> Abstract: The field bus control
technology took the industry standard the new scene solution, it compares with the traditional process control
technology has many obvious superiority. The article has made
the explicit analysis and the comparison from each aspect to the field
bus control technology, and produces selects what kind of
main line standard the suggestion.
Key word: Field bus; Field bus control
system ( FCS) ; Disperser control
system (DCS)
1 introduction
The field bus ( Fieldbus) the
technology realizes the scene cascade control equipment digitization
correspondence one industry scene level network communication;
Is an industry scene level equipment correspondence digitized
revolution. Along with the computer technology, the
communication, the control technology development, causes
this kind of entire digitization, the entire disperser -like, the
entire opening to be possible mutually to operate and the open style
internet new generation of field bus control system ( FCS) obtains the considerable development. It unifies
with the intellectualized scene equipment fully manifests the field
bus control system the superiority. The field bus superiority is
does not need doubt, it also is the oncoming force is
turbulent in each profession application. Therefore we pay
attention to its development tendency, is very much
significant.
2 field buses technology concept
At present, recognition field bus
technology concept description as follows: The field bus
is installs in the production process region scene equipment/measuring
appliance and between the control room automatic control device/system
one kind serial, digital, the multi- spots correspondence data bus.
Among them, "production process" including off and
on production process and continuous production process two kinds.
Or, the field bus is by individually disperses,
digitized, the intellectualized survey and the control device took the
node, connects with the main line, the
realization mutually exchanges the information, completes
the automatic control function together the network system and the
control system.
3 based on field bus control system main characteristic
Compare with the traditional simulation measuring
appliance control system and other field bus measuring appliances, the field bus and the field bus control system has the
enormous superiority in following several aspects.
3. 1 system structure big simplification, reduces
the system and the project cost
The traditional control system (for example DCS) is maintaining a pair of connection way with the
simulation measuring appliance between, all needs to use
a pair of transmission line each scene measuring appliance to the
control system, an unidirectional transmission simulated
signal.
This kind of structure, needs to use the I/O
module, the connecting box, the electric cable in the scene; Must use the massive electric cables, the terminal row in
the control room. Measuring appliance to system connection link
many, thus causes the equipment expense high, takes the space in a big way, wiring
numerous and disorderly, installment expense high, the project cycle is long, maintains the
difficulty.
Between the field bus measuring appliance and the control system
uses is a pair of N connection way, a pair of
transmission line may meet N equipment, two-way transmission many signals. This kind of
structure saves the massive electric cables, does not
need to use the I/O module, the connecting box and the massive
terminal rows, causes the wiring big simplification, reduces by the unreliable factor which 接线?creates.
The equipment takes the space slightly, installment
expense low, project cycle short, maintains
conveniently, the system expansion is easy.
3. 2 true dispersers controls
The field bus control system disperses the tradition
control system control function to the scene measuring appliance
module in, the scene equipment and the measuring
appliance constitute the control loop, no longer like
today process automatic control structure take DCS as a center, no longer relies on the control room, has
cancelled the I/O unit and the control station, realizes
the thorough disperser. In the scene control loop, changes delivering not only to have the signal to change
delivers, compensates and so on the function, but also
has I/O, P the ID adjustment and the operation function; The implementing agency not only has the signal to
transform and to carry out the function, but also may
contain the input level to verify and the compensatory function, also
may have P the ID control and the operation function.
Each kind of function is all made by the modulation the function
block, the user may according to need to select the
function block to install in the scene equipment and the measuring
appliance, the control function block may put in changes
in the delivering module, also may put in the execution
module, or the two establishes, realization redundancy control. The control system
still might carry on the long-distance monitoring to the process,
carried on the on-line configuration, the correction to the scene
measuring appliance and the equipment and so on, meanwhile might use the control system to complete some
complex controls and the management function. Like this enhances
the system the reliability, the autonomy and the flexibility.
