An integrated approach to real-time distributed control systems over fieldbuses

The increasing application of flexible and powerful real-time distributed control systems is presently characterizing the industrial automation field. Such systems involve three main disciplines: control systems, real-time systems, and communication systems. Control systems, due their stringent timing constraints, demand real-time computing technology. In addition, communication systems are needed for the data messaging between field devices. We propose an integrated approach to the design and implementation of such systems. We show that by a separate control design and its posterior distributed implementation, the system performance may suffer degradation. That is, when control loops are closed over communication networks, timing problems, as communication induced varying delays, can appear, decreasing the control system performance, and even leading the system to instability. However, we show that by an adequate integrated approach, that takes advantage of control theory, real-time communication properties, an adequate timing analysis, and an appropriate distribution of the control functions, the system performance increases dramatically.