1. Introduction Programmable Logic Controllers (PLCs) have long been widely used in industrial automation, providing reliable control and overall solutions for various control devices, meeting enterprises' needs for automatic control, and facilitating convenient and flexible on-site setup, detection, and monitoring of production parameters for various equipment. With the development of network technology, control system architectures are also evolving towards networking and openness. More and more PLC suppliers are offering Ethernet interface devices, thus forming Ethernet control systems in industrial environments. The adoption of Industrial Ethernet completely breaks down the traditional "island" concept of industrial automation, organically connecting the entire plant into a remote monitoring network based on production nodes. Industrial Ethernet (IHE) is a unit network designed for industrial applications according to the IEEE 802.3 (Ethernet) international standard. It allows automation systems to connect to each other and provides communication between PCs and workstations of the same and different machine types. It boasts high communication performance and can serve as a solution for implementing a wide range of open networks. Compared to fieldbus, Industrial Ethernet offers backward compatibility, enabling switching, full-duplex transmission, and bandwidth ranging from 10MB/s to 100MB/s to 1000MB/s. It is primarily used in network systems within industrial environments. Industrial Ethernet offers advantages in automation, including low cost, easy integration with the Internet, and widespread technical support. In a port expansion project involving a 200,000-ton iron ore terminal, the wastewater treatment and storage yard spraying systems utilize a PLC control system based on Industrial Ethernet. Schneider Electric's PLCs can interact with their programming software, Concept, via an Industrial Ethernet control network. Technicians can modify the program in a relatively comfortable environment via Ethernet, eliminating the need to operate in harsh field conditions. Schneider Electric's Transparent Factory technology has enabled the successful application of Industrial Ethernet in PLC control systems. This paper will study how to implement a Schneider Electric MODICON PLC network control system in this system. 2 System Analysis and Design 2.1 Control Requirements Control requirements for the wastewater treatment system: The wastewater treatment station's collection tank is equipped with two submersible pumps that automatically start and stop based on the tank's liquid level, with the two pumps operating alternately. Simultaneously with starting the submersible pump, the metering pump is also started. After the wastewater is lifted to the intermediate water tank, two submersible pumps operate in rotation, and can be started if one pump fails. The sludge tank has two sludge pumps, which automatically start and stop based on the status of the float valve. The water levels in the collection tank and clear water tank, the pressure of the containers, sludge booster pumps, and the outlet pipe, and the flow rate of the outlet pipe can be monitored on the host computer. The sprinkler system control requirements are: water spraying can be controlled from the on-site control cabinet and remotely controlled by the host computer. Remote control allows for inching of the sprinkler valves and cyclical water spraying of the stockpile area. There are two modes: single-stockpile spraying and full-stockpile circulation. Single-stockpile circulation involves the host computer selecting a specific stockpile for spraying; full-stockpile circulation involves spraying the entire stockpile once based on whether there is stockpile material, whether there is a bucket wheel excavator cantilever signal, and whether spraying is selected. 2.2 System Design This wastewater treatment and yard spraying automatic control system consists of one field PLC master station and ten remote I/O substations. The computer monitoring workstation is located in the central control room and connected via industrial Ethernet. An industrial computer for spraying control is installed in the central control room, running a human-machine interface to monitor and manage the wastewater treatment system and the yard spraying system. It monitors, controls, and manages the entire production process and technological flow of the wastewater treatment system and the yard spraying system. The system uses a 100Mbps fiber optic industrial Ethernet, connecting all field control master stations, operator stations, and all remote I/O stations via industrial Ethernet optical transceivers. A MODICON QUANTUM series PLC is installed at the wastewater treatment system's field control master station, and a MODICON MOMENTUM series PLC is equipped as a remote I/O station for each of the ten valve control boxes in the yard spraying system. These are connected to the field control stations via fiber optic industrial Ethernet. The monitoring industrial computer connects to the field control PLC master station via Ethernet to achieve data communication between the wastewater treatment system, the yard spraying automatic control system, and the main control system. Because Schneider Electric's Modbus TCP/IP (1998) is currently the de facto standard for industrial Ethernet, enabling its widespread application at the sensor and device levels, this control system utilizes Schneider Electric's TSX Quantum and Momentum series PLCs. An industrial control computer serves