1. Introduction A Programmable Logic Controller (PLC) is a new type of industrial control device based on a microprocessor, integrating computer technology, communication technology, and automatic control technology. It emerged in the 1960s and continues to experience rapid development. It boasts advantages such as small size, rich functionality, flexible configuration, adaptability to harsh environments, strong anti-interference capabilities, high reliability, convenient programming, and low cost, making it widely used in automatic control of various industrial processes in power, machinery, metallurgy, chemical, and textile industries. It can not only replace traditional relay control systems but also form complex process control networks. Fieldbus technology, developed in the late 1980s, is currently a hot topic in the field of automation and represents the development direction of next-generation control systems. It integrates digital communication technology, computer technology, automatic control technology, network technology, and intelligent instruments, fundamentally breaking through the limitations of traditional point-to-point analog or digital-to-analog signal control, forming a fully distributed, fully digital, multi-variable, and multi-node communication and control system. Fieldbus is a digital, bidirectional, multi-branch communication network that connects field intelligent devices and automated control equipment. Its foundation is digital intelligent field devices. Digital intelligent field devices scattered in various fields are connected together through the fieldbus and together with the controllers and monitors in the control room, they form a fieldbus control system (FCS). Fieldbus technology actually uses serial data transmission and connection methods to replace the traditional parallel signal transmission and connection methods. It realizes data transmission between the control layer and the fieldbus device layer in sequence, while ensuring the reliability and openness of information while ensuring the real-time transmission. A typical fieldbus has the following characteristics: (1) simple wiring; (2) openness; (3) real-time performance; (4) reliability; (5) efficient diagnostics; (6) flexible hardware. At present, there are many kinds of fieldbuses in the world, and a unified international standard has not yet been established. Among them, those with strong capabilities and influence include: FF (Foundation Fieldbus), HART (Highway Addressable Remote Transducer), CAN (Controller Area Network), Profibus (Process Fieldbus), INTERBUS, LonWorks (Local Operating Network), WorldFIP, MODBus, DeviceNet, ControlNet, and ASi (Actuator Sensor Interface). Electrical control systems based on PPC industrial computers, PLCs, and fieldbuses are widely used in industrial automation fields such as metallurgy, power, petrochemicals, mining, cement, water treatment, dairy and beverage, beer bottling, tobacco processing, machinery assembly, and product packaging. However, they are not yet widely used in electrical control systems for large-scale railway track maintenance machinery. This paper proposes a design scheme for an electrical control system for large-scale railway track maintenance machinery based on PPC industrial computers, PLCs, and INTERBUS fieldbuses, based on the characteristics of such control systems. 2. Current Situation Mechanized track maintenance is a crucial technical means to modernize railway maintenance and ensure uninterrupted railway transportation and safe train operation. To adapt to the technological development requirements of high-speed, heavy-haul, and heavy-duty railways, developed countries have successively adopted large-scale track maintenance machinery for railway line maintenance. By the late 1980s, a pattern had been basically formed where large-scale track maintenance machinery was the primary means of operation. At this time, however, China was still relying on manual labor, small machinery, and non-standard self-made equipment for line maintenance, resulting in poor work quality and low efficiency. This was particularly evident on busy trunk lines, where the contradiction between line maintenance and operation was especially prominent. In the early 1980s, China introduced advanced large-scale track maintenance machinery manufacturing technology from the Austrian company Plasser-Taylor, establishing a development path for large-scale track maintenance machinery that involved "technology introduction—digestion and absorption—domestic production—development and innovation." Through more than 20 years of technology introduction and domestic production, we have learned advanced technologies from foreign large-scale track maintenance machinery, updated traditional design concepts, broadened development ideas, and enhanced our ability to develop products with independent intellectual property rights. With the rapid development of railways and intensified market competition, accelerating the introduction, digestion, and absorption of advanced foreign technologies for large-scale track maintenance machinery, speeding up the research and development of products with