1. Volume selectionProduct placement is to be tested when tested designate environment, were tested in order to ensure an atmosphere around the productAble to meet the test specification test conditions specified in the environment, climate chamber size and work products were testedBetween dimensions should follow the following 3 points:A. products were tested volume (W × H × D) shall not exceed the effective working space chamber for 20% to 30%(Recommended to select 20%); the heat in the test products, then recommended to select no more than 10%.B.windward tested products with the cross sectional area of ??the work on the experimental box test total area ratio of not more than 35% to 50% (35% of the recommended choice)C. Test Product outline chamber wall surface distance and the distance to maintain at least 100mm ~ 150mm (recommended choice 150mm)2. Temperature range At present, foreign chamber temperature range substantially -73 ℃ ~ +177 ℃ or -70 ℃ ~ +180 ℃. The majority of domestic manufacturers to provide a temperature of -80 ℃ ~ +130 ℃, -60 ℃ +130 ℃ or -40 ℃ ~ +130 ℃, there are high temperatures reached +150 ℃. These temperature range already meet most domestic military and civilian product temperature testing needs, unless there are other special needs, such as: installation location near heat sources such as generators products, otherwise, not blindly raise the temperature limit. Because, the higher the upper limit temperature, the greater the temperature difference between inside and outside the test case, the test flow inside the box have poorer uniformity. In contrast, the available experimental phase the smaller body aircraft. Other hand, the higher the value of the maximum temperature of the tank wall insulation sandwich requires higher heat resistance; box sealing requirements are also higher. So, the chamber will be a substantial increase in production costs.3. Humidity range Domestic and international environmental chamber humidity index mostly given release 20 ~ 98% RH or 30 ~ 98% RH, if the heat chamber without dehumidification system, the humidity range of 60 ~ 98% RH, can only do this type of environmental chambers humidity test, however, its price is low. It should be noted that in the back of humidity indicator should indicate the appropriate temperature range, the minimum dew point temperature or labeled. Because the relative humidity and temperature are directly correlated. For the same absolute moisture content, the higher the temperature, the smaller the relative humidity. For example: the absolute moisture content of 5g/KG, (intended to mean 1 kg of dry air containing 5 grams of water vapor), when the temperature is 29 ℃, the relative humidity of 20% RH; temperature 6 ℃, the relative humidity of 90% RH, when the temperature dropped below 4 ℃, relative humidity exceeds 100%, the test cabinets cause condensation phenomenon.4. Control mode selectionTemperature / humidity chamber with temperature chamber BA-T80, high and low temperature heat chamber BA-TH80 In both cases, the ordinary high and low temperature generally refers to a constant high temperature chamber, its control mode is: setting a target temperature, the chamber has an automatic thermostat's ability to point to the target temperature. Constant temperature control chamber is similar, set a target temperature and humidity point, the chamber has an automatic thermostat to a target temperature and humidity point capability. High and low temperature test chamber has a set of one or more high and low temperature changes, recycling programs, the chamber has the ability to complete according to a preset curve during the test, and can be at the maximum heating and cooling rate capability range, precise control of heating, cooling rate, which can be set to control the slope of the rate of heating and cooling. Similarly, the high and low temperature heat chamber also has a preset temperature, humidity curve, and the ability to control according to preset. Of course, the chamber has a constant alternating chamber functions, however, alternating chamber higher manufacturing costs, due to alternating chamber must be configured with curves automatic recording device programmer, need to solve the interior chamber at work the case of high temperature, automatically open refrigerator and other issues, so the price is higher than the alternating chamber chamber constant prices are generally higher than 20%. In the pragmatic context, the experimental method as a starting point needed to decide whether to use a constant or alternating chamber chamber.5. Non-linear loadsLinear rate that is variable temperature control, high and low temperature is not an ordinary pointer cool, cool down from ambient temperature to a nominal minimum time, usually 90 to 120 points. High and low temperature test chamber with alternating high and low temperature heat chamber has a variable temperature requirements of speed, its temperature rate of 1 ℃ / min, at this rate range, speed adjustable. The rapid temperature changes faster variable temperature chamber, heating, cooling rate up to 3 ℃ / minute ~ 15 ℃ / min heating in certain temperature ranges, the cooling rate can even reach 30 ℃ / min or more.Various specifications, rapid changes in the speed of the temperature range of temperature chambers are generally the same, namely -60 ℃ ~ +130 ℃, but the assessment of the cooling rate of the variable temperature range is not the same, according to experiment with different test requirements Rapid Temperature Change Test Some boxes variable temperature range -55 ℃ ~ +80 ℃, while some -40 ℃ ~ +80 ℃.Rapid temperature changes on the chamber temperature rate, there are two references, one is full average heating and cooling rate, one is a linear ramp speed (actually the average speed every 5 minutes). The average speed is the entire variable temperature range in the chamber, the maximum temperature and the minimum temperature difference between the comparison and time. At present, foreign various environmental test equipment manufacturers to provide temperature rate refers to the technical parameters are full average speed. The Company BA-80H, for example, refers to a linear ramp speed every 5 minutes in any period of time, to ensure that the temperature rate. In fact, the chamber for rapid temperature changes, ensuring a linear rise, cooling rate of the most difficult, the most important final H.264/AVC SVC segments are: cooling section in the last 5-minute period, the chamber of the cooling rate can be up to. To a certain perspective, linear ramp speed (average speed every 5 minutes) more scientific. Therefore, the test device preferably has a full average ramp rate and linear heating rate of these two parameters. As for the non-linear annexed to the actual discussion with the sales staff can also, in order to understand the manufacturer's professionalism.6. WindsRelevant standards, environmental test, temperature and humidity inside the wind speed should be less than 1.7m / s, the test itself, the smaller the better wind. Wind speed is too large, will accelerate the test piece surface and the heat exchange air flow cabinets, the authenticity of the experiment negative. But in order to ensure the chamber temperature uniformity of the working chamber, the test chamber with circulating air is a must. However, the rapid temperature changes as well as chamber temperature, humidity, vibration and other factors integrated environmental test chamber, temperature and velocity in order to pursue it, we must accelerate the test cabinets circulating air flow, wind speed is usually 2 ~ 3m / s. Therefore, for a variety of purposes, speed limit is not the same.7. Temperature fluctuationTemperature fluctuation is relatively easy to achieve a parameter, so the majority of environmental test equipment manufacturers test box actual temperature fluctuations, are able to control within the range of ± 0.3 ℃.8. Temperature uniformityFor more correct analog products are physical in nature environment, must ensure that the test in the environment, surrounding the products tested in the same temperature conditions, therefore, necessary to test chamber temperature gradient and temperature fluctuation be limited. In GB GJB150.1-86 military environment Equipment General test method clearly states: the test sample shall be measured near the temperature of the system at the test temperature within ± 2 ℃.9. Humidity controlMost environmental chambers to test humidity test using dry and wet bulb law, environmental test equipment manufacturing standards GB10586 requirements, relative humidity deviation should be within ± 2 ~ 3% / RH inside. Does not meet the requirements of precision humidity control, humidity chamber temperature control precision is high. Otherwise, it is difficult to achieve humidity control accuracy requirements.10. Environmental RequirementsRecommend ventilated to avoid the sun, the surrounding environment temperature and humidity will affect the test equipment, temperature and humidity cause instability and even cause the compressor heater burden, wasting power consumption and increase the impact of the snow kind of life.
Article From http://www.bangtest-china.net Author Bang Instrument co.,ltd
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