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Control Systems Engineering - Block Reduction Help

  1. Apr 7, 2015 #1
    1. The problem statement, all variables and given/known data


    I'm trying to reduce the following block diagram


    2. Relevant equations

    3. The attempt at a solution

    I appear to be having some issues in doing this. The first thing that I did to reduce this block diagram was to take the forward path that has 2/(s+4) with negative feedback of 2, and reduce this by

    (K G(s))/(1 + K*G(s)*H(s)) = (3/(s+4))/(1 + 6/(s+4)) = 3/(s+4 + 6) = 3/(s+10)

    I also moved the 1/s block to the left of the summation. This resulted in a parallel path with a gain of one. I reduced this to simply a forward path with 1/s + 1.

    I then did the following with 6s and the negative feedback with a gain of 1

    This resulted in a reduced diagram with

    (1/s +1)*3/(s+10)

    in the forward path with a negative feedback of 6s+1

    I guess I have done something wrong, and I'm not exactly sure what. Below is a picture of what I did.


    Thanks for any help. I guess I'm doing something wrong, but am not exactly sure what it is I'm doing wrong.
  2. jcsd
  3. Apr 8, 2015 #2
    When you did this, did you remember to adjust the 6s path as well? TBH I worked hard to forget all this stuff. But I'm pretty sure I got stuck on this exact question as well =D
    Could you try moving the 1/s instead to the right? That way you'd only need to adjust the foward path 1 to S

    You could also try moving the 6s into the 1 feedback, but would have to adjust that forward back then to 1-6s

    I really hated these was always much better with the equations :)
  4. Apr 8, 2015 #3


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    Gold Member

    like cpscdave said there is your problem
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