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  • A distributed control system refers to a control system of a process plant and industrial process

  • wherein control elements are not only located in central location but are also distributed

  • throughout the system with each component sub-system controlled by one or more controllers

  • so the intelligence is distributed across the sections of the plant. DCS follows hierarchy

  • in its control philosophy with various function spread across .

  • DCS is a computerized control system used to automate processes in various industries.

  • The entire system of controllers is connected by networks for communication and monitoring.

  • DCS is a very broad term used to monitor and control distributed equipments in process

  • plants and industrial processes . Chemical plants

  • Petrochemical industries and refineries Boiler controls and power plant systems

  • Nuclear power plants Environmental control systems

  • Water management systems Oil refining plants

  • Metallurgical process plants Chemical plants

  • Pharmaceutical manufacturing Sugar plants

  • Dry cargo and bulk oil carrier ships

  • Elements

  • A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections

  • and standard communications protocol for communication. Input and output modules form component parts

  • of the DCS. The processor receives information from input modules and sends information to

  • output modules. The input modules receive information from input instruments in the

  • process and the output modules transmit instructions to the output instruments in the field. The

  • inputs and outputs can be either analog signal which are continuously changing or discrete

  • signals which are 2 state either on or off . Computer buses or electrical buses connect

  • the processor and modules through multiplexer or demultiplexers. Buses also connect the

  • distributed controllers with the central controller and finally to the Humanmachine interface

  • or control consoles. See Process automation system.

  • The elements of a DCS may connect directly to physical equipment such as switches, pumps

  • and valves and to Human Machine Interface via SCADA. The differences between a DCS and

  • SCADA is often subtle, especially with advances in technology allowing the functionality of

  • each to overlap. Applications

  • Distributed control systems are dedicated systems used to control manufacturing processes

  • that are continuous or batch-oriented, such as oil refining, petrochemicals, central station

  • power generation, fertilizers, pharmaceuticals, food and beverage manufacturing, cement production,

  • steelmaking, and papermaking. DCSs are connected to sensors and actuators and use setpoint

  • control to control the flow of material through the plant. The most common example is a setpoint

  • control loop consisting of a pressure sensor, controller, and control valve. Pressure or

  • flow measurements are transmitted to the controller, usually through the aid of a signal conditioning

  • input/output device. When the measured variable reaches a certain point, the controller instructs

  • a valve or actuation device to open or close until the fluidic flow process reaches the

  • desired setpoint. Large oil refineries have many thousands of I/O points and employ very

  • large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also

  • include things like paper machines and their associated quality controls, variable speed

  • drives and motor control centers, cement kilns, mining operations, ore processing facilities,

  • and many others. A typical DCS consists of functionally and/or

  • geographically distributed digital controllers capable of executing from 1 to 256 or more

  • regulatory control loops in one control box. The input/output devices can be integral with

  • the controller or located remotely via a field network. Today’s controllers have extensive

  • computational capabilities and, in addition to proportional, integral, and derivative

  • control, can generally perform logic and sequential control. Modern DCSs also support neural networks

  • and fuzzy application. DCSs are usually designed with redundant processors

  • to enhance the reliability of the control system. Most systems come with canned displays

  • and configuration software which enables the end user to set up the control system without

  • a lot of low level programming. This allows the user to better focus on the application

  • rather than the equipment, although a lot of system knowledge and skill is still required

  • to support the hardware and software as well as the applications. Many plants have dedicated

  • groups that focus on this task. These groups are in many cases augmented by vendor support

  • personnel and/or maintenance support contracts. DCSs may employ one or more workstations and

  • can be configured at the workstation or by an off-line personal computer. Local communication

  • is handled by a control network with transmission over twisted pair, coaxial, or fiber optic

  • cable. A server and/or applications processor may be included in the system for extra computational,

  • data collection, and reporting capability. History

  • Early minicomputers were used in the control of industrial processes since the beginning

  • of the 1960s. The IBM 1800, for example, was an early computer that had input/output hardware

  • to gather process signals in a plant for conversion from field contact levels and analog signals

  • to the digital domain. The first industrial control computer system

  • was built 1959 at the Texaco Port Arthur, Texas, refinery with an RW-300 of the Ramo-Wooldridge

  • Company The DCS was introduced in 1975. Both Honeywell

  • and Japanese electrical engineering firm Yokogawa introduced their own independently produced

  • DCSs at roughly the same time, with the TDC 2000 and CENTUM systems, respectively. US-based

  • Bristol also introduced their UCS 3000 universal controller in 1975. In 1978 Metso(known as

  • Valmet in 1978) introduced their own DCS system called Damatic. In 1980, Bailey introduced

  • the NETWORK 90 system, Fisher Controls introduced the PROVoX system, Fischer & Porter Company

  • introduced DCI-4000. The DCS largely came about due to the increased

  • availability of microcomputers and the proliferation of microprocessors in the world of process

  • control. Computers had already been applied to process automation for some time in the

  • form of both direct digital control and set point control. In the early 1970s Taylor Instrument

  • Company, developed the 1010 system, Foxboro the FOX1 system, Fisher Controls the DC2 system

  • and Bailey Controls the 1055 systems. All of these were DDC applications implemented

  • within minicomputers and connected to proprietary Input/Output hardware. Sophisticated continuous

  • as well as batch control was implemented in this way. A more conservative approach was

  • set point control, where process computers supervised clusters of analog process controllers.

