Abstract: This paper discusses the concept and characteristics of fieldbus technology from the perspective of factory-level automation and information integration technology, and analyzes the changes in the structure of automation systems based on fieldbus technology and the changes in the product market pattern. The author believes that China's automation product manufacturing industry is facing a new opportunity. Keywords: Fieldbus; PROFIBUS; Automation monitoring system 1. Fieldbus Technology 1.1 Concept of Fieldbus Technology According to the definition of the International Electrotechnical Commission IEC1158, 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". In other words, fieldbus is a network system and control system that uses individual distributed, digital, and intelligent measurement and control devices as network nodes, connected by a bus, to exchange information and jointly complete automatic control functions. Among them, "production process" should include both discontinuous production processes and continuous production processes. Field devices/instruments refer to sensors, drivers, actuators, and other devices located at the field layer. Therefore, fieldbus is a digital network technology for factory-level automation and information integration. Automation systems based on this technology are called FCS (Fieldbus Control System). 1.2 Key Features of Fieldbus Technology 1.2.1 Digital Communication Replaces 4-20mA Analog Signals: In traditional technology, the connection between field devices and the controller is one-to-one (one I/O point to one control point of the device). This I/O wiring method transmits 4-20mA (analog information) or 24VDC (switching information) signals. Fieldbus technology allows the controller to be connected to field devices (intelligent devices with communication interfaces) using a single communication cable, fulfilling the communication and control requirements of the underlying devices through digital communication. 1.2.2 Intelligent Field Devices: Fieldbus technology requires field devices (sensors, drivers, actuators, etc.) to be intelligent (programmable or parameterizable) devices with serial communication interfaces. Therefore, fieldbus technology is based on the development of large-scale integrated circuits in computers. 1.2.3 Integrating remote control, parameterization, and fault diagnosis of field devices: Fieldbus uses computer digital communication technology to connect intelligent field devices. Therefore, the controller can obtain a wealth of information from the field devices, enabling the transmission of equipment status, fault, and parameter information, and completing remote control, parameterization, and fault diagnosis. 1.2.4 Fieldbus is an extension of computer network communication to the field level: Traditional communication between field devices and controllers uses a one-to-one connection, transmitting 4-20mA/24VDC signals. This communication technology has limited information capacity, making it difficult to achieve information exchange between devices and between the system and the outside world, turning the automation system into an "information island" in the factory, severely restricting the realization of enterprise information integration and comprehensive automation. Fieldbus technology uses computer digital communication technology, enabling the automation system and devices to join the factory information network, becoming the bottom layer of the enterprise information network, extending the coverage of enterprise information communication all the way to the production site. 1.2.5 Fieldbus technology is a key technology for realizing factory-level information integration: To successfully implement CIMS, the information integration at each level and its supporting technology—computer network issues—must be well resolved. Fieldbus is an extension of factory computer networks to field-level devices, and it serves as the technological foundation for supporting the integration of field-level and workshop-level information. 1.3 Fieldbus Technology Development and Standards 1.3.1 Rapid Development of Fieldbus Technology and Products Internationally Internationally, fieldbus technology, products, and systems have developed rapidly. Taking PROFIBUS as an example, there are currently over 1500 products supporting the PROFIBUS standard, from more than 250 manufacturers worldwide. More than 2 million PROFIBUS devices have been installed and are in operation globally, with an annual growth rate of 25%. A market survey of fieldbus systems (FBS: a fieldbus system consisting of ten or more devices) provided by CONSULTIC (in the European market, 1996) showed that 427,500 FBSs had been installed, with 146,400 new FBSs added. Fieldbus systems account for an average of 25% of the entire automation system market share. Currently, internationally renowned automation, instrumentation, and electrical manufacturers all offer fieldbus products and systems, such as Rockwell, Siemens, Schneider Electric, Rosemount, Honeywell, and Yokogawa. 