Selection method of environmental testing machine

The following five basic principles should be followed when selecting environmental and reliability testing equipment:
1. Reproducibility of environmental conditions
It is unreachable to reproduce the environmental conditions that exist in nature in a complete and precise manner 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, transportation, etc. This passage is summarized in engineering language, which means "the environmental conditions (including platform environment) created by the test equipment around the test product should meet the environmental conditions and tolerance requirements stipulated in the product test specifications." For example, the temperature box used for military product testing must not only meet the requirements of the national military standards GJB150.3-86 and GJB150.4-86 according to different uniformity and temperature control accuracy. Only in this way can the reproducibility of environmental conditions in environmental testing be ensured.
2. Repeatability of environmental conditions
An environmental testing equipment may be used for multiple tests of the same type of product, while an engineering product of the subject may also be tested in different environmental testing equipment. In order to ensure the comparability of the test results obtained by the same product under the environmental testing conditions stipulated by the same test specification, the environmental conditions provided by the environmental testing equipment must be reproducible. This means that the stress levels (such as thermal stress, vibration stress, electrical stress, etc.) applied to the product to be tested are consistent with the requirements of the same test specification.
The repeatability of environmental conditions provided by environmental testing equipment is guaranteed by the national metrology and verification department in accordance with the verification procedures formulated by the national technical supervision agency after passing the verification. 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 use time shall not exceed the time limit specified in the verification period. For example, the very common electric vibration table must not only meet the technical indicators such as excitation force, frequency range, and load capacity, but also meet the requirements of accuracy indicators such as lateral vibration ratio, tabletop acceleration uniformity, and harmonic distortion stipulated in the verification regulations. Moreover, the service period after each verification is two years. It must be re-checked and qualified before it can be put into use after more than two years.

3. Measurement and controllability of environmental conditions parameters
The environmental conditions provided by any environmental testing equipment must be observable and controllable. This is not only a requirement to limit environmental parameters to a certain tolerance range and ensure the reproducibility and repeatability of the test conditions, but also necessary to start from the safety of product testing, so as to prevent environmental conditions from being out of control and causing damage to the subject's product and causing unnecessary losses. At present, various test specifications generally require that the accuracy of parameter tests should not be less than one-third of the error allowed by the test conditions.

4. Exclusiveness of environmental test conditions
Each environmental or reliability test is conducted, strict regulations are provided on the categories, magnitude and tolerance of environmental factors, and environmental factors that are not required for the test are eliminated, so that when judging and analyzing product failure and failure modes during or after the test is completed, the environmental test equipment is required to not allow other environmental stress interference to the test product except for the specified environmental conditions. For example, the table surface leakage magnetic field is defined in the verification procedures for electric vibration tables, the acceleration signal-to-noise ratio, and the total root mean square ratio of the internal and external accelerations of the band. The inspection of random signals, harmonic distortion and other accuracy indicators are all verification items formulated to ensure the nature of environmental test conditions.

5. Safety and reliability of test equipment
Environmental testing, especially reliability testing, has a long test cycle, and the test objects are sometimes very valuable military products. During the test, the test personnel often have to operate inspections or test work around the site. Therefore, environmental testing equipment must have the characteristics of safe operation, easy operation, reliable use, and long working life to ensure the normal progress of the test itself. Various protection, alarm measures and safety chain devices of the test equipment should be perfect and reliable to ensure the safety and reliability of the test personnel, the test products and the test equipment themselves.