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I dont want to know that we have two types of feedbacks and why it was invented,I just want an explanation in simple words of what feedback is.

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Feedback is nothing more than looking at the output of some system and using that information to control one of the inputs on that same system for the next time interval.

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Feedback is a phenomenon by which the signal at input of a system is affected by change in output.

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Try Google, there are lots of references on the web.

Here's a particularly good one: http://www.cds.caltech.edu/~murray/books/AM05/pdf/am08-complete_22Feb09.pdf

I think one of the first applications of feedback in a complex system was to regulate the speed of Watt's steam engine.

If my memory is correct there was a spinning device with 2 balls attached (called a governor). As the speed increased the balls tended to spin outwards which opened a valve that slowed the engine. The system reached equilibrium at the desired speed. So the speed was measured with the spinning device, which fed control signal back into the engine to slow it to keep the speed constant. Any load on the engine would cause the spinning to slow, which the governor would react to providing more power to the output.

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  • \$\begingroup\$ I don't know if this is the first example of feedback in control, but it's certainly an early one. Interestingly, it is the origin of the phrase "Balls out", though its tempting to place the origin on other things. \$\endgroup\$ – Scott Seidman Jun 9 '14 at 15:27
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Just two?

Feedback is readout of the reaction of the system to your control.

Example 1: You drive a GPIO pin high. The pin activates an actuator. There is an edge switch that detects the actuator started moving and it works as input on another pin. When both conditions are met, a warning light is lit to inform the actuator is in motion. This is your feedback: light informing of the actuator in motion.

Example 2: You switch a heater on, and your feedback is the resistance of a thermistor attached to the heater, letting you determine the temperature and switch it off when it's hot enough.

Example 3: You drive an AC motor through PWM. You output a signal that gets converted to current at some duty cycle. You read in the current flowing to the motor to determine the motor's torque, and you read a rotary encoder that gives you the motor position. Your control is duty cycle = power provided to the motor. Your feedback is the torque and position of the axle. Knowing this you can position the motor precisely and drive it to desired state in optimal time.

Generally, any system has inputs and outputs. Any input whose state is determined by your output - be it directly or indirectly - is called a feedback,

If you use that feedback to determine the control (like, regulate temperature by switching the heater on and off), you have a feedback loop. If the feedback just provides information (like that warning light), it's monitoring - reading and providing the state of the system output without affecting it.

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Just one sentence: We have feedback when the result of a certain process acts back to the source that has caused the process. This is not necessarily restricted to technical systems. We also have feedback effects in biology, social sciences and other areas.

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Suppose you have a system and you want something at the output, now the system is not ideal and it gets affected by its environment or surrounding like temperature, light or anything that can affect the behavior of the system, if you keep the input constant then there's no guarantee that you'll get the desired output due to certain things perturbing the system, so what you do is sense the output, feed it back to the controller whose controlling your system(providing input to the system, it could be a microprocessor controlling a servo motor or whatever) and the controller changes the input to the system accordingly to get the desired the output, that's feedback.

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