Measurement of Thermal Response Time of Thermocouples in Temperature Instruments

As a kind of temperature instrument, thermocouple is widely used in the industry. Here we will explore the thermal response time of thermocouple, which is a question that everyone is more concerned about.
Measuring the thermal response time of thermocouple is actually quite complicated. Different test conditions will produce different measurement results. This is because it is affected by the heat exchange rate between the thermocouple and the surrounding medium. The higher the heat exchange rate, the shorter the thermal response time.
In order to make the thermal response time of temperature instrument thermocouple products comparable, the national standard stipulates that the thermal response time should be carried out in a dedicated water flow test device. The water flow rate of the device should be maintained at 0.4±0.05m/s, the initial temperature should be in the range of 5-45℃, and the temperature step value should be 40-50℃. 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 tested thermocouple is 150mm or the planned insertion depth (select the smaller value and indicate it in the test report).
Because the installation is relatively complicated, only a few units have this equipment now. The national standard stipulates that the manufacturer can negotiate with the user and adopt other test methods, but the given data must indicate the test conditions.
Because the thermoelectric potential of the B-type thermocouple is very small near room temperature, the thermal response time is not easy to measure. Therefore, the national standard stipulates that the thermoelectrode assembly of the S-type thermocouple of the same specification can be used to replace its own thermoelectrode assembly, and then the test is carried out.
During the test, the time T0.5 when the output of the thermocouple changes to a temperature step change equivalent to 50% should be recorded. If necessary, the thermal response time T0.1 when the change is 10% and the thermal response time T0.9 when the change is 90% can be recorded. The recorded thermal response time should 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 should be within ±10%. In addition, the time required to form a temperature step change should not exceed one tenth of T0.5 of the tested thermocouple. The response time of the recording instrument or meter should not exceed one tenth of T0.5 of the thermocouple being tested.