Thermocouples
Thermocouples are devices that measure temperature by using two dissimilar metal wires joined at one end to form an electrical junction. They produce an electrical output that can be measured and used to determine the temperature of the junction. They are used in a wide range of applications, including laboratories, industrial control systems, automotive and aerospace systems, and medical equipment.
Thermocouples are so named because they are formed by two conductors of different materials, often stainless steel and copper, joined at one end to form a thermoelectric junction. This junction produces a small electrical potential when the temperature of one junction is different from the temperature of the other junction. The more dissimilar the two materials, the more sensitive the thermocouple is to a given temperature change. The most common material used for the two conductors is type K (chromel-alumel).
In general, thermocouple material is selected based on the application and the environment it will be used in. The material needs to be able to withstand high temperatures and be highly resistant to corrosion and oxidation. In some cases a thermocouple material other than type K may be required for improved accuracy, such as when measuring very low or very high temperatures. Specialty thermocouples may be made with gold-platinum wire, iridium-rhenium alloys, or tungsten-rhenium alloys.
The selection of the proper thermocouple is important, as it must be able to accurately measure the temperature range needed, be able to withstand the environmental conditions, and be compatible with the other components in the system. Additionally, the thermocouple must be connected to the proper measuring device, such as a controller or meter, to measure the appropriate range.
The accuracy of a thermocouple is affected by the material of the two conductors, the gauge of the wire, and the environment it is used in. The calibration of the thermocouple must be accurate for the temperature range being measured and the environment in which it will be used. Calibration involves testing the thermocouple and comparing the results to a known reference, such as a calibrated thermocouple standard.
Thermocouples are a versatile, reliable and relatively inexpensive method of measuring temperature, and are used in a wide range of industries and applications. They are easy to install, and can be used in tight spaces and in harsh or hazardous environments. When selecting and installing a thermocouple, it is important to select the proper thermocouple for the application and take into consideration accuracy, calibration, environment and compatibility with other equipment.
