【 Weak current College 】 PLC, DCS, FCS three control system features and differences---Power By 【 China power house network 】

1. preface

The 1990s toward practical use of fieldbus control system, is the rapid development of rapid momentum, is the world's most innovative control system. FCS is the automation technology in a hotspot, being foreign and domestic automation equipment manufacturers and users increasingly strong concern. Fieldbus control system, will provide Automation brings another revolution, its depth and breadth to more than any time in history, thereby creating a new era of automation.

In some industries, FCS is PLC developed; in other industries, FCS is evolved by DCS, PLC and DCS FCS and inextricably links between, and the existence of differences in the nature. This article on the PLC, DCS, FCS three control system features and differences for analysis, pointed out that their origins and development.

2.PLC, DCS, FCS three control system's basic features

At present, in a continuous process of production of automatic control (PA) or custom claims of industrial process control, there are three control systems, PLC, DCS and FCS. Their basic characteristics are as follows:

2．1PLC

(1) from the switch quantity control development to sequence control, delivery address, is a bottom-up.

(2) continuous PID control, multi-purpose, PID in break point.

(3) available on a PC as the main station, multiple identical PLC to from the station.

(4) may also be a PLC-based terminals, multiple identical PLC to from the station, constitute a PLC network. Than a PC as the main station is easy: there are user programming, you don't have to know the communication protocol, as long as written by manual formatting.

(5) PLC grid both as independent DCS/TDCS, can also be used as DCS/TDCS subsystems.

(6) with large systems, such as DCS/TDCS TDC3000, CENTUMCS, WDPFI, MOD300.

(7) PLC networks such as Siemens SINEC L1 company — — SINEC H1, S4, S5, S6, S7, etc, GE's GENET, Mitsubishi MELSEC-NET company, MELSEC-NET/MINI.

(8) is mainly used for industrial process control, in order also new PLC and a closed-loop control function.

(9) manufacturer: GOULD (USA), AB (United States), GE (US), OMRON (Japanese), MITSUBISHI (Japan), Siemens (Germany), etc.

2.2DCS or TDCS

(1) decentralized control system DCS and distributed control system is set 4C TDCS (Communication, Computer, Control, CRT) technology in a monitoring technology.

(2) from the top to the bottom of the tree topology systems, communication (Communication) is the key.

(3) PID in break point, break station joins computer and field instrumentation and control equipment.

(4) is a tree-like topology and parallel continuous link structure, there are a large number of cables from the relay to the scene to instruments in parallel.

(5) analog signal, A/D-D/A, mixed with microprocessor.

(6) an instrument of a snapline, receiving the I/O control station on the local area network LAN.

(7) DCS is control (engineer), operation (operator stations), site meter (field control station) 3-level structure.

(8) the disadvantage is the high cost, the company's products are not interchangeable, Interop, DCS systems are all different.

(9) for massive continuous process control, such as petrochemical, etc.

(10) manufacturer: Bailey (United States), Westinghous (United States), HITACH (Japanese), LEEDS & NORTHRMP (US), SIEMENS (Germany), Foxboro (United States), ABB (Switzerland), Hartmann & Braun (Germany), Yokogawa (Japanese), Honewell (United States), Taylor (USA), etc.

2．3FCS

(1) basic tasks are: nature (eigenvalue) security, dangerous areas, volatile and difficult to deal with the process, the very environment.

(2) full digital, smart, multifunctional replace analogue single-function devices, instrumentation and control equipment.

(3) use two lines join dispersed field instrument, control devices, the PID and the control centre, replace each instrument two lines.

(4) in the bus on the PID and instruments, meters, control devices are equal.

(5) multiple variables, multiple nodes, serial, digital communication system replaced the single variable, single points, parallel, simulation systems.

(6) is an Internet-only, bidirectional, open replace one-way, closed.

(7) with dispersed virtual control station instead of centralized control station.

(8) consists of onsite computer manipulation, can also be linked to a host computer, on the level of the same bus.

(9) LAN, and then communicates with the internet.
BR > (10) to change traditional signal standards, communication standard and system standards in the enterprise management network.

(11) manufacturer: Honeywell, Smar, Fisher-Rosemount, AB/Rockwell, Elsag Bailey, Foxboro,-Yamatake, Siemens, Yokogawa, Europe, GEC-Alsthom, Schneider, ABB proces — Data, etc.

(12) the typical 3 class FCS

1) continuous automatic control of the process such as petrochemical industry, including "controlnet" technology is absolutely crucial, typical products is FF, WorldFIP, Profibus-PA;

2) discrete process actions automatically control such as car manufacturing Robotics, automotive, typical products of the Profibus-DP, CANbus;

3) multipoint control such as building automation, typical products is LONWork, Profibus-FMS.

