Module 3 : Product Quality Improvement
Lecture 2 :What are component and system reliability and how it can be improved?
 
In a special case, where all components have the same failure rate,, the system reliability for parallel component is given by
For such specific situation, the mean-time-to-failure for the system with n identical components in parallel, and also assuming that each failed component is immediately replaced by an identical component, can be expressed as

Systems with Components in Series and in Parallel

Real life systems often consist of components that are mixed and consist of both series and parallel configuration. For such system, reliability calculation is primarily based on the previously discussed concepts, and assumption of components operating independently. Parallel systems are first collated to get a composite reliability, and then the overall components are considered as series to calculate system reliability. Systems can also consist of standby component, which operates as and when base component fails. Reader may refer to book by Amitava Mitra (2008)  or Besterfield et al (2004 ) for further details on. K-out-of-N system (parallel system is 1 out of N system) is another possible system configuration.