Abstract: Addressing the challenges of complex operating environments, high failure rates, and numerous influencing parameters in submersible motors, this paper introduces a design scheme for a distributed monitoring system for submersible motors based on a CAN bus. The hardware circuitry, software initialization program, and communication flow of the intelligent monitoring nodes are presented. System testing and actual operation demonstrate that the system is easy to install and use, exhibits high reliability, meets design requirements, and possesses certain reference and promotional value. Keywords: CAN bus; distributed system; intelligent node; P87C591 Abstract: Countering the problems existing in the submersible motor, such as the complex condition of running, high malfunction ratio, many parameters influenced, this paper introduces the design of the distributed monitor system about the submersible motor based on CAN bus, and presents the hardware schematic circuits, software initial programs and communications flow of the intelligent monitor node. Practical use shows that this monitor system has the better control effect and is suitable for similar practical engineering. Keywords: CAN bus; distributed system; intelligent node; P87C591 1 Introduction Fieldbus control system (FCS) is a new type of control system after direct digital control (DDC) and distributed control system (DCS). It is a fully open, fully digital, multi-point communication low-level control network with a fully distributed control architecture [1]. Its significant feature is that it connects field devices into a network through an open bus. Each intelligent device can complete automatic control and self-diagnosis of its operating status, and can communicate with each other through the bus, thereby simplifying the system structure and improving reliability. CAN (Controller Area Network) bus, also known as Controller Area Network, is a serial communication network that effectively supports distributed control or real-time control. Due to its high performance, high reliability, unique design, and reasonable price, it is widely used in industrial field control, intelligent buildings, medical devices, transportation vehicles, and sensors, and has been recognized as one of the most promising fieldbuses. Traditional distributed control systems (DCS) have obvious limitations due to their closed system, large hardware investment, complex wiring, and inconvenient maintenance. This paper presents a design scheme for intelligent node hardware and software based on the CAN bus, applied to a distributed monitoring system for submersible motors. 2 System Overall Scheme Design [align=center] Figure 1 Overall Structure of Distributed Monitoring System[/align] The entire system consists of a monitoring computer, a PC-CAN adapter card, intelligent monitoring nodes (n<110), and a CAN bus network. Its system structure is shown in Figure 1. Distributed monitoring nodes on-site can independently perform intelligent control and protection of the motor; the monitoring computer can communicate in real time with each control node via a CAN bus network, thereby realizing decentralized control and centralized monitoring of the submersible pump unit. The control nodes in the monitoring system consist of a CAN controller, a CAN transceiver, and peripheral circuits (such as optocoupler isolation, I2C, LED displays, etc.). The monitoring computer can be a regular PC or an industrial IPC. A PC-CAN adapter card is used to perform protocol conversion between the CAN bus and the monitoring computer; a PCI bus adapter card, an ISA bus adapter card, or an RS232 serial communication adapter can be used. The control nodes are interconnected via shielded twisted-pair cables to form a CAN bus network. 120Ω impedance matching resistors are connected at both ends of the bus to improve system stability and enhance its anti-interference capability. 3. Hardware Design of the Monitoring Node Currently, there are two types of CAN bus devices available on the market: one is a microcontroller with integrated CAN, such as the P8XC591/2, 87C196CA/CB, and MC68376; the other is a standalone CAN controller, such as the Philips SJA1000, 82C200, Intel 82526, and Microchip MCP2510. However, standalone CAN controllers require an external microprocessor to operate. This design uses the Philips P87C591 microcontroller with an on-chip CAN controller, which greatly simplifies the node's hardware circuit design, reduces program complexity, and improves system reliability. 3.1 Composition of the Monitoring Node The monitoring node hardware circuit design adopts a modular structure, consisting of a microcontroller, CAN communication module, sensor components, data acquisition module, motor control module, LED display module, and field setting module. Its overall structure is shown in Figure 2. Depending on the specific situation, only some modules may be selected. For example: the display module and the field setting module can be removed, and the monitoring computer can be used to realize the functions of data display and parameter setting. When running in stand-alone mode, the CAN communication module can be omitted. [align=center] Figure 2 Block diagram of monitoring node[/align] 3.2 Functions of monitoring node The functions of each component of the monitoring node are as follows: (1) Sensor components: used to detect the operating status of the submersible motor, including: temperature sensor, current transformer, and liquid level sensor. They are used to detect the temperature of the three-phase stator of the motor, the three-phase main current, and the water level in the pump chamber, respectively. They can effectively monitor abnormal phenomena such as overcurrent, overheating, phase loss, short circuit, and leakage of the submersible motor. (2) Data acquisition module: converts the analog signals collected by the sensors into digital signals and sends them to the microcontroller through a multi-channel analog switch. The CPU obtains the motor stator temperature, current, and liquid level information, makes corresponding judgments, and sends them to different subroutines for corresponding processing. (3) Motor control module: When the CPU determines that