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A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers are connected by a network for communication and monitoring. It has been suggested that this article or section be merged with Control theory. ...
Synonymous with Manufacturing Execution Systems Manufacturing Execution Systems (MESs) are critical to the success of large manufacturing operations today. ...
Illustration of a physical process: a geyser in action. Process (lat. ...
In engineering and mathematics, a dynamical system is a deterministic process in which a functions value changes over time according to a rule that is defined in terms of the functions current value. ...
Basic Principles A controller is the brain component of a system that monitors certain input variables and adjusts other output variables to achieve the desired operation. ...
For other uses, see Brain (disambiguation). ...
DCS is a very broad term used in a variety of industries, to monitor and control distributed equipment.
Description of an electrical power grid Electrical power is generated in many locations and created by various technologies in the form of alternating current. ...
Itaipu Dam is a hydroelectric generating station Electricity generation is the first process in the delivery of electricity to consumers. ...
Traffic lights will sometimes differ where there are several lanes of traffic. ...
Refining is the process of purification of a substance, usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. ...
A Chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. ...
Pharmacology (in Greek: pharmacon is drug, and logos is science) is the study of how chemical substances interfere with living systems. ...
A sensor network consist of many spatially distributed sensors, which are used to monitor or detect phenomena at different locations such as temperature changes, pollutant levels, etc. ...
For other uses, see Ship (disambiguation). ...
Elements
A DCS typically uses computers (usually custom designed processors) as controllers and uses both proprietary interconnections and protocols for communication. Input & 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 (a.k.a. field) and output modules transmit instructions to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexers/demultiplexers. Buses also connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles. See Process Automation System. In the field of telecommunications, a communications protocol is the set of standard rules for data representation, signalling, authentication and error detection required to send information over a communications channel. ...
In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ...
An electrical bus (sometimes spelled buss) is a physical electrical interface where many devices share the same electric connection. ...
Schematic of a 2-to-1 Multiplexer. ...
The term multiplexer has uses in several fields of application: Electronics In electronics, a multiplexer or mux is a device that combines several electrical signals into a single signal. ...
Human-Machine Interface (HMI) is a term that refers to the layer that separates a human that is operating a machine from the machine itself. ...
Console may be: An organ term for the area of an organ including the keys, stops, and foot pedals manipulated by the organist. ...
It has been suggested that this article or section be merged with Manufacturing Execution Systems. ...
Elements of a distributed control system may directly connect to physical equipment such as switches, pumps and valves or or may work through an intermediate system such as a SCADA system. SCADA is the acronym for Supervisory Control And Data Acquisition. ...
Applications Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central station power generation, pharmaceuticals, food & 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 (I/O) 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 variable speed drives and motor control centers, cement kilns, mining operations, ore processing facilities, and many others. Control valves are valves used within industrial plants and elsewhere to control operating conditions such as temperature, pressure, flow, and liquid level by fully or partially opening or closing in response to signals received from sensors that monitor changes in such conditions. ...
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 (I/O) 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 (PID) control, can generally perform logic and sequential control.
DCSs may employ one or several 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 had been applied for control of industrial processes since the beginning of the 1960's. These systems relied on gathering all process signals in a plant to a central point for conversion from field contact levels (for digital points) and analog signals to the digital domain. Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ...
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[1] systems, respectively. US-based Bristol also introduced their UCS 3000 universal controller in 1975. In 1980, Bailey (now part of ABB) introduced the NETWORK 90 system. Honeywell Heating Specialties Company Stock Certificate dated 1924 signed by Mark C. Honeywell - courtesy of Scripophily. ...
Yokogawa Electric Corporation (横河電機, Yokogawa Denki) (TYO: 6841) is a Japanese manufacturer of test and measurement products and factory automation systems. ...
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 Set Point Control, where process computers supervised clusters of analog controllers. The proliferation of microprocessors allowed suppliers to take this mode to the next step by deploying minicomputers in a supervisory role, controlling several digital loop 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 long way away.
Central to the DCS model was the inclusion of control function blocks, which were introduced by the Foxboro company. 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[2] today.
Digital communication between controllers and supervisory computers was one of the primary advantages of the DCS, and 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 The DCS brought distributed intelligence to the plant and established the presence of computers and microprocessors in process control, but it still did not provide the reach and openness necessary to unify plant resource requirements. In many cases, the DCS was merely a digital replacement of the same functionality provided by analog controllers and a panelboard display. This was embodied in The Perdue Reference Model (PRM) that was developed to define Manufacturing Operations Management relationships. PRM later formed the basis for ISA95 standards activities today.
In the 1980s, users began to look at DCSs as more than just basic process control. It was believed that if openness could be achieved and greater amounts of data could be shared throughout the enterprise that good things could be achieved, although few were sure what these benefits would be. 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 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 (COTS) 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 (RTOS) 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 invasion of Microsoft at the desktop and server layers resulted in the development of technologies such as OLE for Process Control (OPC), 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 '90s 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 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 ABB with System 800xA[3], Emerson Process Management[4] with the DeltaV control system, Siemens[5] with the Simatic PCS7[6] and azbil[7] from Yamatake with the Harmonas-DEO system. For other uses, see Delta-v (disambiguation). ...
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, Schnieder and Siemens, were able to leverage their expertise in manufacturing control hardware to enter the DCS marketplace with cost effective offerings. 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 solution -- named "Process Automation System/Controller".
To compound the issue, suppliers were also realizing that the hardware market was becoming saturated. The lifecycle 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 (PAM), Real Time Performance Management (RPM) 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. DCS supplier such as azbil known as Yamatake services have also expanded in scope to the point where many suppliers can act as Main Automation Contractors (MACs), providing a single point of responsibility for all automation-related facets of a project.
References - ^ [1] CENTUM
- ^ [2] Foundation Fieldbus
- ^ ABB System 800xA
- ^ [3] Emerson Process Management
- ^ [4] Siemens
- ^ [5] Simatic PCS5
- ^ [6] Yamatake's azbil
See also SCADA is the acronym for Supervisory Control And Data Acquisition. ...
PLC & input/output arrangements A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ...
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