Process control is a statistics and engineering discipline that deals with architectures, mechanisms, and algorithms for controlling the output of a specific process. See also control theory. This article is about the field of statistics. ... Engineering is the discipline of acquiring and applying knowledge of design, analysis, and/or construction of works for practical purposes. ... This article is about building architecture. ... A mechanism is some technical aspect of a larger process or mechanical device, a part or combination of parts designed to perform a particular function. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will terminate in a defined end-state. ... Illustration of a physical process: a geyser in action. Process (lat. ... For control theory in psychology and sociology, see control theory (sociology). ...

For example, heating up the temperature in a room is a process that has the specific, desired outcome to reach and maintain a defined temperature (e.g. 20°C), kept constant over time. Here, the temperature is the controlled variable. At the same time, it is the input variable since it is measured by a thermometer and used to decide whether to heat or not to heat. The desired temperature (20°C) is the setpoint. The state of the heater (e.g. the setting of the valve allowing hot water to flow through it) is called the manipulated variable since it is subject to control actions. For other uses, see Temperature (disambiguation). ...

A commonly used control device called a programmable logic controller, or a PLC, is used to read a set of digital and analog inputs, apply a set of logic statements, and generate a set of analog and digital outputs. Using the example in the previous paragraph, the room temperature would be an input to the PLC. The logical statements would compare the setpoint to the input temperature and determine whether more or less heating was necessary to keep the temperature constant. A PLC output would then either open or close the hot water valve, an incremental amount, depending on whether more or less hot water was needed. Larger more complex systems can be controlled by a Distributed Control System (DCS) or SCADA system. 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. ... 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... SCADA is the acronym for Supervisory Control And Data Acquisition. ...

In practice, process control systems can be characterized as one or more of the following forms:

• Discrete – Found in many manufacturing, motion and packaging applications. Robotic assembly, such as that found in automotive production, can be characterized as discrete process control. Most discrete manufacturing involves the production of discrete pieces of product, such as metal stamping.

• Batch – Some applications require that specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. One example is the production of adhesives and glues, which normally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples are the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds).

• Continuous – Often, a physical system is represented though variables that are smooth and uninterrupted in time. The control of the water temperature in a heating jacket, for example, is an example of continuous process control. Some important continuous processes are the production of fuels, chemicals and plastics. Continuous processes, in manufacturing, are used to produce very large quantities of product per year(millions to billions of pounds).

Applications having elements of discrete, batch and continuous process control are often called hybrid applications.

Examples

A thermostat is a simple example for a closed control loop: It constantly measures the current temperature and controls the heater's valve setting to increase or decrease the room temperature according the user-defined setting. A simple method switches the heater either completely on, or completely off, and an overshoot and undershoot of the controlled temperature must be expected. A more expensive method varies the amount of heat provided by the heater depending on the difference between the required temperature (the "setpoint") and the actual temperature. This minimizes over/undershoot. Bi-metallic thermostat for buildings A thermostat is a device for regulating the temperature of a system so that the systems temperature is maintained near a desired setpoint temperature. ...

An anti-lock braking system (ABS) is a more complex example. An anti-lock braking system (ABS) (translated from German, Antiblockiersystem) is a system on motor vehicles which prevents the wheels from locking while braking. ...

See also

An actuator is a mechanical device for moving or controlling a mechanism or system. ... This article does not cite any references or sources. ... Automatic control is the research area and theoretical base for mechanization and automation, employing methods from mathematics and engineering. ... Computer-Aided Acquisition and Logistic Support (CALS) is a strategy for paperless process control. ... A Proportional-Integral-Derivative controller is a standard feedback loop component in industrial control applications. ... Control engineering is the engineering discipline that focuses on the mathematical modelling systems of a diverse nature, analysing their dynamic behaviour, and using control theory to make a controller that will cause the systems to behave in a desired manner. ... Control panel of the engines of the Clémenceau. ... It has been suggested that this article or section be merged with Control theory. ... For control theory in psychology and sociology, see control theory (sociology). ... Controllability is an important property of a control system, and the controllability property plays a crucial role in many control problems, such as stabilization of unstable systems by feedback, or optimal control. ... 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. ... Cruise control (sometimes known as speed control or Autocruise) is a system to automatically control the speed of an automobile. ... A current loop describes two different electrical signalling schemes. ... Digital control is a branch of control theory that uses digital computers to act as a system. ... 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... For the superhero, see Feedback (Dark Horse Comics). ... Feed-forward is a term describing a kind of system which reacts to changes in its environment, usually to maintain some desired state of the system. ... A fieldbus or field bus is an industrial computer network for real-time distributed control. ... A flow control valve regulates the flow or pressure of a fluid. ... A Fuzzy control system is a control system based on fuzzy logic - a mathematical system that analyzes analog input values in terms of logical variables that take on continuous values between 0 and 1, in contrast to classical or digital logic, which operates on discrete values of either 0 and... In the branch of mathematics called functional analysis, the Laplace transform, , is a linear operator on a function f(t) (original ) with a real argument t (t ≥ 0) that transforms it to a function F(s) (image) with a complex argument s. ... Captain Nemo and Professor Aronnax contemplating measuring instruments in Twenty Thousand Leagues Under the Sea In physics and engineering, measurement is the activity of comparing physical quantities of real-world objects and events. ... Model Predictive Control, or MPC, is an advanced method of process control that has been in use in the process industries such as chemical plants and oil refineries since the 1980s. ... This article does not cite any references or sources. ... Non-linear control is a sub-division of control engineering which deals with the control of non-linear systems. ... An open-loop controller does not use feedback to control states or outputs of a dynamic system. ... A proportional-integral-derivative controller (PID controller) is a generic control loop feedback mechanism widely used in industrial control systems. ... abbreviated as P&ID ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... The Process Capability Study answers the question, is my process good enough? This is quite different from the question answered by a Control chart, which is, has my process changed? Properly, use of a Control Chart to establish that a process is stable and predictable precedes the use of a... 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. ... In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. ... SCADA is the acronym for Supervisory Control And Data Acquisition. ... Small R/C servo mechanism 1. ... Setpoint is the target value that an automatic control system, for example PID controller, will aim to reach. ... The Simatic S5 PLC is an automation system based on Programmable Logic Controllers. ... In control theory sliding mode control is a type of variable structure control where we try to alter the dynamics of a nonlinear system via application of a high-speed switching control. ... Temperature control is a process in which the temperature of an object is measured and the passage of heat energy into or out of the object is adjusted to achieve a desired temperature. ... A transducer is a device, usually electrical or electronic, that converts one type of energy to another. ... // These water valves are operated by handles. ... A governor (device) invented by James Watt to control (or govern) the speed of various machines: for example, pumps of the kind used in agriculture. ...

External links

• NETPROG - industrial automation company - PLC programing
• The Michigan Chemical Engineering Process Dynamics and Controls Open Textbook
• Process Control Training