independent intellectual property rights, accelerating the development of new products, developing core technologies, and striving for innovation and transcendence have become the top priorities and cannot be delayed. Large-scale railway track maintenance machinery is a specialized railway machine integrating mechanical, hydraulic, pneumatic, electrical, computer, and laser technologies. Functionally, it includes the following series: rail cleaning machines, tamping machines, ballast distribution machines, stabilization machines, rail grinding machines, rail flaw detection machines, track inspection machines, overhead line erecting machines, rail welding machines, and turnout replacement units. The essential difference between the electrical control systems of different types of large-scale railway track maintenance machinery lies in the operation monitoring and control system. To date, the technology of my country's large-scale railway maintenance machinery, such as ballast cleaning machines, tamping machines, ballast distribution machines, and stabilizing machines, has been mainly developed based on the introduction, digestion, and absorption of the technology of large-scale railway maintenance machinery from the Austrian company Plasser-Taylor. It belongs to the analog centralized control system, which mainly consists of the following subsystems: (1) vehicle power supply subsystem; (2) diesel engine monitoring and control subsystem; (3) high-speed running monitoring and control subsystem; (4) operation monitoring and control subsystem; (5) auxiliary equipment subsystem: including lighting, communication, heating, and air conditioning. Among them, the operation monitoring and control subsystem is the core of the electrical control system of various large-scale railway maintenance machinery. It completes the monitoring of the status of the operating mechanism and the control of the operation mechanism's actions. The complexity of the operation monitoring and control system of large-scale railway maintenance machinery with different functions varies greatly. For example, the operation monitoring and control system of ballast cleaning machines and ballast distribution machines is relatively simple. However, the operation monitoring and control subsystems of tamping machines, stabilizing machines, rail grinding machines, rail flaw detection machines, track inspection machines, and overhead line machines are more complex. The following is an introduction to the operation monitoring and control subsystem of the stabilizer car, which consists of the following parts: (1) Computer control part: consisting of upper computer control board, keyboard and display; (2) Program control part: consisting of microcomputer system consisting of lower computer control board, I/O board and power output board; (3) Analog quantity control part: consisting of A/D conversion board, D/A conversion board, frequency measurement board and various functional analog control boards; (4) Measurement part: consisting of left and right leveling sensors, acceleration sensor, vibration frequency sensor, etc.; (5) Track parameter recording part: consisting of recorder, front and rear electronic pendulum, versine sensor, measuring wheel, etc. The characteristics of the Prass-Taylor analog centralized control system are as follows: (1) The monitoring part of each subsystem uses analog instruments or digital displays or indicators and alarm lights; (2) The control part of the operation monitoring and control subsystem of complex models uses plug-in analog circuit boards and microcomputer systems composed of plug-in circuit boards; (3) The wiring method of each I/O signal in the operation monitoring and control subsystem is the traditional wiring method of "terminal (switch, sensor/solenoid valve, relay) - operation main control cabinet" or "terminal element (switch, sensor/solenoid valve, relay) - intermediate transition box - multi-core cable - operation main control cabinet" (as shown in Figure 1); (4) The track parameter recording system is an independent system and has no communication and data exchange with the microcomputer and computer system. [align=center] Figure 1: Traditional Wiring Method[/align] The Prass-Taylor analog centralized control system has the following shortcomings: (1) The installation positions of monitoring instruments, indicators and alarm lights are scattered; the analog instrument signals are only used for display and do not enter the process control; (2) The vibration resistance, impact resistance and dust resistance of the plug-in circuit board are not good; the adjustment of the analog circuit board (such as calibration) is completed by multiple potentiometers, which is relatively complicated; the analog quantity is used in the control system to convert and transmit the transmission and control signals, which has poor accuracy and is greatly affected by interference signals, so the control effect and system stability of the entire control system are poor; (3) The centralized control mode makes the main control cabinet of the operation larger in size; the traditional wiring method of I/O signals makes a large number of connecting cables in the main control cabinet of the operation, which increases the number of breakpoints and contacts and thus increases the number of fault points, making inspection and maintenance complicated. 