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Feedback Loops

05/10/2015

Feedback helps control a system in either a good way or a bad way.

Inappropriate feedback can lead to erratic behaviour or even collapse of the system.

Always try to provide feedback based on desired output.

Can be either direct or indirect (from another system).

Feedback loops enhance, decrease or buffer changes within system.

Feedback can be negative or positive.

Positive feedback loops enhance or amplify changes – moves system from equilibrium state making it unstable.

Too much positive feedback will render the system in a permanent undesirable state incapable of change except from outside influence.

Negative feedback dampens or buffers system changes.

This has the opposite effect to excess positive feedback and holds the system in a stable state of equilibrium.

Example: automatic gain control. If average output volume rises over time for standard input, take portion of average output value, invert it and apply to input resulting in a reduce output.

Positive feedback connection – an increase or decrease in one variable results in matching change in second variable.

Negative feedback connection – increase or decrease in one variable results in an opposite change in second variable.

Example: world population. Birth rate increases at fixed percentage results in unlimited population growth, known as vicious circle. Further growth in population results in even large growth in population. Also known as exponential growth.

Not all positive feedbacks result in exponential growth but all result in unlimited growth unless modified by another event.

Example of positive feedback connection: an increase in the force applied to the accelerator of a motor car results in an increase in speed.

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