A New Approach for PLC Ladder Diagram Design

Programmable controllers (PLCs) were developed to solve the problems of automating and manufacturing control systems and they have found wide applications in industrial control fields. Ladder diagram is the most adopted programming language for PLC control. Process sequence and flow charts can be used for simple PLC ladder diagram design. For complex PLC controls, state diagrams have been proposed for PLC ladder diagram programming. However, state diagram method has some limitations. In this paper, based on the analysis and design techniques of digital systems, we proposed a new PLC design approach. In this method, first we need to identify the functions of datapath and controller and the inputs/outputs of both. Second, Algorithmic State Machine(ASM) charts are used to draw the state transitions for the controller. Finally, a ladder diagram is designed from the ASM chart. The best practices with this approach are also discussed in the paper.