1, the choice of volume
When the test product (components, components, components or complete machine) is placed in the climatic environment box for testing, in order to ensure that the atmosphere around the test product can meet the environmental test conditions specified in the test specification, the working size of the climate chamber and the product to be tested The following points should be observed between the dimensions:
2, the choice of temperature range
At present, the range of foreign temperature test chambers is generally -73 to +177 °C, or -70 to +180 °C. Most domestic manufacturers generally have -80 to +130 ° C, -60 to +130 ° C, -40 to +130 ° C, and high temperatures to 150 ° C. These temperature ranges usually meet the needs of most domestic military and civilian products for temperature testing. Unless there are special needs, such as installing products close to the heat source such as the engine, the temperature upper limit should not be blindly increased. Because the higher the upper limit temperature, the greater the temperature difference between the inside and outside of the tank, the worse the uniformity of the flow field inside the tank. The smaller the available studio volume. On the other hand, the higher the upper limit temperature value, the higher the heat resistance requirement for the heat insulating material (such as glass wool, etc.) in the tank wall interlayer. The higher the sealing requirements of the cabinet, the higher the manufacturing cost of the cabinet.
3, the choice of humidity range
The humidity indicators given by the environmental test chambers at home and abroad are mostly 20-98% RH or 30-98% RH. If the damp heat test chamber does not have a dehumidification system, the humidity range is 60-98%. This type of test chamber can only be high. Wet test, but its price is much lower. It is worth noting that the corresponding temperature range should be indicated after the humidity indicator or the minimum dew point temperature should be given. Because the relative humidity is directly related to the temperature, for the same absolute moisture content, the higher the temperature, the smaller the relative humidity, such as the absolute moisture content of 5g / Kg (refers to 1 kg of dry air containing 5 grams of water vapor) ), when the temperature is 29 ° C, the relative humidity is 20% RH, the temperature is 6 ° C, the relative humidity is 90% RH, when the temperature drops below 4 ° C, the relative humidity exceeds 100%, condensation will appear in the box phenomenon. To achieve high temperature and high humidity, it is only necessary to spray water vapor or atomized water droplets into the air of the cabinet to humidify. Low temperature and low humidity are relatively difficult to control because the absolute moisture content at this time is very low, and sometimes it is much lower than the absolute moisture content in the atmosphere. It is necessary to dehumidify the air flowing in the tank to make the air dry. At present, most of the temperature and humidity chambers at home and abroad adopt the principle of cooling and dehumidification, and a set of cooling tubes are added in the air pre-conditioning room of the cabinet.
4, the choice of control methods
The temperature and humidity test chambers have two conditions: constant test chamber and alternating test chamber. Ordinary high and low temperature test chambers generally refer to constant high and low temperature test chambers, which are controlled by setting a target temperature and the ability of the test chamber to automatically constant temperature to the target temperature point. The control method of the constant temperature and humidity test chamber is similar. Set a target temperature and humidity point. The test chamber has the ability to automatically adjust the temperature to the target temperature and humidity point. The high and low temperature alternating test chamber has the program of setting one or more high and low temperature changes and circulation. The test chamber has the ability to complete the test process according to the preset curve, and can accurately control within the range of maximum heating and cooling rate capability. The rate of temperature rise and temperature drop, that is, the temperature rise and temperature drop rate can be controlled according to the slope of the set curve.
5, the choice of temperature change rate
Ordinary high and low temperature test chambers have no index of cooling rate, and the time from ambient temperature cooling to the nominal minimum temperature is generally 90 to 120 minutes. The high and low temperature alternating test chamber and the high and low temperature alternating damp heat test chamber all have the requirements of variable temperature speed, and the variable temperature rate generally requires 1 ° C / min, and the speed is adjustable within the range of this rate. The rapid temperature change test chamber has a faster temperature change rate, and the temperature rise and temperature drop rate can reach 3 ° C / min ~ 15 ° C / min. In some temperature ranges, the temperature rise and temperature drop rate can even reach 30 ° C / min or more. The temperature range of the rapid temperature change test chamber of various specifications and speeds is generally the same, that is, -60～+130°C, but the variable temperature range of the evaluation cooling speed is not the same. According to the different test requirements of the test, the rapid temperature change test The temperature range of the box is -55 to +80 °C, and some are -40 to +80 °C.