Thermocouple is widely used in industrial electric furnace, silicon carbon rod electric furnace and salt bath furnace because of its wide temperature range and convenient measurement. But the interference generated by these equipment is larger, resulting in abnormal temperature measurement instrument, error, instability, indicating speed is slowed down and so on, especially the leakage of thermocouple is a common problem. Must be solved, otherwise can not guarantee the quality of the product, resulting in losses.

Cause analysis of thermocouple leakage

1. Furnace wire and thermocouple contact, platinum-rhodium thermocouple protection tube is alumina porcelain tube, porcelain wire wear for separation insulation, insulation performance should be reduced at high temperature, resulting in leakage, leakage to the thermocouple, so that there is AC leakage signal on the thermocouple. 2. The insulation of firebrick on electric furnace is poor at high temperature, and the thermocouple with metal tube inserted into the furnace wall equipped with the furnace wire is easy to make the furnace wire contact with the thermocouple. The firebrick is good insulation and disassembly at room temperature, but the insulation performance will decrease significantly as the temperature rises. The lining of resistive electric furnace is mostly made of alumina firebrick, and its resistance decreases significantly with the increase of temperature.

Prevention of thermocouple leakage

1. Keep thermocouple out of contact with firebrick.

2. Ground the negative electrode of the thermocouple to eliminate the leakage signal on the thermocouple.

3. Install a filter device at the output end of the thermocouple.

4. Ground the ground wire from the hot contact of the thermocouple.

5. Add heat-resistant steel tube or silicon carbide tube on the thermocouple tube, and ground it.

For the above methods we are completely verified by experiments, completely for the instrument in use to ensure that the instrument accurate temperature, temperature control, record, so that various instruments play their due roles.