A Graphical Language for Batch Control

University dissertation from Depatment of Automatic Control, Lund Institute of Technology, Box 118, 22100 Lund, Sweden

Abstract: In this thesis a graphical language for sequential control is presented and its application to batch control is examined and discussed. The name of the language is Grafchart. Its main feature is that it makes it possible to express complicated control problems in a compact and intuitive manner. Grafchart exists in two versions; a basic version and a high-level version. The basic version was available when the work presented in this thesis started. The basic version of Grafchart is mainly based on Grafcet, i.e., it has a clear and intuitive syntax. In addition to this it has support for parameterization and methods and message passing as well as extended facilities for exception handling. The high-level version of Grafchart takes the concepts of the basic version one step further. The concepts of object tokens and multi-dimensional charts are introduced. These features are inspired by high-level Petri nets and constructs from object-oriented programming languages. The main application area of Grafchart is batch control. In the thesis it is shown how Grafchart can be used for recipe structuring and recipe analysis. By using the features of Grafchart in various ways, recipes can be given different structures with different advantages and disadvantages. All structures comply with the international batch standard IEC 61512 (also refered to as ISA S88.01). To test and evaluate the different recipe structures, a real-time batch plant simulation platform was used. The batch recipe structures can be combined with resource allocation and a visualization of the allocation is thereby achieved. By transforming the recipes into an equivalent Petri net structure, formal analysis methods that exist for Petri nets can be used to look for possible deadlock situations. Several commercial batch control systems exist today. They all have a similar approach to recipe structuring, resource allocation and user presentation. The advantages of using Grafchart compared to some of these systems, regarding these features are presented in the thesis. A toolbox implementation of Grafchart exists. It is implemented in G2, an object-oriented programming environment. G2 is also an industrial environment, this makes the toolbox and the results of this thesis directly usable in industry.

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