From the above description of the basic elements, we noticed that, for process control of the three systems, no one is developed for power station, or, in the early stages of their development, are not to be the preferred system power station control objects. These systems use description will not put the station as the preferred application, application there is no mention in the power station. Now the strange thing is that these three control systems, in particular the DCS, PLC, are in the power station has been widely applied, and the effect is verygood.

3. three major differences between the control system

We already know, FCS is the development by DCS and PLC, DCS and FCS not only possess the characteristics, and PLC a revolutionary step forward. At present, new DCS and PLC, has drawn close to each other. New DCS have a very strong order control functions; and a new type of PLC in disposal no closed-loop control aspects, and both can make up a large network, DCS and PLC, a big crossover. The next section will only to DCS and FCS. In the previous sections, have actually been involved to DCS and FCS differences, the following will architecture, investment, design, use, etc.

3.1 difference points

·DCS

DCS system communication is the key. It can be said that the data highway is DCS distributed control system of the spine. Because of it's mission is to provide all communication networks between the parts, so the data highway's own design determines the overall flexibility and security. Data highway media can be: a twisted pair cable, coaxial or fibre optic cable.

Through data highway design parameters, basically can understand a specific DCS system relative strengths and weaknesses.

(1) the system can handle the number of I/O information.

(2) the system can handle and control the control loop.

(3) can adapt to many users and devices (CRT, control stations, etc.).

(4) the integrity of transmitted data is thoroughly checked.

(5) data highway for the maximum allowed length.

(6) data can support the number of branch roads.

(7) data highway is supported by other factory production hardware (programmable controller, computer, data recorder, etc.).

In order to ensure the integrity of the communication, most of the DCS manufacturers are able to provide redundant data highway.

In order to guarantee system security, use a complex communication protocols and error detection technology. The so-called communication protocol is a set of rules to ensure the transmission of data is received and understood it and send data.

At present in the DCS system generally use two categories of communication means that synchronization and asynchronous, synchronous communication relies on a clock signal to regulate data transmission and reception, asynchronous network uses no clock of the reporting system.

·FCS

The key points of the FCS has three

(1) FCS system is the core bus protocol, i.e. bus standard

The preceding chapters have described, a type of bus, as long as its bus protocol is established, the related key technologies and related equipment are determined. The basic principle of bus protocol, various types of bus are the same, to solve the bidirectional serial transmission of digital distribution as basis. For various reasons, various bus bus protocol there is a big difference.

In order for the fieldbus meet interoperability requirements, making it a truly open system, the IEC international standards fieldbus protocol layer in the model of the user, expressly provide user level has the device description. In order to achieve interoperability, each fieldbus devices are used to describe a device description DD. DD can be considered to be one of the drive, it includes all the necessary parameter description and main station the required steps. Because the DD including description of the device to communicate all the information you need, and has nothing to do with the main station, so you can make the field devices achieve true interoperability.

The actual situation as above, the answer is no. Current through the fieldbus international standards including 8 type, and the IEO international standards is just one of the eight types, and other 7 type bus status are equal. Other 7 bus, irrespective of its market share numbers, each bus protocol has a set of software and hardware support. They can form a lineCommission, the formation of product, andthe international standard IEC field bus, is a free software support or hardware support of empty shelves. Therefore, in order to achieve these bus compatibility and interoperability, for the purposes of the present state, is almost impossible.

Through this, we can conclude that a mapping: an open fieldbus control system interoperability, a specific type of the field bus, as long as you follow the type fieldbus bus protocol, its product is open and interoperable. In other words, no matter what the manufacturers of the products, nor a family is the fieldbus products, as long as you follow the bus bus protocols, products are open and interoperable, can make up bus network.

(2) FCS system is based on the field of digital smart device

Digital intelligent field devices is FCS system hardware support is the Foundation, the reason is simple, FCS system performing an automatic control device and field device for bi-directional digital communications between the fieldbus signal system. If on-site installations do not follow unified bus protocol, i.e. related communication protocols that do not have a digital communication functions, the so-called bidirectional digital communication just empty words, you cannot call the fieldbus control system. Then, a large field bus is to increase the field-level control function. If the site system is not a multi-function intelligent products, fieldbus control system features that do not exist, the so-called simplified system, which makes it easy to design and facilitate the maintenance advantage is virtual.

