![]() The testing process is largely the same though users should note that with an additional variable in the model it is highly desirable to have more failure data to fit the model accurately. In dual stress models, there are two stresses being tested, such as temerature and humidity. This means the ALT test needs sufficient stresses (usually 3 or more) and sufficient failures (as many as you can afford to test) at each stress.ĪLT tests may either be single stress or dual stress. As with any model fitting the analyst must ensure there is sufficient data to fit the model such that the results are meaningful. This will be evidenced by the shape parameter of the distribution as a changing shape parameter will show the failure mode is changing, though it is desirable that each failed component be examined to ensure that the failure mode being studied was the failure mode experienced. To ensure the ALT test is performed correctly, the analyst must ensure that the failure modes are the same at each stress. How much the component life will be extended can be quantitatively measured using an ALT test to find the life-stress model. Derating is the process of reducing the load (typically voltage or current) on a component below its “rated” load, or equivlently selecting a component that is rated above the design load. The electronics manufacturer can collect failure data at a variety of stresses, fit the appropriate life-stress model, and then enter the “use stress” into the life-stress model to determine the failure distribution that is expected to occur at the use stress.ĪLT testing is also a very useful way to determine the effectiveness of derating. Done correctly, this is equivalent to speeding up the passage of time. By increasing the stress on the component, failure will be induced more rapidly. If the component being tested has a mean life of 30 years, the manufacturer cannot reasonably spend several years performing a reliability test as they are ready to release their product on the market soon. ALT is often used when we can not afford to wait for failures to occur at their normal rate but we need to know how failures are likely to occur in the future.Ĭonsider an electronics manufacturer who wants to know how many failures will occur in 10 years (possibly for warranty purposes). ALT is a popular method of testing because of its ability to “speed up time”. How are the confidence intervals calculatedĪccelerated life testing (ALT) is a method of test and analysis to determine how failures would likely occur in the future.How does Maximum Likelihood Estimation work.How are the plotting positions calculated.Solving simultaneous equations with sympy.Converting data between different formats.What does an ALT probability plot show me.Fitting all available models to ALT data.Fitting a dual stress model to ALT data.Fitting a single stress model to ALT data.Getting your ALT data in the right format.Fitting all available distributions to data.Fitting a specific distribution to data.Introduction to the field of reliability engineering. ![]()
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