Home entertainment audio-visual equipment and automotive electronics are one of the key commodities of many manufacturers. In the process of product development, we must simulate the adaptability of products to temperature and electronic characteristics under different temperatures. However, when using ordinary ovens or high and low temperature test chambers to simulate the temperature environment, both ovens and high and low temperature test chambers have a test area equipped with circulating fans, so the problem of wind speed will occur in the test area. During the test, the temperature uniformity is balanced by rotating the circulating fan. Although the temperature in the test area can reach uniformity through air circulation, the calorific value of the product to be tested itself will also be taken away by the circulating air, which is obviously inconsistent with the actual product in the windless environment (such as living room and indoor). Because of the wind circulation, the temperature difference of the tested object with power transmission will be close to 10 ℃. In order to simulate the actual use environment, many people will misunderstand that natural convection test can be carried out only if the test machine can produce temperature (such as oven and high and low temperature test chamber), which is not the case. In the specification, there are special requirements for wind speed, and a test environment without wind speed is required. Through the natural convection test equipment (no forced wind circulation test), the temperature environment (natural convection) without passing through the fan is generated, and then the test integration test of the relevant temperature detection of the test object is carried out. This solution can be applied to the actual ambient temperature test of household related electronic products or confined spaces (such as large-size LCD TVs, car cockpit, car electronics, notebook computers, desktop computers, game consoles, audio, etc.).
The difference between the test environment with and without air circulation for the test of the object to be tested:
If the test object is not powered on, the test object itself will not heat, and its heat source is only to absorb the air heat in the test furnace. If the test object is powered on and heated, and there is air circulation in the test furnace, the heat of the test object itself will be taken away. For every 1 meter increase in wind speed, the heat will be reduced by about 10%. Suppose we want to simulate the temperature characteristics of electronic products in the indoor air-conditioned environment. If we use an oven or a constant temperature and humidity machine to simulate 35 ℃, although the environment in the test area can be controlled within 35 ℃ through electric heating and freezing, the air circulation of the oven and the high and low temperature test chamber will take away the heat of the tested product, so that the actual temperature of the tested product is lower than the temperature in the real airless state. Therefore, the natural convection test machine without wind speed must be used to effectively simulate the actual windless environment (such as indoor, car cockpit without startup, instrument chassis, outdoor waterproof box, etc.).
Indoor environment with no wind circulation and solar radiation:
Note: through the natural convection test chamber, simulate the real non forced air-conditioning convection environment actually used by the client, the hot spot analysis and heat dissipation characteristics evaluation of the product. For example, the LCD TV in the photo should not only consider its own heat dissipation, but also evaluate the impact of the thermal radiation outside the window on it. The thermal radiation may produce an additional radiant heat temperature rise of more than 35 ℃ for the product.
Hot spot improvement of analysis circuit board under natural convection constant temperature environment:
Note: provide a windless environment for the circuit board through the natural convection testing machine. Measure the temperature of each hot spot of the circuit board with the multi track temperature record. It is found that due to the rise of hot air, the heat released by the LSI IC by the SSI accumulates to 50 ℃ to θ According to the 10 ℃ rule, the higher the temperature, the shorter the service life of the product, and its reliability will also be greatly reduced. After thermal analysis and improvement, the LSI IC is designed at the bottom of the circuit board, the temperature of the LSI is greatly reduced, and its service life and reliability are also greatly improved.
No forced air circulation test:
Note: according to the specification requirements of iec60068-2-2, in the high temperature test process, the test conditions of forced air circulation need to be carried out. The test process needs to be maintained under the airless circulation component, and the high temperature test is carried out in the test furnace. Therefore, this test cannot be carried out through the oven or high and low temperature test chamber, and the free air condition can be simulated only through the natural convection test machine.
No forced air circulation test specifications: iec-60068-2-2, GB2423.2, gb2423.2-89 3.3.1 in IEC 60068-2-2-2007, GB2423.2
No need to use computer to directly measure the multi-point temperature of the product to be tested: the natural convection testing machine produced by Hongzhan has built-in RS-232 communication interface and the temperature control program of Agilent 34970A data collector. It can record the temperature values of each point measured by the product to be tested in the test curve of the controller at the same time, except that the controller can directly view the curve, And the curve can be copied out with the portable disc, and the detailed curve analysis can be carried out on the computer (the machine does not include the Agilent 34970A data collector, which needs to be purchased).。
Description of test conditions:
no forced air circulation test specifications: iec-68-2-2, GB2423.2, gb2423.2-89 3.3.1
No forced air circulation test: the test conditions without forced air circulation can well simulate the free air conditions
Gb2423.2-89 3.1.1:
when measured in free air, when the temperature of the test sample is stable, and the temperature of the hottest spot on its surface is more than 5 ℃ higher than the temperature of the surrounding heater, it is a heat dissipation test sample, otherwise it is a non heat dissipation test sample.
Gb2423.2-8 10 (high temperature test of temperature gradient of heat dissipation test sample): provide a standard test procedure to determine the adaptability of heat dissipation electronic products (including components, equipment level and other products) to use at high temperature.
Test requirements:
a. Testing machine without forced air circulation (equipped with fan or blower)
b. Single test sample
c. The heating rate shall not be greater than 1 ℃ /min
d. After the temperature of the test sample reaches stability, the test sample is powered on or loaded with electrical load for electrical performance testing
