Explosion-proof thermocouple measurement method The thermal response time of an explosion-proof thermocouple is more complicated, 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. If the heat exchange rate is high, the thermal response is 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 performed on a dedicated water flow test device. The water flow speed of the device should be maintained at 0.4±0.05m/s, the initial temperature should be within 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 exceed ±1% of the temperature step value. The insertion depth of the tested thermocouple is 150mm or the designed insertion depth (choose the smaller value and indicate it in the test report).　　　　Because the device is relatively complicated, only a few units have this set of equipment at present, so the national standard stipulates that the manufacturer is allowed to negotiate with the user and other test methods can be used, 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, so 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 50% of the temperature step change should be recorded. If necessary, the thermal response time T0.1 with a 10% change and the thermal response time T0.9 with a 90% change 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 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 meter should not exceed one-tenth of the T0.5 of the thermocouple under test. Generally, the thermocouple processing program and the instrument store the temperature-potential correspondence table. This is also the manufacturer automatically realizes the comparison relationship, without artificial setting, what we have to do is to pass the on-site electric potential signal to the The device or program can be used. For routine maintenance, you can use rough data to judge whether the temperature measurement of the on-site thermocouple is correct. In order to save maintenance time, you do not need to use the thermocouple comparison table. You can remember the electric potential of the commonly used thermocouple-the temperature correspondence relationship. For example, the corresponding relationship of K-type thermocouple, the couple is usually 0.4mV corresponding to 10 degrees, the field uses a multimeter to detect the thermoelectric potential at the end of the thermocouple divided by 0, 4 multiplied by 10 plus the temperature at this time to know what the measured temperature is. Although there are errors, it is sufficient to judge the quality of the on-site thermocouple during maintenance.
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