1.3.2 The Lack of a Unified International Standard for Fieldbus A key issue in the realization of fieldbus technology is the need for a common fieldbus communication protocol standard that manufacturers in the automation industry adhere to. Leading international manufacturers of automation products and field devices, recognizing fieldbus technology as the future direction, have formed alliances to launch their own bus standards and products, cultivate users and expand their influence in the market, and actively support international standards organizations in developing international fieldbus standards. The ability to secure a significant share of their bus technology standard in future international standards is crucial to the future of their products, user trust, and corporate reputation. Historical experience shows that international standards are based on one or a few of the most successful technologies in the market. Therefore, the competition among major international companies in developing international fieldbus standards reflects a competition for technological leadership, ultimately stemming from competition in market strength. It is said that there are currently no fewer than two hundred different buses and bus standards internationally. Several fieldbuses with significant influence and market share include: PROFIBUS Fieldbus: Approved as a European standard on March 15, 1996, as DIN 50170 V.2. PROFIBUS products are widely accepted in the global market, holding the largest market share in Europe with an annual growth rate of 25%. Currently, over 1500 products support the PROFIBUS standard, from more than 250 international manufacturers. Over 2 million PROFIBUS devices are installed and operational worldwide. By May 1998, PROFIBUS-PA instrumentation equipment suitable for process automation was in operation at 40 user factories in 19 countries. In December 1989, companies voluntarily adopting the PROFIBUS standard in their products formed a User Organization (PNO), and in 1995, the PROFIBUS International Organization (PI) was established. Currently, the PI has regional organizations in 20 countries and regions, with over 800 members. In July 1997, the China Fieldbus (PROFIBUS) Professional Committee was established, along with a laboratory for PROFIBUS product demonstration and certification. PROFIBUS is primarily used in manufacturing automation, process control automation, power automation, building automation, and railway traffic signaling systems. FF Fieldbus: Established in 1994 through the merger of the ISP Foundation and World FIP (North America), the FF Foundation aims to develop a unique international fieldbus conforming to IEC and ISO standards. The low-speed bus (H1) protocol was published in 1996. In May 1997, the China Fieldbus (FF) Professional Committee was established, and an FF Fieldbus product certification center was planned. FF Fieldbus is mainly used in process automation, such as in chemical, power plant experimental systems, wastewater treatment, and oilfield industries. LONWORKS Bus: LONWORKS stands for LONWORKS NetWorks, a distributed intelligent control network technology. It aims to provide a measurement and control network suitable for various fieldbus applications. Currently, LONWORKS has a wide range of applications, including industrial control, building automation, data acquisition, and SCADA systems. In China, it is mainly used in building automation. CANBUS Fieldbus: CANBUS fieldbus has been approved by ISO/TC22 technical committee as an international standard ISO 11898 (communication rate less than 1Mbps) and ISO 11519 (communication rate less than 125Kbps). CANBUS products are mainly used in automotive manufacturing, public transportation vehicles, robotics, hydraulic systems, and distributed I/O. It also has applications in elevators, medical devices, machine tools, and building automation. WorldFIP Fieldbus: Became a European standard in 1996 (EN 50170 V.3). WorldFIP fieldbus has a wide range of applications, with excellent results in process automation, manufacturing automation, power, and building automation. P-NET Fieldbus: In 1987, the P-NET standard became an open and complete standard, becoming a Danish national standard. In 1996, it became part of the European bus standard (EN 50170 V.1). The international P-NET user organization was established in 1997 and currently has nearly 100 corporate members. Headquartered in Siekeborg, Denmark, it also has regional branches in Germany, the UK, Portugal, and Canada. P-NET fieldbus is widely used in Europe and North America, including in petrochemical, energy, transportation, light industry, building materials, environmental engineering, and manufacturing sectors. 1.2.3 It is impossible to use a single fieldbus standard to address the diverse range of automation industries and application needs. Automation technology has different requirements for communication networks than computers; automation is not isolated from specific industries. Therefore, it is impossible to use a single fieldbus standard to address the diverse range of automation industries and application needs. A particular fieldbus standard may be suitable and offer a high performance-price ratio in certain areas, but may not be optimal or even suitable outside of these areas. The idea and practice of attempting to cover all application areas with a single fieldbus standard is unrealistic. 