Validation of logic controllers from events observation in a closed-loop system

Numerous worthwhile results have been published in the last two decades on validation of logic controllers by using formal methods like model-checking or conformance testing. Whatever the merits of these contributions, the first approach considers only a model of the control code while the second one focuses on an isolated controller that executes this code. However, from a control engineering point of view, validation of a logic controller requires also to analyze the behavior of the controller when it is connected to the plant it must control to form a closed-loop system. This paper proposes a method to check, from observation of I/O events, whether the behavior of such a controller conforms to its specification. The principle of this method is to build a model of the closed-loop system from the observed I/O events then to compare this model to the specification model. A criterion to terminate the observation step is defined by using previous results on identification of discrete event systems. This method is illustrated on a small example.