IRCAM LN2 Autofill Service

This document describes connections and service for the IRCAM LN2 autofill system. When IRCAM is on the telescope, at the beginning of each night the system will need to be disconnected, and reconnected at night's end.

Disconnecting the system

It should be possible for the 160-l supply dewar to remain in a fixed position that does not interfere with the telescope, as shown in this image. However, these instructions assume that the supply dewar must be moved.
  1. Unplug the solenoid valve 3-prong power cord from the black and white autofill control box, which piggybacks on the IRCAM power supply.
  2. Using an 11/16 inch open-end or crescent wrench, disconnect the flare fitting on the IRCAM dewar base, indicated in the following image:

  3. Hook the cryo line to the storage dewar. If necessary, wheel the supply dewar E of the pier.

Connecting the system

  1. The telescope must be at the home position. Wheel the supply dewar to a position just NE of IRCAM. Extend and support the fill line, and hand-screw the F flare fitting onto its mate on the dewar base until tight; this may require moving the fill line around slightly. Tighten with an 11/16 inch open-end or crescent wrench.
  2. Plug in the solenoid valve to the black and white autofill control box mounted on the IRCAM power supply.
  3. Make sure that the supply valve on the 160-liter dewar is open.

System description

The autofill system consists of a control timer and circuit that starts a fill at 0800 daily, and fills to overflow of the dewar where a sensor stops the fill cycle. The timer will switch off the solenoid after 20 minutes in the event of sensor or circuit failure. When filled and stored vertically, the dewar has a hold time of more than 34 hours. When on the telescope, the fill level and hold time will be reduced by a small, undetermined amount.

It has been observed that the dewar begins to dump LN2 within 2 hrs of being filled when at a zenith distance less than 59 degrees. With a normal morning fill schedule dumping LN2 should not be a concern.

Monitoring the IRCAM temperature

The IRCAM temperature is logged at 10 minute intervals, stored in the file mesa:/var/local_logs/ircam_temp.log. To view the log real-time, use the perkins pulldown-menu selection "Instruments - IRCAM Temperature Monitor", which will launch an xterm with an active tail of the file.

Programming the timer

The timer is a consumer-level unit that occasionally has its memory reset when AC power is applied to it. If this occurs, the display time will reset to 12:00 AM, and autofills will not occur. Follow these instructions to reprogram the time and autofill cycle.
  1. Set DAY, HOUR, and MIN by holding down the TIME SET button and simultaneously setting these buttons. Make sure AM or PM displays appropriately.
  2. Hit the PROG button, and the LCD display will update with Prg 1, and the light bulb symbol on the display will be on.
    To set the program 1 ON time, first hit the DAY button several times until all 7 days of the week are highlighted. Then, hold down the HOUR button until it reads AM 08:00.
    To set the program off time, hit the ON/OFF button, and the light bulb symbol will change to off. Now, hit the DAY button again several times until all 7 days of the week are highlighted. Then, hold down HOUR and MIN until the OFF time reads AM 08:20.
    To exit program mode, hit the TIME SET button again.
  3. Hit the MODE button until the display reads Auto.