BOTO GROUP is manufacturer of environmental test chambers with over 20 years of experience.
Focusing on the production of various environmental test chamber, include: temperature humidity test chamber, UV aging test chamber, Xenon aging test chamber, salt spray test chamber, etc.
Although environmental testing and reliability testing are closely related, they are completely different in terms of test purpose, amount of environmental stress used, environmental force value selection criteria, test type, test time, and test termination criteria.
Test purposes
Environmental testing examines the product's adaptability to the environment, determines whether the product's environmental adaptability design meets the contract requirements, and provides a basis for decision-making on acceptance or rejection.
The reliability test is a quantitative assessment of the reliability of the product, that is, the probability of the product completing the specified function within the specified time under specified environmental conditions.
Number of environmental stresses used
As far as environmental testing is concerned, GJB 150 specifies 19 test items, MIL-STD-810 D specifies 20 environmental test items, and 810F increases to 24 test items, including environmental stresses that have a more important impact on products, such as : Temperature, humidity, salt spray, vibration shock, pressure, solar radiation, sand and dust, rain, etc. Test items should be selected based on the product being tested based on its future environmental conditions of use and degree of impact. Generally, more than 10 environmental stresses should be examined.
Since the reliability test requires comprehensive simulation, it only combines comprehensive environmental stress (temperature, humidity, vibration) and electrical stress for testing. It can be seen that the number of environmental stresses selected for reliability testing is much smaller than that for environmental testing.
Criteria for Selection of Environmental Stress Values
Environmental tests basically use extreme conditions, replacing mild with harshness, that is, using the most extreme environmental conditions that a product may encounter during its life cycle as test conditions. Many tests are destructive to a certain extent and it is generally not necessary to simulate the working state of the product during the test process.
The reliability test adopts actual test, which truly simulates the main environmental conditions encountered during storage, transportation and use and its dynamic change process. GJB-889 and the corresponding MIL-STD-781 D stipulate a set of methods to determine the environmental profile based on the mission profile, and then simplify the environmental profile into a test profile to conduct long-term reliability assessment of the product. Reliability testing generally does not cause damage to the product. It needs to simulate the working state of the product. Most of the test conditions used simulate the milder stress environment commonly encountered in work, and the values are much lower than those of environmental testing.
Test type
Environmental testing usually uses single-factor testing and multi-factor combination testing, which act on the product in a certain order.
Reliability tests often use comprehensive stress tests, which apply multiple environmental stresses to the sample in the same space and at the same time to more realistically simulate the impact of environmental conditions. In order to improve the accuracy and reliability of test results, environmental testing has also begun to focus on the development of comprehensive testing, and actively develop large-scale multi-functional environmental testing equipment that can simultaneously apply temperature, humidity, vibration, radiation, sand, dust, wind, rain and other stresses.
Test time
In environmental testing, the time of each test basically depends on the selected test and the specific test procedures. There are only some differences due to the different time required for performance testing at each stage. The test time is much shorter than the reliability test.
The reliability test time depends on the reliability index value to be verified and the selected statistical test plan as well as the quality of the product itself. The time cannot be determined until the total operating hours of the tested product reaches the specified value or a decision of acceptance or rejection can be made.
Test termination criteria
Failures are not allowed in environmental tests. Once a product fails, it is considered to have failed the test. The test will be stopped and fault analysis will be carried out to take corrective measures and improve the design. This is the TAAF process for environmental testing.
The reliability test is a test in which the results are expressed with a certain statistical probability. The allowable number of failures is determined based on the quantitative reliability indicators required by the contract and the selected statistical scheme. The test must be carried out until the specified total number of hours is reached before it can be stopped. A fault reporting, analysis and corrective action system (FRACAS) should be established throughout the testing process.