Closed-loop transfer function

(Redirected from Open-loop transfer function)

In control theory, a closed-loop transfer function is a mathematical function describing the net result of the effects of a feedback control loop on the input signal to the plant under control.

Overview

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The closed-loop transfer function is measured at the output. The output signal can be calculated from the closed-loop transfer function and the input signal. Signals may be waveforms, images, or other types of data streams.

An example of a closed-loop block diagram, from which a transfer function may be computed, is shown below:

 

The summing node and the G(s) and H(s) blocks can all be combined into one block, which would have the following transfer function:

 

  is called the feed forward transfer function,   is called the feedback transfer function, and their product   is called the open-loop transfer function.

Derivation

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We define an intermediate signal Z (also known as error signal) shown as follows:

Using this figure we write:

 
 

Now, plug the second equation into the first to eliminate Z(s):

 

Move all the terms with Y(s) to the left hand side, and keep the term with X(s) on the right hand side:

 

Therefore,

 
 

See also

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References

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  •   This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22.