A comparison of relay ladder logic programming and Petri net approach for sequential industrial control systems

For about the past two decades programmable logic controllers (PLC's) using relay ladder logic (RLL) programming have been the workhorse for sequential industrial control systems. Petri nets are a methodology for modeling, evaluating and controlling discrete event systems (DES). This paper uses a theoretical Petri net based controller for an industrial control application. These two design methodologies are compared using an industrial design example. Comparisons are made on the ability to evaluate the programmed logic, flexibility of the logic and the ability to troubleshoot/debug the system.