Abstract: This paper introduces the hardware configuration and software implementation of a wastewater treatment monitoring system based on an industrial Ethernet hybrid model. At the field level, a Siemens S7-300 series PLC is used as the master station, and distributed I/O ET200s are used as slave stations, forming a PROFIBUS-DP bus control system. An industrial PC is used as the host computer, and WinCC configuration software is used to develop monitoring screens for process flow, parameter settings, and real-time curves. Industrial Ethernet based on TCP/IP protocol is used to communicate with the PLC and connect to the building's architecture (BA), achieving integrated control. Operational results show that the system ensures the process quality of wastewater treatment, operates stably and reliably, and improves management efficiency. Keywords: Sewage Disposal Monitoring Fieldbus Industrial Ethernet[b][align=center]Supervisory Control System Based on Mixed Model of Industrial Ethernet for Sewage Disposal[/align][/b] Hui Hong-zhong Abstract: This paper introduces the hardware configuration and the software achievement of monitoring and control system based on mixed model of industrial Ethernet for sewage disposal. SIEMENS S7-300 PLC is used as master station and ET200 distributed I/O device as slave station to compose PROFIBUS-DP control system. Industrial personal computer is chosen as the upper computer and WinCC is used to develop monitoring and control picture such as technologic flow, parameter setting, real-time curving. PLC and IPC is communicated via industrial Ethernet based on TCP/IP to form a hybrid control system, which realize the integrating management and control by linking the BA together. The results of operation prove that this system ensures the technical quality of the sewage disposal and works steadily as well as improves the management level. Key words: Sewage Disposal Monitoring and Control Fieldbus Industrial Ethernet 1 Introduction Ethernet and TCP/IP communication technologies are mainly suitable for information management and information processing systems. They have achieved great success in the IT industry and have become the preferred network communication technology in IT applications. Due to their defects of uncertain queuing delays in message transmission, they cannot guarantee the real-time requirements of data transmission and therefore cannot be effectively used in industrial control. However, with the development of integrated management and control technology, there is an urgent need to extend the Ethernet of the management layer down to the device layer, thereby forming a unified transparent data link without data conversion, in order to achieve the best economic benefits for enterprises. Therefore, Ethernet and TCP/IP technologies have been gradually applied in the automation industry and have developed into a technological trend. 2 Industrial Ethernet Design Model In order to apply Ethernet to industrial sites, many companies and research institutions at home and abroad are making various attempts to improve the existing Ethernet and establish new communication protocol models. In general, there are two models of industrial Ethernet: one is the hybrid model (Ethernet is connected to other buses); the other is the so-called "Transparent Factory" model, which adopts a unified industrial Ethernet communication protocol from the top to the bottom. (1) Hybrid Model. This model is actually a compromise and a relatively easy-to-implement solution. Many companies have launched industrial network architecture models, as shown in Figure 1. Ethernet is used at the management and workshop levels in the industrial field. It can connect to the Internet at the top and read the status information of various control subsystems in the workshop at the bottom. At the equipment level, independent fieldbus technologies such as CAN, PROFIBUS, and ASI are still used. They are connected to Ethernet through dedicated gateways. This solution makes the most of the communication functions provided by the existing Ethernet. Each gateway is an Ethernet node and also the master station of the subsystem below. The gateway can realize real-time control of the subsystem and preprocess the information inside the subsystem, sending only some important information to the Ethernet in the format of TCP/IP frames. The advantage of this solution is that it avoids direct access of Ethernet to sensors and actuators and other low-level devices, reduces the amount of real-time data transmitted on the Ethernet, reduces the chance of collisions, and to a certain extent avoids the problem of delay in transmitting real-time data under harsh industrial conditions. This model is still a transitional structure. The numerous protocols of the equipment fieldbus also affect the user's use. The idea of ​​unified and open fieldbus has not been fully realized. (2) "Transparent Factory" type. This model represents a complete solution for industrial Ethernet, meaning the enterprise network is entirely composed of Ethernet from top to bottom. It achieves complete transparency of the entire factory to the user, as shown in Figure 1 with the gateway removed and the lines dashed. Because the entire network uses a unified protocol, users can access any device from the top management layer to the bottom equipment layer without needing to know how this access is performed. Ordinary sensors and actuators connect to the Ethernet via industrial Ethernet I/O modules, and the management layer host can communicate with various devices via IP access. Currently, some experimental networks have been reported, achieving some results, but practical application is still some distance away. The advantage of this solution is its comprehensive solution for on-site monitoring networks, but its implementation is relatively difficult. The main challenge is modifying Ethernet for real-time control and introducing real-time control algorithms above the network layer to compensate for Ethernet's inherent limitations in transmitting deterministic data. 3. Wastewater Treatment Process This wastewater