(3) FCS system is essentially information processing field of

For a control system, whether used DCS or fieldbus, system needs to address at least the same amount of information. In fact, the use of fieldbus to from the site for more information. The amount of the fieldbus system is not reduced, or even increasing, and transport information cable is greatly reduced. This requires on the one hand to greatly enhance the ability of cable transmission of information, on the other hand to allow large amounts of information in the scene-place finishes processing, reducing the site and the information between the control room. It can be said that the essence of the fieldbus is information processing field.

Reduce information from network design and system configuration of an important principle. Reduce information to and from the often leads to improved system response time. Therefore, the network design time should give priority to the mutual information exchange capacity of node, in the same slip.

Reduce information return and reduce system cable sometimes contradictory. This should save investment principles to make a choice. If you choose a system response time allows, would save cable programmes. If the selected system response time comparison, slightly reducing the point information transmission is sufficient, that would reduce the transmission of information.

Now some strip fieldbus field instrument itself has a number of functional blocks, although different products with a function block in performance is slightly different, but a network of branch, there are many functional similarity function block is objective and existent. Choose which field instrument of function block, is the system configuration in order to solve the problem.

This principle is: as far as possible reduce the information on the bus. Usually you can select that feature information about the output up to that one of the function block on the gauge.

3.2 typical system comparison

Through the use of fieldbus, users can significantly reduce the field wiring, using a single field instrument for many variables, different factory production of appliances can complete interoperability, increase site level control capabilities, simplify system integration, and maintenance is very simple.

3.3 design, investment and the use of

Comparison of the DCS system and typical, ideal FCS system. Why are you such a hypothesis. For DCS system till today, the early development of the technical requirements have been met and perfection, the current situation is further enhanced, thus ideal for typical, does not exist. But as an FCS system, have just entered the 1990s, as the early development of the practical use of technology requirements: compatible with open, two-way digital communication, digital intelligent field devices, high-speed bus, are also not ideal to be improved. This State and fieldbus international standards could not be said that there is no relationship. The last ten years, the bus is busy developing the standards organization, develop products, occupying more market, the goal is to participate in international standards, legitimate occupation market. Now the international standard for war has come to an end, all major corporate organizations have realized that to truly dominate the market, you'll have the perfect system and related products. We can do such a forecast, the not-too-distant future, the perfection of the fieldbus system and the related products have become the mainstream of fieldbus technology.

Comparisons:

(1) DCS system is a great system, the controller features the strong and the role of the system is very important that the data highway is the key to the system, therefore, must be the overall investment in one step, after the expansion difficult. While decentralization more thorough FCS features, information processing field of digital intelligent field devices for widely adopted, makes the controller function and importance relative to abate. Therefore, the starting point for FCS systems investment is low, you can expand with, edge, edge commissioning.

(2) DCS system is a closed system, the basic products are not compatible. The FCS system is an open system, the user can select different manufacturers, different brands of all kinds of equipment to the fieldbus, achieve the best system integration.

(3) DCS systems are binary or analog form, you must have a D/A and A/D conversion. The FCS system is fully digitized, eliminates D/A and A/D converters, high integration and high performance precision from ± 0.5% to ± 0.1%.
BR > (4) FCS system can be closed-loop control function loads the PID transmitter or actuators, shortens the control cycle, available from DCs 2 ~ 5 sec, raised to the FCS of 10 ~ 20 sec, thus improving performance.

(5) DCS it can control and monitor the process of the entire process, on its own for diagnostic, maintenance and configuration. However, because of its Achilles ' heel, its I/O signal using the traditional analog signal, therefore, it cannot stand in the DCS engineers on field instrument (including transmitter, actuators etc.) for remote diagnosis, maintenance and configuration. FCS adopts all digital technology, digital intelligent field devices send multiple variable information, not just the single variable information, and also have the ability to detect errors in the information. FCS is bi-directional digital communication fieldbus signal system. Therefore, it can be on site installation (including transmitter, implementing agencies, etc.) for remote diagnosis, maintenance and configuration. The advantages of this point FCS is DCS.

(6) FCS because information processing field, compared with DCS can save considerable amount of isolators, Terminal Cabinet, I/O Terminal, i/o card, file I/O and I/O Cabinet, while also saving I/O devices and equipment room space and floor space. Some experts believe that can save 60%.

(7) and (6) for the same reason, a large number of FCS reduces cable and the Cable Tray Cable laying, etc., while also saving design, installation and maintenance costs. Some experts believe that can save 66%.

For (6), (7), two points should be added, using FCS system, saves the investment result is no doubt, but if some of the experts have said upto 60 ~ 66%. These figures appear in several articles, the authors believe that this is the result of mutual reproduced, is still not found the original source of the figures, so that readers refer to these figures with caution.

