Ten important points when doing experimental testing

1.Low temperature switch off time

How long is the appropriate shutdown time for a low-temperature switch? This is the key to this test. The basic principle is that the temperature rise caused by the heat after the product is turned on can be reduced to the same temperature as the ambient temperature in the environmental test chamber during the shutdown time. The consistency here refers to the temperature of all parts of the product, not certain specific parts. For some complex products that cannot be estimated, this time can be determined through experiments. The test method is to place temperature sensors on different devices inside the product, conduct actual tests to understand the rate of change of temperature recovery, and finally determine how long it will take to recover to the same ambient temperature.

2.Recovery of test temperature

The time it takes for the test sample to reach equilibrium when the temperature test conditions are restored depends on its thermal inertia, that is, the shape, mass and structure of the test sample. The recovery time is usually 1 hour. For specific samples, especially equipment test samples, it may be necessary to re-evaluate and determine the corresponding recovery time. For working constant temperature tests, the end time of the test is often at night or on weekends. At this time, you will encounter the problem of how to deal with such problems. It is generally recommended to restore to normal temperature (25 degrees) after the test time is over, and keep the temperature test chamber working to maintain this temperature until the next day or working day. In order to maintain the temperature test chamber studio, because for some products with high heat generation, if the air is not circulated after the temperature test chamber is turned off, the ambient temperature will rise due to the heat of the product. It is very likely that the ambient temperature will exceed the range of the test and cause failure, and even cause fire in severe cases. In addition, it should be noted that the sample needs to be kept working continuously, and the power cannot be cut off or the executed program or function cannot be terminated. For some times, it is required to perform a functional check before the end of the test. At this time, it is necessary to consider whether to continue to maintain the test temperature and wait until all functions are checked after the working time before returning to normal temperature. Of course, extending the test time by one night or one or two days generally has little effect on the test results, and the risk is very low. If the temperature is restored to normal temperature in advance, the temperature of the temperature test chamber needs to be adjusted to the test temperature again after the working hours return. Consumer electronic products need to work for at least one hour before relevant functional tests can be carried out.

3.Principles for placing samples in temperature test chamber

The placement of test samples in the test chamber should not affect the air convection in the test chamber. They can be placed in multiple layers. Different test chambers can accommodate different test samples. The following table shows typical test chambers and corresponding size recommendations. For detailed sizes, refer to the figure below. The most critical thing is the minimum distance between the sample and the four walls of the test chamber. When preventing multiple samples, the minimum distance between samples can also refer to the recommended value in the table below.

4.Sample pre-test

Samples must be pre-tested before testing. The most important thing is to test the software or other tools needed in the test for more than half an hour at room temperature before the test. Any problems that occur during the test need to be recorded. It is not recommended to use constant temperature tests for samples that have problems during the test, unless the test is only used to find problems, and the test results cannot be used as the final judgment basis. It is generally recommended to conduct constant temperature tests for samples that have problems under room temperature conditions after solving the problems.

5.Test chamber wind speed

It is recommended that the test chamber wind speed affect the sample surface temperature below 5 degrees. If possible, it is recommended that the test chamber wind speed be lower than 0.5m/s. This applies to all temperature and humidity environment test items.

6.Test chamber temperature change rate

The average temperature change rate of the test chamber shall not exceed 1 degree per minute. This value is based on the average value of the temperature change rate for no longer than 5 minutes.

7.Test chamber inlet air temperature

After the test chamber temperature stabilizes, the inlet air temperature must be within ±2 degrees of the specified temperature. If this accuracy cannot be guaranteed due to dimensional factors of temperature and humidity, an accuracy of ±3 degrees is acceptable for temperatures above -25 degrees, and an accuracy of ±5 degrees is acceptable for temperatures between -25 degrees and -65 degrees.

8.Setting the temperature curve

Some manufacturers' temperature test chambers provide two options for temperature settings. One is that when a certain range of the set temperature is reached, it is considered that the set temperature has been reached and the execution time of the next program will be calculated. The other is that the set temperature is considered to have been reached only after the set temperature has been reached. It is recommended to choose the latter setting if there is a choice to ensure that the test time meets the requirements. Although the difference of a few minutes is within an acceptable range, the latter should be chosen for safety reasons. This recommendation applies to all temperature-related tests using temperature and humidity test chambers.

9.Trial interruption

If the interruption time of the test condition is within the allowable error range, it will not be counted as an interruption (for example, the power supply of the temperature test chamber is restored after a short interruption, but the ambient temperature in the temperature test chamber is not affected). If the interruption time of the test condition exceeds the allowable error range, it is necessary to continue to restore the test conditions to ensure that the sum of the time before the test interruption and the continuous test time after the test conditions are restored after the test interruption meets the test requirements. However, if the test is interrupted, it is recommended to invalidate the test and the test needs to be completely re-executed, and the final result of the re-executed test shall prevail.

10.Test product bracket

Generally, the test chamber is equipped with a multi-position stainless steel bracket. The purpose of the test is to simulate the actual use environment. Usually, the possibility of placing the product on a metal rack or a good thermal conductor is low, so it is not recommended to place the product directly on the bracket during the test. Usually, it is necessary to prepare a material with poor thermal conductivity and place it on the bracket, and the final product is placed on the material with poor thermal conductivity for testing. It is recommended to use Teflon or wood to place the sample on the metal rack for testing.