The selection of high and low temperature test chamber environment and reliability test equipment should follow the following basic principles

1. Reproducibility of environmental conditions The complete and accurate reproduction of environmental conditions existing in nature in the laboratory is elusive. 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, transportation, etc. This paragraph is summarized in engineering language. The environmental conditions created by the test equipment around the tested product (including the platform environment) should meet the environmental conditions and tolerance requirements specified in the product test specification. For example, the temperature box used for military product testing must not only meet the national military standard GJB150.3-86, GJB150.4-86 according to different types of products in the high temperature, low temperature test value, test time, but also meet the test specifications for the uniformity of temperature field and temperature control accuracy requirements. Only in this way can the reproducibility of environmental conditions in environmental tests be guaranteed. 2. Repeatability of environmental conditions An environmental test equipment may be used for multiple tests of the same type of product, and an engineering product under test may also be tested in different environmental test equipment. In order to ensure the comparability of test results obtained by the same product under environmental test conditions specified in the same test specification, The environmental conditions provided by the environmental test equipment must be reproducible. That is to say, the stress level (such as thermal stress, vibration stress, electrical stress, etc.) applied to the product being tested by the environmental test equipment 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 procedures formulated by the national technical supervision agency. To this end, it must be required that the environmental test equipment can meet the requirements of the technical indicators and accuracy indicators in the verification regulations, and the use time does not exceed the time limit specified in the verification cycle. Such as the use of very common electric vibration table in addition to meet the exciting force, frequency range, load capacity and other technical indicators, must also meet the requirements of the verification regulations stipulated in the lateral vibration ratio, table acceleration uniformity, harmonic distortion and other accuracy indicators, and the service cycle after each verification is two years, more than two years must be re-verified before it can be put into use. 3. 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, to ensure the reproducibility and repeatability of the test conditions, but also to start from the safety of the product test is necessary. In order to prevent the uncontrolled environmental conditions leading to the damage of the tested products, resulting in unnecessary losses. At present, various test specifications generally require that the accuracy of parameter testing should not be less than one-third of the allowable error of test conditions. 4. Exclusivity of environmental test conditions Each environmental or reliability test has strict regulations on the category, magnitude and tolerance of environmental factors, and unless the environmental factors required by the test penetrate into it, in order to provide an exact basis for judging and analyzing product failure and failure modes during or after the test. Therefore, in addition to providing the specified environmental conditions, the environmental test equipment is not allowed to attach other environmental stress interference to the tested product. For example, the mesa magnetic leakage, the acceleration signal-to-noise ratio, and the total RMS value ratio of the in-band plus speed are limited in the verification regulations of the electric vibration table. Random signal test, harmonic distortion degree and other accuracy indexes are designed to ensure the uniqueness of environmental test conditions. 5. The safety and reliability environmental test of the test equipment, especially the reliability test, the test cycle is long, the object of the test is sometimes high value military products, during the test process, the test personnel often have to operate or test work around the site, so the environmental test equipment must have the characteristics of safe operation, easy operation, reliable use, long working life, etc. To ensure the normal conduct of the test itself. Various protection, alarm measures and safety interlocking devices of test equipment should be perfect and reliable to ensure the safety and reliability of test personnel, tested products and test equipment itself.