Abstract: This paper introduces a distributed submersible motor monitoring system based on CAN bus, analyzes the system's structure and implementation method, and briefly describes the communication process of the control node and CAN/RS232 interface. Keywords: CAN bus, submersible motor, distributed system, RS232 bus 1. Overview Submersible motors are an important component of submersible pumps, widely used in farmland irrigation, mine drainage, lake water conservancy, and other industrial and agricultural water supply and drainage fields. The complex working environment of submersible motors, coupled with the special manufacturing processes of some models, makes them more prone to failure than ordinary motors, such as overload, overheating, water seepage, leakage, short circuits, and phase loss. Currently, several domestic companies have developed intelligent electronic protection devices for individual submersible motors. While these devices can protect the motors, they lack centralized management capabilities and have significant limitations. This system, based on CAN fieldbus technology, achieves distributed monitoring and centralized management functions. The performance, structure, and implementation method of this system are discussed below from several aspects, including the system's hardware structure, the design of the monitoring computer software, and the system's communication process. 2. System Hardware Design 2.1 System Overall Structure As shown in Figure 1, this motor monitoring system consists of a monitoring computer located at the monitoring center, a CAN/RS232 conversion card, and control nodes located at the submersible motor's working site. The control nodes distributed at the site can independently monitor and protect the motor, while the monitoring center can communicate with each node via the CAN network to achieve centralized management. This forms a distributed monitoring structure integrating decentralized monitoring and centralized management. 2.2 Control Node Structure Figure 2 shows the control node structure. The hardware design adopts a modular structure, consisting of a microcontroller, communication module, sensor group, data acquisition module, high-voltage control module, and display module. Depending on the specific situation, only some modules can be selected. For example, the display module and field setting module can be removed, and the monitoring computer can be used to implement display and parameter setting functions. In stand-alone operation, the communication module is not required. The structure and function of each component are briefly described below. Sensor Group: Used to detect the motor's operating status, consisting of a platinum resistance temperature sensor, a current transformer, and an electrode-type liquid level sensor. These sensors are used to detect the temperature of the three-phase stator, the three-phase main current, and the water level inside the motor cavity, effectively monitoring abnormalities such as overcurrent, overtemperature, phase loss, short circuit, and leakage in submersible motors. The platinum resistance thermometer and electrode-type liquid level sensor have strong anti-interference capabilities and are suitable for operation in harsh environments. The data acquisition module, based on a 12-bit precision A/D converter and multiplexed analog switches, converts the analog signals acquired by the sensors into digital signals and sends them to the microcontroller. The high-voltage control module triggers the corresponding abnormality handling circuit when any of the stator temperature, liquid level, or current values ​​exceeds the normal range. The display module uses I2C bus-based display technology to show the current three-phase temperature and current values ​​of the motor stator. In setting mode, it displays the values ​​of the parameters to be set. The field setting module uses an 8255-based keyboard and an X25045-based E2PROM to enable on-site setting of operating parameters. The X25045 stores information such as alarm current, shutdown current, alarm temperature, shutdown temperature, and station address. These parameters can all be set via the keyboard. Besides the station address, other parameters can also be set through the monitoring computer. Additionally, the X25045 acts as a watchdog timer, resetting the system after a timeout period when a system fault occurs. The X25045 low VCC detection circuit protects the system from low voltage conditions. 2.3 CAN/RS232 Interface Card Structure Figure 3 shows the structure of the CAN/RS232 interface card, enabling communication between the monitoring host and the CAN network. It converts data sent from the control node into RS232 protocol format and sends it to the host, and converts data sent from the host into CAN protocol format and sends it to the control node. 3. Design of Monitoring Computer System Software The computer system software performs management functions for the entire system and some monitoring functions. It uses MFC window programming based on VC++ and the RS232 serial communication protocol based on API, providing an intuitive and easy-to-understand graphical interface. The implemented functions include: 1. Displaying the working status of each node; 2. Broadcasting settings for the working parameters of all nodes, and also setting parameters for a specific node; 3. Providing error references when a motor malfunctions, facilitating maintenance; 4. Automatically detecting newly added or removed pump stations during operation; 5. Recording the day's work status into a file named by date for easy management. 4. System Communication Flow 4.1 CAN Bus Overview The CAN fieldbus is an open real-time system with a three-layer network structure—physical layer, data link layer, and application layer. The CAN bus transmits information in message units and can use a multi-master approach, allowing any node on the network to actively send information. It abandons traditional address encoding and uses communication data blocks for encoding. A powerful bus arbitration function ensures reliable data transmission and avoids bus conflicts. The CAN bus has good reliability, real-time performance, and anti-interference capabilities. At a communication rate of 5Kbps, the theoretical communication distance can reach 10,000 meters. Due to these advantages, CAN has been widely used in measurement and control systems. 4.2 Brief Description of the Communication Flow of the Control Node The CAN bus communication hardware interface circuit of this system mainly consists of an 89C52 microcontroller, an SJA1000 CAN controller, a 6N137 high-speed optical isolator, and an 82C250 CAN transceiver (see Figure 3). The 89C52 completes the application layer functions of the CAN protocol, while the SJA1000 completes the physical layer and data link layer functions. The 82C250 provides differential data transmission and reception functions for the bus, effectively improving the bus's anti-interference capability and realizing functions such as bus protection and reduction of radio frequency interference. The 6N137 isolation control circuit and transceiver circuit further improve the system's anti-interference capability. The communication medium is shielded twisted-pair cable, and a 120Ω resistor must be added at both network terminals for line matching. In this system, the CAN bus communication software is written in C51 language and uses the CAN2.0A protocol, mainly consisting of three parts: initialization, data transmission, and data reception. The initialization section is crucial for communication, and its main steps are: entering reset mode -> initializing the Acceptance Code Register (ACR), Mask Code Register (AMR), Bus Timing Register (BTR), and Output Control Register (OCR) -> clearing reset mode -> initializing the control register and command register. ACR, AMR, BTR, and OCR can only be accessed in reset mode. The data transmission and reception sections are written according to specific requirements. The communication flow of the control nodes is shown in Figure 4. Figure 4 shows that the system uses a method where each node actively sends data to the monitoring computer at regular intervals. This utilizes the multi-master communication feature of the CAN bus. Since real-time monitoring is performed by each control node, and the monitoring computer mainly performs management functions, a method of periodically uploading data is used instead of uploading all data collected by sensors in real time, thus reducing the bus load. This is also an advantage of distributed control methods compared to centralized control methods. 4.3 Brief Description of CAN/RS232 Communication Flow Figure 5 shows a simplified communication flow of the CAN/RS232 conversion card. The above communication flow quickly and accurately realizes the conversion between the CAN bus protocol and the RS232 protocol. 5. Conclusion After on-site debugging, this system maintained data reliability over a transmission distance of 1500 meters at a transmission rate of 20kHz. It effectively achieved the monitoring and management functions of the submersible motor. Experiments demonstrate that the CAN bus has superior performance and is a mature technology with broad application prospects.