Abstract: This paper introduces the application of PROFIBUS-DP networks in a clean water treatment system. The hardware configuration, software design, and implementation functions of the control system are described in detail, meeting production requirements. Practice has proven that the system is rationally designed and operates stably and reliably.
Keywords: Profibus-DP hardware and software functions
Abstract: The application of Profibus-DPinwatertreatmentcontrolsystemisintroduced,emphaticallydissertatedamethodofS7-300PLCsystemofapplication,hardwareconfiguration,softwareconfigurationandfunction.
Keywords:Profibus-DPhardwaresoftwarefunction
1. Introduction
The automated water treatment control system is the water supply system for a steel plant's continuous hot-dip galvanizing and color coating project. Automated monitoring and real-time control of water treatment are key to improving efficiency and reducing energy consumption. The system employs a PLC-based process automation monitoring system to automatically monitor all pumps and valves, and programmatically control the operation of aeration and drainage equipment. Based on the process requirements, it can control cooling tower fans, water pumps, electric valves, and other equipment in real time. This ensures that water flow and temperature meet industrial water requirements, achieving the goal of automated water treatment process control.
2 System Description
This system has four control stations: a clean circulation pump station, a galvanizing furnace cooling return water booster pump station, a color steel plate cooling return water booster pump station, and a rainwater and sewage pump station. Its system process flow diagram is shown in Figure 1.
Figure 1 System process flow diagram
3. Hardware composition of the control system
The overall system structure is shown in Figure 2. The main parts and their functions are described below.
Figure 2 System Overall Structure
(1) Profibus-DP network
Based on application characteristics, PROFIBUS can be divided into three compatible versions: PROFIBUS-DP, PROFIBUS-FMS, and PROFIBUS-PA.
PROFIBUS-DP: An optimized, high-speed, and inexpensive communication connection designed for communication between automatic control systems and distributed I/O at the device level. Using PROFIBUS-DP modules can replace expensive 24V or 0-20mA parallel signal lines for data transmission in distributed control systems. The clean-loop pump station, galvanizing furnace cooling return water lift pump station, color-coated steel sheet cooling return water lift pump station, and stormwater/sewage pump station are connected via a PROFIBUS-DP network. The clean-loop pump station is station #2, the galvanizing furnace cooling return water lift pump station is station #3, the color-coated steel sheet cooling return water lift pump station is station #4, and the stormwater/sewage pump station is station #5.
(2) PLC control system
Based on the operational requirements of the equipment, the Siemens S7-300 series programmable logic controller (PLC), known for its cost-effectiveness, was selected to construct the control system. The CPUs in the PLCs for the clean-loop pump station and the stormwater/sewage pump station are CPU315-2DP, and the clean-loop pump station PLC has two expansion racks. The CPUs in the PLCs for the color-coated steel cooling return water lift pump station and the furnace cooling return water lift pump station are CPU313C-2DP. Communication between these four systems is achieved via a Profibus-DP network. The PLC system hardware configuration diagram is shown in Figure 3.
Figure 3 PLC system hardware configuration diagram
(3) Monitoring station
The monitoring station utilizes Siemens industrial control computers and high-performance industrial monitoring software WinCC (Windows Control Center) to display and monitor the entire system's process flow and equipment operating status, display curves, save historical data, manage access permissions, query operations, generate alarms, and print data. One host computer monitors the production processes of the clean circulating water pump station, the galvanizing furnace cooling return water booster pump station, and the color steel plate cooling return water booster pump station, while the other monitors the production of the rainwater and sewage pump station. The two host computers serve as backups for each other, improving system reliability.
(4) Instrumentation System
The instrumentation system consists of transmitters, distributors, isolators, regulators, and actuators. It mainly acquires flow and pressure signals and controls valves. The regulator serves as a backup control mechanism for the computer system, allowing manual control when the computer malfunctions.
4. Automation Software Design
The software of the automated control system for clean water treatment includes two parts: the host computer and the slave computer design.
4.1 Host Computer Software Design
The design goals of the host computer system are: to have the ability to communicate with multiple slave computer systems, monitor the working status of multiple slave computers in real time, and display the working curves in the production process in real time; to have remote control capabilities; to collect data from slave computers and store, query, display, and print historical data.
