Modeling of Sequential Control System with Cyclic Scan by Petri Net

We propose the modeling method of a ladder diagram (LD) with the cyclic scan of a programmable controller (PC) by Petri net (PN). First, some experiments are conducted to examine the relationship between the cyclic scan and the behavior of LDs. Second, PNs are used for the qualitative modeling of the behavior of LDs based on the IEC61131-3 PC programming languages standard. Especially, in addition to LD Boolean logic expressions previously modeled by PNs, we consider the PC control components, such as cyclic scan, peripherals, memories, scanning ladder rungs. Moreover, the experimental results are qualitatively explained by the PNs.