Sensors and feedback loops — Technology, 14–17 years
Many technologies do not simply obey one command; they measure what is happening and adjust their action. This is a feedback loop.
Idea
A sensor measures something, such as temperature, light or movement. A controller compares the measurement with a target and changes an output, such as a heater or motor. The loop repeats, so the system responds to changing conditions rather than following one fixed command.
Why
The problem is that the world does not stay still. A heater switched on for exactly ten minutes may leave one room cold and another too hot. Engineers used feedback to make machines respond to real conditions, building on control systems developed for devices such as steam engines and thermostats.
Worked example
A thermostat targets 20 °C. The sensor reads 18 °C, so the controller switches the heating on. Later it reads 20.5 °C, so the controller switches it off. If the room falls to 19.5 °C, the loop turns heating on again; it keeps checking instead of guessing once.
Trap
A reasonable mistake is to assume that a sensor tells the exact truth. It only measures where it is, with limited precision, and can be blocked, delayed or badly calibrated. A thermostat near a radiator may think the whole room is warm, even when the far corner is cold.
Use
Feedback controls cruise control, phone brightness, camera focus, washing-machine cycles and many robots. It is useful when conditions change and a device must keep near a target. It is not magic: a poor sensor or a badly chosen target can still produce poor behaviour.
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