# Feedback Block Diagram Reduction

For this diagram reduction question, I thought pushing the summing junction to the left past the G1(s) is can be a solution but is it correct that pushing to number 2 then we can collapse the summing junctions?

• If you would simply write down the transfer functions of the system before and after the change you propose then you would know if the change makes will affect the system or not. Shortcut: assume $G_3(s)$ and $H(s)$ are both zero and determine the transfer functions. – Bimpelrekkie Mar 18 '19 at 12:31

## 1 Answer

To do what you want to do you need to modify the feedback path involving G4(s): -

Now you can collapse the summing junctions!

• So there is no difference pushing the sum junction to 1 or 2 we can collapse summing junctions in both conditions? – Jamesflo97 Mar 18 '19 at 13:12
• In the original circit, the input for G3 is the difference R-(output H). In the modified circuit - after combining both sum junctions - G3 will get an additional term: -(outputG4/G1). Or - what is ment with "collapsing"? – LvW Mar 18 '19 at 14:35
• @Jamesflo97 take note what LvW says about G3's input. – Andy aka Mar 18 '19 at 15:01