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    PIDs

    PID Temperature Control for the βNMR cryostat


    Temperature control is done by a LakeShore model 330 and/or 331 temperature control operating one or two heaters and using feedback from on of the two thermometers (see thermometry).

    These controllers are shown below: The 330 is on top and has a red coloured LED readout. The 331 is below and has a blue LED readout. They are located on the rack at the southwest corner of the platform.

    LakeShore Temperature Controllers

    For some fundamentals of PID temperature control see this excerpt(pdf) from the LakeShore 331 manual. There is also a general discussion with references here(pdf).

    In order to cool, one must have helium (or nitrogen) getting to the cryostat. The helium cools the cryostat by being pumped through the needle valve and capillary into the block by the Sogevac pump.
    The cooling power produced by this refrigerant is balanced by heat input from the electrical heater(s). The amount of heat applied is altered adaptively by the PID controller to keep the temperature at the constant value chosen as the "setpoint"

    Experience has shown that the numeric values of the optimal PID parameters characterizing the response of the controller depend on temperature but are mainly determined by the response characteristics of the thermometer.

    Thus Bassam recommends the following PID values for the associated temperature ranges:

    Temperature Range
    		 P
    		 I
    		 Heater Range
    4-10 K
    		 1
    		 600
    		 Medium
    10 - 20 K
    		 5
    		 200
    		 Medium
    20 - 30 K
    		 8
    		 100
    		 High
    30 - 40 K
    		 20
    		 60
    		 High
    40 - 60 K
    		 80
    		 40
    		 High
    60 K - Room Temp
    		 500
    		 20
    		 High

    Note: D is invariably better left at ZERO.

    The temperatures of the sample and radiation shield and block dropped on a typical experiment as
    Cooling Time
    and the temperatures of the sample and the radiation shield are graphically shown below
    Cooling Time

    The Lakeshore Controllers are GPIB devices attached to the CAMP interface.

    CAMP Lakeshore Device 'Sample1'

    The output produced by the controller to the heater has 4 distinct ranges: off, low, medium and high. This parameter can also be set remotely from CAMP with the parameter "heat_range" see fig. above.

    The CAMP system chooses PID values based on the zone, but these can be changed by going into setup within camp and altering the PIDs. From CAMP settings of the controller can be adjusted remotely from the counting room. Go into the "setup" menu (see above) to get to the following menu (where the PIDs) can be set:

    CAMP LakeShore Setup


    Page last modified: 07/23/09 02:45 by Andrew MacFarlane.