Environmental test is to expose materials or products to artificial or natural environment and evaluate their performance under storage, transportation and various conditions. From these aspects, we can see the correlation between environmental testing and reliability. Environmental test equipment is used to test and verify the reliability of any product in terms of environmental factors, just like taking a ruler with a scale to measure the length of other objects. If the scale is inaccurate, the measured length will not be accurate. Therefore, the reliability of environmental test equipment is particularly important.
1.Reliability overview of environmental test equipment
The reliability of environmental test equipment refers to the ability of environmental test equipment to complete specified functions under specified conditions and within specified time. Environmental test equipment includes electrical equipment and mechanical equipment. The principle of reliability engineering is the same for electrical equipment and mechanical equipment, but they have their own characteristics.
In environmental test equipment, the performance of electrical equipment parts and mechanical equipment components have different effects on reliability. In terms of the structure of electrical equipment and mechanical equipment, there are different emphases on the reliability of environmental test equipment. For example, the control part of vibration test equipment belongs to electrical equipment, and the reliability characteristics of electrical equipment should be taken into account; while the vibration table part is mainly a mechanical structure, the reliability characteristics of mechanical equipment should be taken into account.
Therefore, for the whole vibration test, electrical equipment and mechanical equipment shall be comprehensively considered when considering reliability, that is, the reliability method of the whole system shall be adopted. The key to improve the reliability of environmental testing equipment in China is to improve the reliability of electrical equipment. To improve the reliability of electrical equipment, the reliability of element parts must be improved.
2.Reliability index of environmental test equipment
There are many indicators to check the quality of products. For example, the temperature and humidity test chamber has a temperature range and a humidity range, as well as a heating rate and a cooling rate. Such quality indicators are usually called performance indicators, which are necessary for the product to complete its designated functions. There is also a quality index called reliability index, which indicates the ability of the product to maintain the performance index, just like the working time of the temperature and humidity test chamber when there is no failure. Performance indicators do not involve time, while reliability indicators are closely related to time
Common reliability indicators include:
2.1 Reliability: refers to the probability that the product will complete the specified function within the specified time and conditions.
2.2 Cumulative failure probability: it refers to the probability of product failure within the specified time and conditions.
2.3 Failure efficiency: refers to the probability of failure per unit time after a certain time when the product has not failed.
2.4 Average life: the repairable product is called mean time to failure, which reflects the time quality of the product and reflects the ability of the product to maintain its function within the specified time. Specifically, it refers to the average working time between two adjacent failures, which is also called the average failure interval. For non repairable products, it is called the average working time before failure, which is the average working time from the start of using the product to the failure.
2.5 Mean time to repair: the average value of the time to repair.
2.6 Effectiveness: the probability that the maintainable product can maintain the specified function at a certain time.
3.Reliability design of environmental test equipment
The reliability design of environmental test equipment is mainly about design technology and design cost. The purpose of technical design is to improve the reliability index, while the purpose of cost design is to make the reliability index most economical and reasonable.
The design of technical indicators for the reliability of environmental test equipment includes circuit design and environment resistance design. The circuit design should try to use integrated circuits and high reliability components, and the key components should use redundancy technology.
The reliability design of environmental test equipment requires not only the knowledge of engineering technology, but also the theoretical basis of reliability, such as reliability allocation and reliability prediction before design. Stress and other technologies shall be adopted in design.
Reliability work requires a certain cost. When designing reliability cost, we should consider the loss cost and work cost caused by unreliable products. To find the best reliability, we can rely on reliability cost design.
4 Reliability test of environmental test equipment
4.1. Contents of reliability test
The reliability experiment of environmental test equipment is to simulate the low temperature, high temperature, humidity sudden change and other conditions in the natural environment, so that the conditions that may occur in the use of the product can accelerate the reaction, to check whether it meets the expected quality objectives, to detect the performance of the product under various environmental conditions of actual use, transportation and storage, and then to evaluate and improve the product to determine the reliability life of the product.
4.2. Reliability test method
There are two methods for reliability test of environmental test equipment, including laboratory experiment and field experiment. Laboratory experiment, also known as artificial simulation experiment, is a reliability experiment verification or measurement experiment conducted in a manually created controllable environment. It has good reproducibility and comparability. Its disadvantage is that limited by equipment, products with small volume and light weight can be tested generally, while field experiment is based on reliability experiment verification or measurement experiment conducted on the site and the environmental conditions on the site, The working conditions and maintenance conditions need to be recorded one by one, which fully makes up for the shortage of laboratory experiments. The on-site test has the advantage of objectivity and authenticity, but the disadvantage is that its experimental environment cannot be manually controlled, so the experimental conditions and results do not have reproducibility.
The experimental methods used in environmental test equipment should be selected objectively. The experimental methods are different with different equipment. For example, the field experiment method is required for large-scale environmental test equipment, and the field experiment or laboratory experiment can be used for small-scale environmental test equipment, depending on the conditions of test equipment and economic conditions. In general, the reliability experiment of environmental test equipment adopts the method of field experiment.
The reliability analysis of environmental test equipment can improve the quality and reliability of products, which is also of great benefit to industrial production. Environmental tests are interspersed in the development, production and use of products, which are designed, improved and put into operation. The more true and accurate the environmental test results are, the better the reliability of the product is, that is, it should be used for product research performance test, inspection test, type approval test, acceptance test and safety performance test.