as the central operator station (operator station and engineer station). The central operator station is responsible for equipment status monitoring, production information processing, printing, system start/stop command transmission, loop adjustment, and setpoint assignment. Field stations are responsible for field I/O signal acquisition, loop control, and interlocking sequence control; all field signals are routed to the field stations via cables. Field stations and operator stations exchange information and data via industrial Ethernet, truly embodying the principle of distributed control and centralized management. This system adheres to the principle of openness, adopts a structured architecture, and possesses complete compatibility and scalability for future development. Utilizing an industrial Ethernet structure, it offers excellent scalability and openness; any device conforming to industrial Ethernet protocols can connect to the network, and it can be easily integrated with an external production scheduling and management system (MIS). 3. Composition and Implementation of the Control Network 3.1 Construction of the Control Network The hardware composition of the system's control network is as follows: one central control room operator station PC, one field control station Quantum PLC, ten remote control substations Momentum PLCs, eleven Schneider MODICON Ethernet hubs (10Mbps 3TP/FL 499NOH10510), and one industrial Ethernet fiber optic network transceiver. The network construction scheme is designed as follows: The main station Quantum PLC and the substations Momentum PLCs form a redundant ring network with eleven nodes through the fiber optic transceiver and the 499NOH10510 Ethernet hub. Communication between the ring subnet and the host computer is achieved through the fiber optic transceiver and the 499NOH10510 hub. Using a ring network, if the ring fiber optic cable fails, the ring structure will switch to a bus structure with full transmission capacity within less than 500 ms. Therefore, if a problem occurs with one of the Momentum PLCs, the redundancy of the ring network will not affect the normal operation of the entire system, improving the stability of the entire system. The structure is shown in Figure 1. After the network hardware is successfully built, Schneider Electric's Bootp tool is used to assign IP addresses to each PLC forming the ring network. These addresses must be in the same IP segment as the host computer's IP address. 3.2 Solving Communication Problems In this PLC control system, the hardware network is only one part; ensuring the stability and accuracy of network communication is a crucial issue. There are two ways to achieve network communication between Quantum PLCs and Momentum PLCs: 1. Configure the master station and slave stations for information exchange, and set the unit address for the data length to be read and written; 2. Use the FBD function instructions in the Concept programming software to perform read and write operations on the slave stations. In the control network of this system, we used a 499NOH10510 hub for photoelectric conversion. Since the hub receives a message from one port and then broadcasts it to all other ports, for every message from any port, the hub will pass it to all other ports. In terms of message transmission, the hub is slow and inefficient, and message conflicts may occur. Obviously, due to this deficiency of the hub, when information from various PLCs simultaneously occupies a communication channel, it will cause message conflicts, leading to network communication interruption and paralysis of the entire control network. Only by restarting the entire system can it return to normal. However, since information transmission in the control system is frequent, the possibility of system control network paralysis is always present if the information conflict problem is not resolved. Figure 2 shows the program flow of time-sharing read/write information communication. The key to resolving information conflicts is to enable multiple PLCs to use the channel for information exchange in a time-sharing manner, thus avoiding information channel conflicts. In the first solution, simply allocating corresponding storage registers for information communication cannot solve the conflict problem of information simultaneously occupying the channel. Therefore, we adopt the second solution to solve this problem. Schneider PLC programming software Concept 2.6 has powerful functions. Its simple programming language and complete function instructions allow users to easily solve the problems they encounter. In the FBD programming mode, it has powerful FFB function instructions, which can realize all configuration functions and logic ladder diagram functions, including network communication (MB_TCP/IP, MODBUS, etc.). The human-machine interface of the host computer operator station was developed using FameView configuration software from Beijing Jiekong Company. Utilizing the Modbus TCP/IP protocol interface provided by FameView, communication and control between the host computer and the PLC Ethernet control network can be easily achieved. 4. Conclusion The system is now in use. After several months of trial operation, it has proven that the control system meets the design requirements, successfully solving the stability and accuracy issues existing in industrial Ethernet, and demonstrating a very significant control effect. It fully reflects the advantages of PLC network control systems, such as intuitive control and convenient operation.