Transfer Function for a negative feedback loop

S

Thread Starter

smarch

Joined Mar 14, 2009

52

Nov 20, 2010

• #1

Hi guys would appreciate the help.
I am having trouble with this question.

From the JPEG I have a attached:

Determine the equivalent T.F. G(s) in form of G(s) = \(\frac{p}{qs+r}\), where p, q, r are constants.

I have tried working it out, but got into a mess. Help please, how do you do it?

Thanks

 

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Last edited: Nov 20, 2010

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guitarguy12387

Joined Apr 10, 2008

359

Nov 20, 2010

• #2

Can ya post your work?

In general, for a closed loop system, you have:

TF = (direct path gain)/(1 - sum of loop gain)

From there it is just algebra to get into the right form

 

S

Thread Starter

smarch

Joined Mar 14, 2009

52

Nov 20, 2010

• #3

I come to :

C(s) = R(s).(10/3s - 5) - C(s)(40/3s - 20)

Am I on the right track?
I have limited notes on this and have tried to follow it as they are in the notes, but it is quite a different problem to that one.

 

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guitarguy12387

Joined Apr 10, 2008

359

Nov 20, 2010

• #4

Yeah that looks about right i think.

Now just solve for C(s)/R(s)

 

S

Thread Starter

smarch

Joined Mar 14, 2009

52

Nov 21, 2010

• #5

guitarguy12387 said:

Yeah that looks about right i think.

Now just solve for C(s)/R(s)

Click to expand...

How do you complete it all the way through to get G(s) = \(\frac{p}{qs+r}\)

 

Georacer

Joined Nov 25, 2009

5,182

Nov 21, 2010

• #6

First read here:http://en.wikipedia.org/wiki/Control_theory in the section Closed Loop Tranfer Funtion. In your case you have C=5, P=\(\frac{2}{3s}-1\) and F=-4;

Try to calculate the Transfer Function H(s).

Post it and we will discuss more.

 

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krishna chaitanya

Joined Nov 8, 2010

5

Dec 28, 2010

• #7

TF = (direct path gain)/(1 - sum of loop gain)..

it will give ans for this...