Interpretation rules of Petri net models for logic control

This paper focuses on the influence of the semantics of Petri net (PN) models used to represent and design logic controller algorithms. The specific problem addressed is to investigate how the performance and the correctness of a logic controller algorithm are affected by the particular way in which a PN scheme is converted into (thus, interpreted) an algorithm running on a programmable logic controller. The way of executing a PN model is a fundamental part of the model itself and should always be included in the definition of the representation model. This is necessary since the PN model is used to represent an entity (the controller) interacting with other entities (the process). Thus, the model is not autonomous. As a consequence, the model is not complete if the execution rules and the specific way in which input/output signals are treated are not stated. The model of the logic controller is briefly recalled. The considered execution policies are illustrated. We describe the subnets studied and propose some solutions to the highlighted problems