Abstract: This paper takes a glass batching production line as an example to introduce fieldbus technology and fieldbus control system (FCS). The overall structure and working principle of the PROFIBUS-based control system are discussed. The stable operation of this control system demonstrates the broad application prospects of fieldbus technology in the industrial control field. Keywords: Fieldbus technology, Fieldbus control system, Glass batching, PROFIBUS 1 Introduction Raw material batching is the core of the glass production process. Scientific proportioning and precise metering of raw materials are the primary conditions for ensuring glass quality, and the design of the batching control system is crucial to the quality of the batching process. Currently, most glass production lines in China use distributed control systems (DCS), which are mostly analog-digital hybrid systems and have not yet formed a complete network from measurement and control equipment to the operation control computer, resulting in significant technical limitations. Due to the use of single signal transmission, reliability and interoperability are poor, and real-time control of field equipment is not well achieved. Fieldbus is a product of the comprehensive application of microprocessor technology, network technology, communication technology, and automatic control technology. It puts the microprocessor into the field automatic control equipment, so that the equipment has digital computing and digital communication capabilities, and improves the measurement, control and transmission accuracy of signals[2]. In recent years, with the promotion of fieldbus technology, it has become an inevitable trend of technological progress to improve the traditional batching control system into a fieldbus-based control system. This paper combines engineering practice to introduce the design of a glass batching control system based on fieldbus technology and has achieved good results in practical application. 2 Fieldbus and Fieldbus Control System Fieldbus is a serial, digital, multi-point communication data bus between field devices/instruments installed in the production process area and automatic control devices/systems in the control room. Among them, "production process" includes two types: discontinuous production process and continuous production process. Or, fieldbus is a network system and control system that uses a single distributed, digital, intelligent measurement and control device as a network node, connects them with a bus, realizes mutual information exchange, and jointly completes the automatic control function. Fieldbus has developed rapidly, and more than 40 fieldbuses have been developed so far, among which the five influential ones are FF, Profibus, HART, CAN and Lonworks. Fieldbus technology integrates dedicated microprocessors into traditional measurement and control instruments, giving them digital computing and communication capabilities, allowing them to become network nodes that independently undertake certain control and communication tasks. They transmit information through various means such as twisted-pair cables, coaxial cables, and optical fibers, thus forming a network system connected by multiple measurement and control instruments, computers, etc., as nodes. Fieldbus can be considered an extension of communication buses in field devices, allowing bidirectional, multi-variable digital communication between various field devices, such as transmitters, control valves, base controllers, recorders, displays, PLCs, and handheld terminals, and the control system via the same bus. Fieldbus control systems are a new type of industrial control system that emerged after distributed control systems (DCS). It relies on microprocessor chips with detection, control, and communication capabilities to achieve completely distributed control of digital instruments (devices) in the field. These distributed measurement and control devices act as network nodes, connecting these points in a bus configuration to form a fieldbus control system. It belongs to the lowest level of network system and is a network-integrated fully distributed control system. It distributes all the functions of the original distributed control system (DCS) field controllers to various network nodes. Therefore, it can transform the original closed, dedicated system into an open, standard system. It changes the original control architecture, updating the hybrid analog and digital distributed control to fully digital control. It uses an open fieldbus network to interconnect various field controllers and intelligent instruments, forming an operable fieldbus control system. It completely decentralizes control functions to the field, truly achieving distributed control, distributed hazard, centralized monitoring, and full digitalization. Therefore, FCS is essentially an open, interoperable, completely distributed control system, thus representing a further step forward from DCS. A comparison of the fieldbus control system (FCS) and the traditional distributed control system (DCS) is shown in Figure 1. Figure 1: Comparison of FCS and DCS structures. 3. Design of a Glass Dispensing Control System Based on PROFIBUS Bus 3.1 Overview of PROFIBUS Fieldbus PROFIBUS is an open fieldbus standard launched by SIEMENS. It is not dependent on manufacturers, and various automated devices can exchange information through the same interface. PROFIBUS is used for distributed I/O devices, drives, PLCs and PC-based automation systems. PROFIBUS consists of three compatible parts [4], namely PROFIBUS-DP, PROFIBUS-PA and PROFIBUS-FMS. Among them, PROFIBUS-DP is a high-speed, low-cost communication connection used for device-level control systems and distributed I/O communication. It has good real-time performance, with a data transmission rate of 9.6kbps-12Mbps and a response time of hundreds of microseconds to hundreds of milliseconds. The data transmission technology adopts RS-485, and the transmission medium is shielded twisted pair or optical fiber. In addition, PROFIBUS-DP also provides non-periodic communication required by intelligent field devices for configuration, diagnosis and alarm processing and determination of parameters of complex devices during operation. The extended diagnostic function of PROFIBUS-DP can quickly locate faults. Diagnostic information is transmitted on the bus and collected by the master station. It adopts an open communication network, which allows for the formation of a single master station or a multi-master station system. PROFIBUS stands out in terms of performance, openness, interchangeability, interoperability, and industrial performance; therefore, it was chosen as the bus type. 3.2 System Overall Structure and Working Principle The entire control system is based on electronic weighing