Enhancing reliability in IEC/ISA FieldBus

The aim of the paper is to discuss and evaluate the impact of the occurrence of faults on the IEC/ISA FieldBus protocol. This communication system was conceived to be used mainly in process control environment, where robustness to the occurrence of faults is an important requirement. After a survey of the FieldBus protocol's main features, certain types of fault are defined, the occurrence of which may be critical for the communication system. The paper then presents the results of research conducted by the authors to see whether the current protocol is capable of recovering these types of fault. These results show that some types of fault cannot be recovered by the IEC/ISA FieldBus protocol. For this reason, a fault recovery model is presented. It is made up of functional blocks and procedures to be adopted at the System and Network Management Layer of the FieldBus communication stack. The paper concludes by presenting an evaluation of the fault recovery mechanisms proposed, demonstrating their effectiveness. This will be done from two different points of view. For each kind of fault that cannot be recovered by the current fault recovery mechanisms, it will be demonstrated that the proposed fault recovery model is able to recover the fault. This is not enough to evaluate the fault recovery mechanisms, but it is very important to see the effects of the occurrence of a fault on the control processes using the FieldBus communication system. Some of these effects may be the loss of critical information, errors in the reconstruction of analog sampled signals, and so on, An efficient fault recovery model must limit the effects of faults on the control processes as far as possible. The proposed fault recovery model will be evaluated in the paper according to this aim. (C) 1999 Elsevier Science B.V. All rights reserved.