Fieldbus (Fieldbus) was developed internationally in the late 1980s and early 1990s. It is used for field intelligent device interconnection communication networks in fieldbus technology process automation, manufacturing automation, building automation and other fields. It serves as the basis for the plant's digital communications network and communicates the links between the production process site and control equipment and its level of higher control management. It is not only a grassroots network, but also an open, new fully distributed control system. This integrated technology with intelligent sensing, control, computer, digital communication and other technologies has attracted worldwide attention and become a hot spot in the development of automation technology, and will lead to profound changes in the structure and equipment of automation systems. Many internationally powerful and influential companies have developed fieldbus technologies and products to varying degrees. The working environment of the fieldbus device is at the bottom of the process equipment. As the factory equipment level basic communication network, it requires the characteristics of simple protocol, strong fault tolerance, good security and low cost: certain time certainty and high real-time performance. Requires that the network load is stable, and most of them are characterized by short frame transmission and frequent information exchange. Due to the above characteristics, the field bus system has the characteristics of different upper layer high speed data communication networks from network structure to communication technology.
The fieldbus system is generally referred to as the fifth generation control system, also known as FCS, the fieldbus control system. People generally refer to the PCS as the first generation of the Pneumatic Signal Control System before the 1950s. The electric analog signal control system such as 4-20 mA is called the second generation, and the digital computer centralized control system is called the third generation. The distributed distributed control system DCS since the middle of the decade is called the fourth generation. As a new generation control system, the fieldbus control system FCS breaks through the limitations of the DCS system using a communication-dedicated network. It adopts an open and standardized solution to overcome the defects caused by the closed system. On the other hand, DCS The centralized and decentralized system of distributed systems has become a new fully distributed structure, and the control functions have been completely decentralized to the scene. It can be said that openness, dispersion and digital communication are the most prominent features of the fieldbus system.
Fieldbus technology outlook and development trend
The development of fieldbus technology should be reflected in two aspects: one is the continued development and improvement of the low-speed fieldbus field; the other is the development of high-speed fieldbus technology.
At present, the fieldbus products are mainly low-speed bus products, which are applied to fields with low operating speeds, and the performance requirements of the network are not very high. From the application status, both FF and Profibus, as well as other fieldbuses, can achieve better process control with slower rate requirements. Therefore, it is difficult for anyone in the control field with lower rate requirements to unify the entire world market. One of the key technologies of fieldbus is interoperability. The unification of fieldbus technology is the desire of all users. How to develop and unify fieldbus technology in the future is a problem that all manufacturers and users are very concerned about.
High-speed fieldbus is mainly used in the interconnection of control networks, connecting devices such as computers and PLCs with high intelligence and fast processing speed, and realizing the connection between low-speed fieldbus bridges. It fully realizes the full decentralized control of the system. The structure is required. This area is still relatively weak. Therefore, the design and development of high-speed fieldbus will be a highly competitive field, which will also be an important opportunity for the integration of fieldbus technology. The choice of what kind of network technology as the overall framework of high-speed fieldbus will be its primary content.
The development of fieldbus technology has become a focus of attention in the field of industrial automation. The research and development of fieldbus in the world has made the measurement and control system break through the prohibition of long-term closed systems and embarked on the journey of open development. This is the Chinese fieldbus control system. The development is an excellent opportunity and a serious challenge. The networking of automation systems is a major trend in development. The fieldbus technology is deeply influenced by computer network technology. Nowadays, network technology is changing with each passing day, and the development is very rapid. Some new network technologies with significant influence will be further integrated into the fieldbus technology. These fieldbus technologies with promising prospects include software and hardware technologies for intelligent instrument and network device development; State of the art, including network topology, network equipment, network segment interconnection, etc.; network management technology, including network management software, network data operation and transmission; human-machine interface, software technology; fieldbus system integration technology.
As automation technology has evolved from stand-alone control to factory automation FA, it has evolved to system automation. The factory automation information network can be divided into the following three layers: factory management level, workshop monitoring level, field equipment level, and fieldbus is the communication network between the factory bottom equipment. Here, I will introduce Ethernet first. This article refers to Industrial Ethernet. Industrial Ethernet is an industrial network protocol derived from the field of office automation. It refers to the IEEE802.3 protocol according to the habit. If the TCP/IP protocol family is further adopted, the "Ether." Net+TCP/IP†indicates that its technical features are mainly suitable for information management and information processing systems, and have achieved great success in the IT industry. In the field of factory management level and workshop monitoring level information integration, there have been many successful cases of industrial Ethernet. There are many applications in the case where the device layer does not have strict requirements on real-time performance. Due to the wide variety of fieldbus and different standards, many people hope that Ethernet technology can intervene in the lower layers of the device and widely replace the existing fieldbus technology. Schneider is an active advocate and practitioner of this idea. At present, there are a number of industrial grades. Product introduction and practical application. But for now, Ethernet can't really solve real-time and deterministic problems, and most field layers still prefer fieldbus technology. Due to the limitations of technology and the interests of various manufacturers, such a variety of industrial bus technologies coexist, the status quo of continuous penetration of Ethernet technology will remain for some time. Users can choose the solution they need based on technical requirements and actual conditions.
