"Graduation number" in thermocouples and temperature measuring instruments
The "gradation number" in thermocouples and temperature measuring instruments/the graduation numbers of thermocouples mainly include S, R, B, N, K, E, J, T, etc. Among them, S, R, and B belong to precious metal thermocouples, and N, K, E, J, and T belong to cheap metal thermocouples.
The S grade is characterized by strong oxidation resistance and should be used continuously in oxidizing and inert atmospheres. The long-term use temperature is 1400°C and the short-term use temperature is 1600°C. Among all thermocouples, S graduation number has the highest degree grade and is usually used as a standard thermocouple;
Compared with the S-grading type, the heat removal electromotive force of the R-grading type is about 15% larger, and other properties are almost identical;
The thermal electromotive force of the B graduation number is extremely small at room temperature, so compensation wires are generally not needed during measurement. Its long-term use temperature is 1600℃ and short-term use temperature is 1800℃. It can be used in oxidizing or neutral atmospheres and can also be used under vacuum conditions for short periods of time.
The characteristics of the N index number are strong high-temperature oxidation resistance at 1300°C, good long-term stability of thermoelectromotive force and short-term thermal cycle reproducibility, and good nuclear radiation resistance and low temperature resistance. It can partially replace the S index number. thermocouple;
The K-grading number is characterized by strong oxidation resistance and should be used continuously in oxidizing and inert atmospheres. The long-term use temperature is 1000°C and the short-term use temperature is 1200°C. Most widely used of all thermocouples;
The characteristic of the E graduation number is that it has the largest thermal electromotive force among commonly used thermocouples, that is, the highest sensitivity. It should be used continuously in oxidizing and inert atmospheres, and the operating temperature is 0-800°C;
The characteristic of the J index number is that it can be used in both oxidizing atmospheres (the upper limit of the operating temperature is 750°C) and reducing atmospheres (the upper limit of the operating temperature is 950°C), and is resistant to H2 and CO gas corrosion. It is mostly used in oil refining and chemical industry;
The T graduation number is characterized by the highest grade among all cheap metal thermocouples and is usually used to measure temperatures below 300°C.
