Survey article

Process control is based more and more on computers. Fault-tolerance techniques are applied for critical processes to guarantee safety and/or minimize production losses and equipment damage. The increasing safety and production requirements, the constantly dropping hardware prices, the increasing digitalization and the constantly growing capabilities of integrated circuits will widen the application area . To choose the economically-technically best method for your application, an insight in the possibilities and limitations of the different techniques is necessary . This paper considers fault-tolerance for low level process controllers . The methods are however applicable to all kinds of computer systems . An introduction to fault-tolerance and a faultstudy are given first . Subsequently it is possible to study the possibilities and limitations of the different hardware fault-tolerance techniques. The paper concludes with some comments on software faulttolerance, multiprocessor and distributed systems .