Introduction to the measurement method of industrial thermocouple insulation resistance

　　When measuring the insulation resistance of industrial thermocouples, the following technical requirements should be met:

　　1. Industrial thermocouples should be subjected to insulation resistance tests according to the original assembly method at the factory.

　　2. The accuracy of the instrument used to measure insulation resistance shall not be less than ±20%. The method of measuring insulation resistance is: connect the output end of the measuring instrument to the protection tube and the hot electrode of the industrial thermocouple and between the two hot electrodes (when the measuring end is open). For industrial thermocouples using ceramic protection tubes, use metal wire to evenly wrap 15-20 turns around the heated part of the industrial thermocouple ceramic protection as one pole of the upper limit temperature insulation resistance test. The metal wire used should be harmless to the industrial thermocouple. When the test voltage is applied for 60s, record the insulation resistance value indicated by the instrument, then change the direction of the applied test voltage, and record the measurement results separately, and take the smaller value as the insulation resistance value of the tested industrial thermocouple.

　　3. The test voltage of insulation resistance at room temperature is DC (500±50) V. The test voltage of insulation resistance at upper temperature limit is DC (10±1) V.

　　4. The atmospheric conditions for measuring the insulation resistance at room temperature are: temperature 15-35℃, relative humidity 45%, atmospheric pressure 86-106kpa. The industrial thermocouple to be tested should be placed under such atmospheric conditions for at least 2h before testing. When measuring the insulation resistance at the upper limit temperature, the heated length of the industrial thermocouple is 300mm or 50% of the total length (select the smaller value, and allow a deviation of 10%); the temperature non-uniformity of the heating area should be within 10℃; the deviation range of the test temperature from the upper limit temperature is ±10℃; the time the industrial thermocouple to be tested stays at the test temperature should not be shorter than 5 times its thermal response time T0.5.