Thermocouple Types for Thermometers and Temperature Instruments
In thermocouples and temperature measuring instruments, common thermocouple calibration types include S, R, B, N, K, E, J and T. Among them, types S, R and B are precious metal thermocouples, while N, K, E, J and T are base metal thermocouples.
Type S features excellent oxidation resistance and is suitable for continuous service in oxidizing and inert atmospheres. Its long‑term operating temperature is 1400 °C, with a short‑term limit of 1600 °C. It has the highest accuracy among all thermocouples and is commonly used as a standard thermocouple.
Type R has nearly identical performance to Type S, except that its thermoelectromotive force is about 15 % higher.
Type B generates extremely low thermoelectromotive force at room temperature, so compensation cables are generally unnecessary for measurement. Its continuous service temperature is 1600 °C and the short‑term temperature limit is 1800 °C. It can be used in oxidizing or neutral atmospheres and for short periods under vacuum conditions.
Type N offers outstanding high‑temperature oxidation resistance up to 1300 °C, excellent long‑term stability of thermoelectromotive force and good repeatability under short‑term thermal cycling. It also provides good radiation resistance and low‑temperature performance, and can partially replace Type S thermocouples.
Type K has strong oxidation resistance and is suitable for continuous operation in oxidizing and inert atmospheres. The long‑term service temperature is 1000 °C and the short‑term limit is 1200 °C. It is the most widely used thermocouple type.
Type E delivers the highest thermoelectromotive force and sensitivity among conventional thermocouples. It is suitable for continuous use in oxidizing and inert atmospheres, with an operating temperature range of 0 °C to 800 °C.
Type J can be applied in both oxidizing atmospheres (maximum 750 °C) and reducing atmospheres (maximum 950 °C). It resists corrosion by hydrogen and carbon monoxide, and is widely used in petroleum refining and chemical industries.
Type T achieves the highest accuracy among all base metal thermocouples and is mainly used for temperature measurement below 300 °C.