1.2.4 Faced with numerous fieldbus standards, we should actively conduct research on fieldbus technologies suitable for China's national conditions and geared towards manufacturing automation. Faced with various schools of thought on fieldbus and standards internationally, Chinese and foreign experts generally believe that: (1) It is hoped that the IEC can complete the formulation of a unified standard as soon as possible according to the expected goal. However, according to the current progress, it is estimated that the IEC will find it difficult to complete the expected goal in the near future. (2) The proposed solutions put forward by the IEC at present are limited to process automation and are difficult to meet the requirements of other application fields. They are unlikely to become the only standard and are likely to form a coexistence of multiple standard systems. Under the framework of a unified standard, multiple communication protocol interfaces may be a suitable solution for a unified standard. Regarding the development policy of fieldbus technology in my country, I believe that we cannot wait indefinitely for the international standard of the IEC. We should combine my country's national conditions, actively track, introduce, and study the fieldbus standards with mature application experience in the international market, and carry out research on fieldbus technologies, standards, applications, and product development that are suitable for my country's national conditions and geared towards industry. 2. Factory-Level Automation System and Information Integration Technology 2.1 Hierarchical Division of CIMS Architecture and Industrial Data Structure Based on factory management, production processes, and functional requirements, the simplified CIMS architecture can be divided into three layers: factory level, workshop level, and field level, as shown in Figure 1. 2.2 Field-Level and Workshop-Level Automation Monitoring and Information Integration are Indispensable Parts of Factory Automation and CIMS The field-level and workshop-level automation monitoring and information integration systems mainly complete functions such as single-machine control, wired control, communication networking, online equipment status monitoring, and collection, storage, and statistics of production and operation data from field equipment. This ensures that field equipment completes production tasks with high quality and transmits the production and operation data to the factory management level, providing data to the factory-level MIS system database. Simultaneously, it can also receive and execute production management and scheduling commands issued by the factory management level. Therefore, the field-level and workshop-level monitoring and information integration systems are the foundation for realizing factory automation and CIMS systems. 3. The development of fieldbus technology has led to changes in the factory's bottom-level automation system and information integration technology. 3.1 Traditional field-level and workshop-level monitoring systems Traditional field-level and workshop-level monitoring systems are mostly distributed monitoring systems based on PLC. One of their main characteristics is that the connection between the field-level devices and the controller is one-to-one (one I/O point to one measurement and control point of the device). The so-called I/O wiring method transmits 4-20mA (transmitting analog information) or 24VDC (transmitting switch information) signals. As shown in Figure 2: 3.2 Main disadvantages of the system (1) Weak information integration capability: The controller and the field devices are connected by I/O lines to transmit 4-20mA analog signals or 24VDC and other switch signals, and monitor the field devices in this way. In this way, the amount of information obtained by the controller is limited, and it is difficult to obtain a large amount of data such as equipment parameters, faults and fault records. The bottom-level data is incomplete and the information integration capability is weak, which cannot fully meet the requirements of the CIMS system for bottom-level data. (2) The system is not open, has poor integrability, and lacks specialization: In addition to the field equipment, which are all connected by standard 4-20mA/24VDC, other software and hardware in the system can usually only use products from one manufacturer. There is a lack of interoperability and interchangeability between products from different manufacturers, resulting in poor integrability. Such systems rarely leave interfaces to allow other manufacturers to integrate their specialized control technologies, such as control algorithms, process flows, and formulas, into the general system. Therefore, there are very few industry-oriented monitoring systems. (3) Reliability is not easy to guarantee: For large-scale distributed systems, a large number of I/O cables and laying construction not only increase costs but also increase the unreliability of the system. (4) Low maintainability: Due to incomplete information on field-level equipment, the online fault diagnosis, alarm, and recording functions of field-level equipment are weak. On the other hand, it is also difficult to complete the parameterization functions such as remote parameter setting and modification of field equipment, which affects the maintainability of the system. 