It is an all-digital, two-way and multi-station communication system connecting intelligent field devices and automation systems. It mainly solves the digital communication between intelligent instruments, controllers, actuators and other field devices in the industrial field and these problems.
Information transmission between field control equipment and advanced control system.
Mainly used for:
Manufacturing, process industries, transportation, construction and other aspects of automation systems.
In April 2003, the third edition of IEC6 1 158 Ed.3 fieldbus standard officially became an international standard, which stipulated 10 fieldbus.
1 TS6 1 158 fieldbus.
Type 2 Control Network and Ethernet /IP Fieldbus
Type 3 Profibus field bus
Type 4 P-NET field bus
Type 5 FF HSE field bus
Type 6 SwiftNet fieldbus
Class 7 World FIP Fieldbus
Type 8 Interbus field bus
9 FF H 1 fieldbus
10 PROFInet fieldbus
Technical characteristics of field bus
(1) all-digital communication
(2) Open Internet
(3) Interoperability and interoperability?
(4) Intelligent field devices?
(5) The system structure is highly decentralized.
(6) Adaptability to site environment
Characteristics of Fieldbus
The field control equipment has communication function, which is convenient to form the bottom control network of the factory.
The openness and consistency of communication standards make the system open and the devices interoperable.
Standardization of functional blocks and structures enables devices with the same functions to be interchanged.
The control function is dispersed to the site, which makes the control system structure highly dispersed.
Advantages of Fieldbus
Fieldbus makes automatic control equipment and system step into the ranks of information network, which opens up a wider field for its application.
Multiple control devices can be hung on a pair of twisted pairs, which is convenient to save installation costs;
Save maintenance costs;
And the reliability of the system is improved;
It provides users with more flexible initiative in system integration.
Development Trend of Fieldbus Technology
From the analysis of fieldbus technology itself, it has two obvious development trends:
The first is to seek a unified international standard for fieldbus.
Second, industrial Ethernet is moving towards industrial control network?
Unified and open TCP/IP Ethernet is the most successful network technology in the past 20 years. In the past, IT was always thought that Ethernet was developed for the application in the IT field, and there was a gap between Ethernet and industrial network in many aspects, such as real-time, environmental adaptability, bus feeding and so on, so it could only be used in the industrial automation field. In fact, these problems are being solved rapidly, and the domestic EPA technology (Ethernet for process automation) has also made great progress.
With the successful development of FF HSE and the popularization and application of PROFInet, it can be predicted that Ethernet technology will soon enter all levels of industrial control system. ?
Development of industrial Ethernet
There are four industrial Ethernet technology camps in the world:
Mainly used in discrete manufacturing control system is:
Modbus-IDA industrial Ethernet
Ethernet /IP industrial Ethernet
PROFInet industrial Ethernet
Mainly used in the process control system are:
Foundation Fieldbus HSE Industrial Ethernet
With the rapid development of science and technology, great changes have taken place in the field of process control in the past two centuries. The pneumatic signal standard (PCS) based on 5- 13 psi appeared more than 50 years ago, which marked the initial formation of control theory, but there was no concept of control room at this time. In 1950s, with the proposal and wide application of analog process control system based on 0- 10 mA or 4-20 mA current analog signal, it marked the arrival of the era of electrical automatic control, and the establishment of three cybernetics laid the foundation of modern control. The mode of setting control room and separating control functions has been used to this day. In 1970s, with the intervention of digital computer, centralized control computer system came into being. Most signal transmission systems still use 4-20 mA analog signals. Soon, people also found that the system is easy to get out of control and has low reliability, and it soon developed into a distributed control system (DCS). With the wide application of microprocessors and the improvement of computer reliability, distributed control systems have been widely used. Distributed control realized by many computers, some intelligent instruments and intelligent components is its most important feature, and digital transmission signals are gradually replacing analog transmission signals. With the rapid development and wide application of microprocessor, digital communication network may extend to the industrial process site, thus producing intelligent devices with microprocessor as the core and integrated circuits instead of conventional electronic circuits to realize information collection, display, processing, transmission and optimal control. The communication and control between devices require higher accuracy, operability, reliability and maintainability. Therefore, the field bus is produced.
