9 - Fault-tolerant control for safety

Abstract

This chapter discusses fault-tolerant control for safety. Modern control systems frequently involve the use of complex algorithms and extensive empirical data to implement their control strategy. The application of fault prevention recognizes that faults will occur during the development of the system but tries to prevent their inclusion in the operational system. Fault prevention is necessary to a greater or lesser degree for any system. It minimizes the number of faults and, hence, failures that must be handled by fault tolerance. Using fault tolerance to improve reliability may, therefore, be, at least in part, consistent with improving safety. The reliability concerned, however, is reliability with respect to failures that will realize the hazard if they occur. Active and passive redundancy is typical approaches to provide fault tolerance. The distinction between them is important. Passive redundancy typically involves the provision of a stand-by system or subsystem. When a failure is detected the standby system is switched in, either manually or automatically.