Currently the Cryoelectronics board is fully capable of running the cryostat. One of the first things that we would like to be able to do is to automatically cycle the fridge. This requires building a state machine in python that checks the various temperatures inside the cryostat and depending on the readings it should hold its current heater settings or step to the next set of heater values. At the bottom of the page is a copy of the SPT fridge cycle that works quite well in the SPTPOL cryostats, and could easily be adapted to other cryostats.

Channel mappings

Physical device inside cryostat	Cryoelectronics board name
Ultra Head	channel 0
Helium 4 Interpump	channel 1
Helium 3 interpump switch	channel 2
Interhead	channel 4
Helium 3 interpump	channel 5
Helium 3 Ultrapump switch	channel 6
Exchanger	channel 8
Helium 3 Ultrapump	channel 9
Main plate	channel 12
Helium 4 interpump switch	channel 13
Heater He 4 interpump	Heater Channel 3
Heater He 3 Interpump	Heater channel 4
Heater He 3 ultrapump	Heater channel 5
Heater He 4 interpump switch	Heater channel 0
Heater He 3 interpump switch	Heater channel 1
Heater He 3 ultrapump switch	Heater channel 2

The Following is a brief outline of the fridge code that needs to be written

Start cycle

STATE 1

set Heaters 1-6 to zero DAC counts and the Switches to 0 Wait until the heat switches drop below 7 K

STATE 2

Set Heater 3 to 32376 DAC counts (12 volts), Heater 4 to 21584 DAC counts (8 volts) Wait until helium 4 interpump> 44 k

STATE 3

Set heater 3 to 10388 DAC counts ( 2.5 volts), Heater 4 to 32376 DAC counts (12 volts), Heater 5 to 5194 (3.5 volts) (note the resistor for heater 5 is 1/2 the value of heaters 4 and 5) Wait until helium 3 interpump> 35K

STATE 4

Set heater 3 to 10388 DAC counts ( 2.5 volts), Heater 4 to 6745 DAC counts (2.5 volts), Heater 5 to 17808 (12 volts) Wait until helium 3 ultrapump> 35K

STATE 5

Set heater 3 to 6745 DAC counts ( 2.5 volts), Heater 4 to 6745 DAC counts (2.5 volts), Heater 5 to 4722 (3.5 volts) Wait until mainplate< 4.8K

STATE 6

Set heater 3 to 0 DAC counts, Heater 4 to 4047 DAC counts (1.5 volts), Heater 5 to 2698 (2.0 volts) Wait until mainplate< 4.5K

STATE 7

Set heater 0 to 300 DAC counts ( 4.5 volts), Heater 4 to 6745 DAC counts (2.5 volts), Heater 5 to 4722 (3.5 volts) Wait until Helium 4 Interpump< 7K

STATE 8

Set heater 0 to 300 DAC counts ( 4.5 volts), Heater 1 to 300 DAC counts (4.5 volts, Heater 4 to 0 DAC counts, Heater 5 to 0 Wait until 10 minutes has passed

STATE 9

Set heater 0 to 300 DAC counts ( 4.5 volts), Heater 1 to 300 DAC counts (4.5 volts, Heater 2 to 300 DAC counts (4.5 volts) hold

Copy of SPT's fridge cycle

Until the above state code is written/debugged, this is a copy of SPT's fridge cycle slightly adjusted to work on the cryo board. It works quite well to cycle the fridge. Copy of the SPT fridge

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This topic: CryoElectronics > WebHome > PythonFridgeCycle Topic revision: r4 - 2010-07-16 - SouthPoleTelescope

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