1. Preface The fieldbus control system in the 1990s in the 1990s is rapidly developed in a rapid development of rapid momentum. It is currently the latest control system in the world. Fieldbus control systems are a hot spot in automation technology, which is being paid attention to by domestic and foreign automation equipment manufacturers and users more and more intense. The emergence of the fieldbus control system will bring another revolution to the automation, and its depth and breadth will exceed any history of history, thereby creating a new era of automation. In some industries, FCS is developed by PLC; and in other industries, FCS is developed by DCS, so there is a thousand link between FCS and PLC and DCS, and there is essential difference. This article analyzes the characteristics and differences of the three major control systems of PLC, DCS, FCS, pointing out the origin and development direction between them. 2. Basic Features of the three major control systems of PLC, DCS, and FCS are currently in continuous processes. Production Automatic Control (PA) or conventionally, there are three major control systems, pLC, DCS, and FCS. Their basic features are as follows: 2.1 PLC (1) Develop from the switch to sequential control, transport processing, is from bottom to top. (2) Continuous PID control, etc., PID is in the interrupt station. (3) A PC can be used as the master station, and multiple similar PLCs are slaves. (4) You can also a PLC as the main station, multiple similar PLCs are slaves, constitute a PLC network. This is more convenient to use the PC machine, which is: (5) The PLC mesh can be used as a separate DCS / TDCS, and can also be used as subsystems of DCS / TDCs. (6) Large system with DCS / TDCs, such as TDC3000, CentumCs, WDPFI, and Mod300. (7) PLC network such as Siemens company's SINEC-L1, SINEC-H1, S4, S5, S6, S7, etc., GE, GENET, Mitsubishi's MELSEC-NET, MELSEC-NET / MINI. (8) Mainly used in the sequential control in the industrial process, the new PLC also has a closed-loop control function. (9) Manufacturer: Gould (US), AB (US), GE (US), OMRON (Japan), Mitsubishi (Japan), Siemens (Germany). 2.2 DCS or TDCS (1) Dispersion Control System DCS and Distribution Control System TDCS is the monitoring technology of 4C (COMMUNICATION, COMPUTER, CONTROL, CRT) technology. (2) From the top to the tree topology system, communication (Communication) is the key. (3) PID in the interrupt station, interrupting station connection computer and field instrumentation and control device. (4) It is a tree topology and parallel link structure, and there is a large number of cables from the relay station to the field instrumentation. (5) Simulation signal, A / D-D / A, mixing with microprocessor.
(6) A pair of instruments connected to I / O, hung by the control station to the local area network. (7) DCS is the 3-level structure of control (engineer station), operation (operator station), on-site instrument (on-site measuring and control station). (8) The disadvantage is that the cost is high, and the products cannot be interchanged, and it is not possible to interoperate. The big DCS system is different. (9) Used for large-scale continuous process control, such as petrochemical, etc. (10) Manufacturer: Bailey, WESTINGHOUS (US), Hitach (Japan), Siemens, Foxboro, ABB (Switzerland), Hartmann & Braun (Germany), Yokogawa (Japan), Honewell (US), Taylor, etc. 2.3 FCS (1) Basic tasks are: essential (intrinsic) security, dangerous area, volatility process, difficult to deal with very environment. (2) Full digital, intelligent, multi-function replacement analog single functional instruments, instruments, control devices. (3) Use two lines to join the on-site instrument, control unit, PID and control center, replace two lines per instrument. (4) All PIDs and instruments, meters, and control devices are equal. (5) Multivariate, multi-node, serial, digital communication system replaces single variable, single point, parallel, and simulation system. (6) is interconnected, two-way, open substitution, closed, closed. (7) Replace the concentrated control station with a dispersed virtual control station. (8) Manipulated by the on-site computer, can also be hung to the upper computer, and the last level of the previous level of the bus. (9) LAN, can then communicate with the Internet. (10) Change the traditional signal standard, communication standards and system standards into enterprise management network. (11) Manufacturer: Mei Honeywell, Smar, Fisher- Rosemount, AB / Rockwell, Elsag- Bailey, Foxboro, Yamatake, Japanese Yokogawa, Ou Siemens, Gec-Alsthom, Schneider, Proces-Data, ABB, etc. (12) Typical 1 of 3 types of FCS 1) Continuous process process automatically controls petrochemicals, wherein "this security explosion-proof" technology is absolutely important, typical products are FF, World FIP, PROFIBUS-PA; 2) Division of process actions Automatic control, such as automotive manufacturing robots, cars, typical products are PROFIBUS-DP, CANBUS; 3) Multi-point control such as building automation, typical products are LON Work, Profibus-FMS. From the above description of the above basic points, we noticed the three systems used for process control, no one was developed for the power station, or said that in the initial development of their development, it is not the first choice for the system. Object.
