In order to obtain reproducibility, the temperature test must be designed in such a way that the maximum or minimum temperature reached at a certain point of the test sample in the high and low temperature test chamber is the same, regardless of the laboratory in which the test is performed, and the temperature reached relative to the test sample If the time required for stabilization is relatively short-duration, the following precautions should be considered:
1. The air velocity around the test sample:
The heat exchange efficiency between the air in the high and low temperature test chamber and the test sample depends on the air speed. In the high and low temperature test, it is expected to accurately simulate the air speed in the actual environment, but because of the limited knowledge of the actual environment and the difficulty of confirming the test chamber This kind of simulation is usually not possible. Therefore, the test must generally be carried out according to the "worst case" to cover all possibilities. When testing non-heat dissipation test samples, higher air speeds lead to higher / For low temperature test is a lower temperature of the test sample, therefore, it is recommended to use a high air velocity in the test chamber for this test (the measurement is preferably not less than 2M / S under no load). When testing the heat dissipation test sample, if The temperature of the hottest spot of the test sample is higher than the surrounding air temperature, then the higher air velocity will reduce the temperature of that point, so in most cases, whenever possible, this test should be performed without forced air circulation (ie free air conditions) It is carried out in the test box. When the heating or cooling of the test box can only be achieved by air circulation, the forced air method can be used as an alternative method.
In order to obtain reproducibility, the temperature-time process of the test chamber air must be well specified during the entire high and low temperature test chamber test. If the actual environment can be accurately simulated, the temperature can be specially designed to simulate this situation- Time course, it should be noted that the temperature-time course diagram is different from Test A and Test B in the following details:
a. The temperature range at the beginning is narrow (25 degrees plus or minus 3 degrees);
b. The rate of change of the test chamber air temperature during the establishment of the test temperature;
c. The test duration is calculated from when the air temperature of the test chamber reaches the specified value.
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