Basic Principles for Selecting Environmental Test Chamber

Basic Principles for Selecting Environmental Test Chamber

An environmental test chamber refers to a test chamber that simulates the natural environment to guide the environmental and reliability tests of engineering products. The selection should follow the following five basic principles.

 

 

Reproducibility of Environmental Conditions

 

It is impossible to completely reproduce the environmental conditions in the laboratory. However, within a certain tolerance range, people can completely and accurately simulate the external environmental conditions experienced by engineering products during use, storage, and transportation. This paragraph is summarized in the language of engineering, that is, "the environmental conditions (including the platform environment) created by the test equipment around the tested products should meet the environmental conditions and tolerance requirements specified in the product test specifications." For example, the temperature humidity testing equipment used for military product testing must meet the requirements of national military standards GJB150.3-86, GJB150.4-86 according to different uniformity and temperature control accuracy. Only in this way, the reproducibility of environmental conditions can be guaranteed in environmental tests.

 

Repeatability of Environmental Conditions

 

An environmental chamber may be used for multiple tests of the same type of products, and a tested engineering product may also be tested in different environmental test equipment. In order to ensure the comparability of the test results obtained by the same product under the environmental test conditions specified in the same test specification, the environmental conditions provided by the environmental test equipment must be repeatable. This means that the stress level (such as thermal stress, vibration stress, electrical stress, etc.) applied by the environmental test equipment to the tested product is consistent with the requirements of the same test specification. 

The repeatability of the environmental conditions provided by the environmental test equipment is guaranteed by the national metrological verification department after passing the verification according to the verification regulations established by the national technical supervision agency. Therefore, it is required that the environmental test equipment can meet the requirements of various technical indicators and accuracy indicators in the verification regulations, and the service life does not exceed the time limit specified in the verification cycle. For example, in addition to technical indicators such as excitation force, frequency range, and load capacity, the very common electric vibration platform must also meet the requirements of accuracy indicators such as lateral vibration ratio, platform acceleration uniformity, and harmonic distortion specified in the verification regulations. Moreover, the service life after each test is two years. After more than two years, the test must be re-qualified before it can be put into use.

 

 

Measurability and Controllability of Environmental Condition Parameters

 

The environmental conditions provided by any environmental test equipment must be measurable and controllable. This is not only to keep the environmental parameters in a certain tolerance range, ensuring the reproducibility and repeatability of the test conditions. In addition, it is also necessary for the safety of product tests to prevent uncontrolled environmental conditions from causing damage to the tested product and bringing unnecessary losses. At present, various test specifications generally require that the accuracy of parameter testing should not be less than one third of the error allowed by the test conditions.

 

Exclusiveness of Environmental Test Conditions

 

Each time an environmental or reliability test is performed, there are strict regulations on the type, magnitude and tolerance of environmental factors, and the factors that are not required for the test should be precluded, so that we can judge and analyze product failure during or after the test with exact basis. Therefore, the environmental test equipment is not allowed to add other environmental stress interference to the tested product in addition to providing the specified environmental conditions.

 

 

Safety and Reliability of Test Equipment

 

Environmental tests, especially reliability tests, have long test cycles, and the test products sometimes are high-value military products. During the test, testers often patrol or test around the site. Therefore, environmental test equipment must have the characteristics of safety, convenient operation, reliable use, long working life to ensure the normal conduct of the test itself. Various protections, warning measures and safety interlocking devices of the test equipment should be perfect and reliable to ensure the safety and reliability of the test personnel, the tested product and the test equipment itself.