Availability is a property of a system requiring it to be ready for performing its required operation or task at time t. (It is often also referred to as readiness). This is clearly related to the main system property, reliability. The main measure of availability is the so-called availability coefficient, A(t), which is equal to the probability of finding the system in the operational state at the needed moment of time t.
If the process of the system's functioning is described in terms of an alternating sequence of lifetimes (i.e., times to failure) {Xi} and repair times {Yi}, then at any moment t, the availability coefficient can be determined as
For stationary processes, that is, where t goes to ∞, the stationary availability coefficient is defined as
where Ev[·] is the expectation operator.
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References
Kozlov, B.A. and I.A. Ushakov (1970). Reliability Handbook. Holt, Rinehart and Winston, New York.
Ushakov, I.A., ed. (1994). Handbook of Reliability Engineering. Wiley, New York.
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© 2001 Kluwer Academic Publishers
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Ushakov, I. (2001). Availability. In: Gass, S.I., Harris, C.M. (eds) Encyclopedia of Operations Research and Management Science. Springer, New York, NY. https://doi.org/10.1007/1-4020-0611-X_46
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DOI: https://doi.org/10.1007/1-4020-0611-X_46
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