Content abstract: This article introduced the field bus concept, to and its has the background and the most recent development present situation, has made the summary to the field bus essence and the merit, compared with several kind of mainstreams field buses, and has made the simple introduction to the industry ethernet and the field bus relations. The article faces the object for to controls the primary reader which the domain and the field bus is interested, is connected the content basic material.

The field bus is in the process control theory hot topic of discussion, also is connected the domain technical hot spot, has received in the world scope widespread attention. In discusses in front of the field bus we might as well first recollect the process control domain developing process as well as the field bus production background. Perhaps this can to us understand the field bus the essence and the development has the help.

Control system development as well as field bus production

Along with the science and technology fast development, the process control domain has had the huge transformation in the past two centuries. More than 150 years ago appear based on 5 - 13psi air operated signal standard (PCS, Pneumatic Control System pneumatic control system), symbolize the control theory preliminary formation, but this time not yet have the control room the concept; The 20th century 50's, along with based on 0 - 10mA or 4 - 20mA electric current simulated signal simulation process control system were proposed and obtain the widespread application, had symbolized the electrical automatic control time arrival, three big cybernetics establishments have laid the modern control foundation, sets up the control room, the control function separation pattern also continuously continues to use until now; The 20th century 70's, along with the digital computer involvement, has had "the common control" the central control computer system, but the signalling systematic majority is still continues to use 4 - 20mA the simulated signal, soon the people also had discovered is following "the common control", this system easily has out of control, the reliable low shortcoming, and very quickly its development for distributional control system (DCS, Distributed Control System distributional control system); The microprocessor universal application and the computer reliable enhancement, enable the distributional control system to obtain the widespread application, realized the distributional control by many computers and some intelligent measuring appliances as well as the intelligent part is its most main characteristic, but the digital transmission signal also gradually was substituting for the simulation transmission signal. Along with the microprocessor fast development and the widespread application, the digital communication network extends to the commercial run scene becomes possibly, has produced take the microprocessor as the core, the use integrated circuit replaces the convention electronic circuit, implements function the and so on information gathering, demonstration, processing, transmission as well as optimized control intelligent equipment. Between the equipment each other correspondence, the control, in the precision, may be operational as well as the reliability, maintainable and so on all has a higher request. From this, has caused the field bus production.

Field bus essence and merit

In 1984, the field bus concept obtained officially proposed. IEC (International Electrotechnical Commission, international electrician committee) to field bus (Fieldbus) the definition is: The field bus is one kind applies to produces the scene, between the scene equipment, the scene equipment and between the control device implements, the string shape, the multi- points digital communication technology bidirectional.

The different organization and the different person possibly have the different definition to the field bus, but in the usual situation, everybody recognizes the field bus the essential body now following six aspects:

Scene correspondence network
Uses in scene correspondence network which the process automation and the manufacture automation scene equipment or the scene measuring appliance interlocks.

Scene equipment interconnection
Rests on the actual need use different transmission medium the different scene equipment or the scene measuring appliance interdependence.

Mutually operational
The user may act according to the control loop which own demand choice different factory or the different model product constitution needs, thus may freely integrate FCS.

Dispersible function block
FCS has abandoned the DCS input/output unit and the control station, dispersible assigns the DCS control station function block for the scene measuring appliance, thus constitutes the hypothesized control station, thoroughly has realized the disperser control.

Passes the fuse power supply
Passes the fuse power supply way to allow the scene measuring appliance directly from to pass on the fuse to absorb the energy, this way provides uses in the essential security environment low power loss scene measuring appliance, if necessary also has the safety fence.

Open style internet
Field bus for open style internet, also may with with the level network interconnection, also may with the different level network interconnection, but also may realize network database sharing.

