Overview
PLC controllers have been developed as a low cost flexible alternative to old relay logic controllers used in process and automated manufacturing control. They have numerous advantages over the relay logic systems including the lower cost, size, greater reliability and more functions than older systems. The technology that has allowed their development is the microprocessor/microchip technology. This allows for easy reprogramming of the control programs stored within the PLC memory and eliminates the need for any hardware modifications when a different control process is to be implemented. In the interest of simplicity and greater efficiency of programming a common set of programming standards and languages has been adopted across all PLC platforms.
This report focuses on the IEC 1131-3 standard and the set of four graphical and textual languages currently in use in the PLC programming.
The basic PLC system configuration and internal operation is provided, however the main focus is on the actual programming languages which are evaluated in detail. For each language the main application area is defined with the main strengths stressed, followed by a detailed account of the various instructions that are the building blocks of the programming language.
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