Feedback control — Engineering, 14–17
A feedback system measures what is happening, compares it with a target and adjusts its action to reduce the difference.
Measure, compare, adjust
Feedback control keeps a system near a chosen target. A sensor measures the current result, a controller compares it with the target, and an action changes the system. The loop repeats because the system and its surroundings keep changing.
Why feedback was needed
A fixed instruction cannot respond when conditions change. A heater set to run for ten minutes may leave one room cold and another too hot. Feedback developed to make machines respond to results, helping systems such as engines, thermostats and industrial processes stay stable.
A thermostat loop
The target room temperature is 20 °C. The sensor reads 18 °C, so the controller finds an error of 2 °C and switches the heater on. Later it reads 20.5 °C, an error of −0.5 °C, so it switches the heater off; the loop continues checking.
Feedback is not just a command
It is reasonable to think that setting a target is enough: tell a motor to turn and it will turn correctly. But without measuring the result, the system cannot notice friction, a changing load or a sensor error. A command starts an action; feedback checks what actually happened.
Feedback in real systems
Cruise control measures a car’s speed and changes engine power to approach the chosen speed. A drone uses sensors to correct its position, while a refrigerator controls temperature by switching its compressor. These systems work only when their measurements are useful and timely.
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