Quantitative aspects of reliability in process-control systems

In recent years, the study of the reliability of equipment has been put on a more clearly defined statistical basis. This demands the precise definition of the terms used and the development of specialised mathematics. Particularly when considering the availability of systems incorporating redundancy and facilities for repairs, there have been advances that allow sophisticated calculations to be made. The reliability of process-control equipment can usefully be considered at three levels: components, assemblies and systems, and features of each of these should be taken into account. The practical value of reliability studies is shown when they enable predictions of performances to be made, and this has happened in several industrial fields. When the predictions have been based on valid data, they have commonly been found to agree¿within the broad limits set by statistics¿with subsequent observations.