Combined temperature altitude humidity testing, also called low pressure testing. The purpose of the test is, in short, to confirm the effect of low air pressure on the product under test.
The basic concept of high altitude and low pressure:
Air pressure refers to the atmospheric pressure acting on a unit area, which is numerically equal to the gravity of the vertical column of air extending upward to the upper bound on a unit area. The international unit PASCAL, referred to as Pa, symbol PA. From the above definition, it can be seen that in the natural environment, the air pressure gradually decreases with the increase of altitude. At attitudes approaching 5,000 m, the atmospheric pressure drops to about half of the standard atmospheric pressure at sea level. At altitudes approaching 16,000 m, the atmospheric pressure drops to about 1/10 of the standard atmospheric pressure, and to about 1/100 of the standard atmospheric pressure at altitudes approaching 31,000 m.
Atmospheric pressure at the same altitude is also affected by temperature and latitude. Temperature impacts the movement of gas molecules in the atmosphere. The higher the temperature, the more intense the movement, and the higher the temperature, the higher the atmospheric pressure under other equal conditions. Different latitudes are impacted by the centrifugal force of the earth, the lower the latitude, the stronger the effect, and the lower the latitude, the higher the atmospheric pressure under other equal conditions.
correspondence curves of altitude and air pressure
The negative effects of low pressure on the product:
The direct impact of the reduction of air pressure on the product is mainly the pressure effect generated by the change of air pressure. For sealed products, the shell will produce a pressure, under the action of this pressure there is a risk of breaking the seal.
However, the main effect of the reduction of air pressure is that the performance of the product will be greatly impacted by the reduction of atmospheric density due to the reduction of air pressure. For heating products, such as motors, transformers, contactors, resistors, etc. These products will heat up during use, and the temperature of the product will rise due to heat, which is called temperature rise. The temperature rise of heat dissipation products increases with the decrease of atmospheric pressure and increases with the increase of altitude. The performance of the product is reduced, or the operation is unstable.
For equipment that uses air as an insulating medium, low air pressure has a more significant effect on the equipment. Under normal atmospheric conditions, air can be a better insulating medium, and many electrical products use air as an insulating medium. When these products are used in high altitude areas or as airborne equipment, due to the reduction of atmospheric pressure, partial discharge phenomenon is often generated near the strong electrode of the power plant, called corona.
What is more serious is that sometimes air gap breakdown occurs. At low pressure, especially when accompanied by high temperature conditions, the dielectric strength of the air is significantly reduced. That is, the corona initial voltage and breakdown voltage are significantly reduced, which increases the risk of arc surface discharge or corona discharge.
What is combined temperature altitude humidity testing:
Combined temperature altitude humidity testing is mainly used in aviation, aerospace, information, electronics and other fields to determine the environmental adaptability and reliability test of instruments, electrical products, materials, parts, and equipment. It is performed under the single or simultaneous action of low pressure, high temperature and low temperature. At the same time, to measure the electrical performance parameters of the specimen.
Aviation Equipment
Communication Products
PCB
Instrumentation
Automotive Products
The thinner the air, the lower the air pressure. According to this principle, the combined temperature altitude humidity testing operates by pumping air out of the workroom through a vacuum pump, thus bringing the studio to negative pressure conditions. Due to the lack of dispersion medium under vacuum, water mist cannot enter the workroom, so it is not possible to offer the humidity option when conducting low-pressure testing. The humidity test and the low temperature/ low pressure test must be alternated.
Test equipment of combined temperature altitude humidity testing - Altitude Test Chamber
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Internal dimensions D 1500 W 1000 H 970 mm -
Temperature range —40℃ to +150℃ -
Humidity range 20% ~ 95% (more than 50Kpa can be controlled) -
Heating rate 3℃/min -
Cooling speed 2℃/min -
Pressure range Atmospheric pressure to 0.5kPa -
Depressurization time Atmospheric pressure to 0.5k ≤30min
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