Copyright © IFAC Low Cost Automation 1989 Milan, Italy, 1989 A SOFTWARE PRODUCTION METHODOLOGY FOR PROCESS CONTROL P. Cofrancesco * A. Cristoforetti, R. Scattolini + * Lab.oratory N.M.R., Fondazione Mondino, clo Department of Chemistry-Physics, Umverslty of PavIa, VIa Tararnelli 16, I 27100 Pavia, Italy + Department of Computer Science, University of Pavia, Via Abbiategrasso 209, I 27100 Pavia, Italy Abstract. In this paper a software production methodology for process control is presented. The specification phase is carri ed out by resorting to the formalism of Petri Nets . By means of a worked example it is shown how Petri Nets are amenable to describe feedback control structures. The implementation of Petri Net models is performed by the use of a data driven architecture . The presence of system tasks supplying standard functions, such as monitor, display, command acquisition is also considered to ease software production. Keywords. Digital control; software engineering ; development; direct digital control; software tools. software INTRODUCTION In spite of its fundamental role in the transfer of advanced control techniques from theory to application as well as its increasing economical relevance, software production for digital contro l and simulation is often still more an art or a craft than an industrial-type acti v ity . It is therefore necessary to support software development with effective tools which ease the building and testing of control software of high quality, see Sommerville (1982) . In the systematic design of control software, two fundamental phases have to be dealt with, namely its formal specification and subsequent rapid prototyping. The specification phase is required to (i) provide a clear and concise description of the dynamic and lo gic structure of the con tro l system being considered; (ii) associate the main functions supplied by the control software to well defined and autonomous processes; (iii) describe all the aspects concerning concurrency , synchronization and transmission of data among the tasks composing the control software ; (iv) validate the overall system requirements in order to check the presence of possible incongruities in the design. Several languages supporting the specification phase have been described in the literature, e.g. SADT ( Ross and 1977), PLS / PSA (Teichroew and Hershey, 1977), PAISLey (Zave, 1982); however most of them are general purpose tools which either do not cope with the specific features of control software or are not amenable to automatic implementation programming language. in a standard The aim of this work is to develop a methodology which eases the transition from specification phase to implementation. Focusing attention on digi tal control sys terns design and deve lopment, we will present a toolkit which allows to: * define or modify many different control system structures; * introduce new control algorithms in pre-defined structures; * implement tasks where exchange of data with the external environment is minimized; * monitor, display , modify and store the values of variables of any task belonging to the control structure; * compute control values ac c ording to various control strategies ( e.g. manual, PID, adaptive) and select the most appropriate one on line; * simulate and analyze the behaviour of the co ntrol system step-by-step . This feature is particularly useful in the preliminary debugging phase. The specification pha se uses the rigorous , and easy to learn, formalism of Petri Nets (PN) since it lends itself to the description of distributed systems wi th their related concurrency and synchronization aspects. Thanks to their usefullness as a mode ling tool , it is believed that PN are going to play an increasing role in software engineering for control systems. In this field, practical applications of PN have already been proposed by Bruno and Marche teo (1986) and by Brand and Kopainsky (1988). The first paper presents an extension of PN called PROT nets, it then fr?wn how PROT nets can be translated lnto ADA program structures to speed up prototyping of systems for simulation purposes. In the paper by Brand and Kopainsky (1988), a general approach to event-related process control wit h PN is presented with particular emphasis to the modeling aspects . lADA is a registered trademark of the U. S . Departmen t of Defence