Abstract: In existing industrial control system,PLC(Programmable Logic Controller) is often applied to realize sequential control, timing and etc. For the reason that control program often performs synchronous control and the occasions of input switches triggered are undermined, it is inevitably to cause the problem that control program cannot describe real executing process of control program fully. In view of it this paper put forward a method as follows: Firstly, we can use Petri net to construct net model representing the control logic during the process of compiling control program, this model represents executing logic of the PLC program. Secondly, we can dynamically run the net model mentioned above according to the actual execution route of the control program until the program stops executing. So we can find out some of the logical errors.

Key words: Petri net, PLC, Execution model , Prohibit arc