Technical standards for different thermocouples
S type thermocouple: platinum rhodium 10 - platinum thermocouple
S-type thermocouple specifications: for precious metal thermocouples. The diameter of the filament is specified to be 0.5 mm, the allowable deviation is -0.015 mm, and the nominal chemical composition of the positive electrode (SP) is platinum-rhodium alloy, wherein ruthenium is 10%, platinum is 90%, and the negative electrode (SN) is pure platinum. Commonly known as a single platinum rhodium thermocouple. The thermocouple has a long-term maximum operating temperature of 1300 ° C and a short-term maximum operating temperature of 1600 ° C.
Advantages of S-type thermocouple: It has the highest accuracy, the best stability, wide temperature range and long service life. It has good physical and chemical properties, good thermoelectric potential stability and high oxidation resistance at high temperatures, and is suitable for oxidizing and inert atmospheres. Because the S-type thermocouple has excellent comprehensive performance and conforms to the internationally used S-type thermocouple with temperature scale, it has long been used as an interpolation instrument for international temperature scales. Although the "ITS-90" stipulates that it will no longer be used as an internal temperature-testing instrument for international temperature standards. However, the International Temperature Advisory Committee (CCT) believes that S-type thermocouples can still be used to approximate the international temperature scale.
S-type thermocouple is insufficient: it is a thermoelectric potential, the thermoelectric potential rate is small, the sensitivity is low, the mechanical strength is lowered at high temperature, it is very sensitive to pollution, and the precious metal material is expensive, so the one-time investment is large. It is a commonly used product in the metallurgy and glass manufacturing industries.
K-type thermocouple: nickel-chromium-nickel silicon thermocouple
K-type thermocouple specification: It is the most expensive metal thermocouple currently used, and its dosage is the sum of other thermocouples. The nominal chemical composition of the positive electrode (KP) is: Ni:Cr=90:10, and the nominal chemical composition of the negative electrode (KN) is: Ni:Si=97:3, and its use temperature is -200 to 1300 °C.
Advantages of K-type thermocouple: It has good linearity, large thermal electromotive force, high sensitivity, good stability and uniformity, strong anti-oxidation performance and low price. It can be used in oxidative inert atmosphere. Widely used by users.
K-type thermocouple is insufficient: it cannot be used directly in high temperature for sulfur, reducing or reducing, oxidizing in alternating atmospheres and vacuum, and is not recommended for use in weak oxidizing atmospheres.
J-type thermocouple: iron-copper-nickel thermocouple
J-type thermocouple specifications: also known as iron-constantan thermocouple, is also a low-cost cheap metal thermocouple. Its positive electrode (JP) has a nominal chemical composition of pure iron, and its negative electrode (JN) is a copper-nickel alloy. It is often ambiguously called Constantan. Its nominal chemical composition is: 55% copper and 45% nickel and a small amount. However, manganese, cobalt, iron and other elements, although it is called Kangkang, are different from nickel-chromium-constantan and copper-constantan, so they cannot be replaced by EN and TN. The coverage temperature of the iron-constantan thermocouple is -200~1200 °C, but the temperature range is usually 0~750 °C.
Advantages of J-type thermocouple: It has the advantages of good linearity, large thermal electromotive force, high sensitivity, good stability and uniformity, and low price. It is widely used by users.
J type thermocouple is insufficient: it can be used in vacuum, oxidation, reduction and inert atmosphere, but the positive iron is oxidized faster at high temperature, so the use temperature is limited, and it can not be used directly in the vulcanization atmosphere at high temperature without protection.