3. 3 open style, is mutually operational, the
maintainability, may the integration
The different factory product so long as uses the
identical main line standard, has mutually
operationally, the interchangeability, therefore the
equipment has very well may the integration. System for open
style, permits other merchants own specialty control
technology, like the control algorithm, the technical
process, the formula and so on integrate in the general system, therefore, in the market will have many
will face the profession characteristic the supervisory system.
Similarly also strengthened the scene level information
integration ability, the field bus has been possible from the scene
equipment gain massive rich information, could the
better satisfied factory automation and the CIMS system information
integration request. The field bus is the digitized
correspondence network, it not purely substitutes for 4
~ 20 mA signal, but also may realize the
scene level equipment on-line breakdown diagnosis, report to the
police, the recording function, may complete scene
parameter work and so on the equipment long-distance parameter
hypothesis, revision, also strengthened the system
maintainability. Based on field bus automation supervisory
system if uses the computer digitization communication, causes the automatic control system and the equipment
joins the factory information network, the constitution
enterprise information network first floor, causes the
enterprise information communication the cover scope continuously to
extend to produces the scene.
In the CIMS system, the field bus is the factory
computer network to scene level equipment extending, is
supports the scene level information integration the technology base.
3. 4 pair of environment highly compatibility
The field bus is specially for the industry scene
design, it may use the twisted pair line, the coaxial
cable, the optical cable, the electricity line of force and the
wireless way transmits the data, has the very strong
antijamming ability. The commonly used data link is the
inexpensive twisted pair line, and allows the scene
equipment to pass the fuse using the data to carry on the power
supply, but also can satisfy the essential safe
explosion-proof request.
3. 5 scales invariable control system and nimble
network topology
Traditional DCS or PLC divide big, middle, the small
scale and the model, increases when the equipment must
increase the electric cable, the I/O connection and meets 线牌, even increases the controller, also must
use the different machine language to the different system and so on
to carry on the configuration, the system expands for
the design and the construction brings many is inconvenient.
The field bus control system uses the complete disperser -like
structure, the system function unit modulation, in the function block inlays in the field bus equipment
and the measuring appliance or the controller, the scene
equipment and the measuring appliance equally hang as the pitch point
meets on the field bus, if is the relative perfect
condition, from several return routes to several hundred
return routes may. The increase control loop or the unit, only must hang the equipment receives in the node, function formidable software may help us the rapid
configuration scene equipment, and the investment
movement, the system expands extremely simply, therefore is called the scale invariable control system.
The field bus control system may act according to the complex
scene situation composition different network topology, like tree, star, main line and level network
architecture and so on.
It can be said that, the development, the
dispersivity and the low cost are the field bus most remarkable three
big characteristics. Under some special professions, the special
request, the field bus as well as uses the nimble
network architecture to the environment compatibility has the
necessity very much. For instance in the dangerous region, requests the scene equipment the explosion-proof; The conventional explosion-proof method can through the
limit energy avoid because the electromagnetic induction produces
spark energy. Like this had the contradiction with the field bus
main merit, because in order to limit the energy (to
utilize this peaceful method) , then, in each main line branch allows the connection the scene
equipment to be able the big reduction. Also for instance the
main line uses the striation structure, if a main line
leg electric cable broke, this leg was paralysed; If uses the network structure, even if
broke 12 legs, the information also may through other way
transmissions, the system function be able to drop, but
cannot be paralysed.
4 main field buses synopsis
The field bus development is rapid, right
now is at the stage which the independent warlords rises together
simultaneously, hundred school of thought contends, at
present has developed 40 many kinds of field buses, has
the influence to have 4 kinds.
4. 1 foundation field bus FF ( Founda tion Fieldbus)
After the foundation field bus is on the international
several field bus passes through the steep competition forms one kind
of field bus, promotes by the field bus foundation.
Is different with the private network main line agreement, FF main line not attached to any enterprise or country.