We may see from the above content, the field bus has manifested the distribution, the opening, the interconnection, the redundant reliable characteristic, but these are precisely the DCS system shortcomings. DCS usually is a pair one alone transmits the signal, its uses simulated signal precision low, is easy to receive disturbs, the operator which is located the handling room to simulates the measuring appliance often with difficulty to adjust the parameter and the forecast breakdown, is at "out of control" the condition, the very many measuring appliances merchant from decides the standard, interchangeability bad, the measuring appliance function is also more unitary, satisfies with difficulty modern the request, moreover the nearly all control function all is located in the control station. FCS adopts a pair of two-way transmission signal, uses the digital signal precision high, the reliability is strong, the equipment also throughout is at operator's long-distance monitoring and the controllable condition, the user may freely according to have to choose the different brand type the equipment interconnection, the intelligent measuring appliance has the correspondence, the control and the operation and so on the rich function, moreover the control function disperses to each intelligent measuring appliance in. May see from this us FCS is opposite to the DCS huge progress.

Also is precisely because the FCS above characteristic causes it in the design, the installment, to throw transports all has the very big superiority to the regular production: First because disperses in the front end intelligent equipment can carry out a more complex task, no longer needs the independent controller, the computing element and so on, has saved the hardware investment and the useable area; The FCS wiring is simple, moreover a transmission line was allowed to hang meets many equipment, greatly saved the installment expense; Because the scene control device often has from the diagnosis function, and could the breakdown information transmission to the control room, reduce the maintenance work; At the same time, because the user has the high system integration right to independence, may through the quite nimble choice appropriate factory product; The integrated system reliability and the accuracy also greatly are the enhancement. All these helped the user to realize decreased the installment, the use, the maintenance cost, finally achieved the increase profit the goal.

Field bus present situation

As a result of each national each company's struggle benefit, although as early as the international electrician technical committee/international standard association (IEC/ISA) began in 1984 to start to formulate the field bus standard, until now unifies the standard has not still completed. Very many companies also promote its respective field bus technology, but each other openness and operational also with difficulty is mutually unified. Below at present the field bus market has the characteristic:

The many kinds of field bus coexists
At present in the world has the about 40 kind of field buses, like France's FIP, England's ERA, Germany siemens Siemens ProfiBus, Norway's FINT, Echelon Corporation's LONWorks, PhenixContact Corporation's InterBus, RoberBosch Corporation's CAN, Rosemounr Corporation's HART, CarloGarazzi Corporation's Dupline, Danish ProcessData Corporation's P-net, PeterHans Corporation's F-Mux, as well as ASI (ActraturSensorInterface), MODBus, SDS, Arcnet, international standard organization - foundation field bus FF: FieldBusFoundation, WorldFIP, BitBus, US'S DeviceNet and ControlNet and so on. These field buses mostly use in domain and so on process automation, medicine domain, processing manufacture, transportation, national defense, astronautics, agriculture and building, probably does not hold 80% about to ten kind of main lines the market.

Each kind of main line all has its application the domain
Each kind of main line mostly has its application the domain, for instance FF, PROFIBUS-PA are suitable for profession the and so on petroleum, chemical industry, medicine, metallurgy process control domain; LonWrks, PROFIBUS-FMS, DevieceNet are suitable for domain and so on building, transportation, agriculture; DeviceNet, PROFIBUS-DP are suitable for the processing manufacturing industry, but these divisions is not absolute, each kind of field bus all tries hard its application domain to expand, each other seepage.

Each kind of field bus all has its international organization and the support background
The majority field bus all has or several large-scale multinational corporations for the background and the establishment corresponding international organization, tries hard to expand own influence, to obtain the more market share. For instance PROFIBUS take Siemens Corporation as the main support, and established the PROFIBUS international user to organize WorldFIP take Alstom Corporation as the main backstage, has established the WorldFIP international user organization.

The many kinds of main lines become the country and the local standard
In order to strengthen own competitive ability, very many main lines all strive for into national or the local standard, for instance PROFIBUS has become the German standard, WorldFIP has become the norme francais nf and so on.

