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Cryogenic

 
 

Introduction to Cryogenic Temeperature Sensors

Cryogenic, or very low temperature sensors, are in a class of their own. Mainly used in low temperature physics research and in space applications, these sensors employ the same principals as standard temperature sensors but may use different materials.

The electrical properties of many materials changes rapidly, and even abruptly, as their temperature approaches absolute zero. In low temperature physics, the experimental set-ups can force special operating requirements on the sensors. For example, there may be strong magnetic fields or ionizing radiation associated with an experiment. Also, there may be significant temperature gradients, so the sensor must be small, and its wiring must not conduct heat into the system.

Types of cryogenic temperature sensors

A detailed coverage of cryogenic temperature sensors is beyond the scope of this document, however, the following table provides an outline of some available sensors:

Sensor Type

Temperature Range

Tolerance to Magnetic Fields

Tolerance to Nuclear Radiation

Comments

Gallium-Aluminum- Arsenide Diode

1.4K to 325K

good

poor?

10µA excitation

Silicon Diode

1K to 475K

ok

poor

10µA excitation

Capacitive Sensor

-

good

good

Prone to drift

Thermocouple

>5K

ok

ok

Poor over all performance

Carbon-Glass RTD

1.4K to 325K

ok

good

Popular, good sensitivity

Carbon-Ceramic RTD

1.5K to 375K

good

excellent

Stable, good performer

Cernox RTD

-

good

excellent

Good performer

Platinum RTD

30K to 800K

poor below 40K

ok

Ok above 70K, useless below 14K

Germanium RTD

0.05K to 300K

poor

ok

Good performer below 30K where it is a secondary standard

Rhodium-Iron RTD

1.4°K to >325°K

ok

excellent

Thin film types, very fast

Ruthenium Oxide RTD

<50mK to 300K

good

good

Good interchangeability

Thermox thermistor

70K to 300K

-

-

Sensitive

The number of suppliers of cryogenic temperature sensors is limited. Try Lakeshore Cryogenic - their web site provides a reasonably complete coverage in this specialist area.