Its main line system structure is refers to ISO in the OSI model
the physical level, the data link layer and the application level, and increased the correspondence model which the user
level establishes. FF obtained in the world the nearly all
famous measuring appliances manufacturer support, simultaneously
observes IEC the agreement plan, is basic with the IEC
field bus international standard and the draft - sends.
The FF main line has provided Hl and the H2 two physics levels
standard. Hl is uses in the process control low speed main
line,
The transmission speed is 31. 25 kbp s, the transmitting
range is 200 m, 450m, 1 200 m, 1 900 m four kinds (adds
repeater to be allowed to lengthen) , may use the main
line power supply, supports the essence safety equipment
and the non- essential security main line equipment. H2 is the
high speed main line, just started FF to the H2
conception was 1Mbp s (this time
transmitting range is 750 m) or 2. 5 Mbps (this time transmitting range is
500 m) . The decision changed in the
afterwards conference take 100Mbp the s ethernet as a
foundation, and was called high speed ethernet field bus
HSE (High Speed Ethernet Fieldbus) . H1 and the H2 each
section of festivals points may reach 32, after uses the
repeater to be possible to reach 240, Hl and the H2
passable net bridge has interlocked. The FF prominent
characteristic lies in the equipment to be mutually operational, the
improvement process data, the earlier forecast maintenance and the
reliable security. At present, FF field bus
application domain by process automation primarily. For example: Profession and so on chemical industry, power plant
experiment system, waste water processing, oil field.
4. 2 processes field bus Prof ibus
Profibus is by Siemens Corporation proposed and
initiates vigorously, the oneself successively becomes German country
standard D IN19245 and European standard
EN50170, is one kind of opening but the independent main
line standard, at the machine manufacture, in the
commercial run control, the intelligent construction acts as the
correspondence network.
Profibus by Profibus - PA, Profibus - DP and Profibus- the FMS
three series is composed. Profibus - PA ( Process Automation) uses in the process automation
low-speed data transmission, its basic characteristic
with the FF H1 main line, may provide the main line
power supply and the essential security, and obtained
the special-purpose integrated circuit (ASIC) and the
software support. Profibus - DP and
Profibus - PA is compatible, the basic characteristic with the FF H2 main line, may realize the high speed transmission, is suitable between the dispersible external
instrumentation and the automatic control equipment high speed data
transmission, uses in to connect Profibus - PA and the processing automation.
Profibus - FMS is suitable for the
general automated medium speed data transmission, mainly
uses in the sensor, the execution, the electrical transmission, PLC,
the spinning and weaving and the building automation and so on.
The latter two series use the RS485 correspondence
standard, the transmission speed from 9. 6 kbp s to 12 Mbp s, the transmitting range from 1 200 m to 100 m (and transmission speed related) .
The medium access control essential way for the master station
between command sign way and the master station with from the station
host from the way, as well as synthesizes these two ways
the mixed mode.
4. 3 Lonwoks main line
The Lonworks field bus full title is Lonworks NetWorks, namely the distributional intelligent control
network technology, hoped promotes can suit each kind of
field bus application situation the observation and control network.
The intelligent pitch point and the LonTalk communication
agreement are the LonWorks field bus foundation, former
support disperses, the intellectualized characteristic, latter satisfied between the scene intelligence pitch
point not to have the jam, the fast security communication request.
Its most major characteristic is the entire dispersible
intelligent monitoring, entrusts with a scene
intelligence pitch point bigger right to independence, the majority of duties complete, on the
position machine only plays the system construction, the configuration
and the maintenance role. Establishes the system may be
separated from the position machine normal operation, on
the position machine becomes "the hypothesized main engine". At
present the LONWORKS application scope is widespread, mainly includes the industry control, the building
automation, the data acquisition, the SCADA system and
so on. The home mainly applies to the building automation
aspect.
