Einbindung unterlagerter Ebenen in die Steuerlogik des Prozessleitsystems

By using process control systems the single loop control functions generally will be realized as software modules. Each actuator is supervised and controlled by an individual software function block. But certain functions are missing to satisfy requirements such as local operator control, back-up operation, interlocking and mashine-inherent controlfunctions. These functions still have to be realized in a logic beyond the process control system. There exist a lot of functional elements and wiring schemes for the design of this underlaid logic, but it is in the opinion of each planer how to get them together. In praxis the method is a more or less intuitive one. With respect to the experience of the planer, such a procedure leads to a solution which solves the main requirements sufficiently. But the exact analysis shows, that most of these solutions have small logical defects, which under certain conditions lead to an unexpected and undesired behaviour. This article has the aim to describe the problems and to give some examples which may show possible ways for a solution