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In engineering, redundancy is the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe.
In many safety-critical systems, such as fly-by-wire aircraft, some parts of the control system may be triplicated. An error in one component may then be out-voted by the other two. In a triply redundant system, the system has three sub components, all three of which must fail before the system fails. Since each one rarely fails, and the sub components are expected to fail independently, the probability of all three failing is calculated to be extremely small. Redundancy may also be known by the terms "majority voting systems" or "voting logic".
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Forms of redundancy
There are four major forms of redundancy, these are:
- Hardware redundancy, such as DMR and TMR
- Information redundancy, such as Error detection and correction methods
- Time redundancy, including transient fault detection methods such as Alternate Logic
- Software redundancy such as N-version programming
Calculating the Probability of failure of the system
For each component that is doubled in the formula of the probability we use this :
P= 1-[1-p(x)]n where:
- P - probability of failure of multiple component
- p(x) - probability of failure of a single component
- n - number of components
See also
References
- ^ Redundancy Management Technique for Space Shuttle Computers (PDF), IBM Research
- ^ Majority voting systems
- ^ Designing Integrated Circuits to Withstand Space Radiation
- ^ Using powerline as a redundant communication channel