3 System Requirements In view of the shortcomings listed above, it is necessary to design a new electrical control system that meets the following requirements. 3.1 Basic Requirements The new electrical control system for large-scale railway maintenance machinery should have unified display, indication, and alarm functions, process control capabilities, high reliability and stability, good vibration resistance, impact resistance, dustproof performance, and the ability to withstand high temperature and high humidity environments. 3.2 Specific Requirements The new electrical control system for large-scale railway maintenance machinery mainly involves redesigning the diesel engine monitoring and control subsystem, the high-speed running monitoring and control subsystem, and the operation monitoring and control subsystem. The vehicle power supply subsystem and auxiliary equipment subsystem are simple point-to-point controls and do not require redesign. The various input and output signals of these three subsystems are described in detail below. 3.2.1 Diesel Engine Monitoring and Control Subsystem 3.2.1.1 Diesel Engine Monitoring Section Input DI Signals: Oil pressure switch signal, cylinder head temperature (water temperature) switch signal, air filter switch signal, DC generator power generation status switch signal, etc.; Input AI Signals: Speed ​​sensor signal, oil pressure sensor signal, cylinder head temperature (water temperature) sensor signal, battery voltage signal, diesel fuel level sensor signal, etc.; Output DO Signals: Preheating indication signal, etc.; 3.2.1.2 Diesel Engine Control Section Input DI Signals: Idle speed position sensor switch signal, high-speed travel position sensor switch signal, operating position sensor switch signal, etc. Output DO signals: throttle motor drive signals, etc.; 3.2.2 High-speed travel monitoring and control subsystem (hydrostatic transmission mode) 3.2.2.1 High-speed travel monitoring section input DI signals: engagement/disengagement sensor signals for each axle, etc.; Input AI signals: speed-mileage sensor signals, etc.; 3.2.2.2 High-speed travel control section input DI signals: gear engagement switch signal, jog engagement switch signal, forward/reverse travel switch signal, travel handle position signal, etc. Input AI signals: travel handle potentiometer signal, etc. Output DO signals: forward/reverse valve drive signals, gear engagement valve drive signals, etc. Output AO signals: travel pump proportional valve drive signals, etc. 3.2.3 Operation Monitoring and Control Subsystem (Taking the New Stabilizer Vehicle as an Example) Input DI Signals: 125 signals from various switches, limit switches, and inductive switches; Input AI Signals: 7 signals from left and right leveling sensors, front and rear electronic pendulums, versine sensor, measuring wheel, acceleration sensor, and vibration frequency sensor; Output DO Signals: 82 signals from various switch and solenoid valve drive signals; Output AO Signals: 4 signals from proportional solenoid valve drive signals. 4 System Design 4.1 Introduction to INTERBUS Fieldbus INTERBUS Fieldbus was launched in 1984, and its main technology developer was Phoenix Contact in Germany. INTERBUS Fieldbus adopts a very unique lumped frame transmission protocol, with an effective data transmission rate of up to 52%, and powerful fault diagnosis capabilities; it uses twisted-pair cable with no repeater, achieving a transmission distance of up to 12.8 kilometers; a single master station can connect up to 255 slave stations; the time to scan 8192 I/O points is only 7.8 milliseconds (500Kbps). Due to its rapid development and widespread use, INTERBUS has become the standard fieldbus specified in DIN 19258 (German standard), EN 50254 (European standard), IEC 61158 (international standard), and JB/T 10308.8 (Chinese mechanical industry standard). INTERBUS has over 1000 bus device manufacturers worldwide, offering up to 2500 products. To date, INTERBUS fieldbus has been installed at over 7.5 million nodes worldwide, ranking second among various fieldbuses. Today, as a pioneer in fieldbus, PC-based, and industrial Ethernet technologies, Phoenix Contact has also proposed the new automation solution of Fieldbus+Ethernet, constructing a comprehensive industrial enterprise management and control network. The INTERBUS bus includes remote bus networks and local bus networks; both networks transmit the same signals but at different voltage levels. The remote bus network is used for long-distance data transmission, employing RS-485 transmission. The remote network uses full-duplex communication with a communication rate of 500kb/s. The local bus network connects to a remote network, and the BK module on the bus terminal (BT) on the network is responsible for converting remote network data into local network data. The main devices on the INTERBUS bus include the BK module on the bus terminal (BT), I/O modules, and the bus control board installed in a host device such as a PC or PLC. The bus control board is the master device on the INTERBUS bus, used to implement protocol control, error diagnosis, configuration storage, and other functions. The I/O module realizes the reception and data transmission between the bus control board and sensors/actuators, and can handle all standard signals from the machinery manufacturing and process industries. INTERBUS is mainly used in the automotive, paper, tobacco, printing, warehousing, shipbuilding, food, metallurgy, timber, textile, and chemical industries. 