treatment project is the wastewater treatment system for the National Power Dispatch Center. The system consists of three parts: a greywater treatment system, a softened water system, and a drinking water system. The process flow is as follows: 3.1 Wastewater Treatment System: Wastewater from the sludge main pipe passes through a screen in the screen tank to remove impurities, then flows into the equalization tank. A submersible pump then pumps the wastewater to the oxidation tank via a hair collector. After aeration and oxidation, the wastewater flows into the sedimentation tank. The supernatant flows into the drainage ditch, and the settled sludge flows into the sludge thickening tank for treatment. The supernatant with fewer sediment impurities is then pumped back to the oxidation tank for recycling. After oxidation treatment, the wastewater is pumped to a mechanical filter and a deep treatment tank, then into the reclaimed water tank, and finally to the wastewater tank via an effluent pump. Two dosing devices are installed, one for PAC and the other for Cl, primarily for disinfection. (See Figure 2). 3.2 Softening Water System: Water from the wastewater tank is further pumped by a centrifugal pump to an activated carbon filter and a precision filter for filtration. It then enters three sets of softening equipment and is treated with Cl before being sent to the softening tank. The regeneration salt tank regenerates the ion exchanger, improving its activity. 3.3 Water from the soft water tank of the direct drinking water system is pumped to an activated carbon filter and a security filter before being stored in an intermediate water tank. Return water from the high and low zone circulation systems is also sent to the intermediate water tank after passing through a disinfection system. A sodium filtration booster pump sends water from the intermediate water tank to the sodium filtration unit for treatment via a wastewater metering system, then to the oxidation tower for disinfection via another metering system, and finally into the product water tank. Water from the product water tank is supplied to the high and low zone areas by variable frequency pumps. The three sections have a total of 36 pumps, 28 solenoid valves, and 8 continuous control valves. Due to the characteristics of the wastewater medium, all pumps operating throughout the process require one in operation and one on standby. The two pumps must be able to switch on a scheduled basis (weekly or daily) and in case of failure. All pumps and valves are equipped with automatic and manual switching. The start and stop of each pump are mainly controlled by the high, medium, and low liquid levels of the relevant tanks/pools or by pipeline pressure, and a standby pump should be able to start when one pump cannot meet the requirements. All filters can automatically perform forward and backwashing when conditions are met. The analog quantities include liquid level, pressure, flow rate, pH value, hardness, turbidity, residual chlorine, and conductivity. Besides the requirement for display, alarm, and cumulative quantities in the central control room, eight quantities must be continuously controllable. Simultaneously, according to the dispatch center's requirements, this wastewater treatment control system should be connected to the entire building's management system to achieve integrated control from the dispatch center and improve management efficiency. 4. Monitoring System Solution Based on the above process characteristics, equipment distribution, and control requirements, we selected a wastewater treatment monitoring system based on an industrial Ethernet hybrid model. The field-level control system uses a Siemens S7-300 series CPU315-DP as the master station, installed in the central control room along with the host industrial control computer. The PLC is connected to the industrial Ethernet via a network communication module CP343-1. Three distributed I/O modules ET200M are selected as DP slave stations, running in three separate system fields. The ET200M supports the entire S7-300 series of modules and is connected to the PROFIBUS-DP fieldbus via IM153. The host computer is an Advantech industrial PC with an embedded CP1613 network communication card. After setting relevant parameters, it can achieve industrial Ethernet communication between the host computer and the PLC based on the TCP/IP protocol, and can be easily connected to the building's BA (Building Automation) to realize integrated control of the dispatch center. Siemens WinCC 5.0 configuration software is used as the development platform, mainly to complete functions such as process screen, status monitoring, real-time curves, process variable and control parameter setting, alarm display and confirmation. All logic control and simple PID control are completed by the lower-level PLC, which can work safely even when disconnected from the host computer. High and low zone water supply frequency converters are also connected to the DP bus via DP modules. The system configuration is shown in Figure 3. 5 Software Programming 5.1 Lower-Level Computer Program The SIMATIC S7-300 series programmable controller adopts STEP7 standard software programming. Its greatest advantage lies in symbolic programming and hierarchical organization, making the compiled program highly readable and easy to debug on-site. The STEP7 standard software package includes a symbol editor, SIMATIC manager, NETPRO communication configuration, hardware configuration, and three programming languages ​​(LAD, FBD, and STL). It also has hardware diagnostic capabilities. The hierarchical and calling structure of the entire process monitoring program is shown in Figure 4. OB1: This is the system organization block used for cyclic program processing. FC2 is the alarm and data processing function block, used for processing various alarm signals and exchanging data with the upper-level data block (shared) DB20. FC3 is the high, medium, and low level judgment function block, which completes the high, medium, and low level judgment of nine water tanks. This function block calls the level