The Essence and Advantages of Fieldbus
1984 formally put forward the concept of fieldbus. IEC (International Electrotechnical Commission) defines Fieldbus as a bi-directional, serial and multi-node digital communication technology applied to production site, between field equipment and control equipment.
Different organizations and people may have different definitions of fieldbus, but generally speaking, the recognized essence of fieldbus is embodied in the following six aspects:
Field communication network?
A field communication network for interconnecting field devices or field instruments for process automation and manufacturing automation.
Field device interconnection?
According to the actual needs, different transmission media are used to associate different field devices or field instruments.
Interoperability?
Users can choose different manufacturers or different models of products to form the required control loop according to their own needs, so they can freely integrate FCS.
Decentralized function block?
FCS abandoned the input/output unit and control station of DCS, and distributed the functional blocks of DCS control station to field instruments, forming a virtual control station, which completely realized decentralized control.
Communication line power supply?
The power supply mode of the communication line allows the field instrument to directly absorb energy from the communication line, which provides a low-power field instrument for the intrinsically safe environment, and is also equipped with a safety barrier.
Open the internet?
Fieldbus is an open Internet, which can be interconnected with the same layer of networks and different layers of networks, and can also realize the * * * sharing of network databases.
As can be seen from the above, the field bus embodies the characteristics of distribution, openness, interconnection and high reliability, which are the shortcomings of DCS system. DCS usually transmits signals one by one, and its analog signals have low accuracy and are easily disturbed. It is often difficult for operators in the operation room to adjust the parameters of analog instruments and predict faults, and they are in a "out of control" state. Many instrument manufacturers set their own standards, and their interchangeability is poor, so the functions of instruments are too simple to meet the requirements of modernization, and almost all control functions are located in the control station. FCS adopts one-to-many bidirectional signal transmission, and the adopted digital signal has high precision and strong reliability. The equipment is always in the remote monitoring and controllable state of the operator. Users can freely choose different brands of devices for interconnection according to their needs. Intelligent instruments have rich functions such as communication, control and operation, and the control functions are scattered in all intelligent instruments. It can be seen that FCS has made great progress compared with DCS.
It is precisely because of the above characteristics that FCS has great advantages in design, installation and normal production: first, because the intelligent devices scattered in the front end can perform more complicated tasks, there is no need for a separate controller and computing unit, which saves hardware investment and use area; The wiring of FCS is relatively simple, and more equipment can be hung on one transmission line, which greatly saves the installation cost; Because the field control equipment often has self-diagnosis function, it can send fault information to the control room, which reduces the maintenance workload; At the same time, because users have a high degree of autonomy in system integration, they can flexibly choose suitable manufacturers' products; The reliability and accuracy of the whole system are also greatly improved. All these will help users to reduce the installation, use and maintenance costs, and ultimately achieve the purpose of increasing profits.
Present situation of field bus
Due to the interests of various countries and companies, although the International Electrotechnical Commission/International Standards Association (IEC/ISA) began to formulate the standards for fieldbus as early as 1984, the unified standards have not been completed yet. Many companies have also introduced their own fieldbus technology, but it is difficult to unify its openness and interoperability. At present, the fieldbus market has the following characteristics:
Coexistence of multiple field buses?
At present, there are about forty kinds of field buses in the world, such as FIP in France, ERA in Britain, ProfiBus in Siemens, FINT in Norway, LONWorks in Echelon, InterBus in PhenixContact, CAN in RoberBosch and HART in Rosemounr. Dupline of CarloGarazzi, P-net of ProcessData of Denmark, F-Mux of PeterHans, ASI(ActraturSensorInterface), MODBus, SDS, Arcnet, International Organization for Standardization-Foundation Fieldbus FF: Fieldbus Foundation, WorldFIP, BitBus, DeviceNet, ControlNet of the United States, etc. Most of these field buses are used in process automation, medicine, processing and manufacturing, transportation, national defense, aerospace, agriculture and construction, and less than ten kinds of buses occupy about 80% of the market.
