Lake Shore Model 218 Temperature Monitor User’s Manual
Sensor Considerations
2-1
CHAPTER 2
SENSOR CONSIDERATIONS
2.0 GENERAL
Selecting the proper sensor is vital to good temperature monitoring. This chapter covers Temperature
Sensor Selection in Paragraph 2.1, Calibrated Sensors in Paragraph 2.2, and Sensor Installation in
Paragraph 2.3. This chapter describes cryogenic applications, but many ideas apply to other
temperature measurements.
2.1 TEMPERATURE SENSOR SELECTION
This section covers general information about sensor selection. Find additional information on
temperature sensor characteristics and selection in the Lake Shore Temperature Measurement and
Control Catalog.
2.1.1 Temperature
Range
The experimental temperature range must be known when choosing a sensor. Some sensors can be
damaged by temperatures that are too high or too low. Manufacturer’s recommendations should
always be followed. Sensor sensitivity is also dependent on temperature and can limit a sensors
useful range. 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 218
are not able to read some sensors over their entire temperature range. Lake Shore sells calibrated
sensors that operate down to 50 mK, but the Model 218 is limited to operation above 1 K in its
standard configuration.
2.1.2 Sensor
Sensitivity
Temperature sensor sensitivity measures how much a sensor signal changes when the temperature
changes. It is important because so many measurement parameters relate to it. Resolution, accuracy,
and noise floor depend on sensitivity. Many sensors have different sensitivities at different
temperatures. For example, platinum sensor sensitivity is good at higher temperatures, but drops
sharply below 30 K. It may be difficult to determine if a sensor has adequate sensitivity over the
experimental temperature range. Table 1-2 lists sensor sensitivity translated into temperature
resolution and accuracy at different points. This is typical sensor response and can be used as a
guide to choose a sensor for the Model 218.
2.1.3 Environmental
Conditions
Environmental factors such as high vacuum, magnetic field, corrosive chemicals, or even radiation
may limit effectiveness of some sensors. Lake Shore offers sensor packages that withstand
environmental factors found in typical cryogenic cooling systems.
Magnetic field experiments are very common. Field dependence is an important selection criteria for
temperature sensors used in these experiments. Table 1-2 states the field dependence of most
common sensors. The Lake Shore Temperature Measurement and Control Catalog includes detailed
field dependence tables along with specific data on other environmental factors when available.
Summary of Contents for 218S
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