A Blueprint for Implementing a Comprehensive Reliability Engineering Program

Section 3 of 7: Reliability Testing

Reliability testing is the cornerstone of a reliability engineering program. It provides the most detailed forms of data, because the conditions under which the data are collected can be carefully controlled and monitored. Furthermore, the reliability tests can be designed to uncover particular suspected failure modes and other problems. The type of reliability testing a product undergoes will change along different points of its life cycle, but the overriding goal is to insure that data from all or most of the tests were generated under similar enough conditions so that an "apples-to-apples" comparison can be made of the product's reliability characteristics at different points in the product's life. It is for this reason that consistent and thorough reliability specifications and a standard definition of failure are up-front requirements to implementing reliability testing.

A properly designed series of tests, particularly during the product's earlier design stages, can generate data that would be useful in the implementation of a reliability growth tracking program. This will provide information helpful in making management decisions regarding scheduling, development cost projections and so forth. This information will also be useful in planning the development cycle of future products.

Customer Usage Profiling

An important requirement for designing useful reliability tests is to have a good idea of how the product is actually going to be used in the field. The tests should be based on a realistic expectation of the customer usage, rather than estimates or "gut feelings" about the way the customer will use the product. Tests based on mere speculation may result in a product that has not been rigorously tested and consequently may run into operational difficulties due to use stress levels being higher than anticipated. On the other hand, tests that are designed with a strong basis of information on how the product will be used will be more realistic and result in an optimized design that will exhibit fewer failures in the field.

Customer usage profiles can be designed to actively gather information on how the customers are actually using an organization's product. This design can range from a simple questionnaire to a sophisticated instrumentation within the product that feeds back detailed information about its operation. An incentive is often useful to get customers to sign on for a usage measurement program, particularly if it is an intrusive process that involves the installation of data collection equipment. Additionally, customers are often eager to participate in these programs in the knowledge that the information that they provide will ultimately result in a more reliable and user-friendly product.

Test Types

In many cases, the type of testing that a product undergoes will change as the product's design becomes mature and the product moves from the initial design stages to final design release and production. Nevertheless, it is a good practice to continue to collect internally-generated data concerning the product's reliability performance throughout the life cycle of the product. This will strengthen the reliability growth analysis and help provide correlation between internal test results and field data. A brief summary of the various types of reliability tests is presented next.

Development Testing

Development testing occurs during the early phases of the product's life cycle, usually from project inception to product design release. It is vital to be able to characterize the reliability of the product as it progresses through its initial design stages so that the reliability specifications will be met by the time the product is ready for release. With a multitude of design stages and changes that could affect the product's reliability, it is necessary to closely monitor how the product's reliability grows and changes as the product design matures. There are a number of different test types that can be run during this phase of a product's life cycle to provide useful reliability information:

Manufacturing Testing

The testing that takes place after a product design has been released for production generally tends to measure the manufacturing process rather than the product, under the assumption that the released product design is final and good. However, this is not necessarily the case, as post-release design changes or feature additions are not uncommon. It is still possible to obtain useful reliability information from manufacturing testing without diluting any of the process-oriented information that these tests are designed to produce.

 

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