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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Richard Smith ( )
Date posted: Mon May 7 14:02:33 US/Eastern 2001
Subject: Reliability Growth Development Test Help
Hello there, Can anybody please point me to a Reliability Growth Development Test procedure, that will allow me to estimate how many units I need to place under test, and how long I will need to test them etc. in order to meet a required MTBF and confidence level ? Ideally, I would like to fix the test duration to say 6 months, and vary the number of test units required. Any help would be appreciated. Thanks, Richard.


Subject: Growth Testing
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Tue May 8 13:16:19 US/Eastern 2001
For Growth testing, the determination of test length is the primary concern that you need to establish to find the number of samples to test. With this parameter, you can divide up the six months of test time available and determine how many units are necessary. Growth testing is not an exact science, so the exact test length estimation is an estimate. The actual test could be longer, so I would add an extra 10 or 15% to the result to reduce the risk of an over run. From MIL-HDBK-338, Military Handbook, Electronic Reliability Design, I found a section that describes the entire growth program. An equation for determining the test length is available on page 8-141. This equation is: Mr = Mi (Tt / ti)^a where: Mr = required MTBF Mi = initial MTBF Tt = time that the instantaneous MTBF reaches requirement ti = preconditioning time a = growth rate

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