(8) FCS relative to DCs configuration is simple, due to the structure, performance, standardized, easy to install, run and maintain.

(9) for process control design and development of FCS. This is not an comparison with DCS, just a note for process control or that are used to simulate a continuous process of development of FCS in design should focus on.

1) requires bus controlnet function, and is a top priority.

2) basic monitoring such as flow, level, temperature, pressure, etc. change is slow, but also by the lag effect, therefore, the node monitoring does not need faster electronics response time, but requires a complex analog processing. The physical characteristics of the decision to adopt the system essentially Lord a poll from the concentrated between, this is reasonable and economically beneficial.

3) flow, level, temperature, pressure, and other parameters of measurement, its physical principle is classical, sensors, transmitters and controllers should digital intelligent development.

4) as for continuous process and its instruments and the development of FCS, should focus on the design of low-speed bus H1.

4.PLC prospects with DCS

We already know of FCS is evolved by the PLC, and FCS is evolved by DCS, FCS has chores today, PLC and DCS how prospects.

PLC in the United States in the late 60 's first appeared, the aim is to replace relays, execution logic, timing, sequence control functions such as count, establish a flexible process control system. The official naming of 1976 and given definition: PLC is a digital control special electronic computer, it uses the programmable memory storage instructions, such as logical, sequential, timing, count and calculus, and analog and digital input, output, and other components that control various machinery or work procedures. After 30 years of development, the PLC is very mature and perfect and develop analog closed-loop control function. PLC in FCS system status seems to have been determined and no much controversy. IEC recommended PROFIBUS control system architecture, PLC as a stand to hang on a high-speed bus. The editor believes that accessibility workshop of control system should follow the fieldbus Protocol of PLC or communicate with FCS information Exchange PLC as the selection object.

Since 1973 by the first microprocessor-based controller, it gradually improved, and eventually form a full-featured, secure and reliable digital DCS distributed control systems. Its performance is much better to live in any kind of control system. You can meet the DAS, MCS, power plant SCS and APS systems requirements, currently available through industrial Ethernet network building management to meet the increasingly high power plant strengthening management requirements. It can be said that the DCS system monitor can cover large thermal power unit of the whole process.

However, since the FCS, and since the 1990s, chores are arguments in published may be submitted to the Conference, namely: "from now on, new FCs FCS will gradually replace traditional DCS"; "when adjusting functions delegated to the site to go beyond traditional DCS have no existence of necessary and will automatically disappear"; "the next decade, the traditional 4 ~ 20mA analog signal system will gradually be bi-directional digital communication fieldbus signal systems, analog and digital in DCS distributed control system will be upgraded to full digital fieldbus control system FCS". ... These arguments summarized in one word: FCS will replace the DCS, DCS will be extinct.

These arguments are taken from the mouth of the authoritative experts are not unreasonable. Digital communication is a trend, it represents thetechnological progress that is irresistible. Bi-directional digital communication-fieldbus signal and it generated a huge pushPower, acceleration field devices and control instrument of transformation in the development of a more full-featured digital smart field devices. These are the DCS system that does not exist, and the resulting advantages, as well as to the power plant's design, configuration, configuration, operation, maintenance, management benefits is also the DCS system. In addition, FCS is DCS and PLC development, it preserves the characteristics of the DCS or FCS absorbed the DCS development research, as well as the scene for many years practical experience, the course also includes lessons. The resulting conclusion that "the FCS will replace the DCS", seems to be logical.

At the same time we should see that the DCS system development has nearly 30 years, in the application of such a broad range of thermal power plant. Its design, configuration, configuration and function match has reached very perfection (of course, the DCS also exists for the further development of demand, for example, advanced software development to meet the requirements of information integration), has infiltrated the power plant control system for various fields, and also some FCS system. From this perspective, the DCS system seems to be not from extinction. In addition, from the preceding chapters have described that the FCS system cannot give full play to its features and advantages of DCS system is still useful.

We seem to be no need to make the text too much controversy, it is important to emphasize who replaced. As existing DCS and PLC, since new years of development research, in their respective retention self original characteristics, complementary, the formation of a new system, the DCS have not had the same is true of DCS,, type of PLC nor develop initial PLC. We can say is DCS has replaced the PLC or replacing the DCS, PLC are clearly inappropriate.

> 5. conclusions

From the above analysis of the discussion, we can conclude the following simple conclusion: FCS FCS, DCS Digital decentralized control does not disappear, but only about the past is in the Centre of the control system DCS to field bus a site. It can be said that the DCS in control systems Centre situation from this will be broken. Future power plant control system will be: FCS is in central position, the control system with DCs system philosophy a new control system.