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CHAPTER 4:
Basic Operation
Model CRX-6.5K Probe Station
4.5 Temperature
Operation
This section describes basic temperature operation of the probe station; advanced
temperature operation will be discussed in Chapter 5. Before performing any of the
operations, the system must be closed and evacuated as described in section 4.4.2.
Often, there are multiple ways of performing some of these procedures, but we have
chosen steps that represent a good balance between ease of operation and time
efficiency.
The cooling engine in the CRX-6.5K is a two-stage closed cycle refrigerator (CCR). The
sample stage and probes are thermally connected to the CCR 2nd stage through
vibration isolation: the radiation shield stage and probe arms are thermally
connected to the CCR 1st stage through similar vibration isolation.
The recommended operation for variable temperature measurements is to allow the
entire CRX-6.5K station to cool to base temperature and then to warm the sample
stage to the desired measurement setpoint.
4.5.1 Controls for
Temperature Operation
The Model CRX-6.5K uses the CCR and two electronic control loops (one for each
stage) to establish and regulate temperature. This section details the CCR controls
first, followed by the electronic controls.
4.5.1.1 CCR Controls
CCR operation is controlled by the switches located on the CCR compressor control
panel shown in FIGURE 4-10. The default off settings for the various CCR controls are
listed in TABLE 4-1. The compressor supply and return pressures vary according to the
heat load presented to the cold head. During operation, typical supply helium gas
pressure is between 2.00 MPa and 2.14 MPa (290 to 310 psig).
FIGURE 4-10
CCR compressor panel
Switch name
CCR off
CCR on
Supply pressure
2.07 MPa to2.21 MPa at 20 °C
(300 psig to 320 psig at 68 °F)
2.00 MPa to 2.14MPa
(290 psig to 310 psig)
Main power
On
On
CCR on/off
Off
On
TABLE 4-1
CCR compressor default off settings