any of the values ​​of the motor stator temperature, current, or liquid level exceeds the normal range, it will trigger the corresponding abnormal handling circuit through the SSR (zero-crossing triggered AC solid-state relay) to protect the motor. (4) LED display module: It adopts I2C bus-based display technology to display the stator temperature and current values ​​in real time through LED digital tubes during motor operation. It can also display the current value of the parameter to be set in the setting mode. When the motor stops abnormally, the LED can indicate the type of fault, which is convenient for inspection and handling. (5) CAN communication module: The CAN bus communication interface circuit is mainly composed of the on-chip CAN driver SJA1000 of P87C591, 6N137 high-speed optical isolator, and CAN transceiver PCA82C250. P87C591 completes the application layer function of the CAN protocol, and SJA1000 completes the physical layer and data link layer functions. PCA82C250 provides the function of differential transmission and reception of data on the bus, which effectively improves the anti-interference capability of the bus and realizes the functions of protecting the bus and reducing radio frequency interference. The 6N137 isolation control circuit and transceiver circuit can effectively suppress interference introduced by the bus, further improving the reliability of the system. (6) Field setting module: The 8255-based keyboard and the X25045-based E2PROM are used to realize the field setting of node working parameters. The X25045 stores information such as alarm current, shutdown current, alarm temperature, shutdown temperature, node address, baud rate, etc. These parameters can be set by the key. In addition to the node address, other parameters can also be set by the monitoring computer. 4 Software design of monitoring node 4.1 The overall structure of the software design is consistent with the node hardware design. The software design also follows the modular design principle, so that the control software has the advantages of being easy to read, easy to expand and easy to maintain. The corresponding software modules are written in C51 language to realize the various functions of the above monitoring node. The various functional modules of the software are interconnected through the input and output parameters, which are flexible and convenient to combine, reducing debugging time and shortening the development cycle. The software design process of the monitoring node is shown in Figure 3. [align=center]Figure 3 Flowchart of Monitoring Node Software Design[/align] 4.2 Monitoring Node Communication Program Design The communication of the monitoring node adopts the CAN bus 2.0A protocol. The software design of the communication module mainly consists of three parts: initialization program, sending program, and receiving program. Among them, the initialization program is the key to realizing communication. It is mainly used to select the working mode of the CAN controller, that is, to set the registers in the control section of the CAN controller in P87C591, including: setting the bus timing register and output control register; setting the receive acceptance filter register and filter mask register; setting the data frame type (standard frame or extended frame), identifier, and data length. The initialization process is completed in the CAN controller reset mode. The initialization program flowchart of the monitoring node communication is shown in Figure 4. [align=center]Figure 4 Flowchart of CAN Initialization Program[/align] Data exchange between the monitoring node and the CAN bus is realized through the sending program and the receiving program. The sending program flowchart is shown in Figure 5. As can be seen from Figure 5, each node of the system actively sends data to the monitoring computer using a timer interrupt. This takes advantage of the feature of the CAN bus that can communicate in a multi-master mode. Since real-time monitoring is performed by individual control nodes, and the monitoring computer is mainly used for management functions, a timed data upload method is adopted instead of real-time upload of all data collected by sensors, thus reducing the bus load. This is also an advantage of distributed control methods compared to centralized control methods. Figure 6 shows the receiving program flowchart. The receiving buffer is used to store data sent from the CAN bus. After the CPU reads the data, the receiving buffer is cleared, waiting to receive new data. [align=center] Figure 5 Sending program flowchart Figure 6 Receiving program flowchart[/align] 5 Conclusion The intelligent node of the distributed monitoring system based on the CAN bus designed in this paper, after field debugging, can handle overcurrent, overheating, short circuit, and leakage during the operation of the submersible motor, thus protecting the motor; the data communication between the node and the host computer is stable and reliable; the node parameters can be modified through the field setting module. Experiments show the applicability and reliability of the node. The technical solutions and implementation methods proposed in the development process can be promoted and applied in the design of field intelligent nodes in distributed monitoring systems and industrial underlying monitoring networks. The author's innovation lies in designing an intelligent monitoring node based on the P87C591, which adopts a modular structure in both software and hardware design, exhibiting high flexibility and wide applicability. References: [1] Yang Xianhui. Fieldbus Technology and Its Application [M]. Beijing: Tsinghua University Press, 1999. [2] Rao Yuntao, Zou Jijun, Zheng Yongyun. Fieldbus CAN Principle and Application Technology [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2003. [3] Yang Fei, Zheng Guilin. Design of Monitoring System Based on CAN Bus [J], Microcomputer Information (Embedded and SOC), Vol. 21, No. 7, 2005: 34-36 [4] Jiang Jianwen, Lin Yong, Han Jianghong. Analysis and Implementation of CAN Bus Communication Protocol [J], Computer Engineering, No. 2, 2002: 219-221 [5] Li Mao, Qin Tinghao, Yan Shixiao. 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