What does the "type designation" of thermocouples and temperature measuring instruments mean?
Thermocouples mainly have type designations including S, R, B, N, K, E, J and T. Among them, Types S, R and B are noble metal thermocouples, while Types N, K, E, J and T are base metal thermocouples.
Type SIt features strong oxidation resistance and is suitable for continuous service in oxidizing and inert atmospheres. Its long-term operating temperature is 1400°C, and short-term temperature is 1600°C. Among all thermocouples, Type S has the highest accuracy class and is commonly used as a standard thermocouple.
Type RCompared with Type S, it delivers approximately 15% higher thermoelectromotive force, while almost all other properties remain identical.
Type BIts thermoelectromotive force is extremely small at room temperature, so compensating cables are generally not required for measurement. It can be used continuously up to 1600°C, with a short-term limit of 1800°C. It can operate in oxidizing or neutral atmospheres, and can also be used for short periods under vacuum conditions.
Type NIt boasts excellent high-temperature oxidation resistance at 1300°C, good long-term stability of thermoelectromotive force and repeatability during short-term thermal cycling. It also has good nuclear radiation resistance and low-temperature performance, and can partially replace Type S thermocouples.
Type KIt has strong oxidation resistance and is suitable for continuous use in oxidizing and inert atmospheres. Its long-term operating temperature is 1000°C, and short-term temperature is 1200°C. It is the most widely used thermocouple type.
Type EAmong commonly used thermocouples, it produces the largest thermoelectromotive force, meaning it has the highest sensitivity. It is suitable for continuous operation in oxidizing and inert atmospheres, with an operating temperature range of 0–800°C.
Type JIt can be used in oxidizing atmospheres (maximum service temperature 750°C) as well as reducing atmospheres (maximum service temperature 950°C). It resists corrosion by hydrogen and carbon monoxide gases and is mostly applied in oil refining and chemical industries.
Type TIt achieves the highest accuracy class among all base metal thermocouples and is typically used to measure temperatures below 300°C.
