The cryostat controls the temperature of the CCD chip and it regularly needs
to be filled (about once every 10 hours). As a result, you must fill the
cryostat before commencing observing and before leaving for bed in the
morning. If the weather interferes with observing and you leave early,
you must file a
fault report
to have the cryostat filled in the morning.
Filling The Cryostat
To fill the cryostat, follow the step by step procedure below:
Firstly:
Raise the dome floor (using the control pad) while checking that
everything is clear from the edge and that all trip switches (gate,
ladder and sliding door) are closed. Also make sure that the
emergency stop on the control pad is not pressed in while doing this.
Put on the safety equipment (helmet and gloves).
Unzip the black bag.
Connect the earthing cable on the nitrogen dewar to the earthing point
on the side of the telescope.
Insert the long thin pipe on the nitrogen dewar all the way into the
cryostat.
All valves mentioned below are on the nitrogen dewar. A valve is open
if it is parallel to the pipe it is attached to and a valve is closed
if it is perpendicular to the pipe it is attached to.
To fill up the cryostat:
Close all the valves.
Open the unlabelled valve.
Open valve 5.
Open valve 1.
Use valve 5 to keep the pressure on the guage below 1 bar. The cryostat
is full when you can see and hear the nitrogen pouring onto the floor.
To stop filling up the cryostat:
Close valve 1.
Close valve 5.
Close the unlabelled valve.
Open valve 4, the safety valve, which releases the pressure in the dewar.
To finish:
Wait for the pipe to defrost slightly.
Remove the pipe and the earthing cable.
Zip up the black bag.
Lower the dome floor (using the control pad).
Log the filling of the cryostat in the log book in the control room.
