A Study, Design And Application Of The Computer-Monitored PLC Systems

PLC is an industrial equipment with microcomputers as its core. It integrates electrical control, electrical equipment, and electrical communication into one system, and plays a very important role on modern industry. PLC is widely used in automatic control for its strong function, high reliability, wide applicability, modular structure and etc. Many customer services, such as showing process-flow charts, displaying dynamic-data-base interfaces, editing tables, generating charts, managing production and etc, can be provided by connecting personal computers (PCs) to a PLC network. In a PLC-PC system, PLCs, which serves as the low-level units, are used to collect and control the data, (for example, the ON/OFF quantities and analog input/output quantities). A PC compliments the function of PLCs by providing an excellent human-machine interface, hi the system, one PC can be used to monitor one or many PLCs. By taking advantage of both the excellent reliability and flexible control functions of PLCs, and the good human-machine interface and data process functions of PCs, the automation of the whole system is improved.In this thesis, we apply the theory of computer control systems, programmable controller, database, and OpenGL to a practically important problem. We implemented a computer-monitoring system for PLCs to control lights and springs in the square in Shanghai Minhang Sports Park, using SMG-III intelligent control system. The first chapter briefly introduces the research background, purpose, and importance. The second chapter discusses the related theories and technologies. A systematic economy analysis, the recent advances and trend of programmable controller, and the software link to the graphical hardware (OpenGL) are also discussed. The third chapter introduces the overall design. Because the computer monitoring system for PLCs plays a central role in the whole SMG-III intelligent control system, in this chapter, we show how to define the system modules based on analysis of SMG-III intelligent control system and the practical condition of ShanghaiMinhang Sports Park. Based on the partition of system modules, Chap. 4 and Chap. 5 discuss each module of the computer monitoring system in detail. These two chapters are also the most important parts of the whole thesis. Chapter 4 shows the design of the system interface, the real-time, vivid simulation using OpenGL, and the design and implementation of the database. In Chap. 5, we introduce the physical links between PLCs and the monitoring computer, define the communication protocol, give the address assignment of the PLC registers, and develop the communication modules using Visual C++. Chapter 6 summarizes the whole thesis and discusses possible future developments of this technology.In summary, we proposed a systematic, efficient method for designing, developing, and managing PLC computer-monitoring systems, based on the theories for those systems. The work is important for guiding practical applications.