In the instructions in these systems, it will never be used as the preferred scope of application, and some do not power the station at all in the applicable range. It is strange that these three major control systems, especially DCS, PLC, are widely used in the power station, and the effect is also very good. 3. The difference between the three control systems We already know that FCS has been developed by DCS and PLC, but FCS has the characteristics of DCS and PLC, but also a revolutionary step. At present, the new DCS and new PLC have a trend toward the opponent. The new DCS has a strong sequential control function; the new PLC is also in line with closed loop control, and both can form large networks, the scope of DCS and PLC, have a large cross. The next section is only compared with the FCS. In the previous chapter, the difference in DCS and FCS has actually been described, and the architecture, investment, design, usage, etc. will be described below. 3.1 Difference points? The key to the DCS DCS system is communication. It can also be said that the data is the spine of the DCS of the DCS. Since its mission is to provide a communication network between all components of the system, the design of the data highway determines the overall flexibility and security. The media of the data can be: a coupled strand, coaxial cable or fiber optic cable. By the design parameters of the data road, you can basically understand the relative advantages and weaknesses of a particular DCS system. (1) How much I / O information can be handled. (2) The system can handle information about how many control loops related to control. (3) Can adapt to how many users and devices (CRT, control stations, etc.). (4) How is the integrity of transmitted data thoroughly examined. (5) What is the maximum allowable length of the data road. (6) How much support can be supported by data highways. (7) Can data highway support hardware produced by other manufacturing plants (programmable controllers, computers, data recording devices, etc.). In order to ensure the integrity of communications, most DCS manufacturers can provide redundant data roads. In order to ensure the safety of the system, complex communication statics and error detection techniques are used. The so-called communication statute is a set of rules to ensure that the transmitted data is received and is understood to be as understood. At present, two types of communication means in the DCS system, that is, synchronized and asynchronous, synchronous communication rely on one clock signal to adjust the transmission and reception of data, and the asynchronous network uses a report system with no clock. • The key points of the FCS FCS are three points (1) The core of the FCS system is the bus protocol, that is, the chapter in front of the bus standard has been described, a type of bus, as long as its bus protocol is determined, the relevant key technology and related equipment It is determined. For the basic principles of its bus agreement, all types of bus are the same, all to solve two-way serial digital communication transmission as a basic basis. However, due to various reasons, there is a big difference in the bus protocol of all types of bus. In order to satisfy the interoperability requirements to make the fieldbus, it becomes a real open system, in the user layer of IEC international standards, fieldbus communication protocol models, clearly stipulates that the user layer has a device description function. In order to achieve interoperability, each fieldbus device is described in the device to describe DD. DD can be considered a driver of a device that includes all necessary parameter descriptions and the operational steps required for the primary station. Since DD includes all information required to communicate, it is independent of the master station, so that the field device can realize true interoperability. The actual situation is as the above, the answer is negative.
