The average annual temperature in most area of the earth is between 0°C and +40°C, among which the high temperature in summer is usually between +30°C and +49°C, and the average high temperature that often occurs is +43°C, which is the ambient temperature (Air temperature).
 

For consumer electronics application, the environmental test temperature is usually between +35°C and +45°C; and telecommunication and industrial products, are usually between +45°C and +55°C, considering their longer service life. In the other hand, outdoor product is recommended that their environmental temperature resistance should be at least +70°C to have good reliability and automotive electronics are vary depending on their installation conditions. In addition, the thermal radiation produced by sunlight must also be considered. The exposure product may increase about 17°C~33°C by solar radiation, and the thermal radiation effect will be different form the product surface color and ground heat reflection conditions. Thus, if you would like to have long-using duration of outdoor product, it’s the other way to carefully select the surface coating color in order to reduce the radiant heat effect.
 

In order to correctly observe and verify the thermal effect under the product in a high-temperature environment, while avoiding the influence of humidity effects, the International Electrotechnical Commission (IEC) recommended that the dry heat test executes in the temperature cabinet and the absolute humidity should not exceed 20g/m³. At the same time, the pre-test treatment, post-test treatment, heating rate, temperature load conditions, and the volume ratio of the test object in the temperature chamber are all described.
 

Dry Heat Test Application:

Generally, test applications are divided into High Temperature Storage Test and High Temperature Operating Test. It is recommended to use ambient temperature and high temperature cycling for High Temperature Storage Test and a stabilized temperature for High Temperature Operating Test. The application in the MIL standard suggests:

  • Simulation of the real life environmental conditions
  • Environmental testing should start with Dry Heat Test
  • Sequential test : from Vibration, Shock, High Temperature, to High Altitude ( this method is usually used in the product design evaluation stage)

General phenomenon caused by high temperature: 

Expansion coefficients of different materials cause parts damage/stuck, poor heat dissipation, overheating of parts, electrical failure, belt slack, accelerated aging and color degradation/yellowing, plastic softening, performance reduction, characteristic changes, creep rupture, oxidation, etc..


 

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