III. Reliability in Design and Development
A. Reliability design techniques
9. Reliability optimization (Apply)
Use various approaches, including redundancy, derating, trade studies, etc., to optimize reliability within the constraints of cost, schedule, weight, design requirements, etc.
Reminds me of the Oliver Wendall Holmes poem, The Wonderful One Hoss Shay – perfect reliability for 100 years and a day. We can make a system better such that every part is as strong as every other part.
Additional References
What is Reliability Optimization? (article)
Solving a Reliability Optimization Example (article)
Product Reliability Design Guidelines: The Design for Reliability Manual (article)
The Derating & Safety Margin Manual (article)
Derating Value (article)
Product Reliability Design Guidelines: The Design for Reliability Manual (article)
Standby Redundancy, Equal Failure Rates, Imperfect Switching (article)
Standby Redundancy with Equal Failure Rates and Perfect Switching (article)
Quick Quiz
1-13. Which of the following would not enhance software reliability?
(A) structured programming
(B) redundant code programming
(C) programming for fault tolerance
(D) modular programming
(B) redundant code programming
Replicating the same code would replicate any faults within the code. Instead use redundancy with program diversity, where the elements in parallel are different sets of code, the employ a voting routine to determine the correct result if the alternative sets of code do not agree.
Structured programing constrains the programmers to use specific clear, well-defined design practices. Fault tolerance programming attempts to identify and mitigate, or if possible avoid, software failures. Modular programs breaks down complex software projects into smaller, easier to define portions of code, making debugging less complex.
O’Connor and Kleyner, Practical Reliability Engineering section 10.5 page 268 – 270 5th ed.
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