80% of the body shops and welding workshops in the European automotive industry use INTERBUS control systems. The Passat production line at Shanghai Volkswagen, the Audi A6 production line at FAW-Volkswagen, and the new production line at the Hongta Group Yuxi Cigarette Factory have all fully adopted INTERBUS as their control solution. 4.2 System Network Structure Based on the characteristics of the railway large track maintenance machinery control system, the system network structure of the railway large track maintenance machinery control system based on PPC industrial control computer, PLC and INTERBUS fieldbus is shown in Figure 2. It is divided into two layers: monitoring layer and field control layer. 4.2.1 Monitoring Layer The monitoring layer consists of high-speed Ethernet, PPC industrial control computer, TP touch screen display and printer connected to PPC. The monitoring layer mainly performs the following functions: (1) Display of diesel engine speed, oil pressure, cylinder head temperature (water temperature), battery voltage and diesel oil level in the diesel engine monitoring and control subsystem; alarm indication of low oil pressure, high cylinder head temperature (water temperature), air filter blockage status and DC generator power generation status; preheating indication; idle position, high speed travel position and working position indication, etc. (2) Display of speed-mileage and engagement/disengagement status of each axle in the high-speed travel monitoring and control subsystem (hydrostatic transmission mode); display of engagement switch, jog engagement switch, forward and backward travel switch, travel handle potentiometer, and travel handle position. (3) Display of various switches, various limit switches and induction switches of the working mechanism in the operation monitoring and control subsystem (taking the new stable vehicle as an example); display of left and right leveling sensor signals, front and rear electronic swing signals, versine sensor signals, acceleration sensor signals, vibration frequency sensor signals, and working speed. (4) Setting of system parameters. (5) System fault diagnosis. (6) Recording and printing of track parameters. 4.2.2 Field control layer The field control layer consists of four parts: master station (PLC controller, bus branch module, local I/O), fieldbus, slave station (bus coupler BK, remote I/O), and field equipment. The master station is installed in the work room, and the number of slave stations depends on actual needs. They are distributed in different positions on the vehicle body. The field control layer mainly performs the following functions: (1) acquisition of various input signals; (2) output of various control signals; (3) processing of various signals; (4) communication with the monitoring layer. [align=center] Figure 2: Railway large track maintenance machinery control system based on PPC, PLC and INTERBUS[/align] 4.3 System hardware configuration This system is based on the automation products of Phoenix Contact. The main configuration is as follows: PPC industrial computer: PPC 5115 TP touch screen display: TP 15T PLC controller: ILC 370 ETH 2TX-IB, with 2 Ethernet ports and 1 RS232 port. Bus branch module: IBS IL 24 RB-T-PAC; Bus coupler BK: IBS IL 24 BK-T/U-PAC; Various Inline I/O modules: IB IL 24 DI 16-NPN-PAC, IB IL 24 DI 2-NPN-PAC, IB IL 24 DI 32/HD-NPN-PAC, IB IL 24 DI 4-PAC, IB IL 24 DO 2-2A-PAC, IB IL 24 DO 2-NPN-PAC, IB IL 24 DO 32/HD-NPN-PAC, IB IL 24 DO 4-PAC, IB IL 24 DO 8-NPN-PAC, IB IL 24 TEMP 2 RTD-PAC, IB IL AI 2/SF-PAC, IB IL AO 2/U/BP-PAC, IB IL CNT-PAC, etc. 4.4 System Software Configuration The system software configuration includes a Windows NT operating system, IBS OPC SERVER, Diag+ fault diagnosis software, track parameter recording and printing program, upper-level computer monitoring software Visu+, and lower-level computer programming software PC WORX 5. 