Object Oriented Simulation of Relay Ladder Logic

Since their appearance, Programmable Logic Controllers (PLCs) have gain a very strong position in the industrial automation field. The growing complexity of the applications using this type of equipment strongly depends on programmers and maintenance personnel, and so more and better PLC education is of great demand nowadays. The present work deals with an object oriented simulator for the relay ladder logic language. The simulator is a module of a more general system that emulates a real PLC. This system provides a user friendly graphical interface and allows PLC programming and debugging. The simulator runs as a Microsoft Windows application and was developed using C++. With the same algorithm two simulation modes, allowing different analysis of PLC programs, were implemented: fast simulation and real time simulation.