The causes of thermocouple leakage include:
(1) The refractory bricks on the electric furnace have poor insulation at high temperatures. Inserting a thermocouple with a metal tube into the furnace wall with the furnace wire can easily make the furnace wire and the thermocouple contact. The refractory brick is a good insulation disassembly at room temperature. But as the temperature rises, the insulation performance will decrease significantly. Alumina refractory bricks are mostly used for the lining of resistance electric furnaces, and the resistance value decreases significantly as the temperature rises.
(2) The contact between the furnace wire and the thermocouple. The platinum-rhodium thermocouple protection tube is an alumina porcelain tube, and the couple wire is worn with a porcelain tube for separation and insulation. The insulation performance will also be reduced at high temperatures, resulting in leakage, and finally leaking to the thermoelectric In the even place, there is an AC leakage signal on the thermocouple.
Methods to prevent leakage of thermocouple:
(1) Keep the thermocouple not in contact with the refractory bricks.
(2) Ground the negative pole of the thermocouple to eliminate the leakage signal on the thermocouple.
(3) Install a filter device at the output end of the thermocouple.
(4) Lead the ground wire from the hot junction of the thermocouple to ground.
(5) Add a heat-resistant steel tube or silicon carbide tube to the thermocouple tube and ground it.