4.4.1 Upper-Level Computer Monitoring Software This system uses Visu+ as the upper-level monitoring software. For process configuration, all Phoenix Contact HMI devices use the powerful configuration software Visu+. In addition to full SCADA functions (e.g., operation and monitoring, trend charts, alarm information, etc.), it also provides features such as data acquisition, recording, recipe management, database connection, and Enterprise Resource Planning (ERP) system connection. The Visu+ software's development interface is clearly designed, intuitive to operate, and all configuration screen elements can be easily implemented through mouse clicks or drag-and-drop. 4.4.2 IBS OPC SERVER Software OPC is suitable for a visual standard operating phase interface. Through the INTERBUS OPC server, this interface can be used in INTERBUS master stations and PC WORX programming control systems, PC interfaces, and embedded solutions. In this way, it can be easily connected to visualization software using OPC clients, such as Genesis 32, Visu+, etc. 4.4.3 Diag+ Fault Diagnosis Software INTERBUS provides comprehensive diagnostic functions with ease of use, and the Diag+ software tool fully supports these functions. Diag+ enables simple yet comprehensive diagnostics, as well as basic INTERBUS functions. Diag+ can operate as a standalone diagnostic tool or as an ActiveX component integrating INTERBUS diagnostics into the visualization software of devices and systems. The graphical design allows for low-resolution display of diagnostic functions, making it suitable for small handheld diagnostic devices. These diagnostics can be performed through any interface on the INTERBUS master station (Ethernet, V.24, and ISA/PCI bus). Thus, through a single INTERBUS master station, diagnostics can be performed on every control system in the control system network from any location. This means that INTERBUS system diagnostics become simpler and more versatile. 4.4.4 Lower-Level Programming Software Configuration This system uses PC WORX 5 as the lower-level programming software. PC WORX 5 provides a modern development tool for the control system. When PC WORX 5 is connected to a fieldbus-based control system, it not only provides convenient programming tools conforming to IEC 61131-3 and IEC 61131-5 standards, but also facilitates INTERBUS configuration. PC WORX 5 also includes simple INTERBUS diagnostics. 4.4.5 Track Parameter Recording and Printing Program The track parameter recording and printing program is a dedicated program developed to realize the functions of traditional recorders in the electrical control system of large railway maintenance machinery. It can record, query, analyze, and print track parameters. 5 Conclusion In today's era of rapid scientific and technological development, various new technologies, new products, and new control concepts are constantly emerging. The design concept of the electrical control system of large railway maintenance machinery should also keep pace with technological development, adopting new design concepts and the world's most advanced control technologies. In the past, bus systems have been successfully applied in the electrical control systems of large-scale railway maintenance machinery. For example, the CEM 100 gantry crane manufactured by Plasser-Taylor uses a complete RS-485 industrial bus control system; the CMG-16 turnout grinding machine uses a control system based on RS-485 industrial bus combined with Profibus-DP fieldbus; the CPH turnout replacement unit uses a "one-to-many" control system consisting of a wireless transmitter, wireless receiver, CANBUS bus, and PLC; and a program control system composed of PLC and local I/O has been successfully used on the D0832 tamping machine after more than six months of testing. Currently, industrial computer technology, PLC technology, fieldbus technology, and network technology have all experienced significant development and widespread application. This paper proposes an electrical control system for large-scale railway maintenance machinery based on a PPC industrial computer, PLC, and INTERBUS fieldbus. It integrates diesel engine monitoring and control, high-speed travel monitoring and control, and operation monitoring and control, achieving centralized monitoring, centralized processing, and distributed control. This represents a new design and attempt in the application of large-scale railway maintenance machinery. It is applied to the worst working condition of the stable car, and will comprehensively test the various indicators of the system: reliability, stability, shock resistance, ability to withstand high temperature and high humidity, especially the ability to resist frequency vibration. If the application of this control system on the new stable car is successful, then its design concept and method will be fully promoted and used in railway large track maintenance machinery; as a design concept and method that is completely different from the electrical control system of the large track maintenance machinery products of Plasser-Taylor Company, it will become a new model and direction for the development of new products with independent intellectual property rights in the future. References [1] Yuan Renguang. Programmable Logic Controller Application Technology and Examples [M]. Guangzhou: South China University of Technology Press, 2001. [2] Yang Xianhui. Fieldbus Technology and Its Application [M]. Beijing: Tsinghua University Press, 1999. About the author: Qiu Xuefei, male, Han nationality, born in February 1976, from Xuanwei, engineer, has been engaged in the electrical system design of railway large track maintenance machinery products for five years. Contact Address: No. 384, Jinma Town, Guandu District, Kunming, Yunnan Province, China. Postcode: 650215. Contact Number: 0871-3920888 ext. 71109, 15925202983