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Test Design Folio Example


 ReliaWiki: Reliability Demonstration Test Design for Repairable Systems

Test Design Folio

In a zero-failure reliability demonstration test (RDT), the engineer aims to demonstrate a specified target metric (e.g., an MTBF of at least 500 hours with 90% confidence) by testing a specified number of systems for a predetermined time. If no failures occur, then the target metric is demonstrated. This method has been adapted for scenarios where the target metric can be demonstrated even if some failures occur, so long as a specified number of allowable failures is not exceeded. For example, in a demonstration test where the number of allowable failures is 2, the target metric is demonstrated if no more than 2 failures occur during the test.

The test design folio can assist you in using the NHPP model to design a demonstration test for repairable systems by solving for either the test time required per system or the number of systems that must be tested. To create a test design folio, choose Home > Insert > Test Design.

IMPORTANT: The test design folio in RGA (known as the "Repairable Systems - Design of Reliability Tests" tool in prior versions of the software) is based on the non-homogeneous Poisson process (NHPP), so it is suitable only for designing tests involving repairable systems. For tests involving non-repairable items, use the RDT utility in Weibull++, which provides four test design methods that are suitable for non-repairable systems: parametric binomial, non-parametric binomial, exponential chi-squared and non-parametric Bayesian.

Follow the steps outlined next to use the utility:

In the last input field, enter the maximum number of failures that you will allow to occur during the test. For example, if you want to demonstrate the target metric with 2 failures or less (e.g. two systems fail once, but no other failures occur), then you would enter 2 in this field.

After you have made all of the required inputs, click the Calculate icon to solve for the specified value. To examine other possible test scenarios, you can also create a table and plot based on the inputs.

See Repairable Systems RDT Example.

 

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