A Study on Execution Time of Ladder Diagram in Programmable Controller

Abstract

In this paper, we discuss the experimental method to evaluate the execution time of Ladder Diagram (LD), which is the most commonly used language in programmable controllers (PCs). First, the fundamental LD is proposed to examine the cyclic scan of PCs. Using real samples of PCs, it is clarified that dispersion of the cyclic scan can not be necessarily neglected. Second, relationship between the execution time of LD and the number of ladder rungs, logical AND and OR operations, which are important components in ladder programming, is examined by adding some rungs and contacts to the fundamental LD. Some experiments are conducted, and then the means and standard deviations are obtained through some measurements. Moreover, the stochastic tests are conducted to verify the relationship between the execution time and the LD components.