The international standards currently passed through the fieldbus include 8 types, while the original IEO international standard is only one of eight types, and the status of other seven types of bus is equal. Other 7 bus, regardless of its market share, each bus protocol has a software, hardware support. They can form a system, forming a product, and the original IEC fieldbus international standard is an empty shelf for both software support and hardware support. Therefore, to achieve the mutual compatibility and interoperability of these buss, it is almost impossible to state. By the above, we can draw such a image: an open fieldbus control system interoperability, in terms of a specific type of fieldbus, as long as the bus protocol of this type of field bus is open to its product And have interoperability. In other words, no matter what manufacturer's products, no family is the product of the live bus company, as long as the bus protocol is followed, the product is open, and the interoperability can form a bus network. (2) The foundation of the FCS system is that the digital intelligent field device digital intelligent field device is the hardware support of the FCS system. It is the foundation. The reason is very simple. The FCS system executes the two-way digital communication fieldbus signal between the automatic control device and the field device. system. If the field device does not follow the unified bus protocol, that is, the relevant communication protocol, does not have digital communication function, then the so-called two-way digital communication is only an empty talk, and it cannot be called a fieldbus control system. One point, a major feature of the fieldbus is to increase the first-level control function. If the field device is not a multi-functional intelligent product, the characteristics of the fieldbus control system do not exist, the so-called simplified system, convenient design, beneficial to maintenance, etc. is also empty. (3) The essence of the FCS system is that the information processing site is for a control system, whether using DCS or an on-site bus, the system needs to be processed at least as much. In fact, after using the fieldbus, you can get more information from the site. The amount of information on the fieldbus system has not decreased, and even increased, and the cable transmitted is greatly reduced. This requires the one hand to greatly improve the ability of cable transmission information, on the other hand, to make a lot of information to complete the handling on site, reduce the information round trip between the site and the control machine room. It can be said that the essence of the fieldbus is the fieldization of the information processing. Reducing information round-trip is an important principle of network design and system configuration. Reducing the information roundback often can improve the benefits of improving system response time. Therefore, the network design should be preferred to exchange the nodes in the same manner in the same branch. Reducing information round trip and reduced systems can sometimes contradict each other. At this time, it should still be selected as the principle of saving investment. If the response time of the selected system is allowed, the program is saved. If the response time of the selected system is more tense, the transmission of a little less information is sufficient, then the scheme of reducing information transmission should be selected. Now some live meters with fieldbus are under many functional blocks, although the same function blocks of different products will be slightly different in performance, but there are many functional minimalizes on a network branch, which is objective. Which field meter is selected, which is a problem that the system is configured to solve. Considering the principle of this problem is to minimize the information round trip on the bus. You can generally select the function block on the meter that is most related to this function. 3.2 Typical System Comparison By using the fieldbus, the user can reduce the on-site wiring, with a single field meter to realize multivariate communication, and the devices produced by different manufacturing plants can fully interoperate, increase the control function of the field level, system integration It is greatly simplified and maintained very simple. 3.3 The topic of design, investment and comparison is a comparison of the DCS system and a typical, ideal FCS system. Why do you want to do so.
As the DCS system developed to this day, the technical requirements proposed in the initial development have been met and improved, and the current situation is further improved, so there is no typical, ideal statement. As the FCS system, I have just entered practicalization in the 1990s, as a technical requirement for the initial stage of development: compatible, two-way digital communication, digital intelligent field devices, high-speed bus, etc., is not ideal to be improved. This state is not related to the development of international standards for fieldbus. In the past ten years, all bus organizations are busy formulating standards, developing products, occupying more markets, and the purpose is to be crowded in international standards and legal occupation of larger markets. Now that the competition for international standards has been reported that major companies have realized that they must improve the system and related products to improve the system and related products. We can do such predictions, soon, in the near future, the perfect fieldbus system and related products must be the mainstream of the world's live bus technology. Specific comparison: (1) The DCS system is a large system, its controller is functional and is very important in the system. The data is the key to the system. Therefore, it is necessary to invest in an overall investment in place, and afterwards. The FCS function is more complete, and the information processing is widely adopted, and the digital intelligent field device is widely used, so that the controller function is relatively weakened. Therefore, the starting point of the FCS system investment is low, and it can be used while expanding, while being transported. (2) The DCS system is a closed system, and the products of each company are basically incompatible. The FCS system is an open system. Users can choose different manufacturers, various devices of different brands into fieldbus, and achieve the best system integration. (3) The information of the DCS system is all binary or analog signals, and there must be D / A and A / D conversion. The FCS system is full-digital, which is exempt from D / A and A / D transform, high integrated high performance, enhance the accuracy from ± 0.5% to ± 0.1%. (4) The FCS system can load the PID closed loop control function into the transmitter or actuator, shorten the control cycle, and can now be 2 to 5 times from DCS, raise 10 to 20 times per second of FCS, thus Improve adjustment performance. (5) DCS It can control and monitor the whole process of the process, diagnose, maintain, and configure itself. However, due to its own fatal weaknesses, its I / O signal uses traditional analog signals, so it cannot conduct remote diagnostics, maintenance, and configurations on the DCS engineer station. . The FCS uses full digital technology, and the digital intelligent field device transmits multivariate information, not just single variable information, but also features a function of detection information error. FCS uses a two-way digital communication fieldbus signal system. Therefore, it can perform remote diagnosis, maintenance, and configuration on field devices (including transmitters, actuators, etc.). This advantageousness of FCS is that DCS cannot match. (6) FCS can save a considerable number of isolators, terminal cabinets, I / O terminals, I / O card pieces, I / O terminals, I / O cards, I / O files, I / O cards, and I / O cabinets compared to DCS. The space and footprint of the I / O device and the device room. Some experts believe that you can save 60%. (7) and (6) the same reasons, FCS can reduce the bridge of a large number of cables and laying cables, while saving design, installation, and maintenance costs. Some experts believe that you can save 66%.
