Redundancy (engineering)

In engineering, redundancy is the duplication of critical s 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.ref|spaceshuttle 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"ref|votinglogic1 or "voting logic".ref|votinglogic2

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)] nwhere:
* P - probability of failure of multiple component
* p(x) - probability of failure of a single component
* n - number of components

See also


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* Common mode failure
* Data redundancy
* Double switching
* Fault tolerant design
* Radiation hardening


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* Reliability engineering
* Reliability theory of aging and longevity
* Safety engineering
* Self-healing ring
*MTBF

References

# [http://www.research.ibm.com/journal/rd/201/ibmrd2001E.pdf Redundancy Management Technique for Space Shuttle Computers] (PDF), IBM Research
# [http://www.elecdesign.com/Articles/ArticleID/6886/6886.html Majority voting systems]
# [http://www.aero.org/publications/crosslink/summer2003/06.html Designing Integrated Circuits to Withstand Space Radiation]
# [http://www.yamar.com/The-Vehicle-Power-Line-as-a-Redundant-Channel-fo-CAN-Communication.pdf Using powerline as a redundant communication channel]

External links

* [http://www.eu-sparc.net Secure Propulsion using Advanced Redundant Control]


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