Design of Safe and Low Cost Automation Systems: Application to a Three-Tank Control System

Design of an automation system does not consist only in establishing an architecture of components with the lower cost. Indeed, with an industrial point of view, dependability is a significant factor. Untimely stops, incidents occurrences or the unavailability of the control system have important economical consequences. Therefore, these two aspects (cost and dependability) have to be studied simultaneously. This paper presents a methodology to design an automation system (or eventually to improve an existent system), which takes into account these two aspects. From a functional model, the method aims to detennine the operational architecture that respects a set of constraints relative to the dependability with the lower cost. One advantage of the presented method is that it can be used despite a lack of data concerning the reliability of components. The dependability is considered with a semiqualitative point of view and consists in defining some limits in terms of number of failure components, which don't entail the failure or the unavailability of the system.