Industrial Control Systems
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Industrial control system (ICS) is a general term that encompasses several types of control systems, including supervisory control and data acquisition (SCADA) systems, distributed control systems (DCS), and other smaller control system configurations such as skid-mounted Programmable Logic Controllers (PLC) often found in the industrial sectors and critical infrastructures. ICSs are typically used in industries such as electrical, water, oil and gas, data. Based on information received from remote stations, automated or operator-driven supervisory commands can be pushed to remote station control devices, which are often referred to as field devices. Field devices control local operations such as opening and closing valves and breakers, collecting data from sensor systems, and monitoring the local environment for alarm conditions.
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[edit] DCSs
DCSs are used to control industrial processes such as electric power generation, oil and gas refineries, water and wastewater treatment, and chemical, food, and automotive production. DCSs are integrated as a control architecture containing a supervisory level of control overseeing multiple, integrated sub-systems that are responsible for controlling the details of a localized process. Product and process control are usually achieved by deploying feed back or feed forward control loops whereby key product and/or process conditions are automatically maintained around a desired set point. To accomplish the desired product and/or process tolerance around a specified set point, specific programmable controllers are used ONLY.
[edit] PLCs
PLCs provide boolean logic operations, timers, and (in some models) continuous control. The proportional, integral, and/or differential gains of the PLC continuous control feature may be tuned to provide the desired tolerance as well as the rate of self-correction during process upsets. DCSs are used extensively in process-based industries. PLCs are computer-based solid-state devices that control industrial equipment and processes. While PLCs are control system components used throughout SCADA and DCS systems, they are often the primary components in smaller control system configurations used to provide regulatory control of discrete processes such as automobile assembly lines and power plant soot blower controls. PLCs are used extensively in almost all industrial processes.
[edit] A Historical Perspective
Industrial Control System terminology has evolved over the past three to four decades. The differences are subtle but important. They are not easily understood without a good historical perspective . For example, there are Distributed Control Systems in the architecture sense in airplanes, but it would be generally agreed that aircraft do not have DCS systems. DCS systems generally refer to the particular functional distributed control system design that exist in Industrial Process plants (Oil & Gas, Refining, Chemical, Pharmaceutical, some Food & Beverage, Water & Wastewater, Pulp & Paper, Utility Power, Mining, Metals, etc...) Although PLC (Programmable Logic Controller) systems can be considered distributed in architecture, they are not DCS systems in the sense that they are generally applied to Discrete Factory Automation applications.. (Plants that make "Things" rather than "Stuff"). SCADA's history is rooted in pipeline and power distribution applications where there was a need to gather a lot of remote data and do a little bit of control with sites that were widely geographically separated. Each of these types of systems have their particular functional needs that are different. DCS systems used in hazardous explosive environments in Oil production have different requirements than PLC based systems that are controlling the manufacturing and packaging of auto parts for example. Although what you might see in the plants as Boxes that look alike, are in fact quite different in a bunch of ways. As proof of this, companies who are strong on the Process side like Emerson and Foxboro/invensys have had difficulty trying to leverage their systems into Factory Automation. Rockwell Automation, the US leader in PLCs, has always wanted to leverage their strength in factory automation into the process automation side, but similarly has not been able to do that. Having said all of this, the boundaries between these systems are becoming more gray as time goes on and technology provides more and more bridges between them.
