1 sewage generation process simulation
Simulation generated by the sewage plant effluent generator, liquid storage tanks and emergency kits of three parts, shown in Figure 1.
Figure 1 sewage plant diagram of generated
Water generator to clean water and other substances (including acid, alkali, grease, carbon, such as sugar, guano, etc.) through two pre-mixed and mixed stirring motor. Liquid storage tank as a temporary unit in synthetic wastewater to ensure that the upstream inflow is interrupted, continuous follow-up process can still achieve. Emergency kits for the failure to detect water, the experiment can be used as interference signals required by the quantitative variables to return to the water pump generator.
Intelligent instrument control system through the level of sewage, PH value, conductivity, flow values and other analog and digital position of various switches to automatically detect and upload test results to the next slave PLC, calculated by the data processing and then sent to the implementing agencies to implement the corresponding operations.
2 system hardware
According to the operation of sewage generation device simulation and control requirements, control system by Siemens S7-300 series CPU314PLC, SM321 Digital input module, SM322 digital output module, SM331 SM322 analog input module and component analog output module [2]. The hardware configuration shown in Figure 2.
Figure 2 Underground Water Control System PLC and generate functional modules
3 analog control
Analog systems include PH, conductivity, flow, temperature, level and so on. This traditional PID control and PLC combined with logic instructions, so PID control more flexible.
PH value to the control, for example, during PID regulator, the ratio adjustment to reflect the size of systematic bias, as long as biased, and the ratio adjustment will have an effect to reduce the deviation. Differential regulation according to the trend deviationControl, to improve the dynamic response speed. Integral bias points according to changes in regulation to control, control of the system there is a lag effect, to eliminate static error. Increase the integration time constant can improve the static accuracy, but the points too strong, especially in the systematic error is large the system will overshoot and large, and even cause oscillation. Therefore, the system uses the following control strategy, the composition of intelligent control systems. Figure 3 PH deviation of different control strategies
Figure 3 PH deviation of different control strategies
1) lower than the actual PH PH1, in order to speed up response time, increase base flow valves fully open, acid flow valve closed.
2) PH value in the actual [PH1 ~ PH2] range, to avoid the integral saturation, separation of integral term, using PD control with base flow, acid flow valve closed.
3) PH value in the actual [PH2 ~ PH3] range, adaptive PID control with base flow, acid flow valve closed. Figure 4 for the PH value of the adaptive control
Figure 4 PH value of the adaptive control
When measured PH > PH0 A7 and the sampling cycle, PH value continued to rise, then the additional base flow valve is closed (a ???? b, g ???? h); PH < PH0-A7 and the sampling cycle, PH value continued to decline, then add base flow valve connected to (d ???? e); other cases the implementation of PID control. (Dead-set threshold A7 of the system 0.2).
This control method is not only taking into account the measured PH value PH value and set the deviation, but also consider the trend of the measured PH value can reduce the overshoot and volatility, with the adaptive effect.
4) the PH value in the [PH3 ~ PH4] range, the use of PD control with acid flow, increase base flow valve closed.
5) PH value is higher than the actual PH4, in order to speed up the response speed, acid flow valves fully open, plus base flow valve closed.
4 PLC Software
S7-300 user program by the Organization block (OB), function block (FC, FB), data blocks (DB)Form. Block OB1 which is the operating system and user application interface for various conditions, is used to control program execution [3]. OB100 block for the system initialization, the system starts first call (only called once) the block will be cleared some memory address unit. Function block FC1 ~ FC8 were used as starting, stopping, level adjustment, PH value and the conductivity of regulation, and subroutine block. Used to store data blocks from the PLC analog input module receives to the data and the processing of these data [4]. PLC flow chart shown in Figure 5.
In which the subprograms as follows:
Take data subroutine: will come from the PLC analog input module of the data processed into quantities and stored in data blocks.
Level adjustment subroutine: the water level inside the generator with a given value of ultrasonic liquid level detection sensor PID value adjustment calculation and its calculation results as the flow rate adjustment signal to maintain a reasonable level within; to clean water , emergency kits and water flow for a given value of PID detected value of the deviation adjustment calculation and its calculation results as the degree of valve opening adjustment signal to maintain the water flow within a certain range, so that level to meet the requirements of this control is the cascade control.
PH value and the conductivity value adjustment subroutine: the PH for a given value, the value of conductivity for a given value of deviation and detection PID adjustment calculation and its calculation results as the charging port valve opening degree and the transportation of motorPressure regulation signal to PH value and the conductivity in the qualifying range.
The system uses PID FB10 block adjustment as a subroutine block, computing process in order to ensure accuracy, all the parameters that are 4-byte floating point.
Figure 5 PLC program flow chart
5 man-machine interface design
PC using WindowsXP operating system, with Siemens WinCC configuration software to design human-computer interface and control procedures. Operator interface through the local machine and the hardware keyboard membrane switch, down-bit machine the various control commands issued. Same procedure is completed by the main control unit from the real-time acquisition, processing simulation, switch, alarm data and operational data, historical data archiving time, real-time records, failure and switching change information, operator s operation to record and output Dayin. Operator interface can process sewage generated on the monitor box level, according to the different experimental conditions with different levels of user rights to the parameter setting interface landing PH value of water to modify or set [5].
<STRONG> 6 The innovation of this article
Programmable Logic Controller (PLC) and computer (PC) The combined application of simplified field operations, improve the control precision and flexibility of human-machine interface, but also improve the control system stability and security, with potential applications . This traditional PID control and PLC combined with logic instructions, so PID control more flexible. The system has been put into operation and working well, small-scale sewage treatment greatly increased the automation of test equipment.
References:
[1] Water Industry Engineering Design Manual: Wastewater treatment and reuse [M] Beijing: China Building Industry Press, 2002.
[2] SIEMENS.S7-300 Programmable Controller System Manual [M] Beijing: Siemens (China) Co., Ltd., 2004.
[3] SIEMENS.S7-300 automation system CPU31xC technology feature uses manual [M] Beijing: Siemens (China) Co., Ltd., 2001.
[4] XIAO Zuo-free, Chen Zhu, Xiao Aiwu. PLC based control system for sewage purification treatment design [J]. Computer ,2006,10-1:31-32.
[5] Su Kunzhe.Layman Siemens WinCC V6 [M] Beijing: Beijing University of Aeronautics and Astronautics Press, 2004.
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