Thermocouples — What are they?

A thermocouple is a type of sensor used for measuring temperature. Thermocouples are a popular choice for temperature sensing, due to their low cost, versatility and ruggedness. They are used across a wide range of industries including steel, aerospace, pharmaceutical, petrochemical, power generation, food, packaging, metal processing, plastics and most environments where a temperature needs to be managed. They are even found in household appliances including hot water heaters, stoves and toasters.

The construction of a thermocouple consists of two different metals joined together to make a continuous circuit. When a temperature difference takes place, between any 2 points in the circuit, an electromotive force (voltage) occurs.

There are various types of thermocouples. Each are constructed from different materials, with differing temperature ranges and levels of accuracy. Selecting the right thermocouple for the application is critical.

Type B thermocouples are used extensively in the iron and steel industry to monitor temperatures and chemistry during the steel making process.

Type C thermocouples are typically used in extremely high temperatures. Type C thermocouples are the sensor of choice in space vehicles, industrial heating and nuclear reactors. They are well suited for vacuum furnaces at extreme temperatures and in high-pressure research.

Type E thermocouples are used in sub-zero, oxidising or inert applications. They are ideal for pharmaceutical, cryogenic, and chemical applications where critical measurements are required in small increments.

Type J thermocouples are recommended for vacuum, inert, and reducing atmospheres. The thermocouple can be used exposed or unexposed.

Type K thermocouples are the most common general-purpose thermocouple. They can be used for measurements in many different types of environments such as water, mild chemical solutions, gases, and dry area. Found in engines, oil heaters, and boilers. Used as thermometers in hospitals and the food industry.

Type N thermocouples have outstanding thermoelectric stability. Can be used in vacuum or controlled atmospheres. Developed to replace type K in nuclear applications.

Type R and type S thermocouples are used for heat treating and control sensors, semiconductor industry, glass manufacturing, ferrous and non-ferrous metals.

Type T thermocouples are used in food monitoring and environmental applications.

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