ABSTRACT

With the rapid development of economy and society, energy resources are seriously lacking．At the same time，the demands for quality and reliability of water supply system are increased continually．So it is inevitable tendency to design one kind of water supply system which is high reliable and saves on energy well，with the help of advanced technique of automation and control ．

Direct towards the problems of actual water supply system，such as electric power and water resource waste and low quality of water supply, this paper mainly studied and designed a controller of the VF speed regulating constant-pressure water supply system．With the core of Mitsubishi FX2NPLC，this controller combined transducer and pressure sensor . The pressure value of the water-supply pipeline was set, and the number of running pumps and the rotate speed of motor to implement the closed—loop control of water pressure was controlled in this system，namely constant—pressure water supply．

This paper explained the principle of constant—pressure water supply on the basis of characteristic curve of pipeline resistance and water pump head．And water supply system’ energy—saving principle of water pump VF speed control Was clarified according to characteristic curve of running pipelines and water 'pump．Then the structure and work principle and control flow of VF speed regulating constant pressure water supply system Was analyzed in the paper．Based on the research of PID control theory, this paper has designed a PID controller．The design of the system’S hardware and software Was introduced thoroughly, and system EMI problems and relevant restraining methods were put forward in the end．

The water supply system is designed for a residential area in An yang city．After on—site commissioning and operation shows the real time control performance to the water pressure of water supply system designed in this paper Was proved to be all-right according to the experimentation validated．The hardware module is steady—going and reliable，and the PID controller is proper and valid and can guarantee the better stability of water pressure．And this control system is perfect． Keywords：PLC，Variable frequency，Water supply，Constant pressure