Abstract: With the continuous development of computer technology and network technology, control systems are developing in the direction of integration, networking and intelligence. This paper reviews the development of control systems and expounds the similarity of the development between the control system and the information network. The existing problems and structure of FCS are analyzed. This paper also introduces the Ethernet and advances the development trend of control network structure. Keywords: Control system networking information network Fieldbus 0 Introduction With the development of computer technology, communication technology and control technology, the traditional control field is undergoing an unprecedented transformation and is beginning to develop in the direction of networking. The structure of control systems has evolved from the initial CCS (Computer Centralized Control System) to the second-generation DCS (Distributed Control System), and now to the popular FCS (Fieldbus Control System) [1]. The requirements for large data volume and high-speed transmission of data such as images and voice signals have spurred the combination of Ethernet and control networks, which are currently popular in the commercial field. This wave of industrial control system networking has also integrated a variety of popular technologies such as embedded technology, multi-standard industrial control network interconnection, and wireless technology, thereby expanding the development space of the industrial control field and bringing new development opportunities. 1 Development of Computer Control Systems Computer and network technology are closely related to the development of control systems. As early as the mid-to-late 1950s, computers were already being used in control systems. In the early 1960s, a control system in which computers completely replaced analog control appeared, which was called Direct Digital Control (DDC). In the mid-1970s, with the advent of microprocessors, computer control systems entered a new period of rapid development. In 1975, the world's first distributed computer control system based on microprocessors was introduced. It used multiple microprocessors for distributed control and centralized management through a data communication network, and was known as a Distributed Control System (DCS). In the 1980s, microprocessors and peripheral circuits were used to construct digital instruments to replace analog instruments. This DDC control method improved the system's control accuracy and flexibility, and offered a performance-price ratio unmatched by traditional analog instruments in multi-loop cyclic sampling and control. In the mid-to-late 1980s, with the increasing complexity of industrial systems and the further increase in control loops, single DDC control systems could no longer meet the requirements of on-site production control and management. At the same time, the performance-price ratio of small and medium-sized computers and microcomputers improved significantly. Therefore, hierarchical control systems using small and medium-sized computers and microcomputers were widely adopted. Since the 1990s, the rapid development of computer network technology has led to further advancements in DCS systems, improving their reliability and maintainability. DCS still dominates the industrial control field today. However, DCS lacks openness, has complex wiring, high costs, and presents significant challenges in integrating products from different manufacturers. Starting in the late 1980s, the development of large-scale integrated circuits led to the intelligentization of many field devices such as sensors, actuators, and drives. This prompted the search for a single communication cable to connect field devices with unified communication protocols and interfaces. At the device layer, the signals transmitted were no longer I/O (4-20 mA/2 4VDC) signals, but digital signals – this is the fieldbus. Because it solved the reliability and openness issues of network control systems, fieldbus technology gradually became the development trend of computer control systems. Since then, developed industrial countries and multinational corporations have launched their own fieldbus standards and related products, creating a highly competitive market. 2. The Relationship Between Information Networks and Control Systems From a developmental perspective, the development of information network architecture and control system architecture share similarities. The development of enterprise information networks has generally gone through the following stages: ① Centralized host-based model: Powerful hosts completed almost all computing and processing tasks, with minimal interaction between users and hosts. ② Hierarchical workgroup-based structure: The development of microcomputers and local area networks (LANs) enabled groups of people with similar job functions to share certain public resources, strengthening communication and collaboration among users. ③ Networked enterprise organizations based on the Internet/Intranet/Extranet: The development of computer network technology has made it the mainstream of modern information technology, especially the development and widespread application of the Internet, which has become a recognized prototype of the future global information infrastructure. Adopting mature Internet technologies and standards, the concepts of Intranet and Extranet were proposed for the implementation of enterprise intranets and extranets, respectively, thus forming a new generation of enterprise information infrastructure (enterprise networks) centered on Intranets, supplemented by Extranets, and relying on the Internet. Computer control systems have also gone through several development stages, including centralized control, hierarchical control, and fieldbus-based network control, with very similar development processes. With the deepening application and increasing perfection of enterprise information networks, the entry of field control information into information networks for real-time monitoring is an inevitable trend. To improve the social and economic benefits of enterprises, many companies are striving to establish comprehensive management information systems. These systems must include real-time data from the production site to ensure real-time monitoring of the production process, enabling more scientific management decisions and achieving optimal production, operation, and management. Information-control integration will create favorable conditions for realizing enterprise integrated plant automation (CIPA) and enterprise informatization. The similarity in the architectural development of enterprise information networks and control systems is not accidental. In the development of computer control systems, the emergence of each control system structure has always lagged behind the development of corresponding computer technology. In fact, in most cases, people only begin to study how to apply a new technology to the control field after its emergence in the computer field. Given the differences between the two application environments, the technical details have been appropriately modified and supplemented, but they share many commonalities in the principles and implementation of key technologies. It is precisely because of this relationship in their development process that information-control integration becomes possible. 3. Current Status of Fieldbus Technology Research In the 1940s, process control was based on 3-15 PSI pneumatic standard signals. Subsequently, the use of 4-20mA analog signals led to the widespread application of analog controllers. However, not all sensors and drive devices used a unified 4-20mA signal. In the 1970s, the pioneering use of computers in detection, analog control, and logic control led to centralized control. In the 1980s, the advent of microprocessors ushered in the era of digitalization and intelligence for industrial instruments. 4-20mA analog signal transmission was gradually replaced by digital communication. Furthermore, the rapid development of distributed control and network technology promoted the integration of control, scheduling, optimization, and decision-making functions. However, since most detection, transmission, and execution mechanisms use analog signal connections with a one-to-one transmission structure, wiring becomes complex, engineering costs are high, and maintenance is difficult. Signal transmission accuracy is low, susceptible to interference, and instrument interchangeability is poor, all of which hinder the functionality of upper-level systems. On the other hand, intelligent instruments offer far greater capabilities than field analog instruments, such as remote range and zero-point setting, self-diagnosis of instrument operating status, multi-parameter measurement, and compensation for environmental impacts. Therefore, the development of intelligent instruments and control systems requires digital communication between upper-level systems and field instruments. To overcome the technical bottlenecks of DCS systems and further meet field needs, fieldbus technology emerged. It is essentially a bidirectional serial, digital, multi-node communication network connecting intelligent field devices and automated control equipment, also known as the field-level device control network (INFRANET). Unlike information networks such as the Internet and Intranet, control networks directly face the production process, thus requiring high real-time performance, reliability, data integrity, and availability. To meet these characteristics, fieldbus simplified standard network protocols, omitting some intermediate layers and including only the three layers of the ISO/OSI 7-layer model: the physical layer, the data link layer, and the application layer. In the early stages of fieldbus development, various companies proposed their own fieldbus protocols. On December 31, 1999, the IEC voted to establish eight major buses as international fieldbus standards, including CAN Bus, Profit Bus, InterBus-S, Mod Bus, FOUNDATION Fieldbus, etc. Based on these, a new Fieldbus Control System (FCS) was formed. 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 signal or digital-to-analog signal control, and forming a fully distributed, fully digital, intelligent, bidirectional, interconnected, multi-variable and multi-connection communication and control system. The corresponding control network structure has also undergone significant changes. The typical structure of FCS is divided into three layers: device layer, control layer and information layer. Although fieldbus technology has developed very rapidly, there are also many problems that restrict its further expansion. (1) First is the selection of fieldbus. Although the IEC organization has reached an international bus standard, there are still too many types of buses, and each fieldbus has its own most suitable application area. How to combine different levels of fieldbuses according to the application object in practice, so that each part of the system selects the most suitable fieldbus, is still a relatively difficult problem for users. (2) System