Study On The DCS Of Sewage Simulative Generation Device

The sewage simulative generation device is the prepositive part of the sewage treatment experimental device. The device generates different ingredients sewage by changing the feed quantity and proportion, it realizes the automatic control of the feeding, PH, electric conductivity and experimental disturbing signals.According to the analysis on the principle and technique of the sewage simulation, this thesis studied all kinds of electrical controllers in the distributed marks, put forward the control idea and plan of the sewage simulation, and finally designed and developed the distributed control system of the sewage simulative generation device. This DCS makes use of S7-300 programmable logic controller from Siemens, personal computer and WinCC, HMI designing software to realize centralized management, distributed control and on-line supervision.Based on the arithmetic of PID parameters adjustment and control rule of solid-state relays, the subdivision PID control algorithm was presented according to the PH deviation, and the control plan of 4-PH limited value was put forward. The feeding rate is controlled with changing the relay's switch-on time converted from the analogue output of PID algorithm, therefore the quality of sewage water is controlled. The thesis realized the conversion from "analogue output of PID algorithm" to "On/Off control of relays", with using the normal electromagnetic on off valves instead of electromagnetic regulating valves. This plan has characteristics of lower cost, simple system constitution, high control accuracy and is easy to realize.Based on the principle of the "losing-weight" measurement, the powder supplying and calculating device was developed, which uses the losing weight of the materials in the hopper during a unit time to convert the number into the real-time output.Based on the WinCC configuration software, a whole set of the friendly supervision terminals are designed. It can supervise these real-time parameters in order to make the device more robust, stable and safe, facilitate the users more flexible and improve the control precision and productivity.