A fault tolerant controller for high integrity systems

Abstract

Reliability is an essential factor in computer based process control systems. In these systems, fail-safe operation against a single fault would be a necessary requirement. Furthermore, a high degree of continuity of operation would also be a desirable feature; such a system may be classified as High Integrity [1]. Fail-safe operation for the interface (i.e. transducers, actuators etc.) between the computer and the control system can be achieved relatively easily, without a significant increase in cost. The requirements of high integrity operation and protection against processor failure can be achieved by the use of fault tolerance. The hardware redundancy approach to fault tolerance involves replication with majority voting at the computing system level. This has been limited in the past due to the cost. With the availability of low cost single board computers ( sbcs), it is realistic to consider replication at the computing system level. A Basic Fault Tolerant Controller ( basftc) is presented which allows the realisation of a triplicated system ( tmr) configuration based upon sbcs for high integrity control system applications. The controller protects the control system against the existence of a single fault in the triplicated system. The controller has been implemented as two gate arrays, and a demonstrator constructed to provide verification of the concepts.