comparison function block FC4. OB35 is the cyclic interrupt subroutine with an interrupt priority of 12. Its interrupt time can be set between 5ms and 60000ms; in this case, it is set to 1 minute. FC10 is the system main program. Various alarms are handled in function block FC2 and can be confirmed by the upper-level computer. It also prepares and processes the data required by the main program. FC4 is the level comparison subroutine function block. DB21 is also a shared data block, allowing the host computer to set pump switching time and various configuration data. STEP7 standard control functions include multiple PID control modules that can be directly selected, such as function block FB41 in Figure 5.1, where DB41 is the background data block. Users can easily implement simple PID control through connection and parameter settings, with parameters adjustable via the host computer. The system implemented programming to control the start, stop, and 24-hour automatic switching of two submersible sewage lift pumps; sequential control of two secondary sedimentation effluent lift pumps and the submersible sewage lift pump; pressure and time control of forward and backwashing of the steel mechanical filter and activated carbon filter; start, stop, and automatic switching of the greywater effluent lift pump, sludge return pump, and Grundfos centrifugal pump; control of residual chlorine, hardness, turbidity, and pH value by controlling the opening of the dosing metering pump to control the dosage; and closed-loop control functions such as high and low zone variable frequency circulating water supply for water pressure, level, and conductivity control are achieved through six calls to the PID control module FB41 and data blocks DB41, DB42, DB43, DB44, DB45, and DB46, whose parameters can be set via the host computer. 5.2 Host Computer Program The host computer uses Siemens WinCC5.1 configuration software to develop the monitoring program, which mainly realizes the following functions: (1) Control and display of process flow diagram and operating parameters: process flow diagrams for reclaimed water, soft water and direct drinking water are developed respectively, and the operating status of various pumps, valves and other equipment and various monitoring data are displayed in real time. The liquid level, pressure, time, residual chlorine content, pH value and other data can be set and controlled. The main screen simulates the on-site working conditions, which can intuitively and accurately understand the on-site working conditions. Figure 5 shows the flow diagram of the reclaimed water treatment system. (2) Data query function: On the host screen, the collected data can be observed in real time through real-time data curves, which is convenient to understand the specific working conditions; the collected data can be stored in the database through historical data curves, which is convenient to understand the historical trend of long-term work. The query can be accurate, convenient and fast. (3) Alarm function: alarms are triggered for parameters exceeding the set value range and equipment malfunctions. When a real-time data exceeds the set value or a device malfunctions, an audible and visual alarm is triggered, and corresponding processing is performed. After the alarm, the required parameters are stored in the database for future reference. (4) Report function: reports are generated for data that needs to be reported, compared, or stored for a long time, and are printed and archived on a timed or real-time basis. 6 Conclusion The SIMATIC S7-300 series programmable controller is used for wastewater treatment. The hardware can be configured by software, the software programming hierarchy is clear, and on-site debugging is convenient. Its powerful communication function can be used to form various distributed monitoring and management systems. PROFIBUS-DP fieldbus is suitable for industrial fields. It has high reliability, good real-time response, and low environmental requirements. It is a fieldbus suitable for system networking in industrial environments. Ethernet based on TCP/IP protocol has advantages such as high transmission speed, low power consumption, easy installation, and good compatibility. It supports almost all network protocols and is a communication network widely used by enterprise management. The system's operation in the wastewater treatment project of the National Power Dispatch Center demonstrates that combining industrial control computers with PLCs, and fieldbus with industrial Ethernet, to form a hybrid industrial control system not only leverages the advantages of each component but also facilitates network expansion and heterogeneous connections, achieving integrated control. The innovation of this paper lies in applying the hybrid model of industrial Ethernet and fieldbus to the wastewater treatment computer monitoring system, realizing integrated system control. References [1] SIMATIC S7-300 series programmable controller hardware installation manual [2] SIMATIC S7 STEP7 V5.2 programming manual [3] WinCC5.1 user manual [4] Huang Zhaolong. Design of automatic control system in wastewater treatment process of aerated biological filter [J]. Microcomputer Information. 2005.2. [5] Yang Qing et al. Design of distributed wastewater treatment monitoring system based on industrial Ethernet [J]. Microcomputer Information. 2005.11-1. [6] Tang Jiyang. Ethernet and fieldbus technology [J]. Domestic and foreign mechatronics technology. 2002.5.7～14 [7] Chen Yilei et al. Research and development of industrial Ethernet [J]. Low voltage electrical appliances. 2002.5.35～38 Author Introduction Hui Hongzhong, male, master, lecturer, research direction: research and development of industrial process control, computer monitoring system and intelligent control monitoring system. Contact Information: Mailing Address: Unit 3, Building 25, Longshan South District, Dongchangfu District, Liaocheng City, Shandong Province, 252000, China Email: [email protected] Downloadable materials for a wastewater treatment monitoring system based on an industrial Ethernet hybrid model