May 30, 2004

Negative Feedback

A brief illustration of negative feedback:

If you want to design a car to go from point X to point Y there are two possible ways to do it. One way is to point the car at point Y (remember it’s already sitting at point X) and calibrate all the systems very carefully to make sure that it veers neither left nor right. You better make sure that you do an excellent job, because any imperfection will keep it from reaching its destination.

Another way is to not worry so much about the calibration of the systems. Instead add a feedback system that tells the car to turn left if it veers to the right, and right if it veers to the left. This is a much more robust way to design a system, because it will work even when the calibrations are off. Notice that the feedback is opposite in direction to the car’s deviation, that’s why it’s called negative feedback.

(For the sake of completeness, negative feedback will not work if it results in a greater deviation than the original one – for example, if veering to the right results in a deviation to the left that is greater than the original deviation to the right.)

Posted by David Boxenhorn at May 30, 2004 09:55 AM
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