integration problem. Since a system may use multiple forms of fieldbus in actual application, how to seamlessly integrate the industrial control network and the data network, so that the whole system can achieve integrated management and control, is a key link. When designing the network layout of a fieldbus system, it is necessary to consider not only the distance between each field node, but also the functional relationship between field nodes and the flow of information on the network. Since the functions of intelligent field instruments are very strong, many instruments will have the same function blocks. When configuring, it is necessary to carefully consider which function block to select; the information flow on the network should be minimized. At the same time, the configuration of communication parameters is also very important. A balance should be made between the real-time performance of the system and the network efficiency. (3) There are technical bottleneck problems [2]. The main problems are: a. When the bus cable is cut, the entire system may be paralyzed. Users hope that the system performance can be reduced at this time, but it cannot collapse. At present, many fieldbuses cannot guarantee this. b. The constraint of intrinsic safety explosion protection theory. Existing explosion protection regulations limit the length of the bus and the number of loads on the bus. This limits the advantages of fieldbus in saving cables. At present, countries are strengthening research on the intrinsic safety concept (FISCO) of fieldbus and striving for breakthroughs. c. The system configuration parameters are too complex. There are many configuration parameters of fieldbus, which are not easy to master. However, the quality of the configuration parameters has a great impact on the system performance. 4. Ethernet Control Networks The basic trend in the development of control networks is towards open and transparent communication protocols. The aforementioned problems stem from the fact that the openness of fieldbuses is conditional and incomplete. Ethernet offers advantages such as high transmission speed, low power consumption, ease of installation, and good compatibility. Because it supports almost all popular network protocols, it is widely used in commercial systems. In recent years, with the development of network technology, Ethernet has entered the control field, forming a new type of Ethernet control network technology. This is mainly due to the development of industrial automation systems towards distributed and intelligent control, making open and transparent communication protocols a necessary requirement. Current fieldbuses, due to their diverse types and incompatibility, cannot yet meet this requirement. The openness of Ethernet's TCP/IP protocol gives it an unparalleled advantage in this crucial communication link of industrial control. 5. Current Problems When considering networking control systems, we typically link networking with fieldbuses. Currently, influential fieldbus systems in the control field include: FF, LonWorks, Profibus, CAN, HART, and RS485 bus networks. The Fieldbus Foundation has established a unified standard (FF), with its slow bus standard H1 having been adopted as an international standard, while its high-speed bus standard H2 is still under development. However, due to commercial profits and technological monopolies, the fieldbus product market remains highly fragmented, which negatively impacts cost reduction and application expansion. Ethernet has been widely adopted, with mainstream products reaching speeds of 100Mbps and Gigabit Ethernet already in use. Its network products and software are developing rapidly. Ethernet has gained widespread recognition for its low cost, convenient networking, rich hardware and software offerings, and high reliability. The rapid development of the Internet is primarily due to the widespread application of Ethernet and TCP/IP protocols. TCP/IP is extremely flexible, and almost all underlying network technologies can be used to transmit TCP/IP communication. Ethernet using TCP/IP has become the most popular packet-switched LAN technology and also the most open network technology. Therefore , integrating the Internet and related technologies into existing control systems, utilizing open and mature technologies on the Internet to upgrade existing control systems, and accelerating the information-control integration process of industrial enterprises is a feasible solution. Summary From the current trend, it is undeniable that industrial Ethernet will enter the field control level. But at least for now, it is difficult to completely replace the fieldbus as the single standard for real-time control communication. The existing fieldbus will continue to exist, and the most likely development is a hybrid control system [6]. References [1] Jia Dongyao, Wang Renhuang. Development trend of industrial control network structure [J]. Industrial Instrumentation and Automation Device, 2002 (5): 12-14. [2] Fan Kai. Development trend of fieldbus [J]. Automation Instrumentation, 2000·2. [3] Zheng Wenbo. Innovation of network technology and control system [J]. Measurement and Control Technology, 2000·6. [4] Peng Ke, Chen Jida et al. Networking of control system and integration technology of control system and information network [J]. Information and Control, 2002, 31 (5): 441-445. [5] Hao Xiaohong, Su Yuan. Ethernet and fieldbus control system [J]. Electrical Automation, 2002 (4): 4-7. [6] Fan Kai. Application of fieldbus technology in China [J]. Automation Expo, 2001.4.