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Application of SCADA Systems in Water Treatment Author: Liu Guohong, Guangdong Shunde Keli Water Supply and Drainage Engineering Development Company. The SCADA system used at the water treatment plant in Enping City, Guangdong Province, employs Rockwell Automation’s A-B SLC 500 and MicroLogix 1000 as programmable controllers, with ControlNet, DFl radio communication, and Profibus as the communication networks. RSView32 and RSView32 ADS are used as the monitoring and configuration software, enabling automatic monitoring of the water treatment plant, detection of pressures in the water supply network, as well as management and scheduling of the entire plant. The water treatment plant in Enping City, Guangdong Province is a key project in that region; its successful completion has enabled the residents of Enping to have access to high-quality tap water, with the water output meeting the standards of the European Community. By establishing a complete SCADA system, as well as an integrated management and control system that combines an automatic control system, a dispatching system, and an enterprise Intranet system—taking into account their integration with the radio dispatching system—the automatic control of the entire water treatment production process is achieved. Through the radio dispatch system for monitoring the pressure in urban pipeline networks, it is possible to manage these networks effectively, while simultaneously sending the production data from water treatment plants and the monitoring data from pipelines back to the company’s internal network in real time. Any terminal on the company’s intranet can, with proper authorization, monitor the operation of the water treatment plant and the pressure levels in the urban water distribution network. By using this system, it is possible to keep a dynamic overview of the operating conditions regarding pressure in water treatment plants and urban pipeline networks, thereby enabling informed decision-making and efficient scheduling, which reduces production costs, improves production efficiency, and enhances the company’s production management level. Composition of the SCADA system 1. Overall system structure As shown in Figure 1, the SCADA system of Enping Water Treatment Plant consists of the plant’s automatic control system, pressure measurement points along the urban water supply network, and the internal network of the water supply company’s office building. Ethernet is used for the management layer of the system, while ControlNet and wireless communication are used for control layer communication between various PLC controllers and computer operation stations. The management layer and the control layer exchange information through the Active Display System (ADS) server, which is based on the client/server HMI configuration software RSView32. The ControlNet network uses shielded coaxial cables for communication, featuring easy connection and long communication distances; it is a stable industrial network that is widely used for PLC communication. Wireless communication utilizes the DF1 master-slave protocol with SCADA capabilities; the PLC establishes wireless communication with the radio transmitter via its standard RS232 interface, with a communication rate of up to 960 Obps. 2. Composition of the water treatment plant’s automatic control system: Based on the classification of equipment in the water treatment plant and the control requirements, its automatic control system consists of PLC1 for the water intake pump station, PLC2 for the chemical dosing station, PLC3 for the filter station (including routine backwashing), PLC4 for the water delivery pump station, and the central control room. The automatic control system of the water treatment plant consists of three layers: the management layer, the control management layer, and the field control layer. The control system adopts a distributed control system architecture to facilitate three-level control based on \"centralized management and decentralized control\". Command is centralized, control is decentralized, and emphasis is placed on functional decentralization to achieve flexible control and improve the reliability of the entire system. PLC1 is used to monitor the operation of the water intake pumps in the water intake pump room; it includes detecting the operating temperature of the pumps and electrical parameters, as well as water quality parameters such as the pH, turbidity, and temperature of the raw water. The PLC2 dosing station is used to monitor the operation of the alum dosing pump, lime pump, and chlorination unit; it includes sensors for measuring parameters such as SCD, pH, and residual chlorine in the water after dosing. Through feedback, the PLC’s PID control mechanism adjusts the dosage of these chemicals to achieve automatic control. This enables the water to achieve better sedimentation as well as disinfection and sterilization effects, while also maintaining the water’s pH level. This is the most critical control stage in the water treatment plant. PLC3 is used to control automatic constant-level filtration and automatic common backwashing of the filter tank. PLC4 is used to monitor the operation of the water supply pumps in the water supply pump room. This includes monitoring the operating temperature of the pump, electrical parameters, as well as parameters of the water leaving the plant such as pH, turbidity, residual chlorine, pressure, and flow rate, in order to ensure an adequate supply of water and its quality in urban areas. The PLCs in the water treatment plant form a ControlNet network throughout the plant via shielded coaxial cables. The central control room of the water treatment plant is equipped with two HMI operation stations that serve as hot backups for each other. These stations consist of two computers, each fitted with a 1784KTCX15 card, which run the RSView32 system to function as a human-machine interface for monitoring and controlling the production and operation of the entire water treatment plant, as well as for monitoring the pressure levels in the urban water distribution network. Configure the printer to print alarms, production reports, and curves, etc. 3 Composition of pressure measurement points in urban pipeline networks: In SCADA systems, the PLC5-PLC12 units used for monitoring pressure in urban pipeline networks are the most cost-effective and reliable micro programmable controllers, namely the MicroLogix 1000; these controllers collect parameter data from the measurement points and serve as DF1 slaves in the SCADA system. 