AWWA IMTECH51422

Practitioners using a structured approach in the coding of programmable logic controllers (PLCs) provide benefits to themselves and the end users of the PLC. These include productivity, quality, maintainability and scalability. Two different types of structured approaches are described in this paper. The first, and more prevalent, can be used when code is organized by control loop. Using a structured approach in this context offers the practitioner many productivity and scalability benefits; however, the organization by control loop can often result in long repetitive code which consumes large amounts of memory. The second approach organizes the program code into a function-based structure that provides a single, logical pattern for many similar loops. Function programming offers the practitioner a reduction in file size and development time, but reduces scalability. The relative advantages and disadvantages of the two approaches are discussed. The paper concludes with recommendations for application of either approach. Includes figures.