  • A CRT-based workstation provided visibility into the process using text and crude character

  • graphics. Availability of a fully functional graphical user interface was a way away.

  • Central to the DCS model was the inclusion of control function blocks. Function blocks

  • evolved from early, more primitive DDC concepts of "Table Driven" software. One of the first

  • embodiments of object-oriented software, function blocks were self-contained "blocks" of code

  • that emulated analog hardware control components and performed tasks that were essential to

  • process control, such as execution of PID algorithms. Function blocks continue to endure

  • as the predominant method of control for DCS suppliers, and are supported by key technologies

  • such as Foundation Fieldbus today. Midac Systems, of Sydney, Australia, developed

  • an objected-oriented distributed direct digital control system in 1982. The central system

  • ran 11 microprocessors sharing tasks and common memory and connected to a serial communication

  • network of distributed controllers each running two Z80s. The system was installed at the

  • University of Melbourne. Digital communication between distributed

  • controllers, workstations and other computing elements was one of the primary advantages

  • of the DCS. Attention was duly focused on the networks, which provided the all-important

  • lines of communication that, for process applications, had to incorporate specific functions such

  • as determinism and redundancy. As a result, many suppliers embraced the IEEE 802.4 networking

  • standard. This decision set the stage for the wave of migrations necessary when information

  • technology moved into process automation and IEEE 802.3 rather than IEEE 802.4 prevailed

  • as the control LAN. The Network Centric Era of the 1980s

  • In the 1980s, users began to look at DCSs as more than just basic process control. A

  • very early example of a Direct Digital Control DCS was completed by the Australian business

  • Midac in 1981–82 using R-Tec Australian designed hardware. The system installed at

  • the University of Melbourne used a serial communications network, connecting campus

  • buildings back to a control room "front end". Each remote unit ran 2 Z80 microprocessors

  • whilst the front end ran 11 in a Parallel Processing configuration with paged common

  • memory to share tasks and could run up to 20,000 concurrent controls objects.

  • It was believed that if openness could be achieved and greater amounts of data could

  • be shared throughout the enterprise that even greater things could be achieved. The first

  • attempts to increase the openness of DCSs resulted in the adoption of the predominant

  • operating system of the day: UNIX. UNIX and its companion networking technology TCP-IP

  • were developed by the US Department of Defense for openness, which was precisely the issue

  • the process industries were looking to resolve. As a result suppliers also began to adopt

  • Ethernet-based networks with their own proprietary protocol layers. The full TCP/IP standard

  • was not implemented, but the use of Ethernet made it possible to implement the first instances

  • of object management and global data access technology. The 1980s also witnessed the first

  • PLCs integrated into the DCS infrastructure. Plant-wide historians also emerged to capitalize

  • on the extended reach of automation systems. The first DCS supplier to adopt UNIX and Ethernet

  • networking technologies was Foxboro, who introduced the I/A Series system in 1987.

  • The application-centric era of the 1990s The drive toward openness in the 1980s gained

  • momentum through the 1990s with the increased adoption of commercial off-the-shelf components

  • and IT standards. Probably the biggest transition undertaken during this time was the move from

  • the UNIX operating system to the Windows environment. While the realm of the real time operating

  • system for control applications remains dominated by real time commercial variants of UNIX or

  • proprietary operating systems, everything above real-time control has made the transition

  • to Windows. The introduction of Microsoft at the desktop

  • and server layers resulted in the development of technologies such as OLE for process control,

  • which is now a de facto industry connectivity standard. Internet technology also began to

  • make its mark in automation and the DCS world, with most DCS HMI supporting Internet connectivity.

  • The 1990s were also known for the "Fieldbus Wars", where rival organizations competed

  • to define what would become the IEC fieldbus standard for digital communication with field

  • instrumentation instead of 4–20 milliamp analog communications. The first fieldbus

  • installations occurred in the 1990s. Towards the end of the decade, the technology began

  • to develop significant momentum, with the market consolidated around Ethernet I/P, Foundation

  • Fieldbus and Profibus PA for process automation applications. Some suppliers built new systems

  • from the ground up to maximize functionality with fieldbus, such as Rockwell PlantPAX System,

  • Honeywell with Experion & Plantscape SCADA systems, ABB with System 800xA, Emerson Process

  • Management with the Emerson Process Management DeltaV control system, Siemens with the SPPA-T3000

  • or Simatic PCS 7,Forbes Marshall with the Microcon+ control system and Azbil Corporation

  • with the Harmonas-DEO system. Fieldbus technics have been used to integrate machine, drives,

  • quality and condition monitoring applications to one DCS with Metso DNA system.

