Fieldbus is a bidirectional, serial, fully digital communication network used to connect instruments, controllers, and other automation devices in a production field. It is the core technology of a new generation of fully distributed control systems that emerged internationally in the 1990s. With the advent of the digital age, Fieldbus Control Systems (FCS) will inevitably replace traditional distributed control systems (DCS) and become the mainstream of industrial automation .
The "Foundation Fieldbus Protocol Software and Style Controller" project has completed the development of the Foundation Fieldbus Network Controller (commonly known as a network interface card) and its running fieldbus protocol software. This achievement represents the core technology of fieldbus and forms the foundation for developing fieldbus control products. The fieldbus protocol software developed in this project has become the first in China to pass international certification testing, making my country one of the few countries in the world to master core fieldbus technology and filling a domestic gap.
Fieldbus technology
The development of automatic control system technology has greatly improved the efficiency and quality of modern industrial production. Looking back at the development of process industries since the 1930s, it is easy to see that in the process of production systems evolving from pneumatic, electric, and unit control to computer control, automatic control system technology has constituted the main theme of the development and technological progress of process industries.
Since the 1980s, distributed control systems have been the dominant product in process industry main control systems. In the mid-to-late 1980s, due to the rapid development of microelectronics and software technology, modern communication technology gradually penetrated into industrial control systems, leading to the gradual replacement of 4-20mA analog signal transmission lines by fieldbuses, which triggered a technological revolution in the field of control systems. The main manifestations are: (1) intelligent field instruments - with the ability of local control and bus communication; (2) the structure of control systems is completely decentralized.
Fieldbus technology broadly refers to a bidirectional, serial, fully digital communication network connecting field devices such as sensors , transmitters, and actuators. It is a low-level device network for industrial control. Internationally, there are eight fieldbus technology standards, such as FF, Profibus, CAN, Lonwork, WorldFIP, and P-NET. However, in the field of process automation, the Foundation Fieldbus (FF) and Profibus-PA Fieldbus are the main standards. While they share a fundamentally similar architecture, they are competitors in the market. FF is the only international organization dedicated to unifying global fieldbus standards and has the greatest impact on the development of process control systems. Fieldbus-based distributed control systems have many advantages over DCS, primarily:
1. Fully digital
The organic integration of enterprise management and production automation has long been a dream of the industrial sector, but this ideal could only be realized efficiently and at low cost with the advent of fieldbus control systems. In enterprises employing fieldbus control systems, the local area network used for production management can be seamlessly integrated with the fieldbus network used for automatic control. Furthermore, the inherent high precision and anti-interference characteristics of digital signals also improve the reliability of the control system.
2. Total distribution
In FCS, each field device has sufficient autonomy and can communicate with each other. Various control functions can be distributed among various devices, eliminating the need for a central control computer and achieving true distributed control.
3. Bidirectional transmission
Traditional DCS control systems typically use 4–20mA current signals, with only one signal transmitted per line. Fieldbus devices, on the other hand, can transmit sensor signals upwards and control information downwards on a single line.
4 Self-diagnosis
Fieldbus instruments have self-diagnostic capabilities, and this diagnostic information can be sent to the central control room for maintenance, which is not possible with traditional instruments that can only transmit one signal.
5. Saves wiring and control room space
Traditional DCS systems require each instrument to be connected to the central control room via a separate cable, necessitating a large patch panel in the central control room. In contrast, fieldbus control systems allow multiple field devices to be connected serially on a single bus, requiring only a minimal number of cables to enter the central control room, significantly reducing wiring costs and lowering the overall cost of the central control room.
6. Multifunctional Instrument
Digital and bidirectional transmission methods enable fieldbus instruments to break free from the limitations of traditional instruments with single functions. Multiple functions can be integrated into one instrument to create multi-variable transmitters, or even transmitter controllers that integrate detection, calculation, and control.
7. Openness
In late 1999, the fieldbus protocol was officially approved by the IEC as an international standard, thus making fieldbus an open technology.
8 Interoperability
Fieldbus standards ensure interoperability between products from different manufacturers. This allows users within a single enterprise to select products from different manufacturers based on performance and price, integrating them together. This avoids the limitation of traditional DCS systems that require products from the same manufacturer, promotes effective competition, and reduces the cost of the control system.
9. Intelligence and Autonomy
Fieldbus devices can process various parameters, operating status information, and fault information. They are highly intelligent and can work independently in the event of component or even network failures, greatly improving the reliability and fault tolerance of the entire control system.
In recent years, the research and development of fieldbus technology has become an international hot topic, with many well-known foreign companies investing significant human and financial resources and already launching some products. The Chinese government has also attached great importance to fieldbus technology, listing it as a key national science and technology project during the Ninth Five-Year Plan period. This achievement was completed based on the national key research project undertaken by the Shenyang Institute of Automation.
