Iron copper nickel (constantan) thermocouple wire (J)
Iron copper nickel thermocouple (J-type thermocouple) is also called iron constantan thermocouple. The nominal chemical composition of its positive pole (JP) is pure iron, and the negative pole (JN) is copper nickel alloy, which is often vaguely called constantan. Its nominal chemical composition is 55% copper, 45% nickel, and a small amount of very important cobalt, iron, manganese and other elements. Although it is called constantan, it is different from nickel chromium constantan and copper constantan, so it cannot be replaced by EN or TN. The temperature range covered by iron constantan thermocouple is - 210~1200 ℃, but the commonly used temperature range is 0-750 ℃.
J-type thermocouple has the advantages of good linearity, large thermoelectric electromotive force, high sensitivity, good stability and uniformity.
Type J thermocouples can be used in vacuum, oxidation, reduction and inert atmospheres, but the positive iron oxidizes rapidly at high temperatures, so the use temperature is limited, and they cannot be directly used in the sulfurization atmosphere at 500 ℃ without protection.