European Southern Observatory New Technology Telescope

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SOFI cooling down procedure

SOFI COOL-DOWN PROCEDURE
------------------------
 

This is the procedure to cool down SOFI when the Closed Cycle Cooler
looses efficiency and the instrument tends to warm up:

1) Lock the Rotator with the key in Cabinet #1.

2) Disconnect the remote control cable from the CCC compressor.

3) The alarm will trigger - Don't panic! -> Acknowlege the alarm in Cabinet #1.

4) Remove the lid on the LN2 tube on SOFI.

5) Connect the LN2 transfer line to SOFI and toghten well the nut.

6) Tighten the LN2 transfer tube on the LN2 supply dewar.

7) Push 'COOL-DOWN' on the upper left corner of the control panel in Cabinet #1.

8) Watch that the green light 'Valve open' lits.

9) Open the LN2 supply by turning the knurled knob on the dewar tranfer head .

10) Observe the temperature on the Omega Cool-Down Controller to decrease.

11) Leave the system for some hours, and watch the RTAP temperature plot.
 

To shut down:

Proceed in reverse order:

1) Shut off the LN2 valve on the dewar transfer head.

2) Retrieve the transfer tube on the dewar side by ~5mm,
   in order to close the tranfer valve completely.

3) switch to 'COLD' and watch that the green light 'Valve open' goes out.

4) remove the transfer tube on the SOFI side. If LN2 spills out, retrieve
   the transfer tube further from the dewar. (see 2)
 
5) Put the lid onto the LN2 port on SOFI. This will de-activate the
   compressor interlock. The blue light 'CCC' will go on in Cabinet #1
 
6) Reconnect now the remote control line on the compressor.
   If the compressor shuts down, remove the remote cable again and check
   active interlocks...
 
7) Enable the rotator by turning the key in Cabinet #1.

8) Check temperatures, if everything is normal.
 

Remarks:
-------
o The OMEGA controller set-point is at 82 K. The cool-down temp. will never
  reach this value, as the LN2 is heated up to the instrument temp at ~100K.
  However, the tempshould stabilize somewhere at 90...95 K.
 
o There is no way to speed up the cool-down, because the LN2 line is possibly
  clogged with water ice!
 
o If the instrument warms up to fast during the night, it might suddently
  become impossible to cool it down again during day time.
  In this case, SOFI will have to be warmed up definitely.
 
    Follow the procedures described in the emergency manual
    *******************************************************  

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