Since its inception in the 1970s, fieldbus technology has attracted widespread attention and been widely adopted due to its advantages in reducing system cabling, simplifying system installation, maintenance and management, reducing system investment and operating costs, and enhancing system performance, leading to a revolution in the field of automatic control.
Introduction to Fieldbus
Fieldbus refers to an open, internationally standardized, digital, bidirectional transmission and communication network that connects intelligent instruments and control systems. As the foundation of the factory digital communication network, it connects the production process field and control equipment and their higher control and management levels. It is not only a basic network, but also an open, new type of fully distributed control system. It is a comprehensive technology with intelligent sensing, control, computer, digital communication and other technologies as its main contents. It is an applicable technology that promotes industrialization through informatization and informatization through industrialization. It is an industrial bus that can be applied to various computer control fields. Because fieldbus has huge potential business opportunities, major companies around the world have invested a lot of manpower, material resources and financial resources in its development and research [1]. Fieldbus technology has always been a field of fierce competition among major companies in the world. Due to the continuous innovation of fieldbus technology, the process control system has evolved from the fourth generation DCS to the current FCS (Fieldbus Control System) system, which is called the fifth generation process control system. The real difference between FCS and DCS lies in their fieldbus technology. Fieldbus technology replaces analog signals with digital signals. Based on 3C (Computer, Control, Communication) technology, it enables the on-site acquisition, processing, and use of a large amount of field detection and control information, moving many control functions from the control room to field devices. Due to competition among major international companies in the field of fieldbus technology, a unified standard has not yet been formed, and current fieldbus network interconnection follows the OSI reference model. Because fieldbus is based on computer, microelectronics, and network communication technologies, this technology is fundamentally changing the concepts and methods of control systems, and will greatly promote technological progress throughout the industrial sector, with a positive and far-reaching impact on industrial automation systems.
Fieldbus technology is a cutting-edge technology in contemporary industrial digital communication, integrating computer technology, communication technology, and automation control technology. It also embodies information technology and measurement technology in the information age. After 10 years of research, development, testing, and local application, fieldbus technology is now being widely used in small and medium-sized systems and is beginning to be applied in large-scale automation system engineering projects. Fieldbus technology is a pioneer of the industrial digital communication era, and its emergence is triggering an unprecedented technological revolution in the field of industrial control. Fieldbus is not merely a communication system distributed across the lowest-level control systems, but rather a communication system built upon the entire industrial system. Its communication protocol is built upon control strategies, and its standard programming language (DDL) and powerful communication functions make fieldbus control systems the most effective tool for implementing operator commands. Due to its significant technological advantages, it is considered an inevitable trend in the development of industrial control and will gradually replace traditional control methods.
Introduction to several mainstream fieldbuses
1. Foundation Fieldbus (FF)
This is the merging of the ISP protocol, developed by Fisher-Rousemount (USA) in conjunction with 80 companies including Yokogawa, ABB, Siemens, and Invensys, and the WorldFIP protocol, developed by Honeywell (USA) in conjunction with over 150 companies in Europe and other regions, in September 1994. This bus has been widely used in process automation and has promising development prospects. The Foundation Fieldbus adopts a simplified OSI model (layers 1, 2, and 7) from the International Organization for Standardization (ISO), namely the physical layer, data link layer, and application layer, with the addition of a user layer. FF offers two communication rates: low-speed H1 and high-speed H2. The former has a transmission rate of 31.25 Kbit/s and a communication distance of up to 1900m, supporting bus power supply and intrinsically safe explosion-proof environments. The latter has transmission rates of 1 Mbit/s and 2.5 Mbit/s, communication distances of 750m and 500m respectively, supports twisted-pair cabling, fiber optic cable, and wireless transmission, and conforms to the IEC 1158-2 standard. The physical medium of FF uses Manchester encoding for signal transmission.
2. CAN (Controller Area Network)
Originally introduced by the German company Bosch, CAN is widely used in discrete control applications. Its bus specification has been standardized by the ISO international standards organization and is supported by companies such as Intel, Motorola, and NEC. The CAN protocol consists of two layers: the physical layer and the data link layer. CAN signal transmission uses a short frame structure, resulting in short transmission times, automatic shutdown, and strong anti-interference capabilities. CAN supports multi-master operation and employs non-destructive bus arbitration technology, avoiding conflicts by setting priorities. The maximum communication distance is 10 km/5 Kbps/s, the maximum communication rate is 40 Mbps/1 Mbps/s, and the actual number of network nodes can reach 110. Currently, several companies have developed communication chips compliant with the CAN protocol.
3. Lonworks, launched by Echelon Technologies AG and co-sponsored by Motorola and Toshiba, adopts all seven layers of the ISO/OSI model's communication protocol. It employs an object-oriented design approach, simplifying network communication design to parameter settings through network variables. It supports various communication media, including twisted-pair, coaxial, fiber optic, and infrared, with communication speeds ranging from 300 bit/s to 1.5 Mbps and direct communication distances up to 2700 meters (78 Kbit/s), earning it the reputation of a universal control network. The LonTalk protocol used in Lonworks technology is encapsulated within the Neuron chip. Products utilizing Lonworks technology and Neuron chips are widely used in building automation, home automation, security systems, office equipment, transportation, and industrial process control.
