What causes leakage of armored thermocouples? How can we avoid it?

Armored thermocouples have the advantages of bending, high voltage resistance, fast thermal response time, and durability. Like prefabricated thermocouples, armored thermocouples are commonly used as temperature sensors in conjunction with display instruments, recorders, and electronic regulators. Additionally, armored thermocouples can also serve as temperature sensing elements for prefabricated thermocouples. Armored thermocouples can directly measure the temperature of liquid, vapor, gas media, and solid surfaces within the range of 0 ℃ to 1100 ℃ in various production processes.
Armored thermocouples are widely used measurement tools, and leakage may occur during use, which not only affects the use but also endangers the personal safety of operators. So, what are the reasons for its leakage? How can we avoid it?
Reason:
(1) The insulation of refractory bricks on electric furnaces is poor at high temperatures. Inserting thermocouples with metal tubes into the furnace wall containing furnace wires can easily make the wires come into contact with the thermocouples. Refractory bricks are good insulation materials at room temperature. The lining of a resistance electric furnace is mostly made of alumina refractory bricks, and its resistance value decreases significantly with increasing temperature.
(2) The contact between the furnace wire and the thermocouple, the platinum rhodium thermocouple protection tube is an alumina ceramic tube, and the thermocouple wire is insulated with a ceramic tube for separation. The insulation performance also decreases at high temperatures, causing leakage, which then leaks to the thermocouple, resulting in an AC leakage signal on the thermocouple.
Avoidance measures:
Keep the thermocouple out of contact with refractory bricks, ground the negative electrode of the thermocouple, and eliminate the leakage signal on the thermocouple. Install a filtering device at the output end of the thermocouple. Lead the grounding wire from the hot junction position. Install a heat-resistant steel pipe or silicon carbide pipe on the thermocouple tube and ground it.