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4.5.1.2 Electronic Temperature Controls
The Model 336 temperature controller provides the electronic control for the Model
CRX-6.5K stage temperatures. The Model 336 has four sensor inputs and two
independent control outputs. Only the two PID (proportional, integral, derivative)
control outputs of the Model 336 are used in the standard Model CRX-6.5K
configuration (refer to Chapter 2 of the instrument manuals for details).
Each stage includes a temperature sensor and a heater. The temperature sensor is the
control input for each loop, and the heater is the control output for each loop. The
controller balances its heater power against the cooling power of the CCR at a desired
temperature setpoint. Since the controller cannot contribute cooling power, the
setpoint must be higher in temperature than the base temperature of the stage for
the controller to operate properly.
If the controller is configured improperly, the controller can provide enough heat to
damage the probe station.
The Model 336 temperature controller is configured at Lake Shore as described in the
temperature controller configuration table (TABLE 4-2). However, the settings should
be re-verified any time the system is moved, serviced or reconfigured
(section 3.8.1.3).
The sample stage is the only stage actively controlled to a temperature setpoint
during normal operation. The other control loop setpoints should be set to zero or the
heaters should be turned off. The sample stage control operates with different control
settings at different temperatures. Nominal values for operation are described in
each of the following sections and summarized in the temperature controller
configuration table (TABLE 4-2). Some adjustments to these settings will be required
during operation. Control of the other three stages is generally limited to warming
the system for sample exchange. They are most often operated by turning the heater
output on and off.
4.5.2 Cooling the Probe
Station
Follow this procedure to cool the probe station. This procedure assumes the probe
station is at room temperature and that the vacuum chamber has been evacuated
following section 4.4.2.
4.5.2.1 Preparing the System
1. Use the z-axis micrometers to raise all probes 3 mm to 4 mm above the sample.
Failure to do so will potentially cause damage to the probe tip or scratch the sam-
ple surface.
2. Turn off the heater outputs by pressing ALL OFF on the Model 336 temperature
controller.
To minimize condensation on the sample, the sample stage can be maintained at room
temperature while the radiation shield is cooled. Refer to section 5.2.1.2 for the
procedure to do this.
4.5.2.2 Starting the CCR
Due to precision tolerance of the CCR second stage moving parts (displacer), the CCR must
not be started if the CCR second stage temperature is above 300 K.
Turn on the CCR using the CCR On switch.
If the CCR compressor does not operate as expected, or if the probe station does not begin
to cool, refer to the troubleshooting information in section 6.3.2.