4. 4 CANBUS field bus
The CANBUS field bus technical committee has authorized by ISO the /TC22 for international
standard IOS 11,898 (communication speed
to be smaller than 1 Mbp s) and ISO 11,519 (communication speed is smaller than 125 kbp s) . Its agreement
is the workstation field bus - - intelligence scene equipment more
than two main structures networks. It has the standard
communication agreement, the open function is good;
Not damages the structure to carry on the main line by the
position arbitration way the priority visit; The powerful error
processing ability, the breakdown pitch point
automatically is separated from the main line; Has
characteristic and so on stronger network antijamming ability.
The CANBUS main product applies to the automobile manufacture,
the mass transit vehicles, the robot, the hydraulic system, disperser
I/O. Moreover in situation and so on elevator, medical
instrument, tool engine bed, building automation has the application.
How 5 chooses the field bus the suggestion
(1) whether selects the field bus.
In any domain, not actually has used "the new
things", the people often are holding one kind of
suspicion and the discrete manner, much less formerly
used was one kind of quite mature technology or the product. May
be day by day thin along with the field bus standard, field bus system product gradually improving, causes it to disperse, the control level opening, the
cost drop in the risk and so on various aspects superiority appears
suddenly day by day, the choice uses the field bus the
factory and the project gradually increases.
On the other hand, as a result of the historical
reason, our country controls in the profession in the
labor like PLC, DCS falls behind overseas, the basic
reason is the overseas minority several big companies for guaranteed
its monopoly management the status controls the product to its labor
to use the enclosed structure, our country only has to
its essential core technology after the introduction digestion only
then grasps. The field bus technology open strategy has brought
an once in a thousand years equal competition opportunity without
doubt for my national well-known craftsman controlling in the
international market development. We must closely hold this
turning point, takes the lead to promote has the China
field bus product, founds the Chinese international
labor to control the product the name brand.
(2) chooses the standard. Now the field bus
standard comparison diversification, differently
concerns with each profession custom. We should choose in this
profession hold the share quite to be big, yield the good result in
the practical application the standard. Such future
International Standardization Organization basis science and
technology rapid development present situation and the merchant user
to the standard formulation request, will make the corresponding
change to the standard formulation and the authorized procedure, and acknowledgement existence so-called in fact standard
- - namely these held a bigger share in the market, has the very big
user success application experience the technical sign standard.
(3) chooses the main line product. In on at
present international field bus
The independent warlords rise together simultaneously
under the aspect, the user should embark from the
practical application project characteristic chooses. Because
does not have one kind to be possible to be comprehensive, to suit all
applications domain the field bus technology and the product.
Should emphatically inspect this kind of main line in this
profession application achievement. If the manufacturing
industry automation, the electric power automation and the process
control automation three domains, greatly are dissimilar
in the data real-time response request aspect. The natural user
may choose the international well-knownness as far as possible big,
has the user many, the product application foundation good company
product, because these companies' field bus technologies
by international standard acceptance possibility big, the post-sale service, and the seamless
promotion product opportunity is big.
In view of the ships profession request security high, the
usability strong, 监控?are many, the monitoring physical quantity
type multi- and so on the characteristic, and many years
practical application foundation and senior's recommendation, generally uses LonWorks or the CANBUS field bus
structure is quite appropriate.
In view of the sea platform application in the process control
continuous working ability request, and its in the
system design emphasized "the breakdown - is safe" the natural and the
habitually used main line standard, generally uses FF or
the ProfiBus these two kind of main lines structure.
6 concluding remark
The field bus technology overcame has simulated the
measuring appliance and the traditional control system (for example
DCS: The collection control system) in
technical and application each kind of flaw, has brought
the long-term benefit which the traditional control technology is
unable to compare. When selects the field bus, must formulate own main point, chooses the
suitable field bus standard and the product. The field bus time
already quietly approached, lets us greets this labor by
the enthusiasm and the initiative posture to control the challenge and
the opportunity which the revolution brought!
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