Open loop transfer function

  • Thread starter erece
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  • #1
erece
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In many books i saw that open loop transfer function is given by KG(s)H(s) , where G(s) is forward path gain and H(s) is the feedback gain. But according to the definition of open loop it does not contain feedback , then why there is a term of H(s) ?


reference url
http://en.wikibooks.org/wiki/Control_Systems/Stability
 

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  • #2
NascentOxygen
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G(s).H(s) is the full path gain of the loop you will use for feedback. Or to put it another way, it is the open loop path gain of the difference signal that you intend to connect in as feedback. Until you close the loop there is no feedback, so by definition G(s).H(s) must be some sort of OPEN LOOP gain.

The difference signal, v(in) - v(f), will be amplified by G(s).H(s) and added to v(in). But until we close the loop there is no feedback, so you have a signal vf(s) = G(s).H(s).vin(s)
 
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