What is the thermal response time of a K-type thermocouple
In the process of using the K-type thermocouple, it is found that the response time of the K-type thermocouple is very important for the whole measurement process. How should the response time of the K-type thermocouple be measured? Let me introduce the method of measuring the response time of K-type thermocouple.
K-type thermocouples have high measurement accuracy and a wide measurement range. Because the thermocouple is in direct contact with the object to be tested, it is not affected by the intermediate medium.
K-type thermocouples are simple in construction and easy to use. Thermocouples are usually made up of two different wires and are not limited by size and opening. They have a protective sleeve and are very convenient to use.
Measuring the thermal response time of a K-type thermocouple is actually quite complicated. Different test conditions will produce different measurement results. This is because the heat transfer rate is high due to the heat transfer rate of the surrounding medium, and the thermal response time is short. .
In order to make the thermocouple's thermal response time comparable, the national standard stipulates that the thermal response time should be performed on a dedicated water flow test device. The water flow rate of the device should be maintained at 0.4 ± 0.05 m / s, the initial temperature is in the range of 5-45 ° C, and the temperature step is 40-50 ° C. During the test, the temperature change of the water should not exceed ±1% of the temperature step value. The thermocouple to be tested was placed at a depth of 150 mm or the depth of the design.
Since the thermoelectric potential is small near the room temperature and the thermal response time is not easy to measure, the national standard stipulates that the hot electrode assembly of the K-type thermocouple of the same specification can be used to replace its own hot electrode assembly, and then the test is carried out.
During the test, the output of the thermocouple should be recorded to a time T0.5 corresponding to a 50% change in the temperature step. If necessary, a thermal response time T0.1 of 10% change and a thermal response time T0.9 of 90% change can be recorded.
The recorded thermal response time shall be the average of at least three test results of the same test, and the deviation of each measurement from the average value shall 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.
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