4 Composition of the company monitoring station The company monitoring station includes the internal network within the headquarters building of the water supply company, as well as server computers equipped with 1784 PCIC cards and a SCADA system. Due to the significant distance between the control room of the water production facility and the building of the water supply company, a ControlNet network composed of coaxial cables was used for connection. The system is equipped with 1784 PCIC cards, and the server computers run RSView32 and RSView32 ADS as monitoring configuration software, which are used to monitor real-time pressure data from the water treatment plant and the urban water distribution network. This setup also enables communication between the company’s internal network and the control network. Thus, through the ControlNet network, radio dispatch system, and internal company network, the water treatment automation system, the urban pipeline network dispatch system, and the internal company network are connected into an integrated network. Monitoring terminals have been installed in functional departments such as the manager’s office; just like any other terminal on the company network, installing an ADS workstation or a Web Browser is sufficient to monitor the operating conditions of water treatment plants and urban pipeline pressures, provided that appropriate authorization is available. The system features Internet/Intranet interfaces, enabling convenient monitoring of production operations from any location at any time via dial-up access, that is, remote monitoring. 5 Composition of system software System software is the core of the entire system, and it directly affects the success or failure of the whole system. System software mainly includes operating systems, monitoring software platforms, etc. The operation station in the water treatment plant’s control room uses the Windows NT operating system and the RSView32 human-machine monitoring configuration software. The ADS server computers in the Water Supply Group Company’s building are equipped with Windows 2000 Server as standalone servers on the intranet, running the RSView32 HMI configuration software as well as RSView32 ADS Server. RSView32 is a human-machine monitoring software developed by Rockwell Automation using open technologies, based on MFC (Microsoft Foundation Classes) and DCOM (Distribution Component Object Model) component technologies. This HMI product makes use of ActiveX, VBA, and OPC for graphical display, and it offers all functions such as monitoring, control, and data acquisition. It is a monitoring and configuration software that is easy to use, highly scalable, and possesses excellent monitoring capabilities. RSView32 ADS extends the RSView32 HMI software into a client/server architecture. The ADS server can be located on-site, or it can be accessed from anywhere in the world via the Internet. The client can use ADS Station software or Internet Explorer as the monitoring software platform. The system security policy takes advantage of the dual security features provided by Windows 2000 and RSView32: Windows 2000 is responsible for managing the login of operators or system administrators at the internal network system level, while RSView32 controls the operational permissions of various users at the application layer by setting different security levels, thereby ensuring the proper operation of the system and preventing unauthorized access. The SCADA system protocol ControlNet is a completely new industrial control network introduced by Rockwell Automation. It is an open, high-speed, deterministic network that can be used to transmit information with strict timing requirements; its communication speed can reach 5 Mbps, enabling real-time control and peer-to-peer communication services. By adopting the producer/client approach, it replaces the traditional network model, in which multiple transmissions are required to reach different sites, with a model that allows for one transmission to be shared among multiple sites; this reduces the number of network transmissions and thus makes the network more efficient and responsive. Use the RSNETworx software to configure the ControlNet network. Due to historical reasons, we are using SLC5/03 PLCs; therefore, to enable ControlNet communication, a 1747-SCNR communication module was added to each PLC rack. Additionally, a 1747-KFC15 communication module was installed on PLC4 in the water pumping station, in order to facilitate communication between the 1784KTCX15 and 1784PCI cards and the PLC CPU. The A-B SLC5/03, SLC5/04, and MicroLogix 1000 programmable controllers from Rockwell Automation come equipped with built-in multi-functional standard RS232 interface channels, whose system mode supports the DFl communication protocol. The DF1 protocol is a communication standard widely supported by the PLC systems of Company A and Company B. All series of PLCs, as well as computers equipped with the RSLinx communication software, support the DF1 protocol; this protocol enables the creation of PLC-based scheduling systems. The Enping urban pipeline network scheduling system employs a point-to-multipoint half-duplex communication mode. PLC4, acting as the master station, uses DFl half-duplex for primary communication, while the other controllers PLC5–PLC12, functioning as slave stations, use DFl half-duplex for secondary communication. The master station PLC facilitates data exchange by polling each station in turn. Functions and Features of SCADA Systems 1 Centralized Management, Decentralized Control: The central control room of the water treatment plant enables centralized monitoring and control of various equipment throughout the system as well as production operation data. Three-level control can be achieved. That is: local manual control, station-based PLC control, and centralized control from the control room. The control room offers both automatic control and remote manual control (remote operation). (1) Local manual control: Manual control of the equipment is carried out