1. Reproducibility of environmental conditions
It is impossible to achieve a complete and accurate reproduction of 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 during use, storage, and transportation. This passage is summed up in the language of engineering, that is, "The environmental conditions (including platform environment) surrounding the tested product created by the test equipment should meet the environmental conditions and tolerance requirements specified in the product test specification." For example, the temperature box used for the test of military products must not only meet the requirements of the national military standard GJB150.3-86 and GJB150.4-86 according to different uniformity and temperature control accuracy. Only in this way can the reproducibility of the 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 a tested engineering product may also be tested in different environmental test equipment, in order to ensure that the same product is tested in the same test specification. The comparability of the test results obtained under the conditions inevitably requires the environmental conditions provided by the environmental test equipment to be repeatable. That is to say, 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 reproducibility of the environmental conditions provided by the environmental testing equipment is guaranteed by the national metrological inspection department after passing the verification in accordance with the verification procedures formulated by the national technical supervision agency. For this reason, environmental testing equipment must be required to meet the requirements of various technical indicators and accuracy indicators in the verification regulations, and the use time does not exceed the time limit specified in the verification cycle. For example, in addition to meeting technical indicators such as excitation force, frequency range, load capacity, etc., a very common electric vibration table must also meet the requirements of accuracy indicators such as lateral vibration ratio, table 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-verified before it can be put into use.
3. The measurable and controllability of environmental condition parameters
The environmental conditions provided by any environmental test equipment must be observable and controllable. This is not only to limit the environmental parameters within a certain tolerance range, but also to ensure the reproducibility and repeatability of the test conditions. Moreover, it is also necessary to proceed from the safety of the product test, in order to prevent the uncontrolled environmental conditions from causing damage to the tested product and causing 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.
4. The exclusivity of environmental test conditions
Every time an environmental or reliability test is performed, there are strict regulations on the category, value and tolerance of environmental factors, and non-tests are excluded.
The environmental factors required for the test penetrate into it, so as to provide an accurate basis when judging and analyzing product failure and failure modes during the test or after the test. Therefore, the environmental test equipment is required to provide the specified environmental conditions, and it is not allowed to The trial product adds other environmental stress interference. For example, the table surface magnetic flux leakage, the acceleration signal-to-noise ratio, and the total rms value ratio of the acceleration inside and outside the band are defined in the verification regulations of the electric vibration table. Accuracy indicators such as random signal inspection and harmonic distortion are all verification items designed to ensure the uniqueness of environmental test conditions.
5. Safety and reliability of test equipment
Environmental tests, especially reliability tests, have a long test period. The objects of the test are sometimes high-value military products. During the test, the testers often have to perform inspections or test work around the site. Therefore, the environmental test equipment must be operational Safety, convenient operation, reliable use, long working life and other characteristics to ensure the normal conduct of the test itself. The various protection, alarm 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.