All kinds of buses have their application fields?
Most of each bus has its application fields. For example, FF and PROFIBUS-PA are suitable for the process control fields of petroleum, chemical industry, medicine, metallurgy and other industries. LonWrks, PROFIBUS-FMS and DevieceNet are suitable for construction, transportation, agriculture and other fields. DeviceNet and PROFIBUS-DP are suitable for manufacturing, but these divisions are not absolute. All kinds of field buses are trying to expand their application fields and penetrate each other.
Each fieldbus has its international organization and support background?
Fieldbus mostly takes one or several large multinational companies as the background, and establishes corresponding international organizations in an effort to expand its influence and gain more market share. For example, PROFIBUS, with Siemens as the main support, established the PROFIP international user organization WorldFIP with Alstom as the main background.
Have multiple buses become national and regional standards?
In order to strengthen competitiveness, many buses strive to become national or regional standards, such as PROFIBUS becoming German standard and WorldFIP becoming French standard.
Equipment manufacturers participate in multiple bus organizations?
Many equipment manufacturers often participate in more than one or even more bus organizations in order to expand the application scope of their products.
Are buses coordinated?
Because of the fierce competition, and no one or several buses can unify the market, many important enterprises are trying to develop interface technology to connect their own buses with other buses, and there has also been a coordinated situation in international standards.
The application of industrial automation technology in all walks of life requires ever-changing requirements. It is difficult to meet the technical requirements of all industries with one fieldbus technology. Fieldbus is different from computer network, and people will face a real world with various bus technical standards. Technological development is largely restricted by market rules and commercial interests; Technical standards are not only technical specifications, but also a compromise product of commercial interests. One of the key technologies of fieldbus is interoperability, and it is the wish of all users to realize the unification of fieldbus technology.
Brief introduction of mainstream fieldbus
The following briefly introduces several mainstream fieldbus.
1 Foundation Fieldbus (FF)
This is the merger of the ISP agreement made by Fisher-Rousemount Company of the United States in conjunction with 80 companies including Yokogawa, ABB, Siemens, Yingwei, etc. and the WorldFIP agreement made by more than 50 companies in Europe and other places in September 1994 in conjunction with Honeywell. This bus has been widely used in the field of process automation and has a good development prospect.
Foundation Fieldbus adopts the simplified model of ISO open system interconnection OSI (1, layers 2 and 7), namely physical layer, data link layer and application layer, and adds user layer. FF has two communication rates: low-speed H 1 and high-speed H2. The former has a transmission rate of 3 1.25Kbit/ s and a communication distance of 1900m, which can support bus power supply and intrinsically safe explosion-proof environment. The latter has transmission rates of 1Mbit/ s and 2.5Mbit/ s, communication distances of 750m and 500m, and supports twisted pair, optical cable and wireless transmission. The protocol symbol is IEC 1 158-2 standard. The transmission signal of FF's physical medium adopts Manchester coding.
CAN(controllerarenetwork)？
It was first introduced by BOSCH company in Germany and widely used in the field of discrete control. Its bus specification has been formulated as an international standard by ISO International Standards Organization and supported by Intel, Motorola, NEC and other companies. CAN protocol is divided into two layers: physical layer and data link layer. CAN signal transmission adopts short frame structure, short transmission time, automatic shutdown function and strong anti-interference ability. CAN supports multi-master working mode, adopts lossless bus arbitration technology, and avoids conflicts by setting priorities. The longest communication distance can reach 10KM/5Kbps/s, the highest communication rate can reach 40M/1Mbp/s, and the number of network nodes can actually reach 1 10. At present, many companies have developed communication chips that conform to CAN protocol.
