The Design And Practice Of PLC-based Waste Water Treatment System

Water resource is fundamental for human. However, in recent years, with the rapid development of national economy, industrial waste water has caused great harm to our environment. Thus industrial waste water treatment is an urgent issue.The thesis divides the controlling system of waster water into two sections: the front section and the rear section. The thesis also describes the two subsystems in terms of need design, practice and testing so as to propose a rational and efficient idea of waste water treatment and propose a positive reflection about increasingly serious environmental pollution problems.With reference to the successful experiences of waste water treatment domestically and abroad and taking the technological requirements into account, this paper addresses the general design scheme as well as the hardware and software of the computer-based controlling system for waste water treatment. The following is a more detailed illustration: Hardware, till now, PLC has gone through several stages with various brands, from logical control to process control and from PLC system with a few points to DCS system with thousands of points. The priority should be given on how to rationally select a hardware system with the better price/ performace ratio.Other issues are also discussed, such as on how to select system’s signal input, on how to collect signals for dangerous devices and on how to decide the hardware composition and structure of the PLC system. Software development: The design of applicable software shall not only meet the requirements of industrial control, but also the requirements for safety, practicality and reliability. The programming design of motor control module, tank level control system and waste water collecting pumping stations of waste water treatment system are mainly introduced, focusing on how to realize the safe and economic operation of these programming design. Management system program: The backstage management system can not only monitor the real-time operation of waste water treatment, but also can analyze the historical data to raise the efficiency of waste water treatment so as to provide basic data for system perfection. The main screen design, accident alarm screen design, tendency screen design are emphasized and variable data for archive are determined.The thesis provides a detailed analysis and design of the framework design, function design database design of the controlling system and illustrates the realization of some functions. To be specific, the whole waste water system includes 2 PLC, 1 operator station and 1 engineering station. The realization of functions such as online control, accident analysis and online data demonstration of the waste water treatment system are emphasized. In addition, the general framework is drawn from need analysis. Following the principles of environment protection and energy conservation, the paper demonstrates the operational process of computer controlling system of waste water treatment by several interlinked subsystems and applicable program instructions. From the viewpoint of technological waste water treatment, the paper writes the PLC program and technological process controlling interface of the project by referring to the international counterparts’ design theory and taking the domestic realities in to consideration. Finally the paper summarizes the features and prospect of the computer controlling system of waste water treatment.