How to measure the thermal response time of type K thermocouple

Measuring the thermal response time of K-type thermocouple is actually more complicated, different test conditions will produce different measurement results, this is due to the influence of the heat transfer rate of the surrounding medium, high heat transfer rate, the thermal response time is short.


In order to make the thermal response time of thermocouples comparable, the national standard stipulates that the thermal response time should be carried out on a special water flow test device. The water flow speed of the device should be maintained at 0.4±0.05m/s, the initial temperature is in the range of 5-45 ° C, and the temperature step value is 40-50 ° C. During the test, the temperature change of the water should not be greater than ±1% of the temperature step value. The insertion depth of the thermocouple tested was 150mm or the designed insertion depth.


Since the thermocouple has a very small thermoelectric potential near room temperature and the thermal response time is not easy to measure, the national standard stipulates that its own thermal electrode assembly can be replaced by the thermal electrode assembly of the same specification type K thermocouple, and then the test is carried out.



During the test, the output change of the thermocouple should be recorded to the time T0.5 equivalent to 50% of the temperature step change. If necessary, the thermal response time of 10% change T0.1 and 90% change T0.9 can be recorded. The recorded thermal response time should be the average of at least three test results of the same test, and the deviation of each measurement result from the average should be within ±10%. In addition, the time required to form a step change in temperature should not exceed one-tenth of the T0.5 of the thermocouple being tested. The response time of the recording instrument or meter should not exceed one-tenth of the T0.5 of the thermocouple under test.