locally via buttons or controllers on the control box or cabinet. (2) Sub-station PLC control: The PLCs at each sub-station execute their own control programs to process the I/O signals at that station. In the event of being offline from the central control room or experiencing communication failures, each sub-station can independently use its own PLC for control as well as for communication between PLCs. (3) Centralized control in the control room: This involves monitoring and controlling the entire production process of the plant as well as the pressure in the urban pipeline network, along with processing data, while also enabling automatic or remote control of the equipment under supervision. In automatic control mode, it is possible to carry out coordinated control of the relevant equipment in the water treatment plant; for example, during pump startup, the pump is started first and then the valve is opened, while during pump shutdown, the valve is closed first and then the pump is stopped. If the water level in the suction well is above the pump shaft, start the pump directly; if the water level is below the pump shaft, create a vacuum before starting the pump. Once the vacuum is established, stop the vacuum pump and then start the pump (with the pump valve operating in conjunction) ； Automatic dosing is carried out through a closed-loop feedback PID control ； As well as PID constant-level automatic filtration for the filter tank, automatic backwashing, etc.; in remote control mode, individual control of various control devices is possible. 2 Strong communication capabilities: The process flow monitoring diagrams of the water treatment plant, along with the entire PLC system used for water treatment, form a ControlNet network. The radio communication rate can reach 960 Obps. The DF1 polling time can be set on the monitoring screen according to actual needs, in order to ensure real-time and accurate data. The company uses 10OM Ethernet, ensuring that the entire system can operate quickly, stably, and reliably. 3. The system boasts strong scalability and openness. The hardware and software used in this system are products that meet international standards and are widely used around the world; for example, the monitoring system is based on Microsoft’s Windows NT, 2000, or 9X platforms, and it supports various standard protocols such as OPC, ODBC, ActiveX, DDE, etc. It provides an interface foundation for integrating management control by enabling information exchange between process control systems and management information systems. 4 Rich visualization functions: The display on the computer operation station includes pipeline network monitoring diagrams, dynamic simulation views of various stations in the water treatment plant, high-voltage distribution diagrams, equipment operation screens, trend charts, alarm displays, and more. By accessing these screens, operators can gain a comprehensive understanding of the overall operation of the system, and can easily operate the equipment. 5 Alarm and protection handling functions: The system records information related to alarms generated by devices and software, such as the name of the fault label, alarm details, and the time of the fault alarm, and enables management of these alarm messages. The system also provides protection functions for critical equipment, such as protection against overload, overtemperature, and three-phase current imbalance. 6 Report Functions The system generates reports such as production logs, daily production reports, monthly reports, quarterly reports, annual reports, and pipeline pressure reports. 7 Remote monitoring function: Based on the client/server HMI configuration software RSView32 ADS, remote monitoring of the entire system is possible. Operators can monitor the production process from the central control room, and company management can even while on business trips keep an eye on and check the operating conditions of water treatment plants and urban pipeline pressures, thereby staying informed about production status in real time and enabling faster decision-making and scheduling to improve production efficiency. Performance and existing problems: Since the Enping water treatment plant was commissioned in November 2001 and put into formal operation, the system has operated relatively stably, with good automated control performance. However, for specific reasons, we opted for the SLC5/03 PLC instead of the A-B ControlLogix5000 series PLCs. Although a ControlNet network is formed by adding 1747-SCNR communication modules to each rack, the 1784KTCX15 and 1784PCI cards on the computer cannot communicate directly with the SLC5/03 PLC CPU. To solve this problem, we added an additional 1747-KFC15 communication module to the PLC4 at the water pumping station. This allows the SLC5/03 PLC CPU at the water pumping station to communicate with the 1747-KFC15 via the RS232 serial port. Meanwhile, the 1784KTCX15 and 1784PCIC cards on the computer communicate with the 1747-KFC15 through the ControlNet network, thereby resolving the communication issue between the 1784KTCX15 and 1784PCIC cards and the SLC5/03 PLC CPU. Since there is only one 1747-KFC15 communication module available, for the SLC5/03 PLCs in the other water intake, chemical dosing, and filter stations, we use the ControlNet network to first transmit the addresses of those PLCs to their respective 1747-SCNR communication modules. Then, the M data from those 1747-SCNR modules is sent to the 1747-SCNR module at the water pumping station. Finally, all the M addresses received from the various water pumping station 1747-SCNR modules are sent to the SLC5/03 PLC CPU at the water pumping station, thus enabling monitoring of all the different stations in the entire water treatment plant. Although the problem has been resolved, there are still shortcomings: the communication rate between the SLC5/03 PLC CPU and the 1747-KFC15 via the RS232 serial port can only be set to 19200bps at most. As a result, the 1784KTCX15 and 1784PCIC cards on the computer can communicate with the SLC5/03 PLC CPU at a maximum rate of 19200bps. In contrast, ControlNet is an open, high-speed, deterministic network that allows communication rates of up to 5Mbps. As a result, the speed, real-time performance, and effectiveness of the ControlNet network cannot be demonstrated.