A control loop consists of three parts: Measurement by a sensor connected to the process, Decision in a controller element, Action through an output device ("actuator") such as a control valve. (Some control loops work in cascaded control, and so produce signals used by other controllers or use signals created by other controllers.) For example, suppose a water tank is used to supply water for several parts of a plant and it is necessary to control the tank level at a constant value. A sens ...

See also:

PID controller, PID controller - Control loop basics, PID controller - Theory, PID controller - Nomenclature, PID controller - Tuning a PID loop, PID controller - Problems, PID controller - How to get one

Read more here: » PID controller: Encyclopedia II - PID controller - Control loop basics

See also:

PID controller, PID controller - Control loop basics, PID controller - Theory, PID controller - Nomenclature, PID controller - Tuning a PID loop, PID controller - Problems, PID controller - How to get one

Read more here: » PID controller: Encyclopedia II - PID controller - Problems

The parameters of PID control were originally named after the adjustments on mechanical controllers and so were called proportional band, reset and rate. These quantities are based on the interacting algorithm. Modern practice is to refer to gain, integral gain, and derivative gain since this better matches the usage in digital controllers. There are two different forms of the PID controller: The standard or "non-interacting" form, which allows independent adjustment of the proportional, integral and derivative constants. ...

See also:

PID controller, PID controller - Control loop basics, PID controller - Theory, PID controller - Nomenclature, PID controller - Tuning a PID loop, PID controller - Problems, PID controller - How to get one

Read more here: » PID controller: Encyclopedia II - PID controller - Nomenclature

Development of PID control originated from the observation that a proportional-only control can only eliminate the error between setpoint and process variable at one particular setpoint. At any other setting, there would be an offset between the setpoint and the true process value. Metaphorically, an operator could reset the controller setpoint by hand, until the actual process eventually stabilized at the desired value. In older control literature this is referred to "reset" action as a result. The derivative term reflects the ability to ob ...

See also:

PID controller, PID controller - Control loop basics, PID controller - Theory, PID controller - Nomenclature, PID controller - Tuning a PID loop, PID controller - Problems, PID controller - How to get one

Read more here: » PID controller: Encyclopedia II - PID controller - Theory

"Tuning" a control loop is the adjustment of its control parameters (gain/proportional band, integral/reset, derivative/rate) to the optimum values for the desired control response. The optimum behavior on a process change or setpoint change varies depending on the application. Some processes must not allow an overshoot of the process variable from the setpoint. Other processes must minimize the energy expended in reaching a new setpoint. Generally stability of response is required and the process must not oscillate for any combination of pr ...

See also:

PID controller, PID controller - Control loop basics, PID controller - Theory, PID controller - Nomenclature, PID controller - Tuning a PID loop, PID controller - Problems, PID controller - How to get one

Read more here: » PID controller: Encyclopedia II - PID controller - Tuning a PID loop