Filling the CCD Dewars with liquid nitrogen and operating the alarm system.

Unscrew the white plastic protective pipe from the filler tube on the roll-around dewar. Insert the filler tube in the bottom of the CCD dewar. ( Make sure you are using the correct fill tube - each CCD dewar has a different fill tube, which is labeled ). Screw the cap down, then back it off one turn so that if ice forms you can wiggle tube up and down . Remove the black & red plug from beneath the loudspeaker (attached to the telescope drive electrical cutoff on the east wall). This disables the telescope drives, in case you forget that the telescope is attached to the dewar. Open the output valve. Dewar should fill in about 10 minutes to fill. Check to see if filler tube is defrosted, then take it out and put the protective plastic pipe back on. Before replacing the black & red plug back in its receptacle, make sure the drive enable switch on the electronics rack in the control room is on "disable". Otherwise, the telescope could run away.

[ Below is out of date - alarm has been disconnected]

There is one alarm for the dewar. There is a box on the north side of the top box labeled "CCD temperature alarm". It has two dip switch blocks with eight individual switches each. Only the six switches on the left of each block are used. Make sure only one switch on each block and the same switch on both blocks is on. The bar graph LED shows the temperature of the chip. If all are on the temperature of the chip is -100 C (or colder). If any LED is out, then the unlit LED tells you the temperature as follows:

LED 1 = -75C    LED 2 = -80C  LED 3 = -85C 
LED 4 = -90C    LED 5 = -95C  LED 6 = 100C 

-105 =  106K         -55 =    3.1K              -5  =   290 Ohm
-100 =   68 K        -50 =    2.3K               0  =   239 Ohm
-95 =    45K         -45 =    1.8K              +5  =   197 Ohm
-90 =    30 K        -40 =    1.4K             +10  =   165 Ohm
-85 =    20K         -35 =    1.1K             +15  =   139 Ohm
-80 =    15K         -30 =    848 Ohm          +20  =   117 Ohm
-75 =    10K         -25 =    672 Ohm          +25  =   100 Ohm
-70 =     7.5K       -20 =    539 Ohm          +30  =    85 Ohm
-65 =     5.5K       -15 =    435 Ohm          +35  =    73.2 Ohm
-60 =     4.1K       -10 =    354 Ohm          +40  =    63.1 Ohm

What to do if the alarm sounds.

If temperature alarm sounds, check temperature as follows. Find the Fluke 77 multimeter. Set all dip switch switches on set temperature dip switch to off. Plug in Fluke into the banana connectors on the alarm box. Checked the resistance. If greater than 1000 ohms fill dewar and hope for the best. If less than 1000 ohms call for assistance as pumping the dewar down and oxygen flooding will probably be required. If the ion pump alarm sounds, check the LED bar display on the ion pump. If the display is stable with 1 to 8 segments illuminated it's OK. Check if nitrogen vapor is coming out of the filling hole. If that's OK fill dewar with liquid nitrogen. Sometimes removing power momentarily from the ion pump and plugging it back in restores operation. If not, call for assistance. Pumping and oxygen flooding may be required.