviated as:
	nuu% m utbn2fil=on
One can also invoke a fill from the pulldown menu. The automatic dewar fill software will automatically terminate the fill operation when the dewar becomes full.

Stopping Fills

To terminate a computer-controlled dewar fill operation manually, use the command:
	nuu% modify -s hires utbn2fil=off  (or m utbn2fil=off)
This will work regardless of whether the computer-controlled dewar fill operation was initiated by the computer or via a m utbn2fil=on command.

Manual Fills

To fill the dewar manually if the computer is down, use the manual fill toggle switch attached to the 50-liter nitrogen tank which is located adjacent to the HIRES electronics vault on the right nasmyth platform. You will need to monitor the status of the fill and turn the toggle switch off when you are done. The sensor electronics module on the 50-liter tank will beep when the 3.8-liter is 97% full.

Dewar Warming

If an LN2 autofill does not complete due to failure in air compression, disconnected wires or fittings, or other hardware problems, the dewar will begin to warm up. The cron job hires.dewar.watch will send verbal messages to the waialea speakers, and email messages to interested persons, at ten minute intervals. Read the messages carefully to help determine the source of the problem. Once failed, the controller software will disable the autofill mechanism, and one will need to reenable it on the CCD crate. Log on to the crate as follows:
	nuu% telnet hccdcrate
	    
	login: target
	password:
At the VxWorks prompt (->), reenable autofilling by setting the value of the global variable auto_fill to 1:
	-> auto_fill=1
If successful, this command will return with no errors (value=0). There is also a keyword mapped to the VxWorks global variable. This keyword (autofill) can be set to 1 or 0 and its value will propagate to auto_fill.

Ion Pump

To check the status of the ion pump attached to the 3.8-liter dewar, use the command:
	show -s hires ionpump		(or s ionpump)
This will return a status of OKAY if the ion pump is on. If it returns a status of FAILED, then the ion pump has switched off, either due to a power failure or due to excessive current, which may be indicative of the dewar warming up. That can be confirmed by checking the detector temperature with 's tempdet'.

The ion pump status can also be checked locally by entering the HIRES electronics vault on the right nasmyth platform. The ion pump is located on the middle shelf to your right as you enter the vault. The meter reads the current in microamperes and should typically read about 6 microamps. A significantly higher reading indicates a probable dewar leak.

Modification history