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1. Reproducibility of environmental conditions
It is an elusive thing to completely and accurately reproduce the environmental conditions in nature in the laboratory. However, within a certain tolerance range, people can correctly and correctly simulate the external environmental conditions experienced by engineering products during use, storage, transportation, and the like. This passage is summarized in the language of the project, that is, "the environmental conditions (including the platform environment) created around the test equipment created by the test equipment should meet the environmental conditions and tolerances specified in the product test specifications." For example, the temperature box used for military product testing should not only meet the requirements of different uniformity and temperature control accuracy in the national military standard GJB150.3-86 and GJB150.4-86. 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 one engineered product may also be tested in different environmental test equipment in order to ensure that the same product is in the same test test. The comparability of the test results obtained under the conditions necessarily requires the environmental conditions provided by the environmental test equipment to be reproducible. That is to say, the stress level (such as thermal stress, vibration stress, electrical stress, etc.) applied to the product under test 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 according to the verification procedures formulated by the national technical supervision agency. To this end, environmental testing equipment must be required to meet the requirements of various technical indicators and accuracy indicators in the verification procedures, and the time limit specified in the verification period should not exceed the time limit. If the use of the very common electric vibration table meets the technical indicators such as excitation force, frequency range, load capacity, etc., it must also meet the requirements of the accuracy index such as lateral vibration ratio, mesa acceleration uniformity and harmonic distortion specified in the verification regulations. And the use period after each verification is two years, more than two years must be re-qualified before they can be put into use.
3. Measureability and control of environmental condition parameters
The environmental conditions provided by any environmental test equipment must be observable and controllable, not only to limit environmental parameters to within certain tolerances, but also to ensure reproducibility and repeatability of test conditions. Moreover, it is necessary to start from the safety of the product test, in order to prevent the damage of the test product caused by the out of control of the environmental conditions, resulting in unnecessary loss. At present, the accuracy of the parameter test generally required in various test specifications should not be less than one third of the error allowed by the test conditions.
4. Exclusivity of environmental test conditions
Every time an environmental or reliability test is carried out, there are strict regulations on the types, magnitudes and tolerances of environmental factors, and the environmental factors required for non-tests are excluded from infiltration to judge and analyze product failures during or after the test. In the case of failure mode, the exact basis is provided. Therefore, the environmental test equipment is not allowed to attach other environmental stress interference to the test product except for the specified environmental conditions. For example, the leakage magnetic field of the table, the acceleration signal-to-noise ratio, and the ratio of the total rms value of the in-band and out-of-band acceleration are defined in the electric vibration table verification procedure. Accuracy indicators such as random signal test and harmonic distortion are all verification items to ensure the uniqueness of environmental test conditions.
5. Safety and reliability of test equipment
Environmental tests, especially reliability tests, have long test cycles. The test objects are sometimes high-value military products. During the test, testers often have to conduct inspections or test work around the site. Therefore, environmental test equipment must be operated. Safe, easy to operate, reliable to use, long working life, etc., to ensure the normal operation of the test itself. The various protection, 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 products and the test equipment itself.
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