Lonworks？
It was introduced by American Echelon Company and advocated by Motorola and Toshiba Company. It adopts all seven-layer communication protocols of ISO/OSI model, adopts object-oriented design method, and simplifies network communication design into parameter setting through network variables. It supports twisted pair, coaxial cable, optical cable, infrared ray and other communication media. The communication speed ranges from 300bit/s to 1.5M/s, and the direct communication distance can reach 2700m(78Kbit/s). It is called universal control network. LonTalk protocol adopted by Lonworks technology is encapsulated in neuron chip. Products using Lonworks technology and neuron chips are widely used in building automation, home automation, security system, office equipment, transportation, industrial process control and other industries.
DeviceNet？
DeviceNet is a low-cost communication connection and simple network solution with open network standards. The direct interconnection of DeviceNet not only improves the communication between devices, but also provides a very important device-level location function. DebiceNet is based on CAN technology, and the transmission rate is 125Kbit/s to 500Kbit/s, and the maximum number of nodes in each network is 64. Its transmission mode is: producer/consumer, and multi-channel broadcasting information is adopted. Devices located on DeviceNet network can be connected or disconnected freely, without affecting other devices on the network, and the installation and wiring costs of their devices are also low. The organizational structure of DeviceNet bus is the open DeviceNet Supplier Association (ODVA).
5PROFIBUS
PROFIBUS is the field bus standard of German standard (DIN 19245) and European standard (EN50 170). Consists of PROFIBUS-DP, PROFIBUS-FMS and PROFIBUS-PA series. DP is used for high-speed data transmission between distributed peripherals, which is suitable for the field of processing automation. FMS is suitable for textile, building automation, programmable controller, low-voltage switch, etc. The type of PA bus used for process automation conforms to IEC 1 158-2 standard. PROFIBUS supports a variety of transmission modes, such as master-slave system, pure master station system and multi-master and multi-slave mixed system. The transmission rate of PROFIBUS ranges from 9.6Kbit/s to 12Mbit/s, the maximum transmission distance is 1200m at 9.6Kbit/s, and it is as small as 200m at 12Mbit/s, which can be extended to 10km through repeaters. The transmission medium is twisted pair or optical cable, which can be hung at most.
6 hart
HART is the abbreviation of Highway Addressable Remote Transducer, which was first developed by Rosemount Company. Its characteristic is to realize digital signal communication on the existing analog signal transmission line, which belongs to the product of the transition from analog system to digital system. Its communication model adopts physical layer, data link layer and application layer, and supports point-to-point master-slave response mode and multicast mode. Because it uses mixed analog and digital signals, it is difficult to develop a universal communication interface chip. HART can use bus to supply power, which can meet the requirements of intrinsic safety and explosion-proof, and can be used in dual-master systems with handheld programmers and management system hosts as the main equipment.
7CC-Link
CC-Link is the control &; The abbreviation of Communication Link (Control and Communication Link System) was launched by many companies headed by mitsubishi electric on June 1996 1 1. Its growth momentum is rapid, and it occupies a large share in Asia. The system can transmit control and information data to the field network at a high speed of 10Mbit/s, which has the advantages of excellent performance, simple use, wide application and cost saving. It not only solves the complex problem of industrial field wiring, but also has excellent anti-noise performance and compatibility. CC-Link is a network based on device layer, which can also cover upper control layer and lower perception layer. In July 2005, CC-Link was approved by China National Standards Committee as the guiding technical document of China's national standards.
8WorldFIP
After WorkdFIP and the North American part of ISP were merged into FF, the European part of WorldFIP remained independent and was headquartered in France. It occupies an important position in the European market, especially in the French market, with a share of about 60%. The characteristic of WorldFIP is that it has a single bus structure to meet the needs of different application fields, and there is no gateway or bridge. It uses software to solve the connection between high speed and low speed. WorldFIP and FFHSE can realize "transparent connection", and the technology of FF H 1 has been expanded, such as speed. WorldFIP has the best connection with IEC6 1 158, and is in the forefront of the world.