4. DeviceNet
DeviceNet is a low-cost communication connection and a simple networking solution with an open network standard. Its direct interconnectivity not only improves communication between devices but also provides crucial device-level infrastructure functionality. Based on CAN technology, DeviceNet offers transmission rates from 125 Kbit/s to 500 Kbit/s, with a maximum of 64 nodes per network. Its communication mode is Producer/Consumer, employing multi-channel broadcast messaging. Devices on the DeviceNet network can be freely connected or disconnected without affecting other devices on the network, and its installation and cabling costs are relatively low. The DeviceNet bus is organized by the Open DeviceNet Vendor Association (ODVA).
5. PROFIBUS
PROFIBUS is a fieldbus standard conforming to German (DIN 19245) and European (EN 50170) standards. It consists of the PROFIBUS-DP, PROFIBUS-FMS, and PROFIBUS-PA series. DP is used for high-speed data transmission between distributed peripherals and is suitable for manufacturing automation. FMS is suitable for textiles, building automation, programmable logic controllers (PLCs), low-voltage switches, etc. PA is a bus type used for process automation and conforms to the IEC 1158-2 standard. PROFIBUS supports several transmission modes, including master-slave systems, pure master systems, and multi-master/multi-slave hybrid systems. PROFIBUS transmission rates range from 9.6 Kbit/s to 12 Mbit/s, with a maximum transmission distance of 1200 m at 9.6 Kbit/s and 200 m at 12 Mbit/s. Repeaters can be used to extend the distance to 10 km. The transmission medium is twisted-pair cable or optical fiber, and up to 127 stations can be connected.
6. HART
HART stands for Highway Addressable Remote Transducer, originally developed by Rosemount. Its key feature is the implementation of digital signal communication over existing analog signal transmission lines, making it a transitional product in the shift from analog to digital systems. Its communication model employs three layers: physical layer, data link layer, and application layer, supporting point-to-point master-slave response and multi-point broadcast modes. Because it uses a mix of analog and digital signals, it is difficult to develop universal communication interface chips. HART can utilize bus power supply, meeting intrinsic safety and explosion-proof requirements, and can be used in dual-master systems where a handheld programmer and a management system host are the primary devices.
7. CC-Link
CC-Link is an abbreviation for Control & Communication Link. Launched in November 1996 by a group of companies led by Mitsubishi Electric, it experienced rapid growth and holds a significant market share in Asia. This system allows control and information data to be transmitted simultaneously to the field network at a high speed of 10 Mbit/s, offering advantages such as superior performance, ease of use, wide applicability, and cost savings. It not only solves the problem of complex wiring in industrial fields but also boasts excellent noise immunity and compatibility. CC-Link is a device-layer-based network that can also cover higher-level control layers and lower-level sensing layers. In July 2005, CC-Link was approved by the China National Standardization Management Committee as a guiding technical document for Chinese national standards.
8. WorldFIP
After the North American portion of WorkdFIP merged with ISPs to form FF, the European portion of WorldFIP remained independent, headquartered in France. It holds a significant position in the European market, particularly in France where it holds approximately 60% market share. WorldFIP is characterized by a single bus architecture to accommodate the needs of various application areas, and it uses software to handle high-speed and low-speed connections without any gateways or bridges. WorldFIP can achieve "transparent connectivity" with FFHSE and has extended the technology of FF's H1 standard, such as in terms of speed. WorldFIP excels in connectivity with IEC 61158 Type I standards, leading the world in this area.
In addition, other influential fieldbuses include P-Net proposed by the Danish company Process-Data A/S, which is mainly used in agriculture, forestry, water conservancy, food and other industries; SwiftNet fieldbus is mainly used in aerospace and other fields; and there are other fieldbuses, which will not be discussed here.
Features of fieldbus
Field control equipment has communication capabilities, which facilitates the formation of a factory's underlying control network.
The openness and consistency of communication standards enable the system to be open and the devices to be interoperable.
The standardization of functional blocks and structures enables interchangeability between devices with the same function.
By delegating control functions to the field, the control system structure becomes highly decentralized.
Advantages of fieldbus
Fieldbus has brought automatic control equipment and systems into the realm of information networks, opening up a wider range of applications for them;
Multiple control devices can be connected to a single twisted pair cable, which saves on installation costs, maintenance expenses, and system reliability; and provides users with more flexible control over system integration.
The current status of fieldbus technology in China:
① Various fieldbus technologies are engaged in fierce competition in the country, with the focus of the competition being application engineering.
② Domestically developed fieldbus products have begun to enter the market;
③ The application of fieldbus in various industries in China has developed rapidly.
The Development Trend of Fieldbus in China
From the perspective of fieldbus technology itself, it has two obvious development trends:
1. To seek a unified international standard for fieldbus;
2. This represents Industrial Ethernet's transition to industrial control networks;
