Measurement method of Thermocouple

Posted by Hemant K on

The thermal response time of the thermocouple is more complex, and different test conditions will have different measurement results, because it is affected by the heat transfer rate of the thermocouple and the surrounding medium, and the heat transfer rate is high, the thermal response time is short. In order to make the thermal response time of thermocouple products comparable, the national standard stipulates that the thermal response time should be carried out on the special water flow test device. The water flow speed of the device should be kept 0.4±0.05m/s, the initial temperature is within 5-45 ℃ range, and the temperature step value is 40-50 ℃. In the course of the test, the temperature change of water should not be greater than the ±1% of temperature step value.

The placement depth of the tested Thermocouple is 150mm or the placement depth of the design (select the smaller value and indicate it in the test report).

Because of the complexity of the device, only a very small number of units currently have this set of equipment, so the national standards stipulate that the production plant can be allowed to negotiate with the user, may use other test methods, but the data given must indicate the test conditions.

Because the thermoelectric potential of B-type thermocouple near room temperature is very small, the thermal response time is not easy to measure, so the national standard stipulates that the thermoelectric polar components of S-type thermocouple with the same specification can be replaced with their own thermoelectric polar components, and then tested. The output of the thermocouple should be recorded at a time T0.5 equivalent to 50% of the temperature step change, and the thermal response time of 10% T0.1 and the thermal response time of 90% change T0.9 can be recorded if necessary. The recorded thermal response time should be the average of at least three test results for 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 temperature step change should not exceed one-tenth of the T0.5 of the thermocouple being tested.

The response time of the recording instrument or instrument should not exceed one-tenth of the T0.5 of the tested thermocouple.