The rise of fieldbus technology has opened up a new world of factory underlying networks. It will promote the rapid development of enterprise networks, bring new benefits to enterprises, and thus will be widely used and promote the development of automation related industries.
The nine most popular fieldbuses on the market
At present, there are more than 40 kinds of fieldbuses in the world, but none of them can cover all application planes. According to the size of the transmitted data, it can be divided into three categories: sensor bus (sensorbus), which belongs to bit transmission; device bus (devicebus) ), belonging to byte transfer; field bus, belonging to data stream transmission. Let me go and get to know these nine current re-buses.
1, FF field bus
The FF Fieldbus Foundation was formed by WORLDFIPNA (North American part, excluding Europe) and ISP FoundaTIon in June 1994. It is an international organization whose goal is to create a single, open, interoperable site. Bus international standard. This organization gave strong support to the IEC Fieldbus Standard Drafting Working Group. The organization currently has more than 100 member units, including the world's leading production companies for process control products and systems. In April 1997, the organization established the China Instrument Association Fieldbus Professional Committee (CFC) in China. Committed to the promotion and application of this technology in China. The establishment of FF was relatively late, and it was later than the introduction of PROFIBUS and WORLDFIP in the launch of its own products and the complete application of this technology to engineering. However, since FF was established in September 1992, it is a combination of two major organizations, ISP (Interoperable Operating System Protocol) and WORLDFIPNA, which are based on FisherRosemount. Therefore, this organization has considerable strength: Currently FF is on IEC fieldbus. The standard formulation process plays a pivotal role.
Since its establishment, the Fieldbus Foundation has formed an open, all-digital industrial communication system after ten years of development. It has entered the Chinese market at the end of the last century, promoted the progress of China's industrial automation technology, and began a large-scale operation. Application of system-wide integration. An open bus protocol, it is important to know how many devices support this protocol. Otherwise, the openness of this agreement is meaningless.
In wireless and remote I/O management, the Fieldbus Foundation has released a preliminary specification for the Foundation's remote operations management. The new specification is part of the Foundation's remote operations management solution for wireless and remote I/O, defining fieldbus transmitter modules that represent Foundation HART devices for remote operations management devices. This module can display wired HART and wireless HART devices.
In addition, the specification describes an ideal way to access HART devices for configuration and asset management through the Foundation High Speed ​​Ethernet (HSE) transport of basic HART command protocols. The specification also defines the structure for identifying and maintaining the state of HART devices in wired multi-contact networks and wireless HART networks that connect to Foundation Remote Operations Management devices.
The new transmitter module specification will benefit end users who need to connect HART and wireless HART devices to FOUNDATION fieldbus and enhance their control systems or foundation equipment," said Dave Glanzer, Director of Technology Development at the Fieldbus Foundation: "They may need to adopt a networked approach to asset management, connecting a large number of HART and wireless HART devices for configuration and maintenance. â€
Within the Fieldbus Foundation architecture, H1 and HSE can provide the ability to distribute functional blocks, forming a larger capacity channel with HSE, accelerating data transfer and throughput. The development of the Foundation's remote operations management establishes an open, non-patented specification for wired and wireless HSE backbone networks, which can be used to integrate different Foundation remote operations management devices and wireless field device networks through interfaces.
High-speed HSE connections enable efficient integration of modular digital and analog field I/O devices into the control room. By using HSE device features such as the Intelligent Remote Terminal Unit (RTU), this technology can easily integrate various forms of traditional I/O into a natural fieldbus environment. This solution supports both digital input, digital output, analog input, analog output and H1 fieldbus on the same Ethernet network.
2, LonWorks field bus
LonWorks Fieldbus is a local operating network introduced by Echelon in 1992. It was originally used for building automation, but it soon developed into an industrial field network. LonWorks technology provides a complete, open, and finished solution for designing and implementing interoperable control networks. At the heart of LonWorks technology is the Neuron Chip. The chip is equipped with three microprocessors: the MAC processor completes the medium access control; the network processor completes the OSI layer 3-6 network protocol; the application processor completes the user field control application. Data is passed between them through a common memory. The acquisition and control functions are required in the control unit. To this end, the neuron chip is provided with 11 I/O ports. These I/O ports can flexibly configure interfaces with peripheral devices according to different requirements, such as RS232, parallel port, timing/counting, interval processing, and bit I/O.
