Abstract: This paper systematically introduces the generation and damage of stray current and the method of connecting an embedded TCP/IP protocol microcontroller system to the Internet. A stray current monitoring system based on an embedded TCP/IP protocol microcontroller is constructed, and the communication error rate and testing accuracy of the entire system are experimentally verified. The results show that the system performs well in stray current monitoring and has advantages such as high reliability and low cost. Keywords: TCP/IP protocol microcontroller, stray current, monitoring 1 Introduction TCP/IP (Transmission Control Protocol/Internet Protocol) is the standard for the fundamental communication protocol of the Internet/Intranet today. TCP is responsible for controlling data flow and ensuring the accuracy of transmission; IP is responsible for transmitting data from one place to another. With the increasing development of the Internet, more and more microcontroller systems require the ability to communicate via the Internet. However, the TCP/IP protocol that supports the normal operation of the Internet is a large and complex protocol family. Due to its own resource and operating speed limitations, it is neither possible nor necessary to fully implement all the functions required by the TCP/IP protocol in ordinary microcontroller systems. At present, there are two major trends in the integration of microcontroller communication and the Internet. First, based on the needs of the microcontroller system itself, certain protocols in the TCP/IP protocol suite are selectively implemented; second, certain advanced concepts and technologies in the TCP/IP protocol are utilized in the microcontroller communication system to improve the communication efficiency and reliability of the microcontroller. The Internet has now become one of the major basic information infrastructures, closely integrated with people's lives, and is the main medium for people to transmit and share information over long distances. Meanwhile, microcontrollers or microcontroller units (MCUs), commonly known as embedded systems, have been used in various fields of homes and industries. 2. The Occurrence and Harm of Stray Currents Metro stray current, also known as metro stray current, mainly refers to the current leaked into the track bed and surrounding soil medium by metro trains using DC-powered traction systems during underground railway operation. The Beijing, Tianjin, Shanghai, Guangzhou, and Hong Kong metro systems all use DC-powered transit systems. In this power supply method, the train's DC traction system uses a positive terminal connected to the contact network, with the running rail also serving as the negative return line. In the early stages of subway construction and operation, the insulation between the running rails and the track bed is relatively high, meaning the rail-to-ground transition resistance is large, and stray currents leaking from the running rails into the soil are minimal. However, as the subway operates, unavoidable pollution, humidity, seepage, leakage, and high ground stress cause the rail-to-ground insulation performance in subway stations and tunnel sections to decrease or the initial protective measures to fail, inevitably increasing stray currents leaking from the running rails into the soil. Subway stray currents primarily cause electrochemical degradation of buried metal pipes, communication cable sheaths, and the reinforcing steel in the main structures of stations and tunnels surrounding the subway. This not only shortens the service life of metal pipes and lines but also reduces the strength and durability of the subway's reinforced concrete structure, even leading to catastrophic accidents. In my country, subways are rapidly developing as a major urban transportation tool. Besides the subways in Beijing, Shanghai, Hong Kong, Tianjin, and Guangzhou already in operation, the Shenzhen and Nanjing subways are currently under construction. Because subways are complex underground engineering projects, their structure is largely finalized after construction. After several years of operation, it is extremely difficult to replace or renovate the main structure due to stray current degradation. Therefore, the monitoring and protection of stray current in subways has significant practical implications. In this paper, based on the current mature construction of subway local area networks, the author conducts an in-depth and detailed study on the monitoring methods and technologies of stray current in subway engineering. Utilizing existing local area networks, a stray current monitoring system based on embedded TCP/IP protocol is developed to realize the monitoring and prediction of stray current in subways. 3 Design of the Stray Current Monitoring System Based on Embedded TCP/IP Protocol 3.1 System Function Description The "Technical Specification for Protection Against Stray Current Degradation in Subways" (CJJ49-92) stipulates that "voltage measurements of subway return systems, tunnel main structures, etc., should be carried out under normal subway operating conditions." That is, it is necessary to measure the positive offset value of the polarization voltage of the structural steel reinforcement (CJJ49-92 stipulates that the average offset value shall not exceed 0.5V) and the voltage change between the running rail and the structural steel reinforcement. Therefore, a comprehensive stray current monitoring system must be designed to monitor whether the main structural steel reinforcement is affected by stray current degradation, so that timely measures can be taken when problems occur to ensure the safety of the main structure of the rail transit and surrounding facilities. This monitoring system uses sensors near monitoring points along the urban rail transit line to promptly convert the collected polarization potential (analog quantity) of the main structural steel reinforcement and the potential of the rail (return rail) relative to the main structural steel reinforcement into digital quantities via short-distance transmission (less than 10m), avoiding errors caused by long-distance analog transmission. The microcomputer system is installed in