What are the precautions for using thermocouples
Oct. 30, 2020
Precautions for using thermocouples
1. According to the upper limit of the temperature to be measured, the thermocouple and protective sleeve are correctly selected, and the specifications and dimensions of the thermocouple are selected according to the structure and installation characteristics of the object to be measured.
2. The position where the thermocouple is inserted into the furnace should be a representative place of the temperature in the furnace, and its temperature can represent the actual temperature in the furnace.
3. The depth of the thermocouple inserted into the furnace should not be less than 8-10 times the outer diameter of the thermocouple protection tube, and it should be placed as vertically as possible to prevent deformation at high temperatures. If it must be placed horizontally, the protective tube must be supported when the length of the projected part is greater than 500mm.
4. The gap between the thermocouple and the furnace wall must be blocked with asbestos rope or refractory mud to prevent air convection from affecting the accuracy of temperature measurement.
5. There should be a proper distance between the thermocouple junction box and the furnace wall, generally not less than 200mm. Otherwise, the temperature of the free end of the thermocouple will be too high. When measuring the temperature of the salt bath furnace, a right-angle wire thermocouple should be used.
6. The installation position and direction of the thermocouple should avoid the interference of strong magnetic field, and the metal shell should be well grounded, so as not to affect the accuracy of measurement. If it is used in the electrode salt bath furnace, be careful not to approach the electrode.
7. The welding method of the positive and negative working ends of the thermocouple can be butt welding or welding after twisting, but the number of twisting turns should not exceed 3 turns.
8. Correctly select the compensation wire. When connecting the compensation wire, be careful not to connect the wire reversely. It is better to install the compensation wire in the iron pipe and ground the iron pipe to avoid mechanical damage and electromagnetic interference.
9. The gap between the compensation wire and the outlet hole of the junction box should be blocked with asbestos rope to prevent insects from entering.
10. Be careful when installing or unpacking the furnace, and do not hit the thermocouple.
11. Since thermocouples will oxidize, corrode and recrystallize at high temperatures, their thermoelectric characteristics will change, so they should be checked regularly; new thermocouples or thermocouples stored for a period of time must be checked before use.
12. In use, pay attention to the condition of the thermocouple protection tube. If the surface of the protection tube is found to have pitting, foam, corrosion, thinning, cracking, etc., it should be replaced immediately.