In an automated monitoring system, the monitoring configuration software in operation serves as the system's data collection and processing center, remote monitoring center, and data forwarding center. The monitoring configuration software, in operation, together with various control and detection devices (such as PLCs and smart meters), constitutes a rapid response/control center.
We selected Siemens WinCC configuration software, which has powerful functions for controlling automated processes. It is a SCADA-level operation monitoring system based on a personal computer and has a very high cost-performance ratio.
To ensure stability in the industrial environment, the host computer uses the Windows 2000 operating system and the WinCC programming platform. The host computer performs the following functions: digital display of flow rate, pressure, temperature, and liquid level; display of the start-up, stop, operation, and fault status of each device; during startup, the device buttons are green; during normal operation, they are red; during a fault, the screen flashes colors and displays the fault type in text format for easy troubleshooting; it can record one month's worth of fault information (fault time, fault type, etc.) for convenient incident analysis; and through a report editor, it can print out relevant information periodically or randomly. The HMI monitoring screen is shown in Figure 4.
Figure 4 HMI monitoring screen
4.2 Lower-level software design
The lower-level machine uses SIEMENS' STEP7 software for programming the PLC and configuring and maintaining the PLC equipment. The software mainly includes the design of signal acquisition and processing, signal control, fault module, and DB block for communication with the upper-level machine.
STEP7 provides programming capabilities to generate standard exported function block libraries or FC libraries, which can be repeatedly called within the application. In this system, due to the large number of detection points, this functionality is widely used. The use of FC function blocks saves significant program space and troubleshooting time. It reduces the complexity of program writing and makes the program structure more organized. It has been proven that the use of FC function blocks improves program execution speed and facilitates software portability and scalability.
5. System Functionality
The four pumping stations are operated using both on-site and centralized methods. Centralized operation is further divided into manual and automatic operation modes.
The galvanizing furnace cooling return water booster pump station and the color plate cooling return water booster pump station have 3 water pumps and 2 cooling towers. Among them, 2 of the 3 pumps are in use and 1 is on standby. When the system needs less water supply, 1 pump is turned on to pressurize the pipeline network. When the water supply is large, 2 pumps are turned on to pressurize the pipeline network simultaneously.
The color-coated steel sheet cooling return water booster pump station and the galvanizing furnace cooling return water booster pump station each have two water pumps. These two pump stations use the same control method. Pump #1 and Pump #2 serve as backups for each other. The working and backup pumps automatically activate. Both the color-coated steel sheet cooling water collection tank and the furnace cooling water collection tank are equipped with level monitoring devices to monitor the water level in the suction tank. The control method for Pumps #1 and #2 is as follows: when the water level h > 2.20m, the motor starts and pumps water away; when the water level h < 2.20m, the motor stalls, and the thermal relay trips to protect the motor.
The stormwater and sewage pumping station is used to discharge rainwater and industrial wastewater. Its pumps are divided into three groups: A, B, and C. Group A has two pumps, which operate only during the rainy season. Group B has two pumps; normally one is the working pump, and the other is a standby pump. When the water level rises to -2.15m, the other pump automatically starts, and both pumps operate simultaneously. Group C has one pump, which is normally not in operation. When both pumps in Group B are operating simultaneously, and the water level drops to less than 0.5m within 10 minutes, the pump in Group C is manually activated, and all three pumps operate simultaneously. When the water level drops to -5.20m, all three motors in Groups B and C automatically stop operating.
6. Conclusion
Engineering practice has proven that this control system, employing PROFIBUS-DP network technology to achieve distributed control, offers advantages such as high network speed, high reliability, good openness, and strong anti-interference capabilities. This facilitates installation, commissioning, and equipment maintenance, improving production efficiency and management level. This network architecture boasts a high performance-price ratio and can be expanded to larger systems according to user requirements.
References
1 Yu Qingguang. Programmable Logic Controller Principles and System Design. Beijing: Tsinghua University Press, 2004.
2. SIMATIC S7-300 Programmable Logic Controller System Manual. Beijing: Siemens, 2001.
Contact Person: Li Xia
Mailing Address: Jinan Iron & Steel Automation Information Technology Co., Ltd., No. 21, Industrial North Road, Jinan City
Telephone: (0531) 88866647
Email: [email protected]
Li Xianu (1979–) holds a Bachelor of Engineering degree and works in the field of electrical automation.
