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:
- TEMPDET - CCD temperature in degrees C
- DWRN2LV - liquid nitrogen level (percent full) of
CCD dewar
- RESN2LV - liquid nitrogen level (percent full) of
50-liter tank
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:
- TEMPDET = 32 degrees C
- DWRN2LV = 108% full
- RESN2LV = 109% full
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
- Bob Kibrick, UCO/Lick, 22 July 1993 Author
- 13Jun95 TAB Added section 5 on reenabling autofill
from crate
- 2000-Jan-09 GDW Converted to HTML