FCS is developed by PLC; in other industries, FCS is developed by DCS, so there are inextricable links between FCS and PLC and DCS, and there are essential differences. This paper tries to analyze the characteristics and differences of the three control systems of PLC, DCS and FCS, and points out the origin and development direction between them.
Abstract: This paper analyzes the characteristics and differences of the three control systems of PLC, DCS and FCS, and points out the origin and development direction of the three control systems.
Foreword
The fieldbus control system that went into practical use in the 1990s is rapidly developing with rapid momentum and is the latest control system in the world. The fieldbus control system is a hot spot in the current automation technology and is receiving increasing attention from automation equipment manufacturers and users at home and abroad. The emergence of the fieldbus control system will bring another revolution to the automation field, and its depth and breadth will exceed any history, thus creating a new era of automation.
In some industries, FCS is developed by PLC; in other industries, FCS is developed by DCS, so there are inextricable links between FCS and PLC and DCS. difference. This paper tries to analyze the characteristics and differences of the three control systems of PLC, DCS and FCS, and points out the origin and development direction between them.
Basic characteristics of three major control systems: PLC, DCS and FCS
At present, there are three major control systems, namely PLC, DCS and FCS, in continuous process production automation (PA) or customary industrial process control. Their respective basic characteristics are as follows:
1 PLC
(1) From the development of switching quantity control to sequential control and transportation processing, it is from the bottom up.
(2) Continuous PID control and other functions, PID is in the interrupt station.
(3) One PC can be used as the master station, and multiple PLCs of the same type are slave stations.
(4) It is also possible to use one PLC as the main station and multiple PLCs of the same type as slave stations to form a PLC network. This is more convenient than using a PC as the main station: when there is user programming, you do not need to know the communication protocol, just write it according to the format of the manual.
(5) The PLC grid can be used as an independent DCS/TDCS or as a subsystem of DCS/TDCS.
(6) Large system is the same as DCS/TDCS, such as TDC3000, CENTUMCS, WDPFI, MOD300.
(7) PLC network such as SINEC-L1, SINEC-H1, S4, S5, S6, S7, etc. of Siemens, GENET's GENET, Mitsubishi's MELSEC-NET, MELSEC-NET/MINI.
(8) It is mainly used for sequential control in industrial processes, and the new PLC also has closed-loop control functions.
(9) Manufacturers: GOULD, AB, GE, OMRON, MITSUBISHI, Siemens, etc.
2 DCS or TDCS
(1) Distributed control system DCS and distributed control system TDCS is a monitoring technology that integrates 4C (Communication, Computer, Control, CRT) technology.
(2) A tree topology system from top to bottom, in which communication is the key.
(3) PID is in the interruption station, the interruption station is connected to the computer and the field instrumentation and control device.
(4) It is a tree topology and a parallel continuous link structure. There are also a large number of cables from the relay station in parallel to the field instrumentation.
(5) Analog signal, A/D-D/A, mixed with microprocessor.
(6) One instrument is connected to the I/O by a pair of wires, and is connected to the LAN by the control station.
(7) DCS is a three-level structure of control (engineering station), operation (operator station), and field instrument (site monitoring station).
(8) The disadvantage is that the cost is high, the products of each company cannot be interchanged, and they cannot interoperate. The large DCS system is different.
(9) For large-scale continuous process control, such as petrochemicals.
(10) Manufacturers: Bailey, Westinghous, HITACH, LEEDS & NORTHRMP, SIEMENS, Foxboro, ABB (Switzerland), Hartmann & Braun (Germany), Yokogawa (Japan), Honewell (USA), Taylor (US), etc.
3 FCS
(1) The basic tasks are: the essence (intrinsic) safety, dangerous areas, volatile processes, and very difficult environments to deal with.
(2) Fully digital, intelligent and multifunctional replacement of analog single-function instruments, instruments and control devices.
(3) Replace the scattered field instruments, control devices, PID and control center with two wires to replace the two wires of each instrument.
(4) The PID on the bus is equal to the instrument, instrument, and control device.
(5) Multi-variable, multi-node, serial, digital communication systems replace single-variable, single-point, parallel, and analog systems.
(6) It is interconnected, two-way, and open to replace one-way and closed.
(7) Replace the centralized control station with a decentralized virtual control station.
(8) It can be operated by the on-site computer, and can also be connected to the upper computer and connected to the upper computer of the same bus.
(9) LAN, and then communicate with the internet.
(10) Change traditional signal standards, communication standards and system standards into the enterprise management network.
(11) Manufacturers: Honeywell, Smar, Fisher- Rosemount, AB/Rockwell, Elsag- Bailey, Foxboro, Yamatake, Japan Yokogawa, Euro Siemens, GEC-Alsthom, Schneider, proces-Data, ABB, etc.
(12) Typical of 3 types of FCS 1) Continuous process automatic control such as petrochemical industry, in which "intrinsically safe explosion-proof" technology is absolutely important, the typical products are FF, World FIP, Profibus-PA;
2) Automatic control of discrete process actions such as automobile manufacturing robots and automobiles, typical products are Profibus-DP, CANbus;
3) Multi-point control such as building automation, typical products are LON Work, Profibus-FMS.
From the description of the above basic points, have we noticed that none of the three systems used for process control were developed for power stations, or, in the early stages of their development, they were not the preferred control system for power plants. Object. In the instructions for use of these systems, the power station is never used as the preferred scope of application, and some do not mention the power station at all. The strange thing is that these three control systems, especially DCS and PLC, have been widely used in power stations, and the effect is very good.
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