Author(s)

G. Vafeidis & S. Manesis

Abstract

A computer-aided design program has been developed to design and test relay ladder diagrams used in industrial applications. By using a personal computer the engineer can develop and extensively test and alter a relay ladder diagram before installing it in the industry. The program can simulate the operation of a diagram, while the user can select the visualized operation to be performed either in real time mode or in a step-by-step procedure. In order to establish the proper operation of the sequential control system, the program has also a verification part which checks sequential logic for various scenarios of inputs and determines possible errors. 1 Introduction Programmable Logic Controllers (PLCs) are

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