WFI LN2 Refill Procedure

• Be sure that the telescope is at Zenith.
• Record temperature (sensor 2) and vacuum values in the log (on the south side of the dome wall). Typical values are 167.0K and 2-3x10-6 mB. Temperatures above 167.5K and pressure values above 8x10-6 mbar should immediately be reported to ODT.
• Remove cap from CCD dewar (on the NE side).
• Open LN2 tank valve for short while so that only LN2 goes into the dewar.
• Connect hose from liquid nitrogen tank to the CCD dewar.
• Open valve and start filling the CCD dewar. Typical refill time is 10-15 min.
• The LN2 tank pressure should be 0.4 mB, the refilling should not be done with high pressure in the tank.
• On the other hand, if you suspect there is not enough pressure in the liquid nitrogen tank or refill is taking too long, you can open the valve (small handle) for 20-30 seconds. Do not forget to close it.
• Close valve when liquid nitrogen starts over flowing from the CCD dewar.
• Unplug hose from CCD dewar and put the cap back on.
• Finally, re-record the temperature and vacuum values in the log.