Temperature Sensor

A Temperature Sensor consists of two different types of metals, joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created that can be correlated back to the temperature. Thermocouple alloys are commonly available as wires.

Thermocouples are simple, resilient and can be used over a wide range of temperatures (from -330°F to 4170°F (-200°C to 2300°C)), and permit great precision.

Thermocouple applications include:

• Temperature sensors in thermostats in home appliances
• Flame sensors in safety devices for gas-powered appliances
• Temperature measurement for kilns, gas turbine exhaust, diesel engines and other industrial processes

In contrast to most other methods of temperature measurement, thermocouples are self-powered and require no external form of excitation. The main limitation with thermocouples is accuracy; system errors of less than 34°F (1°C) can be difficult to achieve.

The following criteria is used in selecting a thermocouple:

• Temperature range
• Chemical resistance of the thermocouple or sheath material
• Corrosion, abrasion and vibration resistance
• Installation requirements

Thermocouples are available in different combinations of metals or calibrations. The most common types of thermocouples are base metal thermocouples, while noble metal thermocouples are used in high-temperature applications. Each calibration has a different temperature range and environment, although the maximum temperature changes with the diameter of the wire used in the thermocouple.