Lake Shore Model 340 Temperature Controller User’s Manual
Cooling System Design
2-1
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. 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 is intended to help the user ask the proper questions about sensor selection, and not to give all
the answers. 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.
Temperature range is discussed in Paragraph 2.1.1. Sensor sensitivity is discussed in Paragraph 2.1.2.
Environmental conditions are discussed in Paragraph 2.1.3. Measurement accuracy is discussed in
Paragraph 2.1.4. Finally, sensor packages are discussed in Paragraph 2.1.5.
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 and
a very high sensitivity is needed for good measurement resolution, 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 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 340 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 340 is limited to 300 mK 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 1-1) 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 340.