Redundancy In Reliability
REDUNDANCY
(Parallel connection increases the reliability when compared to series connective.)
One of the methods for improving the reliability of the system is by utilising the concept of redundancy. To enhance reliability of the system, quite often addition units are built into the system to perform the same function. In such a system, one component failure will not necessarily cause the system failure, since additional components are available to perform the same function.
Redundancy is defined as the characteristic of a system by virtue of which marginal component failures are prevented from causing system failures due to the presence of additional components.
In order to increase the reliability of the system, select the component which has the least reliability and then arrange it parallelly.
RS = RA × RB × RC
RS = 0.8 × 0.5 × 0.7
RS = 0.28.
In order to increase the above system’s reliability, select the component which has the least reliability (0.5) and arrange it parallelly.
RB′ = 1 – (1 – RB)(1 – RB)
RB′ = 1 – [(1 – 0.5)(1 – 0.5)]
RB′ = 0.75
RS = RA × RB′ × RC
RS = 0.8 × 0.75 × 0.7 = 0.44.
It is clear that the R is ↑d from 0.28 to 0.44.
Definition of Improvement Factor :
In the case of ‘n’ parallel redundancies, the improvement factor,
where (1 – R) = Unreliability of each component.
(1 – RS ) = Unreliability of the system.
If ‘n’ components are connected in parallel with the same reliability as shown in fig. below :
RS = 1 – [(1 – RA)(1 – RB) ...... (1 – Rn)]
Since RA = RB = ....... Rn
RS = 1 – [(1 – R)n]
∴ 1 – RS = (1 – R)n