| In this paper, sewage processing is studied, and an automatic control system of that is designed and implemented. According to the process characteristics of CASS sewage processing, combining with the control conditions of field devices, the PROFIBUS-DP and MODBUS were introduced to set up the distributed control system. Also, the Siemens S7-300 series PLC was used as the main controller of the whole system. This paper completed the network configuration, hardware structure, software design and computer control interface of the system.The main work completed could be summarized as following:1.The establishment of communication network. Take the Siemens S7-300 as the master controller, In addition, PROFIBUS-DP fieldbus was designed to complete the communication among the master controller, slaver controller S7-200 and remote sub-station ET200M, and the field devices were controlled via the sub-station. Using MODBUS fieldbus to realize the communication between PLC and power system intelligent instrument, and the operational parameters of power system is monitored in real time.2.Design of control system software. Using ladder programming language to compose the program of PROFIBUS-DP and MODBUS comunication, and field device control.3.Design of the PC monitoring program. With Siemens WINCC 6.2 configuration software as development platform, setting up the PC monitoring program including monitoring,alarm,supervising and other functions.This project began trial operation in April,201 l,the result shows that it is stable and reliable to achieve expected purpose. |
