Measuring method of thermocouple

The thermal response time is complex, and different test conditions will have different measurement results. This is because it is affected by the heat exchange rate between the thermocouple and the surrounding medium. A high heat exchange rate will shorten the thermal response time. In order to make the thermal response time of thermocouple products comparable, the national standard stipulates that the thermal response time shall be conducted on a special water flow test device. The water flow velocity of the device shall be maintained at 0.4 ± 0.05m/s, the initial temperature shall be within the range of 5-45 ℃, and the temperature step value shall be 40-50 ℃. During the test, the temperature change of water shall not be greater than ± 1% of the temperature step value. The insertion depth of the thermocouple under test is 150mm or the designed insertion depth (select the smaller value and indicate it in the test report).

Due to the complexity of the device, only a few units have this set of equipment at present, so the national standard allows the manufacturer to negotiate with the user, and other test methods can be used, but the test conditions must be indicated for the given data.

Since the thermoelectric potential of B type thermocouple is very small near the room temperature, and the thermal response time is not easy to measure, the national standard stipulates that the thermoelectric electrode assembly of S type thermocouple with the same specification can be used to replace its own thermoelectric electrode assembly, and then the test can be carried out.

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