What does it mean by Linear Feed back System?Application?

Answer 1

A control system where you have an input, an expected output, a real output, and an error between the outputs...

based on inputs you expect to get certain output, but you get something close to it, so your system will correct for that error.

Imaginary application: inflating car tires to 32psi based on incoming pressure. If tire 1 had 2psi off the bat, then you would put 30psi, but you get 35psi actual. - your system would feeback the error and the next tire if comes at 2psi, then it would adjust to get 32psi....

Answer 2

A feedback system is one in which the input is controlled by always looking at what the resulting output is. A non-mechanical analogy would be if you wanted to drive your car at a specific speed. You would press on the gas pedal until it got up to that speed and keep changing the pressing if the car slowed going up a hill or accelerated rolling down a hill. By constantly checking you can adjust the car's speed to exactly where you want it. The more typical automated example would be a home thermostat in which the room temperature is measured by a thermostat that keeps the heat on until your room is warm enough.

Specifically a linear feedback system is one in which the amount of the incoming energy is varied directly proportional to the amount of output measured. It requires a sensor and a controllable output element that can be driven by the information from the sensor. If you wanted to keep the light constant in a room you could use a photo sensor that would control the voltage going to the lamps depending upon how much light the sensor was seeing.

In real life even linear systems tend to cheat by using not just an output proportional to the desired results but also by keeping track of how fast the sensed value is changing and how much error it has seen in that value. When the linearity is aided by that additional information the output stays much closer to the desired value.

Answer 3

It means that you have a feedback to a controller that has a constant transfer function, that is output/input. For example, the liquid engines on the space shuttle are moved to control the flight. The position of the engines is fed back to the engine control system. This feedback is in the form of an electrical signal that is a function of the position of the engine(s) with reference to the null position.
The linear feedback transfer function in this case would be volts per degree of engine travel.