Thermocouple types

Thermocouples commonly used in industry include S, B, E, K, R, J, T7 types:

(1) The platinum-rhodium 10-platinum thermocouple has the graduation number of S, the temperature measurement range is 0~1300 °C, the platinum-rhodium wire is the positive electrode, and the pure platinum wire is the negative electrode; platinum-rhodium 10-platinum thermocouple is suitable for oxidizing and neutralizing. used in sexual media. Since high-purity platinum and platinum-rhodium alloys are readily available, the S-type thermocouple has high replication accuracy and measurement accuracy, so it is often used for precise temperature measurement and as a standard thermocouple. The disadvantage is that the thermoelectric potential is small, the thermoelectric characteristics are nonlinear, the price is relatively high, and it is easily eroded by reducing gases and metal vapors and deteriorated at high temperatures, thereby causing changes in thermoelectric characteristics and affecting the accuracy of measurement.

(2) Nickel-chromium-nickel-silicon (nickel-aluminum) thermocouple, the graduation number is K, the temperature measurement range is -200~1300℃; the nickel-chromium is the positive electrode, and the nickel-silicon is the negative electrode. It is suitable for use in oxidizing or neutral media. When the medium temperature is lower than 500 ℃, it can also be used to measure the temperature in the reducing medium. In addition, its thermoelectric potential is large, the linearity is good, the measurement range is wide, and the cost is moderate. It is the most commonly used thermocouple in industrial temperature measurement. The disadvantage is that the measured temperature is affected by the change of the thermoelectric characteristics due to the oxidation and deterioration of nickel and aluminum during long-term use.

(3) Nickel-chromium --- test copper thermocouple, it is composed of nickel-chromium wire and test copper (copper, nickel alloy) wire, the graduation is E, the measuring range is -200~1300℃; is negative. It is suitable for measuring temperature in reducing medium or neutral medium. It is characterized by high thermoelectric sensitivity and convenient price, but the measurement range is not large and the measurement temperature is not high. The alloy wire of copper wall and iron wall is easily oxidized and deteriorated. It is difficult to obtain a uniform wire diameter.

(4) platinum-rhodium 30-platinum-rhodium 6 thermocouple, the graduation number is B, the temperature measurement range is 0~1600 ° C; platinum-rhodium 30 wire (platinum 70%, rhodium 30%)