In the previous session, I covered 3 points of the frequently asked questions about thermocouple and RTD temperature measurement. Today, I will continue with another 2 points.
IV. What is a Mineral Insulated Thermocouple, and what are its advantages?
According to the IEC 1515 standard, it is defined as Mineral Insulated Thermocouple Cable.It is manufactured by integrally drawing the thermoelements, insulating material and outer sheath together. Its outer surface appears to be covered with a layer of "armor", hence the name mineral insulated thermocouple.
Compared with conventional assembled thermocouples, it features higher pressure resistance, excellent bendability, good oxidation resistance and long service life.
V. What are the different thermocouple types, and what are their characteristics?
The common thermocouple types include S, R, B, N, K, E, J, T.Among them, S, R, B are noble metal thermocouples, while N, K, E, J, T are base metal thermocouples.
Type S: Excellent oxidation resistance, suitable for continuous use in oxidizing and inert atmospheres. Continuous operating temperature: 1400℃, short-term: 1600℃. It has the highest accuracy among all thermocouples and is commonly used as a standard thermocouple.
Type R: Similar to Type S in almost all properties, except that its thermoelectric EMF is approximately 15% higher.
Type B: Extremely low thermoelectric EMF at room temperature, so compensation wires are generally not required for measurement. Continuous operating temperature: 1600℃, short-term: 1800℃. It can be used in oxidizing or neutral atmospheres, and also in vacuum for short periods.
Type N: Excellent high-temperature oxidation resistance up to 1300℃, good long-term stability of thermoelectric EMF and repeatability under short-term thermal cycling, good radiation resistance and low-temperature resistance. It can partially replace Type S thermocouples.
Type K: Strong oxidation resistance, suitable for continuous use in oxidizing and inert atmospheres. Continuous operating temperature: 1000℃, short-term: 1200℃. It is the most widely used thermocouple.
Type E: Has the largest thermoelectric EMF (highest sensitivity) among common thermocouples. Suitable for continuous use in oxidizing and inert atmospheres, operating temperature range: 0–800℃.
Type J: Can be used in both oxidizing atmospheres (max. 750℃) and reducing atmospheres (max. 950℃). Resistant to corrosion by hydrogen and carbon monoxide, widely applied in petroleum refining and chemical industries.
Type T: Has the highest accuracy among all base metal thermocouples, typically used for temperatures below 300℃.