For (6), (7) two points should be added, using the FCS system, saving investment is not doubt, but if some experts have said 60 ~ 66%. These numbers appear in many articles, and editors think this is the result of mutual pending, and there is currently no original origin of these numbers. Therefore, readers should be cautious when citing these numbers. (8) FCS is simple relative to the DCS configuration, due to structural, performance standardization, easy to install, operate, and maintain. (9) FCS design development points for process control. This is not compared to DCS, just a problem that the process control or the FCS used to simulate continuous processes should be considered in design and development. 1) Requires the bus in this security explosion-proof function, and is important. 2) Basic monitoring such as flow, level, temperature, pressure, etc. are slow, and there is also a lag effect, and therefore, node monitoring does not require fast electronics response time, but requires complex analog processing capabilities. This physical characterization determines that the system is basically a centralized polling system between the main one, which is technically reasonable, which is economically advantageous. 3) Measurement of parameters such as traffic, level, temperature, pressure, is classical, but sensors, transmitters and controllers should develop towards digital intelligence. 4) As a FCS developed for continuous processes and its instrumentation, it should be highly designed to be designed with low speed bus H1. 4. PLC and DCS prospects We already know that the FCS is developed by PLC, and some FCS is developed by DCS, then, today's FCS has been practical, and the PLC and DCS prospects will. The PLC first appeared in the United States in the end of the 1960s, with the aim of replacing the relay, executing logic, timing, counting sequential control function, and establishing a flexible program control system. In 1976, it was officially named and given a definition: PLC is a digital control-specific electronic computer. It uses a programmed memory storage instruction to perform functions such as logic, order, timing, counting, and calculations, and input by simulation and digital input. Output and other components, control various mechanical or working procedures. After more than 30 years of development, PLC has matured and perfect, and has developed analog closed-loop control. The status of the PLC in the FCS system seems to have been determined and there is no more controversy. The fieldbus control system architecture recommended by the IEC, and the PLC is hung on the high speed bus. Editor's editor, the control system of the auxiliary workshop should be in accordance with PLCs that follow the fieldbus communication protocol or the PLC of communication exchange information with the FCS. Since 1973, the first controller based on the microprocessor has been gradually improved, and finally forms a functional and safe and reliable digital dispersion control system DCS. Its performance is greatly exceeded to live in any control system. It can meet the various requirements of DAS, MCS, SCS, and APS systems in the fire power plant, and currently can also establish management networks through industrial Ethernet to meet the requirements of strengthening management of fire power plants. It can be said that the monitoring of the DCS system can cover the process of the process of large thermal generators. However, since I have FCS, I have continued to publish the following arguments in the public publication in the 1990s, namely: "From now, the new fieldbus control system FCS will gradually replace the traditional DCS"; " After the adjustment function is placed in the scene, the traditional DCS does not have the necessary and automatically disappear ";" For the next decade, the traditional 4 ~ 20mA simulation signal system will gradually be replaced by two-way digital communication fieldbus signal system, simulation Digital dispersion control system DCS will be updated to all digital fieldbus control system FCS "......
