Abstract: In order to effectively utilize water resources and improve various problems in gate monitoring in water conservancy and hydropower projects, a new type of distributed network structure gate monitoring system was studied by means of fieldbus technology, Ethernet technology, programmable controller technology, electrical control technology, sensor technology, hydraulic technology, etc. The gate can realize local control and remote monitoring, effectively improving the real-time monitoring capability and work efficiency. The system has the advantages of high reliability and transmission speed, low cost, convenient use and good maintenance. Keywords: fieldbus; programmable controller; monitoring; hierarchical distributed structure; gate Introduction China has abundant water resources and water conservancy projects have developed rapidly. Gate control systems are widely used in water conservancy and hydropower projects such as reservoirs and pumping stations. They play an important role in flood control and drought relief and water transport scheduling, and are also closely related to direct economic benefits. Gates not only require local control of a single gate, but also require centralized indoor control of multiple gates due to the large number of groups [1]. Traditional gate control systems typically consist of a centralized control unit and field workstations. Because the workstations are geographically distant from the centralized control unit, and the amount of information to be transmitted between them is enormous, the system is costly, involves numerous wiring connections, has low reliability, and is difficult to maintain and manage. With the continuous development of automatic control, communication, and computer technologies, applying telemetry, remote control, communication, and computer technologies to gates has become a major focus and direction for sluice gate monitoring systems. Fieldbus control systems align with the development trend of control systems towards distribution, networking, integration, and intelligence, and have now become the mainstream direction for control system development. In reservoir water conservancy projects, a new type of fully distributed network structure gate monitoring system is constructed using fieldbus technology, integrating PLC technology, computer technology, power electronics technology, automatic control technology, and instrumentation technology. This system enables local manual control, local automatic control, and remote control of different types of gates, ensuring the safe and effective operation of water conservancy projects and maximizing their benefits. 1. Overall Gate Monitoring System Design The entire monitoring system adopts a host computer and slave computer model, establishing a control network that combines remote centralized control with local control. The system is divided into a central management and control level and a local control level, consisting of a central control unit, local control units, transmission and execution units, network communication equipment, and an industrial video monitoring system. The overall system structure is shown in Figure 1. The system is managed centrally by a central computer, which performs automatic monitoring, data recording and storage, status reporting, control command issuance, and human-machine interface operation for the local control level. The gate control stations employ distributed control; each station is managed by its own independent CPU terminal under the control of its local main computer, independently monitoring and controlling its respective gate and communicating with the host computer. The central control level and the local control level are connected via a fieldbus. The central control console sometimes also has communication capabilities with remote control monitoring systems via Ethernet, serving as an I/O station for the remote master control system. 2 System Main Module Design 2.1 Central Control Unit The main functions of the central control layer are to monitor, comprehensively analyze, analyze and process fault information of the entire gate equipment, issue operation instructions, set and change working mode, record, report, communication control, system diagnosis, modify set value, and communicate with the local LCU using CAN bus. CAN bus is a single-chip microcomputer local network suitable for the control field. The multi-machine communication system using CAN controller has the advantages of being able to realize fully distributed multi-machine functions, the system has no master and slave distinction, flexible communication mode, good reliability, high communication rate, and low system cost [2]. The gate central control unit consists of Advantech industrial control computer, CAN card PCL-841, emergency stop control and other parts. It receives information from all local control units and provides data services to the remote control center. The centralized control industrial control computer is the core component of the central control unit. Since the computer cannot communicate directly with the CAN bus, the computer must have a CAN smart adapter card. Only in this way can it communicate with the CAN bus. The PCL-841 card is a dedicated CAN communication card that provides bus arbitration, error monitoring, and automatic data retransmission. It can be directly inserted into the ISA slot of a PC, handling bus communication between the upper and lower computers. 