What are the type of feedback in control system?

Definition


Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence the same event/phenomenon in the present or future. When an event is part of a chain of cause-and-effect that forms a circuit or loop, then the event is said to ';feed back'; into itself.





Feedback is also a synonym for:


Feedback signal: the information about the initial event that is the basis for subsequent modification of the event.


Feedback loop: the causal path that leads from the initial generation of the feedback signal to the subsequent modification of the event.


Audio feedback: the special kind of positive feedback which occurs when a loop exists between an audio input and output.





Types of Feedback in Control System


When feedback modifies an event/phenomenon, the modification will subsequently influence the feedback signal in one of three ways:





1 - the feedback signal increases, leading to more modification. This is known as positive feedback.


2 - the feedback signal decreases, leading to less modification. This is known as negative feedback.


3 - the feedback signal does not change, indicating the phenomenon is in equilibrium.





Note that an increase or decrease of the feedback signal here refers to the magnitude of the signal's absolute value, without regard to the polarity or sign of the signal. For example a change in signal value from +5 to +10 or from -3 to -6 are both considered to be increasing.





Positive feedback, which seeks to increase the event that caused it, as in a nuclear chain-reaction, is also known as a self-reinforcing loop. An event influenced by positive feedback will increase or decrease its output/activation until it hits a limiting constraint. Such a constraint may be destructive, as in thermal runaway or a nuclear chain reaction. Self-reinforcing loops can be a smaller part of a larger balancing loop, especially in biological systems such as regulatory circuits.





Negative feedback, which seeks to reduce the feedback signal that caused it, is also known as a self-correcting or balancing loop. Such loops tend to be goal-seeking, as in a thermostat which compares actual temperature with desired temperature and seeks to reduce the difference. Balancing loops are sometimes prone to hunting: an oscillation caused by an excessive or delayed feedback signal, resulting in over-correction.





The terms negative and positive feedback can be used loosely or colloquially to describe or imply criticism and praise, respectively. This may lead to confusion with the more technically accurate terms positive and negative reinforcement, which refer to something that changes the likelihood of a future behavior.





Negative feedback was applied by Harold Stephen Black to electrical amplifiers in 1927, but he could not get his idea patented until 1937. Arturo Rosenblueth, a Mexican researcher and physician, co-authored a seminal 1943 paper Behavior, Purpose and Teleology that, according to Norbert Wiener (another co-author of the paper), set the basis for the new science cybernetics. Rosenblueth proposed that behavior controlled by negative feedback, whether in animal, human or machine, was a determinative, directive principle in nature and human creations.. This kind of feedback is studied in cybernetics and control theory.