12.3: A Bit on Negative Feedback

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Given Equation 12.3.2, in 18.04 we can ask if there are any poles in the right half-plane without needing any underlying physical model. Still, it’s nice to have some sense of where this fits into science and engineering.

In a negative feedback loop the output of the system is looped back and subtracted from the input.

Example \(\PageIndex{1}\)

The heating system in my house is an example of a system stabilized by feedback. The thermostat is the feedback mechanism. When the temperature outside (input signal) goes down the heat turns on. Without the thermostat it would stay on and overheat my house. The thermostat turns the heat up or down depending on whether the inside temperature (the output signal) is too low or too high (negative feedback).

Example \(\PageIndex{2}\)

Walking or balancing on one foot are examples negative feedback systems. If you feel yourself falling you compensate by shifting your weight or tensing your muscles to counteract the unwanted acceleration.