Chen Gang, Nanjing University of Aeronautics and Astronautics and Beijing Jinghang Research Institute of Computing and Communication
PLC Ladder Logic Testing and its Application in Railway Interlocking

A programmable Logic Controller (PLC) is a computing device widely used in industrial automation control. They are typically employed in the control of manufacturing processes, such as assembly lines and robotic devices. The safety of these control programs are of utmost importance. There are five major PLC programming languages, in which the Ladder Diagram (also called Ladder Logic) is still the most popular one adopted in China. In this talk, we will address the problem of Ladder Diagram testing, and present a vendor-independent Ladder program testing tool. The PLC program faults found by this testing software will be analyzed. Some of them are intricate bugs, and may be considered challenging by general PLC programmers. Furthermore, we use this tool to develop and debug a prototype PLC Ladder Diagram to automatically discover wrong side failure of railway signal equipment, which is one of the major causes of train collisions. This example further illustrates the effectiveness of this novel PLC testing technique.