Improving time performances of distributed PLC applications

PLC applications are extensively used in industry to control and repetitive processes such as manufacturing cell management, fly-by-wire control, or nuclear plant shutdown systems. Because of recent developments in local area real-time networks, distributing PLC applications over such networks has now become feasible. A distributed system consists of network nodes (or stations) connected to each other by a hardware communication medium. However, one known shortcoming of distribution is the data transmission overhead, between processes assigned to different nodes that need to communicate. Such overhead signifies a degradation in time performances. The issue addressed in this paper, is to determine how to improve the time performances of distributed PLC applications. We address the problem from a scheduling point of view, and since it is proven to be NP-complete, we also present heuristics to solve it.

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