the monitoring room of the station. The microcomputer and the converter transmit data using local area network infrastructure, transmitting sensor signals to the microcomputer acquisition system according to a specific time sequence to ensure the accuracy of the read data. This monitoring device mainly monitors the following two parameters: ① Polarization potential – the average value of the potential of a structural steel reinforcement relative to a reference electrode stored by each sensor every 30 minutes; ② Rail potential – the potential signal of the rail relative to the structural steel reinforcement stored by the sensor every minute during locomotive operation. All this data is stored on the monitoring device, can be displayed at any time, and is also memorized. Simultaneously, the data from each station monitoring device can be transmitted to the microcomputer via network communication and printed out. 3.2 System Composition The system composition is shown in Figure 1. It utilizes the most commonly used 8-bit microcontroller, embeds the TCP/IP protocol, and connects the sensors using a standard RS485 interface, enabling all sensors to connect to the local area network (LAN), and further connect to the Internet. The advantages of this system are low cost and simpler interface compared to other embedded equipment, facilitating connection with existing terminal equipment. It also facilitates networking using existing LANs and offers relatively fast transmission speed. [align=center] Figure 1 System Composition Block Diagram[/align] 3.3 Method of Connecting Embedded TCP/IP Protocol Microcontroller System to the Internet [align=center] Figure 2 Method of Connecting Embedded TCP/IP Protocol Microcontroller to the Network[/align] To connect the microcontroller system to the Internet, two preparations are required: ① In terms of hardware, a network interface must be added to the system's main controller—the microcontroller; ② In terms of software, the corresponding communication protocol must be provided. When a system is equipped with an Ethernet card chip and provides TCP/IP and IEEE 802.3 protocols, it can access the Internet via a local area network (LAN). Similarly, if a system is equipped with a DTE/DCE interface device that supports TCP/IP and PPP protocols, it can access the Internet via a modem; if a system is equipped with a network interface (RF) with wireless transceiver capabilities and supports TCP/IP and IEEE 802.11 series protocols, it can also access the Internet wirelessly. Therefore, the key to connecting a microcontroller system to the Internet is how to implement the network interface and provide the corresponding network protocols. The network interface is implemented using a NIC (Network Controller/NIC), and the microcontroller provides the other necessary protocols. In this system, the CPU processor is an Atmel AT89C58 8-bit microcontroller and an RTL8019AS chip. The RTL8019AS is an Ethernet NIC designed according to the IEEE 802.3 MAC layer (Media Access Control) protocol standard. In addition to receiving and transmitting serial data from the physical medium, it also has MAC layer control functions, such as CRC verification of MAC frames and checking input data according to the corresponding verification method. Its internal protocol logic array can implement the IEEE 802.3 protocol, including CSMA/CD protocol (carrier sense multiple access control with collision detection) for collision random backoff, framing (adding frame headers), deframing (removing frame headers), and receiving synchronization. As for higher-level protocols, such as the network layer IP protocol, ARP protocol, ICMP protocol, transport layer UDP protocol, TCP protocol, application layer PPP protocol, FTP protocol, etc., these are implemented by the main controller running the protocol code stored in the system extended ROM. 4 Experimental Verification of the Monitoring System 4.1 Communication Reliability Verification To verify the communication reliability of this system, two communication adapters, 30 intelligent sensors, and upper computer acquisition software were designed, with the communication baud rate set to 9600kbps. The host computer sequentially requests data from each smart sensor. The smart sensors send different data according to different commands. Through long-term testing, the communication error rate is 0, demonstrating the high reliability of this network communication mode. 4.2 Verification of Smart Sensor Testing Accuracy To test the accuracy of the smart sensors, a scale-adjustable signal source was added to the sensor input. The measurement accuracy was confirmed by comparing the signal measured at the sensor input terminal with the signal acquired and displayed by the host computer (U2). The measurement accuracy calculation formula is: All 30 designed smart sensors were tested one by one. The test results showed a measurement accuracy of 0.5%, which meets the accuracy requirements for on-site testing. 5 Conclusion This system fully utilizes the subway network resources, achieving online monitoring of stray current degradation factor parameters without the need to lay communication cables along the subway line. It changes the traditional decentralized acquisition mode, adopting a centralized monitoring method, reducing the workload of daily testing. Currently, this system is in use in the subway, greatly improving the quality and efficiency of maintenance management. References: [1] Wang Yuanyuan. Discussion and research on stray current “source treatment” method, Urban Rail Transit Research, 2001.1:42～45 [2] Wang Yuanyuan. Research on stray current regional protection [J]. Railway Standard Design, 2002 (6):84～85 [3] Zhao Yu, Li Wei. Design and application of stray current real-time monitoring system of Guangzhou Metro. Urban Rail Transit Research, 2001.1:63～65 [4] Technical Specification for Stray Current Degradation Protection of Metro (CJJ49-92). Beijing, China Planning Press, 1993 [5] Zhou Xiaojun, Gao Bo. Experimental study on the degradation of steel bars in reinforced concrete by stray current in metro. Journal of Railway Engineering, VOL.21 NO.5 1999 12～24 [6] Lü Jingjian. 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