3. System Reliability

A system is composed of several components. The system Reliability depends on the number of components, reliability of components and also as to how they are connected. Any structure can be considered as a system of various components put together to serve the purpose for which the structure is built to start with. To determine system reliability, one has to first obtain the component reliability using basic methods. The system reliability depends upon how the various components in the system. The two extremes are – series system and parallel system. In series system, all the components in the system have to function for the system to function successfully. In parallel system, functioning of one component is enough for the system to work. A system can also have combined series-parallel system components. In addition, there is another class of system referred to as k-out-of-n redundancy. In this case, if k components out of the total n components work, the system is considered successful. To start finding, the system reliability, one has to draw RBD (Reliability Block Diagram) depicting the way the components are connected in the actual physical system. Each of the cases is discussed below in detail. Mathematical expressions for system reliability are first derived for each case. This is followed by actual generic examples. Finally, reliability examples in various specific disciplines are discussed. It is to be noted that the extreme cases are series system and parallel system. Most of the real systems are mixed systems.