2.2 Local Control Unit (LCU) The local control unit uses a high-reliability PLC as its control core. It consists of a PLC control device, electrical control cabinet, rotary encoder, display operation panel, industrial detection device, and other intelligent instruments. The lower end of the PLC in the local control unit contains relays and other control components, while the upper end is a monitoring center unit composed of industrial computers. The structure diagram of the local control unit is shown in Figure 2. [align=center] Figure 2 Local Control Unit Structure Diagram[/align] The gate local control unit performs gate opening and closing logic control, position detection feedback, motor segmented switching logic control, communication transmission between nodes, real-time acquisition and processing of local data, and alarm and fault diagnosis functions. Each PLC controls a certain number of gates, each independently with identical functions, and can be operated locally or manually to complete the gate control task. The electrical control cabinet mainly adopts dual-machine hot backup, with two motors serving as backups for each other. They take turns starting, thus making full use of the equipment to ensure that it can be used at any time. This redundancy improves the reliability, scalability and adaptability of the system. Each LCU is equipped with an LCD screen, which can realize local automatic operation control and real-time data display. The local LCU can control the hoist and automatically monitor the gate opening, pressure, oil level, etc., and can communicate with the central control level through the PLC serial communication port. The gate monitoring system can complete the functions of preset gate opening, alarm, calculation and display of actual gate opening through the gate opening detection device or water level gauge on-site. 2.3 Industrial video monitoring system. Establish a video monitoring system to intuitively monitor the gate operation site, upstream and downstream water surface and water flow by switching video signals from different locations, and ensure the safety of the gate operation site [3]. The video monitoring system consists of industrial camera equipment, lens, pan-tilt unit, video matrix switcher, industrial monitor, wireless communication equipment and other hardware equipment with multimedia software to monitor and manage important work positions of water level and gate operation process. At the central control station, the video signal received by the optical receiving device is directly transmitted to the image monitor by the graphic matrix host, and the control signal is transmitted to the control computer to realize the data exchange with the host computer. It has multiple functions such as real-time monitoring, multi-screen video display, PTZ lens control, video alarm processing, automatic recording timetable setting, alarm record query, etc., and is equipped with retrieval and playback software, which can perform all-round retrieval. 3 System software design System software design includes centralized control unit monitoring software design and local control unit PLC program design. The PLC completes the control of a single hoist, the acquisition of gate opening and operating status information, and communication with the host computer of the main station. The centralized control unit monitoring software completes data query and browsing, data curve display, data and graphic printing, multimedia alarm function, and system maintenance functions. The host computer monitoring software development adopts component (COM or DCOM) technology. The host computer configuration software adopts Beijing Kunlun's MCGS configuration software. It has the advantages of simple operation, powerful functions, realistic dynamic simulation, and stable and reliable communication [4]. This can shorten the development cycle. MCGS configuration software uses a real-time database as its core to process and analyze data, and send instructions to lower-level computers. Leveraging its open nature, it calls shell functions to execute inter-node communication programs, enabling the entire system to operate effectively. The software block diagram is shown in Figure 3. The software consists of three main parts: the user interface layer, the data management layer, and the data source layer, each composed of multiple components. The user interface layer mainly consists of four component programs and a main program: the system management component, the graphical monitoring component, the data management component, the alarm system component, and the user interface main control program. The data management layer enables bidirectional data transmission between the data source layer and the user interface layer through components. The data source layer mainly consists of a CAN protocol interface component and a database maintenance and access component, which are responsible for acquiring or sending data from external intelligent units and the local database, respectively. [align=center] Figure 3 Integrated Automation Software Block Diagram[/align] The PLC software design mainly involves operating the gate according to the gate control procedures after the monitoring center provides the gate's monitoring parameters. The PLC communicates with the gate monitoring center computer in a point-to-point manner. The PLC first performs initialization settings. When the PLC receives data, it enters the receive interrupt subroutine, first determining whether the data is intended for this PLC, then executing the procedure and sending a response message to the gate monitoring center computer. During gate operation, the PLC monitors the start-up and running current of the hoist, the gate's speed and direction, etc. If any abnormality is detected, operation is stopped and an alarm is triggered. 4. Conclusion This system applies fieldbus technology to hydropower station gate control, achieving real-time monitoring, local and remote gate control, and water level control. The system boasts advantages such as simplified wiring structure, low cost, good maintainability, high speed, and stable reliability. Furthermore, its modular design ensures easy upgrades, compatibility, and networking capabilities, making the system open, interchangeable, and easy to upgrade, expand, and interconnect. In the technical renovation of newly built and existing hydropower stations in China, this system provides a more rational, effective, and reliable solution for gate engineering construction and management. References [1] Jiang Yuanguang. Design and research of automated monitoring system for sluice gates. Hohai University, 2002.1 [2] Wang Honglei. Application and implementation of CAN bus technology in control system. Guizhou University of Technology, 2003.6 [3] Gu Yan, Xu Lizhong, Sun Baoping et al. Distributed gate monitoring system with fieldbus. Automation and Instrumentation, 2000.5 [4] Chen Mingke. Distributed data acquisition system based on MCGS software development platform. Dalian University of Technology, 2002.3