INTERBUS？
INTERBUS is a field bus introduced earlier by German Phoenix Company, and became the international standard IEC6 1 158 in February 2000. INTERBUS adopts the simplified model of ISO open system interconnection OSI (1, 2, 7 layers), that is, physical layer, data link layer and application layer, which has strong reliability, diagnosability and easy maintenance. Lumped frame data ring communication is adopted, which has the characteristics of low speed and high efficiency, and strictly guarantees the synchronization and periodicity of data transmission; The real-time, anti-interference and maintainability of the bus are also excellent. INTERBUS is widely used in automobile, tobacco, warehousing, papermaking, packaging, food and other industries, and has become the leader of international fieldbus.
In addition, the more influential field bus is P-Net proposed by Danish company Process-Data A/S, which is mainly used in agriculture, forestry, water conservancy, food and other industries. SwiftNet field bus is mainly used in aerospace and other fields, and there are some other field buses which will not be described here.
Development of Fieldbus and Ethernet
Fieldbus technology is the intersection and integration of control, computer and communication technologies, covering almost all continuous and discrete industrial fields, such as process automation, manufacturing automation, building semi-automation, home automation and so on. Its appearance and rapid development reflect the requirements of control field for reducing cost, improving reliability, enhancing maintainability and improving data acquisition intelligence. The development of fieldbus technology is reflected in two aspects: first, the continuous development and improvement of low-speed fieldbus field; The other is the development of high-speed field bus technology. At present, field bus products are mainly low-speed bus products, which are used in areas with low running speed and low requirements for network performance. From the practical application situation, most field buses can well realize the process control that does not require high speed. Therefore, it is difficult for anyone to unify the whole market in the control field that does not require high speed. At present, FF Foundation has concentrated almost all the major manufacturers of automation instruments in the world, and its global influence is increasing day by day. However, its marketing in China seems to be insufficient and its market share is not very high. LonWorks has formed a comprehensive system of division of labor and cooperation, and made some substantial progress in China. LonWorks has unique advantages in building automation, home automation and intelligent communication products. In the field of discrete manufacturing and processing, Profibus and CAN have formed their own advantages and strong competitiveness in this field due to the characteristics of industrial application and historical reasons. Domestic manufacturers are relatively small in scale and have poor R&D capabilities. They rely more on the support of technology suppliers and are easily influenced by the domestic support and marketing efforts of fieldbus technology suppliers (chip manufacturers, etc.). ). Moreover, there is one point that cannot be ignored. When building an automatic management system, the selected upper computer, such as the support degree of configuration software for bus devices, and some monitoring configuration software, such as Zijin Bridge monitoring configuration software or InTouch, have good support for some mainstream bus devices, such as Lonworks, PROFIBUS, CAN and so on. , and communicate and collect data through DDE, OPC or direct connection. This can be convenient for users to choose, but some configuration software supports fewer types, which reduces the range of users' choices.
At present, automation technology has developed from single machine control to factory automation FA and system automation. The factory automation information network can be divided into the following three layers: the factory management layer, the workshop monitoring layer and the field device layer, and the field bus is the communication network between the bottom devices of the factory. This is an introduction to Ethernet. This article specifically mentions industrial Ethernet. Industrial Ethernet is an industrial network protocol derived from office automation. Traditionally, it mainly refers to the IEEE 802.3 protocol. If the TCP/IP protocol family is further adopted, it is represented by "Ethernet +TCP/IP". Its technical features are mainly applicable to information management and information processing systems, and it has achieved great success in the IT industry. There have been many successful cases of industrial Ethernet in the field of information integration at the factory management level and workshop monitoring level, and there are also many applications in occasions where real-time requirements are not very strict at the equipment level. At present, there are many kinds of field buses with different standards. Many people hope that Ethernet technology can be involved in lower-level equipment and widely replace the existing fieldbus technology. Schneider Company is an active advocate and practitioner of this concept, and a number of industrial-grade products have been published and applied in practice. But at present, Ethernet can't really solve the real-time and deterministic problems, and most field layers will still choose fieldbus technology first. Due to the limitation of technology and the interests of various manufacturers, such a variety of industrial bus technologies coexist, and the status quo of Ethernet technology will continue to penetrate for some time. Users can choose the required solution according to the technical requirements and actual situation.