Views: 26 Author: Site Editor Publish Time: 2020-06-01 Origin: Site
Analysis of Condensation in High and low Temperature Environmental Test
High and low temperature tests, rapid temperature change tests, and environmental tests are used as a common means of testing to improve the reliability of electronic products. They are widely used in various research and development cycles of electronic products and they are used to determine the adaptability of communication equipment to the environment. In the course of environmental testing, according to the characteristics of the product, select the appropriate test method to inspect and evaluate the mechanical properties, electrical properties, physical properties, tensile strength and tensile resistance of the material, and insulation properties of the product. Only by choosing the correct test method and standard test conditions can the correct test results be obtained. In the process of constant humidity and heat, the product must be preheated to avoid the appearance of a large amount of condensation and cause additional stress, which affects the correct evaluation of the experimental results.
Overview of a tested communication device
It is an outdoor device that uses natural heat dissipation. It is characterized by large volume, large heat consumption and sealed cavity. Working temperature:
A temperature of 40℃ & 55% requires that the temperature rise in the cabinet is not greater than 20℃, working humidity: 10%-95% (relative humidity); storage temperature:-40 ℃-+85 ℃, storage humidity: ≤ 93% (relative humidity); total weight of the whole machine: 50Kg
The overall structure adopts a box structure. It is composed of cabinet, door, installation accessories and internal power supply module, two power amplifier modules, two low-noise amplifier modules, two duplexers (DUP), lightning protection module and monitoring board.
Analysis of Condensation Problems in Environmental Test
For such a sealed, heat-dissipating, large-volume natural heat dissipation product, if the heat in the product is not transferred to the surrounding atmosphere, the product temperature will continue to rise. In fact, the heat generated by the product is continuously radiated to the surrounding atmosphere. Finally, the heat generated by the product is balanced with the heat dissipated in the surrounding cooling atmosphere to stabilize the product temperature. Only when the ambient temperature rises (or falls) will the temperature inside the product rise (or fall) further until it reaches a new equilibrium.
Because the ambient temperature chamber is affected by the ambient temperature and humidity, in the high temperature test , low temperature test and high and low temperature tests, the humidity is not much different from the ambient humidity, about 48% (at least before reaching thermal equilibrium). The general environmental test chamber has a humidity control function, and the humidification method usually used as follows:
Spray humidification: it is easy to generate a small amount of aerosol in the work space;
Steam humidification: may cause condensation of equipment with lower temperature in the box;
Volatile humidification: a small amount of aerosol;
Humidification of aqueous solution: easy to cause corrosion;
When the sample is put into the box, if the surface temperature of the test sample is lower than the dew point temperature of the air in the test box, condensation will appear on the sample surface. Therefore, the test sample is generally preheated before the experiment. Dew point temperature depends on the amount of water vapor in the air. There is a direct relationship between dew point temperature, absolute humidity, and water vapor pressure. During the experiment, if the moisture content in the air and the temperature of the air are high, and the dew point temperature of the air reaches a certain difference between the surface temperature of the test sample, condensation will occur. In general, in the warm-up phase of the experiment, because the experimental sample has a certain thermal time constant, its surface temperature is often lower than the dew point temperature of the air in the experimental box. Therefore, condensation occurs on the surface of the experimental sample.
During the temperature increase, when the experimental sample will produce condensation, the following physical phenomena exist due to humidity:
Adsorption: Due to the different types of material on the surface of the device, the surface structure of the material, and the size of the water vapor pressure, it determines the number of water vapor molecules on the surface of the experimental sample.
Absorption: Depending on the moisture content of the surrounding environment, the rate of penetration of water molecules increases with increasing temperature.
Diffusion: water vapor enters the inside of the housing through the organic sealing material;
Breathing: Due to temperature changes, the exchange of air and water vapor inside and outside the cavity of the experimental sample. There are experimental samples of poor sealing type. The inhaled moisture makes the internal structure of the experimental sample wet or condenses into aggregated water in the cavity.
The absorption and diffusion processes take a considerable amount of time to reach equilibrium, while the condensation and adsorption processes are shorter. Therefore, the phenomenon of a small amount of condensation on the surface of the sealed communication equipment with large volume and large heat dissipation during the experiment is a normal experimental phenomenon. The amount of water vapor on the surface of the equipment and the length of attachment time vary depending on the temperature and humidity changes in the environmental experiment box. If a large amount of water vapor and condensation occurs, the experimental conditions need to be adjusted to prevent large deviations in the experimental results.
Conclusions and recommendations
1) A small amount of condensation during the environmental experiment will not damage the performance of the device. It will not affect the analysis of the experimental results.
2) In order to prevent the occurrence of a large amount of condensation, the analysis of the experimental results leads to a wrong direction, generally in the process of environmental experiments, in advance
Preheat the product.
3) Environmental experiments have a great influence on the experimental samples, which may change the mechanical properties, physical properties, and electrical properties of the materials. Therefore, in
In the early stage of product design, consider the actual use conditions, select the appropriate components, and use derating design, redundancy design, tolerance design, climatic and environmental protection design, buffer vibration reduction design, thermal design and other means to improve product reliability. In environmental experiments, only by applying appropriate experimental conditions, exposing existing problems, and seeking appropriate improvement measures can the suitability of the product be further determined so that the product can meet the requirements for use.
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