View source for Control system

{{short description|System that manages the behavior of other systems}}
{{Other uses}}
{{Use American English|date=May 2022}}
{{More citations needed|article|date=December 2010}}

[[File:Loaded centrifugal governor (New Catechism of the Steam Engine, 1904).jpg|thumb|The [[centrifugal governor]] is an early [[proportional control]] mechanism.]]

A '''control system''' manages, commands, directs, or regulates the behavior of other devices or systems using [[control loop]]s. It can range from a single home heating controller using a [[thermostat]] controlling a domestic boiler to large [[industrial control system]]s which are used for controlling [[Process (engineering)|processes]] or machines. The control systems are designed via [[control engineering]] process.

For continuously modulated control, a [[feedback controller]] is used to automatically control a process or operation.   The control system compares the value or status of the [[process variable]] (PV) being controlled with the desired value or [[Setpoint (control system)|setpoint]] (SP), and applies the difference as a control signal to bring the process variable output of the [[Plant (control theory)|plant]] to the same value as the setpoint.

For [[Sequential logic|sequential]] and [[combinational logic]], [[Algorithm|software logic]], such as in a [[programmable logic controller]], is used.{{Clarify|date=July 2022}}

==Open-loop and closed-loop control==
{{excerpt|Control loop#Open-loop and closed-loop}}

==Feedback control systems==
{{excerpt|Closed-loop controller}}

==Logic control==
Logic control systems for industrial and commercial machinery were historically implemented by interconnected electrical [[relay]]s and [[cam timer]]s using [[ladder logic]]. Today, most such systems are constructed with [[microcontroller]]s or more specialized [[programmable logic controller]]s (PLCs). The notation of ladder logic is still in use as a programming method for PLCs.<ref name="Kuphaldt LADDER LOGIC">{{cite web|last=Kuphaldt|first=Tony R.|title=Chapter 6 LADDER LOGIC|url=http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_6.html|work=Lessons In Electric Circuits -- Volume IV|access-date=22 September 2010|url-status=live|archive-url=https://web.archive.org/web/20100912090415/http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_6.html|archive-date=12 September 2010}}</ref>

Logic controllers may respond to switches and sensors and can cause the machinery to start and stop various operations through the use of [[actuator]]s.  Logic controllers are used to sequence mechanical operations in many applications. Examples include elevators, washing machines and other systems with interrelated operations. An automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. For example, various electric and pneumatic transducers may fold and glue a cardboard box, fill it with the product and then seal it in an automatic packaging machine.

PLC software can be written in many different ways – ladder diagrams, SFC ([[sequential function chart]]s) or [[Instruction list|statement lists]].<ref name="Ian Brady PLCs">{{cite web|last=Brady|first=Ian|title=Programmable logic controllers - benefits and applications|url=http://www.optimacs.com/wp-content/uploads/2012/03/PLC-report.pdf|work=PLCs|access-date=5 December 2011|url-status=live|archive-url=https://web.archive.org/web/20140202000040/http://www.optimacs.com/wp-content/uploads/2012/03/PLC-report.pdf|archive-date=2 February 2014}}</ref>

==On–off control==
{{main|Bang–bang control}}
On–off control uses a feedback controller that switches abruptly between two states. A simple bi-metallic domestic [[thermostat]] can be described as an on-off controller. When the temperature in the room (PV) goes below the user setting (SP), the heater is switched on. Another example is a pressure switch on an air compressor. When the pressure (PV) drops below the setpoint (SP) the compressor is powered. Refrigerators and vacuum pumps contain similar mechanisms. Simple on–off control systems like these can be cheap and effective.

==Linear control==
{{excerpt|Linear control}}

==Fuzzy logic==
{{main|Fuzzy logic}}

Fuzzy logic is an attempt to apply the easy design of logic controllers to the control of complex continuously varying systems. Basically, a measurement in a fuzzy logic system can be partly true.

The rules of the system are written in natural language and translated into fuzzy logic. For example, the design for a furnace would start with: "If the temperature is too high, reduce the fuel to the furnace. If the temperature is too low, increase the fuel to the furnace."

Measurements from the real world (such as the temperature of a furnace) are ''fuzzified'' and logic is calculated arithmetic, as opposed to [[Boolean logic]], and the outputs are ''de-fuzzified'' to control equipment.

When a robust fuzzy design is reduced to a single, quick calculation, it begins to resemble a conventional feedback loop solution and it might appear that the fuzzy design was unnecessary. However, the fuzzy logic paradigm may provide scalability for large control systems where conventional methods become unwieldy or costly to derive.{{cn|reason=See [[Talk:Control system#Fuzzy logic]]|date=April 2022}}

[[Fuzzy electronics]] is an electronic technology that uses fuzzy logic instead of the two-value logic more commonly used in [[digital electronics]].

==Physical implementation==
[[File:Leitstand 2.jpg|thumb|A DCS control room where large screens display plant information. The operators can view and control any part of the process from their computer screens, whilst retaining a plant overview on the larger screens.]]
[[File:Hydraulic press control panel.jpg|thumb|right|A control panel of a hydraulic heat press machine]]

The range of control system implementation is from [[compact controller]]s often with dedicated software for a particular machine or device, to [[distributed control system]]s for industrial process control for a large [[physical plant]].

Logic systems and feedback controllers are usually implemented with [[programmable logic controller]]s.

==See also==
{{Div col|colwidth=25em}}
* [[Building automation]]
* [[Coefficient diagram method]]
* [[Control theory]]
* [[Cybernetics]]
* [[Distributed control system]]
* [[Droop speed control]]
* [[Education and training of electrical and electronics engineers]]
* [[EPICS]]
* [[Good regulator]]
* [[Guidance, navigation, and control]]
* [[Hierarchical control system]]
* [[HVAC control system]]
* [[Industrial control system]]
* [[Motion control]]
* [[Networked control system]]
* [[Numerical control]]
* [[Perceptual control theory]]
* [[PID controller]]
* [[Process control]]
* [[Process optimization]]
* [[Programmable logic controller]]
* [[Real-time computing]]
* [[Sampled data system]]
* [[SCADA]]
* [[VisSim]]
{{Div col end}}

==References==
{{Reflist}}

==External links==
{{Wikibooks|Control Systems}}
* [https://systemcontrol.readthedocs.io/en/latest/index.html SystemControl] Create, simulate or HWIL control loops with Python. Includes Kalman filter, LQG control among others.
* [http://www.unmannedaircraft.org/f/pat6460810.pdf Semiautonomous Flight Direction - Reference unmannedaircraft.org]
* [http://www.mathworks.com/products/control/ Control System Toolbox] for design and analysis of control systems.
* [http://www.trminternational.com/ Control Systems Manufacturer] Design and Manufacture of control systems.
* [http://reference.wolfram.com/mathematica/guide/ControlSystems.html Mathematica functions for the analysis, design, and simulation of control systems]
* [https://github.com/mck-sbs/PyConSys Python Control System] (PyConSys) Create and simulate control loops with Python. AI for setting PID parameters.

{{Electronic systems}}
{{Authority control}}

[[Category:Control theory]]
[[Category:Control engineering]]
[[Category:Systems engineering]]
[[Category:Systems theory]]
[[Category:Automation|&]]