The equipment manufacturer participates in many main lines organization
In order to expand the oneself product the use scope, the very many equipment manufacturer often participation continues a really at most main line organization.

Each main line each other coordination coexists
Because competes intensely, which moreover doesn't have one kind of or several kind of main lines can a series market, very many important enterprises all try hard to develop the connection technology, enables own main line to be connected with other main lines, also had the coordinated coexistence aspect in the international standard.

The industrial automation technology applies to all the various trades and occupations, the request also ever changing, uses one kind of field bus technology very to be also difficult to satisfy all professions the specification; The field bus is different with the computer network, the people will meet with to a many kinds of main lines technical standard coexistence real world. In the technological development very great degree receives the market rule, the commercial interest restriction; The technical standard not only is a technology standard, also is a commercial interest compromise product. But one of field bus essential technical is each other mutually is operational, realizes the field bus technology unification is all users' desire.

Mainstream field bus synopsis

Under makes a simple introduction on several kind of mainstreams field buses.

1 foundation field bus (FoundationFieldbus is called FF)

This was take American Fisher-Rousemount Corporation as the head union the ISP agreement and take Honeywell Corporation which horizontal river, ABB, Simens, England 维斯 and so on 80 companies formulated as the head the WorldFIP agreement which united places 150 companies such as the Europe formulates merges in September, 1994. This main line obtained the widespread application in the process automation domain, has the good prospects for development.

The foundation field bus uses International Standardization Organization ISO the opening system to interconnect OSI the simplification model (1, 2, 7), namely physical level, data link layer, application level, moreover increased the user level. FF divides low speed H1 and the high speed H2 two kind of correspondences speeds, former transmission speed is the 31.25Kbit/ second, the signal distance may reach 1900m, may support the main line power supply and the essential safe explosion-proof environment. Latter transmission speed is 1Mbit/ second and the 2.5Mbit/ second, the signal distance is 750m and 500m, supports the twisted pair line, the optical cable and the wireless launch, the agreement mark IEC1158-2 standard. The FF physical medium transmission signal uses graceful Chester to code.

CAN (ControllerAreaNetwork controller local area network)
Most early promotes by German BOSCH Corporation, it widely uses in to be separated the control domain, its main line standard already by the ISO international standard organization formulation was the international standard, obtained company's the and so on Intel, Motorola, NEC support. The CAN agreement divides into two: Physical level and data link layer. The CAN signalling uses the short frame structure, the transmission time is short, has the automatic shut-off function, has the stronger antijamming ability. CAN supports the multi- hosts work way, and has used the non- destructive main line arbitration technology, avoids through the establishment priority conflicting, the communication is away from far may reach 10KM/5Kbps/s, communication speed most Gao Keda 40M /1Mbp/s, the link points actually may reach 110. At present had many companies to develop has conformed to the CAN agreement correspondence chip.

Lonworks
It promotes by American Echelon Corporation, and by Motorola, Toshiba Corporation initiates together. It uses the ISO/OSI model completely 7 communications agreements, uses the object-oriented design method, simplifies through the network variable the network correspondence design as the parameter establishment. The support twisted pair line, the coaxial cable, the optical cable and the infrared and so on the many kinds of correspondences medium, the communication speed is different from 300bit/s to 1.5M/s, the direct communication distance may reach 2700m (78Kbit/s), by reputation for general control network. The Lonworks technology uses the LonTalk agreement seals Neuron (neuron) in the chip, and can realize. Uses the Lonworks technology and the neuron chip product, is widely applied in profession and so on building automation, household automation, security system, office equipment, transportation, commercial run control.