3.3 The development of fieldbus technology has led to the emergence of a new generation of automated monitoring systems. With the development of fieldbus technology, a new generation of automated monitoring systems based on fieldbus has begun to emerge. The future field-level and workshop-level automated monitoring systems based on fieldbus technology are shown in Figure 3. 3.4 Main advantages of fieldbus-based automated monitoring systems (1) Fieldbus-based automated monitoring systems enhance field-level information integration capabilities. 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 systems. 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. (2) Openness, interoperability, interchangeability, and integrability. As long as products from different manufacturers use the same bus standard, they have interoperability and interchangeability. Therefore, the equipment has good integrability. The system is open, allowing other manufacturers to integrate their proprietary control technologies, such as control algorithms, process flows, and formulas, into the general system. Therefore, there will be many monitoring systems on the market that are tailored to industry characteristics. (3) High system reliability and good maintainability: The fieldbus-based automated monitoring system uses a bus connection method to replace one-to-one I/O wiring, which reduces unreliable factors caused by connection points for large-scale I/O systems. At the same time, the system has online fault diagnosis, alarm and recording functions for field-level devices, and can complete parameter setting and modification of field devices, which also enhances the maintainability of the system. (4) Cost saving: For large-scale distributed I/O systems, a large amount of cable, I/O module and cable laying engineering costs are saved, reducing system and engineering costs. 3.5 Changes in the structure of fieldbus-based automated monitoring systems: All software and hardware of the system can be provided by multiple manufacturers, and have interoperability and interchangeability, which can facilitate hardware and information integration. The main difference of the system is that it has professional software for different industries. Various industry-specific systems will be seen on the market, such as power generation, power transmission and distribution, manufacturing, chemical industry, building, etc. (1) Controller: Since the controller monitors field devices through standard fieldbus communication, there is no need to use I/O module products bundled with the controller. Any field device with a fieldbus interface can be integrated with the controller. Therefore, the main indicators of the controller are high-speed instruction processing capability, large storage capacity and fieldbus communication interface. Therefore, the controller will be replaced by the standard, general-purpose hardware platform Compact Computer, such as Intel/Windows PC. (2) I/O Module: The I/O modules plugged into the controller rack are replaced by distributed I/O modules connected to the fieldbus. Distributed I/O is no longer a bundled product of the controller manufacturer, but a product of third-party manufacturers; cheap, dedicated I/O modules with special quality (such as high protection level, intrinsic safety, acceptance of RTD, mV, high voltage, high current signals, etc.) will have a broad market. (3) Field Device: Developing towards specialization, with program and parameter storage, intelligent control functions, and fieldbus interface. The controller will delegate some control work to the field device itself, and the controller will only perform parameterization and operation monitoring. Such as drives, sensors, transmitters, regulators with professional control algorithms, actuators, HMIs, motor starting and current protection devices, power transmission and distribution protection devices, high and low voltage switchgear, these devices will be manufactured by manufacturers with advantages in this industry and have interoperability and interchangeability. (4) Software: On the one hand, the software is no longer tied to hardware such as controllers, I/O, field devices, etc., and can run on a general standard controller hardware platform. The software will become a general automation software platform with standard communication protocols, standard basic programming languages ​​(such as IEC1131), unified interface style, standard data format and standard database interface. On the other hand, the software must be open, allowing automation expert manufacturers with unique experience in the industry to embed professional control algorithms, simulation, optimization, scheduling and other special automation software into the general software platform and launch their own industry-oriented professional automation systems. 