vacuum furnace thermocouple structure and type
There are many types of thermocouples. The high-temperature box furnace, vacuum tube furnace, muffle furnace, box atmosphere furnace and other laboratory high-temperature heating equipment that we developed and produced are commonly used. Here we share the structure and types of thermocouples.
The composition of thermocouples in the actual temperature measurement, only two thermoelectric thermocouples are rare. Common thermocouple is usually composed of four parts: thermal electrode, insulating tube, protective sleeve and junction box.
(1) Thermoelectric pole: Thermoelectric pole is the core part of thermocouple. The thermoelectric pole of ordinary thermocouple is usually processed into wire shape and welded at one end. The diameter of the thermoelectric pole is mainly determined by the price of the material, the mechanical strength, the use of the thermocouple and the range of temperature measurement. The diameter of precious metal thermoelectric pole is generally 0.3-0.65mm, and that of low-cost metal thermoelectric pole is generally 0.5-3.2mm. The length of the thermoelectric pole is usually made into various specifications within the range of 100-200mm for practical selection.
(2) Insulating pipe: insulating pipe, also known as insulator, is sleeved on the thermoelectric pole with through-hole, which is used for isolating two electrodes and separating the electrode from the metal protective sleeve. Otherwise, the measurement error will be caused by the loss of thermoelectric potential due to short circuit. Insulators are usually made of high temperature resistant insulating materials such as ceramics, quartz, alumina, magnesium oxide, etc., with circular or elliptical cross section, single hole, double hole, four hole and other forms.
(3) Protective tube: the thermoelectric pole sheathed with insulating tube is installed in a closed protective tube at one end. The function of the protective tube is to prevent or reduce the direct erosion of various harmful gases and substances on the thermoelectric pole and the direct rush of high temperature flame or air flow; to prevent the direct contact between the conductive medium and the thermoelectric pole; in addition, it has the function of fixing and supporting the thermoelectric pole. Therefore, the protection tube of thermocouple plays an important role in prolonging the service life of thermoelectric pole and ensuring the measurement accuracy.