DeviceNet
DeviceNet is one kind of low cost correspondence connection also is one kind of simple network solution, has the opening the network standard. DeviceNet has the direct interconnection not only improved correspondence between the equipment moreover to provide the quite important equipment level position function. DebiceNet based on the CAN technology, the transmissibility is 125Kbit/s to 500Kbit/s, each network biggest pitch point is 64, its correspondence pattern is: The producer/customer (Producer/Consumer), selects the multi- channels broadcast information transmission method. Is located in the DeviceNet network the equipment to be allowed freely to connect or the separation, does not affect the on-line other equipment, moreover its equipment installs the wiring cost to be also lower. The DeviceNet main line organizational structure is Open DeviceNet Vendor Association (open style equipment network supplier association, abbreviation "ODVA").

5PROFIBUS

PROFIBUS is the German standard (DIN19245) with the European standard (EN50170) field bus standard. By PROFIBUS--DP, PROFIBUS - FMS, PROFIBUS - the PA series is composed. DP uses in outside the disperser to suppose the high speed data transmission, is suitable to the processing automation domain. FMS is suitable for the spinning and weaving, the building automation, the programmable controller, the low pressure switch and so on. PA uses in the process automation main line type, obeys the IEC1158 - 2 standards. PROFIBUS supports the host systematically - from, the pure master station system, the multi- hosts are many from the mix system and so on several transmission modes. The PROFIBUS transmission speed is 9.6Kbit/s to 12Mbit/s, the maximum transmitting range under 9.6Kbit/s is 1200m, in 12Mbit/s small is 200m, may use the repeater to lengthen to 10km, the transmission medium for the twisted pair line or the optical cable, are most may hang meets 127 stands.

6HART

HART is the Highway Addressable Remote Transducer abbreviation, most early develops by Rosemount Corporation. Its characteristic is realizes the digital signal correspondence in the existing simulated signal transmission line, belongs to the analogous system the transition product which transforms to the number system. Its correspondence model uses the physical level, the data link layer and application level three, supports the point-to-point host from the reply way and the multi- spots broadcast way. Because it uses the analog-digital signal to mix, develops the general correspondence connection chip with difficulty. HART can use the main line power supply, may satisfy the essential safe explosion-proof the request, and may use in by to grasp the programming and the management system management system main engine makes primarily the equipment double main equipment system.

7CC-Link

CC-Link is Control&Communication Link (control and correspondence link system) the abbreviation, in November, 1996, promoted by the Mitsubishi electrical machinery for leading many companies, its growth tendency was swift and violent, held a bigger share in Asia. In its system, may control and the information data with is by the 10Mbit/s high speed transmission to the scene network, has the performance remarkably, the use is simple, widely applies, merit and so on economical cost. Its not only solved the industry scene to match the line complex question, simultaneously had the outstanding anti- chirp performance and the compatibility. CC-Link is by the equipment level primarily network, simultaneously also may cover a higher level the control level and the lower level 传感 level. In July, 2005 CC-Link by Chinese country standard board approval for Chinese country standard instruction technology document.

8WorldFIP

The WorkdFIP North America part and the ISP merge is after FF, the WorldFIP Europe partial still maintained the independence, the headquarters is located in France. It holds the important status in the European market, specially in French 占有�?probably is 60%. The WorldFIP characteristic is has the sole main line structure to be suitable the different application domain the demand, moreover does not have any gateway or the net bridge, solves high speed and low speed linking up with the software means. WorldFIP and FFHSE may realize "the transparent joint", and has carried on the technical development to FF H1, like speed and so on. In with the IEC61158 first type connection aspect, WorldFIP does well, walks in the world front row.

INTERBUS
INTERBUS is the earlier field bus which German Phoenix Corporation promotes, in February, 2000 becomes international standard IEC61158. INTERBUS uses International Standardization Organization ISO the opening system to interconnect OSI the simplification model (1, 2, 7), namely the physical level, the data link layer, the application level, have the formidable reliability, may the diagnosis and the easy maintenance. It uses the lump frame data link correspondence, has the low speed, the high efficiency characteristic, and strictly has guaranteed the data transmission synchronism and the periodicity; This main line timeliness, the anti-jamming and the maintainability extremely are also splendid. INTERBUS widely applies the automobile, the tobacco, stores in a storehouse, industry and so on papermaking, packing, food, becomes the international field bus being in the lead.