4. New opportunities for independent development and industrialization of field-level and workshop-level automation monitoring systems 4.1 Automation systems based on fieldbus have led to a new differentiation among system manufacturers. The main feature is the separation of controller and system software manufacturers, and a trend towards generalized products. The development and manufacturing of field devices such as I/O and sensors and application software are becoming increasingly specialized. (1) Controllers: Traditional PLCs and process control stations will gradually be replaced by standard, universal controller hardware platforms—Compact Computers. These are industrial-grade, rugged PCs based on PC buses and compatible with Intel/Windows. Products from general-purpose computer manufacturers will dominate. (2) System software: Products developed by specialized monitoring software companies, such as Intellution (FIX), Wonderware (INTOUCH), and PcSoft (WIZCON), will dominate, rather than bundled software products from controller hardware manufacturers. So-called "soft PLCs" based on PC/WINDOWS platforms, paired with industrial-grade, rugged PCs compatible with Intel/Windows, may become the mainstream of controllers or fieldbus control system master stations. (3) Field equipment: Sensors, drives, actuators, remote I/O, etc., are manufactured by different manufacturers with professional advantages, such as instruments from E+H and ROSEMOUNT, drives from SIEMENS, AB, ABB, and Danfoss, power transmission and distribution protection devices from Schneider Electric and SIEMENS, high and low voltage switchgear, and I/O modules from Schneider Electric, SIEMENS, and AB. (4) Systems: More manufacturers will launch industry-oriented systems with professional software and hardware control functions based on general software and hardware platforms and standards in their own professional fields. 4.1 New opportunities for independent development and application promotion of automation systems Whether it is PLC or DCS, the hardware, software, and even field-level equipment of the system are sold in bundles. Because internationally renowned automation system manufacturers have an absolute advantage over domestic manufacturers in terms of development investment, production scale, sales organization, brand promotion, and application support, the vast majority of the domestic product market share is occupied by foreign manufacturers. Due to the closed nature of the system, it is difficult for domestic manufacturers to carry out industry-oriented professional technical development on foreign system products in order to achieve system value-added. Most domestic system integrators can only provide system sets. The success or failure of market competition among system integrators is not primarily driven by technical factors, but rather by price. This makes it difficult for domestic automation companies to survive. The development of fieldbus technology and the emergence of new automated monitoring systems have led to more open systems and more universal system products, possessing interoperability and interchangeability. In short, new automated monitoring systems provide an open, universally standardized hardware and software platform. Therefore, this offers domestic manufacturers opportunities to enter the market. On the one hand, automation system integrators can leverage their advantages in system and software design, as well as their technical, experiential, and knowledge-based strengths in a specific automation field, to develop their own systems on a universal platform. These systems should be tailored to their specific industry needs and possess expert and intelligent control functions. This approach can bring greater benefits to companies than simply providing system integration services. On the other hand, a large number of domestic field device manufacturers (such as drivers, sensors, transmitters, regulators, actuators, HMIs, motor starting and current protection devices, power transmission and distribution protection devices, high and low voltage switchgear, etc.), especially those manufacturers producing special quality products (such as regulators with professional control algorithms, high protection levels, intrinsic safety, and field devices that can accept RTD, mV, high voltage, and high current signals), are modifying their products to have fieldbus interfaces, which can help them expand into a wider market. This is because fieldbus control systems using imported controllers and domestically produced field devices (such as drivers, sensors, transmitters, regulators, actuators, and I/O) balance reliability, functionality, and price, making them popular with users and possessing a broad market. 5. Conclusion: 1. From the perspective of factory-level automation and information integration technology, fieldbus technology is not simply a technology of replacing cables with chips; it is an extension of computer and digital communication technologies to the factory's lower levels, i.e., the equipment layer. Like other fields, fieldbus technology represents a digital revolution in factory-level communication technology. 2. Factory-level automation and information integration technologies are the foundation for achieving plant-wide automation and CIMS systems. The development of fieldbus technology has transformed the traditional system structure and brought unparalleled advantages, such as abundant field information resources, system openness, and product interchangeability. 3. Changes in system structure will ultimately lead manufacturers to readjust their market strategies and strategies. Openness has brought new opportunities to China's automation industry.