Lake Shore Model 331 Temperature Controller User’s Manual
CHAPTER 2
COOLING SYSTEM DESIGN
2.0 GENERAL
Selecting the proper cryostat or cooling source is probably the most important decision in designing a
temperature control system. The cooling source defines minimum temperature, cool-down time, and
cooling power. (Information on choosing a cooling source is beyond the scope of this manual.) This
chapter provides information on how to get the best temperature measurement and control from cooling
sources with proper setup including sensor and heater installation.
Chapter 2 contains the following major topics. Temperature sensor selection is covered in
Paragraph 2.1. Calibrated sensors are covered in Paragraph 2.2. Sensor installation is covered in
Paragraph 2.3. Heater selection and installation is covered in Paragraph 2.4. Considerations for good
control are covered in Paragraph 2.5. PID Control is covered in Paragraph 2.6. Manual Tuning is
covered in Paragraph 2.7. AutoTuning is covered in Paragraph 2.8. Finally, Zone Tuning is covered in
Paragraph 2.9.
2.1
TEMPERATURE SENSOR SELECTION
This section attempts to answer some of the basic questions concerning temperature sensor selection.
Additional useful information on temperature sensor selection is available in the Lake Shore
Temperature Measurement and Control Catalog. The catalog has a large reference section that
includes sensor characteristics and sensor selection criteria.
2.1.1 Temperature
Range
Several important sensor parameters must be considered when choosing a sensor. The first is
temperature range. The experimental temperature range must be known when choosing a sensor.
Some sensors can be damaged by temperatures that are either too high or too low. Manufacturer
recommendations should always be followed.
Sensor sensitivity is also dependent on temperature and can limit the useful range of a sensor. It is
important not to specify a range larger than necessary. If an experiment is being done at liquid helium
temperature, a very high sensitivity is needed for good measurement resolution at that temperature.
That same resolution may not be required to monitor warm up to room temperature. Two different
sensors may be required to tightly cover the range from helium to room temperature, but lowering the
resolution requirement on warm up may allow a less expensive, one sensor solution.
Another thing to consider when choosing a temperature sensor is that instruments like the Model 331
are not able to read some sensors over their entire temperature range. Lake Shore sells calibrated
sensors that operate down to 50 millikelvin (mK), but the Model 331 is limited to above 1 K in its
standard configuration.
2.1.2 Sensor
Sensitivity
Temperature sensor sensitivity is a measure of how much a sensor signal changes when the
temperature changes. It is an important sensor characteristic because so many measurement
parameters are related to it. Resolution, accuracy, noise floor, and even control stability depend on
sensitivity. Many sensors have different sensitivities at different temperatures. For example, a
platinum sensor has good sensitivity at higher temperatures but has limited use below 30 kelvin (K)
because its sensitivity drops sharply. It is difficult to determine if a sensor has adequate sensitivity
over the experimental temperature range. This manual has specifications (Table 1-3) that include
sensor sensitivity translated into temperature resolution and accuracy at different points. This is
typical sensor response and can be used as a guide when choosing a sensor to be used with the
Model 331.
Cooling System Design
2-1