In addition the more influential field bus also has P-Net which Danish company Process-Data A/S proposed, this main line mainly applies to profession and so on agriculture, forestry, water conservation, food; SwiftNet field bus main use in domain and so on aerospace, but also had some other field bus here no longer to give unnecessary detail.

Field bus development and ethernet

The field bus technology is the control, the computer, communication technology intersecting with the integration, nearly has covered all continuously, the separate industry domain, like process automation, manufacture processing automation, building semiautomation, household automation and so on. Its appearance and the fast development manifested the control domain to reduce the cost, to enhance the reliability, the enhancement maintainability and enhances the data acquisition the intellectualization request. The field bus technology development manifests is two aspects: Is the low speed field bus domain unceasing development and the consummation; Another is the high speed field bus technology development. But at present field bus product mainly is the low speed main line product, applies to an operating speed lower domain, to the network performance requirement is not very high. Looking from the practical application condition that, the majority field bus, all can realize the speed to request the lower process control well. Therefore, requests the lower control domain in the speed, everybody very is difficult to unify the entire market. In the present case, because the FF foundation nearly has concentrated in the world the main automated measuring appliance manufacturer, its whole world influence increases day by day, but it is as if insufficient in the Chinese market marketing dynamics, the market share is not very high, LonWorks has formed the comprehensive division of labor and cooperation system, in domestic has some substantive progress, in aspect and so on building automation, household automation, intelligent correspondence product, LonWorks has the unique superiority. In the separate manufacture processing domain, as a result of the profession application characteristic and the historical reason, Profibus and CAN after has formed own superiority in this domain, has the stronger competitive ability. Domestic merchant scale relative smaller, research and development ability worse, what are more relies on the technical supplier's support, compared with easily field bus technology supplier (chip manufacturer and so on) to domestic support and market introduction dynamics influence. Moreover, but also some noticeable is when constructs the automation management system management system, the choice on position machine, for instance configuration software to the main line equipment degree of support, some monitorings configuration software, for instance purple golden bridge monitoring configuration software or InTouch and so on to some mainstreams main line equipment for instance Lonworks, PROFIBUS, CAN and so on has the good support, through way and so on DDE, OPC or direct connection carries on the communication, gathers the data. This may facilitate the user the choice, but some configuration software support the type are less, is the user choice scope also along with it reduction.

Because the present automation technology develops from the single plane control to factory automation FA, develops the system automation. The factory automation information network may divide into following three structures: Plant management level, workshop monitoring level, scene equipment level, but the field bus is between the factory first floor equipment correspondence network. Here first introduced the ethernet, this article refers in particular to the industry ethernet, the industry ethernet is the industry network agreement which grows as the office automation domain, mainly refers to the IEEE 802.3 agreements according to the custom, if further uses the TCP/IP agreement race, then uses "ethernet +TCP/IP" to indicate, its technical characteristic mainly suits the information management, the information management system, and obtained the huge success in IT industry. In the plant management level, in the workshop monitoring level information integration domain, the industry ethernet had many successes the case, also has many applications in the equipment level to the timely not strict request situation. Because the field bus at present the type is many, the standard one, very many people all did not hope the ethernet technology can involve the equipment underlying bed, the widespread substitution existing field bus technology, Shi Naide the company is this idea positive initiator and the practice, at present had one batch of industries levels product to be published with the practical application. But in the present case, the ethernet cannot truly solve timeliness and the definite question, the majority of scenes level still met the first choice field bus technology. As a result of the technical limitation and each factory struggle benefit, this kind of many kinds of industries main line technology coexists, the ethernet technology unceasingly seeps the present situation also can maintain period of time. The user may chooses the solution according to the specification and the actual situation which needs.

Reference: "Field bus And its Application Technology" Li Zhengjun arranges the mechanical industry publishing house to publish in January, 2006 first edition

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