LonWorks offers more than just a high-performance neuron chip, and more importantly, it provides a complete development platform. Communication in the industrial field not only needs to send and receive data in real time, but also more data packaging, unpacking, traffic processing, and error processing. This has forced control engineers to invest a lot of effort in data communications. LonWorks provides a very friendly service in this area, providing a complete network building tool - LonBuild.
First, it provides a set of C compilers, which greatly reduces development time. In this compiler, library functions that are very detailed for 11 I/Os are provided. In terms of communication, it also proposes a new concept - network variables. Through network variables, communication on the network simply connects the network variables on the relevant nodes. A network variable is a special static variable defined by the application. It can be various types defined by ANSIC, or it can be a custom type. It can also specify the priority, response mode, and so on. A network variable is defined as an input or output. When a network variable defined as an output is assigned a new value, the input network variable connected to the output variable is immediately assigned the same new value.
In addition, LonBuild integrates the development environment and compilation, has a C debugger, can debug applications on multiple emulators, and has the functions of network protocol analysis and communication analysis.
Since the late 1980s, a variety of fieldbus technologies have gradually formed their influence and demonstrated their advantages in some specific application areas. They all have their own advantages and show strong vitality. For example, Foundation Fieldbus (FF) is a technology that is widely supported in the field of process automation and has good prospects for development. PROFIBUS is the fieldbus standard of the German national standard DIN19245 and the European standard EN50170. This series has DP. FMS. PA three models, of which DP type is suitable for processing automation; FMS type is suitable for textile. Building automation, Programmable Controller. Low-voltage switches, etc.; PA type is used for process automation. CAN was first introduced by the German company BOSCH for data communication between the internal measurement and execution components of the car. HART was first developed by ROSEmount and supported by more than 80 well-known instrument companies. It is the communication of digital signals on existing analog signal transmission lines. Because they are independent in their respective scopes, it inevitably limits the development of the whole system, which is not conducive to the system integration of the whole system, and the Lonworks products developed by our company are in the wine making. electric power. building. It has been applied in industrial automation and chemical industry with good results.
With the continuous advancement of China's socialist modernization process, China's demand in the field of intelligence has increased dramatically. The inherent limitations of other field-type fieldbuses available internationally make them subject to such constraints when applied. The LON bus combines the functions of today's fieldbus with some features of the LAN, making it widely used in aerospace/aerospace, agricultural control, computer/peripheral, diagnostic/monitoring, electronic measuring equipment, test equipment. , health care, military / defense, office equipment systems, robots, security guards, security, sports / entertainment, telephone communications, transportation equipment and other fields. Its versatility shows that it is not a bus for a particular area, but a network technology that combines control systems from different domains into a more complex system based on LONWORKS.
3, Profibu field bus
Profibus is a fieldbus as the German national standard DIN19245 and the European standard prEN50170. The ISO/OSI model is also its reference model. The Profibus series is composed of Profibus-Dp, Profibus-FMS and Profibus-PA. The DP type is used for high-speed transmission between distributed peripherals and is suitable for applications in the field of processing automation. FMS means on-site information specification for general automation such as textiles, building automation, programmable controllers, low-voltage switches, etc., while PA type is a bus type for process automation that complies with the IEC1158-2 standard. The technology was jointly launched by more than a dozen German companies and research institutes led by Siemens. It adopts the physical layer and data link layer of the OSI model. The two parts form a subset of the first part of the standard. The DP type hides the 3-7 layers, and the direct data connection fitting is added as the user interface. The FMS type only hides the third to sixth layers, and uses the application layer as the second part of the standard. The PA type standard is still in the process of development, and its transmission technology complies with IEC1158-2(1) standard, which can realize bus power supply and intrinsically safe explosion-proof.
Porfibus supports several transmission modes such as master-slave system, pure master station system, multi-master multi-slave hybrid system. The master station has control over the bus and can actively send information. For the multi-master system, the master station uses the token method to transfer information, and the site that obtains the token can have the bus control right within a predetermined time, and the token is preset in the main station for one week. The longest time. According to Profibus's communication specification, tokens are transmitted in the upstream direction in the order of address numbers between the primary stations. When the master station gains control, it can send or request information to the slave station in a master-slave manner to achieve peer-to-peer communication. The primary station can broadcast to all stations (no answer required) or selectively broadcast to a group of sites. Profibus has a transmission rate of 96 to 12 kbps and a maximum transmission distance of 1000 m at 12 kbps and 400 m at 15 Mbps, which can be extended to 10 km with repeaters. The transmission medium can be a twisted pair or an optical cable, and up to 127 stations can be attached.
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