composed of sensors and PANTHER weighing terminals, with an S7-300 PLC as the control core. It uses a PROFIBUS-DP fieldbus and a computer to form an organic whole, integrating peripheral actuators to automatically control the entire process of batching, conveying, and mixing materials from the raw material silo to the melting furnace silo. Simultaneously, it displays and monitors alarms and interlocks throughout the system, and manages the system's formula, production data, and equipment operating status to meet the batching requirements of glass production. The process flow of the glass batching system based on the "reduction method" is shown in Figure 2: Figure 2 "Reduction Method" Glass Batching Process Flow The system has three modes: manual operation, automatic operation (PLC control), and fully automatic operation under computer monitoring. During automatic batching, the on-site weighing station weighs the materials in the silo. The system uses a "subtraction method" to control the discharge according to the formula requirements. The discharge value for the subtraction method is the formula value, and two weighings are performed. Discharge stops when the discharge value is met. Simultaneously, the conveyor belt is started to send the material to the mixing silo for mixing. During mixing, an automatic water addition system is activated to add water at regular intervals. After the mixing meets the requirements, the original melting conveyor belt sends the mixture to the kiln head silo. The system completes the batching task through repeated cycles. 3.3 System Network Control Composition: The system is centered around an S7-300 PLC. The host computer and PLC are connected via an MPI network, and the PLC is connected to the high-precision weighing instrument via a PROFIBUS-DP network. The weighing instrument is a slave station in the system. The PANTHER instrument will complete the network connection with the SIEMENS PLC through a dedicated PROFIBUS fieldbus interface. The network composition of the automatic batching system is shown in Figure 3: Figure 3 Network composition of the automatic batching system The system uses STEP V5.2 for hardware configuration to realize the functions of monitoring system equipment, formula management, and data acquisition and recording. The logic processor of the PLC is Siemens' S7-315 2DP CPU, which has an MPI communication interface and a PROFIBUS-DP interface. The host computer manages the slave computer in a unified manner, and transmits the weighing formula to the slave computer for formula, printing and statistics, starts the weighing operation, and monitors the running status of the slave computer with monitoring software. The slave computer performs on-site control of the batching system. The STEP7 programming software installed on the PC communicates with the PLC through MPI, but these communication protocols are not publicly available, so the PRODAVE toolbox provided by Siemens is required [5]. PRODAVE's dynamic link database (DLL) provides a large number of DDL functions based on the Windows operating system for users to solve the data exchange and data processing problems between the PLC and the PC. The host computer directly reads and writes data in the PLC using communication functions, without writing a communication program on the PLC side. The PROFIBUS-DP interface is responsible for communicating with the weighing instrument and transmitting the weighing data and related parameters to the main control station in a timely manner. The weighing instrument adopts the widely used PANTHER weighing terminal. This instrument collects weighing data through the field junction box, and its built-in PROFIBUS-DP interface can easily complete communication with the PLC. 3.4 System control software design The control system's switch input module receives control field and operation button signals as well as motor status feedback signals. The switch output module realizes the start and stop control of motors, cylinders, solenoid valves, and indicator lights. The analog output module controls the feeding and discharging speed of the feeder at the field weighing station. The weighing results of the weighing instrument are transmitted to the processor through the PROFIBUS-DP bus. The processor calculates the received button signals, status feedback signals, and weighing value signals and issues control signals to the field equipment. The entire system then runs automatically according to the predetermined program. The system control software flowchart is shown in Figure 4: Figure 4 Batching control system software flowchart 3.5 System characteristics analysis (1) Due to the adoption of FCS in the control structure, many hardware devices are saved compared with the traditional DCS. Using FCS can reduce isolators, terminal cabinets, I/O terminals, I/O cards, I/O files and I/O cabinets by 1/2 to 2/3, thus saving space for I/O devices and device rooms; at the same time, it reduces a large number of cables, greatly simplifying construction and commissioning. (2) Fieldbus can obtain a large amount of rich information from field devices, which can better meet the information integration requirements of factory automation and CIMS system. Fieldbus is a digital communication network. It does not simply replace 4-20mA signals, but can also realize the transmission of equipment status, fault and parameter information. In addition to completing remote control, the system can also complete remote parameterization work. Therefore, it improves the accuracy and reliability of the control system. (3) Since the field control equipment has the ability to self-diagnose and handle simple faults, and sends relevant diagnostic and maintenance information to the control room through digital communication, users can query the operation, diagnostic and maintenance information of all equipment, so as to analyze the cause of faults early and quickly eliminate them. It shortens maintenance downtime, and at the same time, due to the simplified system structure and simple wiring, the maintenance workload is reduced. (4) The system adopts STEP7 software for unified programming and configuration, making system debugging simpler and more convenient, while greatly reducing the workload of system maintenance. 4 Conclusion This system uses fieldbus, an open and interoperable network, to interconnect various field controllers and instruments, forming a fieldbus control system. At the same time, control functions are completely decentralized to the field, reducing debugging, installation, and maintenance costs. This system has been put into use in many Mettler Toledo weighing and batching projects, and its operation is good, with stable and reliable communication and control. Therefore, it has great potential for promotion in the field of industrial control.