  • The impact of COTS, however, was most pronounced at the hardware layer. For years, the primary

  • business of DCS suppliers had been the supply of large amounts of hardware, particularly

  • I/O and controllers. The initial proliferation of DCSs required the installation of prodigious

  • amounts of this hardware, most of it manufactured from the bottom up by DCS suppliers. Standard

  • computer components from manufacturers such as Intel and Motorola, however, made it cost

  • prohibitive for DCS suppliers to continue making their own components, workstations,

  • and networking hardware. As the suppliers made the transition to COTS

  • components, they also discovered that the hardware market was shrinking fast. COTS not

  • only resulted in lower manufacturing costs for the supplier, but also steadily decreasing

  • prices for the end users, who were also becoming increasingly vocal over what they perceived

  • to be unduly high hardware costs. Some suppliers that were previously stronger in the PLC business,

  • such as Rockwell Automation and Siemens, were able to leverage their expertise in manufacturing

  • control hardware to enter the DCS marketplace with cost effective offerings, while the stabilityreliability

  • and functionality of these emerging systems are still improving. The traditional DCS suppliers

  • introduced new generation DCS System based on the latest Communication and IEC Standards,

  • which resulting in a trend of combining the traditional concepts/functionalities for PLC

  • and DCS into a one for all solutionnamed "Process Automation System". The gaps among

  • the various systems remain at the areas such as: the database integrity, pre-engineering

  • functionality, system maturity, communication transparency and reliability. While it is

  • expected the cost ratio is relatively the same, the reality of the automation business

  • is often operating strategically case by case. The current next evolution step is called

  • Collaborative Process Automation Systems. To compound the issue, suppliers were also

  • realizing that the hardware market was becoming saturated. The life cycle of hardware components

  • such as I/O and wiring is also typically in the range of 15 to over 20 years, making for

  • a challenging replacement market. Many of the older systems that were installed in the

  • 1970s and 1980s are still in use today, and there is a considerable installed base of

  • systems in the market that are approaching the end of their useful life. Developed industrial

  • economies in North America, Europe, and Japan already had many thousands of DCSs installed,

  • and with few if any new plants being built, the market for new hardware was shifting rapidly

  • to smaller, albeit faster growing regions such as China, Latin America, and Eastern

  • Europe. Because of the shrinking hardware business,

  • suppliers began to make the challenging transition from a hardware-based business model to one

  • based on software and value-added services. It is a transition that is still being made

  • today. The applications portfolio offered by suppliers expanded considerably in the

  • '90s to include areas such as production management, model-based control, real-time optimization,

  • plant asset management, Real-time performance management tools, alarm management, and many

  • others. To obtain the true value from these applications, however, often requires a considerable

  • service content, which the suppliers also provide.

  • New age systems of 2010 onwards In the new world of distributed control system

  • following new technologies are emerging and taking roots :

  • 1.>Wireless systems and protocols - Esp. ISA 100 and Wireless HART 2.>Remote transmissions

  • , logging and data historian 3.>Mobile interfaces and controls 4.>Embedded webservers

  • Increasingly and ironically distributed control systems are getting centralised at plant level

  • and are getting distributed in the ability to log in and access providing a superior

  • man machine interface esp. from remote access and portability standpoint.

  • As wireless protocols are getting refined by the day its is increasingly getting integrated

  • into DCS . Controllers of DCS are coming with embedded servers and provide on the go web

  • access. Most vendors have their HMI mobile ready both for android and IOS . With these

  • interfaces threat of breach of security hence danger to plant and process control are now

  • very real. See also

  • OSIsoft BNF Technology Inc.| ARIDES

  • Building Automation Direct Digital Control

  • SCADA PLC

  • Fieldbus First-out alarm

  • Midac Safety instrumented system,

  • Industrial control systems Industrial safety systems

  • Annunciator panel EPICS

  • TANGO References

  • ^ "Introduction to Industrial Control Networks". IEEE Communications Surveys and Tutorials.

  • 2012.  ^ Stout, T. M. and Williams, T. J.. "Pioneering

  • Work in the Field of Computer Process Control". IEEE Annals of the History of Computing 17. 

  • ^ [1] CENTUM ^ a b [2] Metso DNA

  • ^ [3] INFI 90 ^ [4] DCI-4000

  • ^ [5] Foundation Fieldbus ^ [6] Foxboro I/A Series Distributed Control

  • System ^ ABB System 800xA

  • ^ [7] Emerson Process Management ^ [8] SPPA-T3000

  • ^ [9] Simatic PCS 7 ^ [10] Forbes Marshall

  • ^ [11] Azbil Corporation External links

  • DCS Selection MBA research program with many Links

  • Example of DCS system: Mark VIe by General Electric

  • An even better example of DCS system: Control Design Platform by ICD

  • Proview is probably the first Open Source system for process control and automation

  • in the world. Open Source DCS and automation software

  • FreeDCS is another Open Source Distributed Control System

A distributed control system refers to a control system of a process plant and industrial process

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分散制御システム (Distributed control system)

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    蔡育德 に公開 2021 年 01 月 14 日
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