Basic Principles of Environmental Chamber Selection
The selection of environmental and reliability test chamber shall follow the following five basic principles:
1. Reproducibility of environmental conditions
It is out of reach to completely and accurately reproduce the environmental conditions existing in nature in the laboratory. However, within a certain tolerance range, people can accurately and approximately simulate the external environmental conditions experienced by engineering products in the process of use, storage and transportation. This paragraph is summarized in engineering language, that is, “the environmental conditions around the tested product (including platform environment) created by test equipment” It shall meet the requirements of environmental conditions and their tolerances specified in the product test specifications “. Generally, according to the test quantities and test time of high temperature and low temperature specified for different types of products, it shall also meet the requirements for the uniformity of temperature field and temperature control accuracy in the test specifications. Only in this way can the reproducibility of environmental conditions in the environmental test be guaranteed.
2. Repeatability of environmental conditions
One environmental test equipment may be used for multiple tests of the same type of product, and one tested engineering product may also be tested in different environmental test equipment. In order to ensure the comparability of the test results of the same product under the environmental test conditions specified in the same test specification, it is necessary to require the repeatability of the environmental conditions provided by the environmental test equipment In other words, the stress level (such as thermal stress, vibration stress, electrical stress, etc.) applied by the environmental test chamber to the test object meets the requirements of the same test specification.
The repeatability of environmental conditions provided by environmental test equipment will be recognized by relevant national institutions. Therefore, the environmental test equipment must meet the requirements of various technical indicators and accuracy indicators in the verification regulations, and the service time shall not exceed the time limit specified in the verification cycle. For example In addition to meeting the technical indexes such as excitation force, frequency range and load capacity, the widely used electric vibration table must also meet the requirements of accuracy indexes such as transverse vibration ratio, table acceleration uniformity and harmonic distortion specified in the verification regulations. Moreover, the service cycle after each verification is two years. It can be put into use only after it has been verified qualified for more than two years.
3. Measurability of environmental condition parameters
The environmental conditions provided by any environmental test equipment must be observable and controllable, which is not only to limit the environmental parameters within a certain tolerance range and ensure the reproducibility and repeatability requirements of test conditions, but also necessary for the safety of product test, so as to prevent the damage of tested products caused by out of control environmental conditions At present, various test specifications generally require that the accuracy of parameter test should not be less than one third of the allowable error of test conditions.
4. Exclusivity of environmental test
Each environmental or reliability test has strict regulations on the category, quantity and tolerance of environmental factors, and excludes the penetration of environmental factors not required for the test, so as to provide accurate basis for judging and analyzing product failure and failure modes during or after the test. Therefore, it is required that the environmental test equipment shall not be allowed except providing the specified environmental conditions Add other environmental stress interference to the tested product, such as table magnetic leakage, acceleration signal-to-noise ratio, total root mean square value ratio of in band and out of band acceleration as defined in the verification regulation of electric shaking table. The accuracy indexes such as random signal inspection and harmonic distortion are all verification items formulated to ensure the uniqueness of environmental test conditions.
5. Safety and reliability of test chamber
The environmental test, especially the reliability test, has a long test cycle, and the test object is sometimes high-value military products. During the test process, the testers often have to operate or test around the site. Therefore, the environmental test equipment must have the characteristics of safe operation, convenient operation, reliable use and long service life, so as to ensure the normal operation of the test itself Various protection, alarm measures and safety interlocking devices of test equipment shall be perfect and reliable to ensure the safety and reliability of test personnel, tested products and test equipment.