The "graduation number" in thermocouples and temperature measuring instruments
The "graduation number" in thermocouples and temperature measuring instruments mainly includes S, R, B, N, K, E, J, T, and other graduation numbers. Among them, S, R, and B belong to precious metal thermocouples, while N, K, E, J, and T belong to cheap metal thermocouples.
The characteristic of the S graduation number is its strong antioxidant performance, which is suitable for continuous use in oxidizing and inert atmospheres. The long-term use temperature is 1400 ℃, and the short-term use temperature is 1600 ℃. Among all thermocouples, the S graduation number has the highest accuracy level and is usually used as a standard thermocouple;
Compared with the S index, the R index has almost identical performance except for the fact that the thermal electromotive force is about 15% higher;
The B graduation number has a very small thermal electromotive force at room temperature, so compensation wires are generally not used 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, or for short-term use under vacuum conditions.
The characteristics of the N graduation number are strong high-temperature oxidation resistance at 1300 ℃, good long-term stability of thermoelectric electromotive force and reproducibility of short-term thermal cycles, good resistance to nuclear radiation and low temperature, and can partially replace the S graduation number thermocouple;
The characteristic of K-scale is its strong antioxidant performance, and it is suitable for continuous use in oxidizing and inert atmospheres. The long-term use temperature is 1000 ℃, and the short-term use temperature is 1200 ℃. Widely used in all thermocouples;
The characteristic of the E graduation number is that among commonly used thermocouples, its thermoelectric electromotive force is the highest, which means it has the highest sensitivity. It should be used continuously in an oxidizing and inert atmosphere at a temperature of 0-800 ℃;
The characteristic of J graduation number is that it can be used in both oxidizing atmospheres (with an upper temperature limit of 750 ℃) and reducing atmospheres (with an upper temperature limit of 950 ℃), and is resistant to H2 and CO gas corrosion. It is mostly used in oil refining and chemical industry;
The characteristic of T-scale is that it has the highest accuracy level among all cheap metal thermocouples and is usually used to measure temperatures below 300 ℃.
