Characteristic function of the system

Discussion in 'Homework Help' started by glorimda, Oct 3, 2012.

  1. glorimda

    Thread Starter New Member

    Oct 12, 2011
    17
    0
    Hey, guys.

    I'm studying the Automatic Control Systems and struggling with characteristic fn.

    I'm given a system diagram as an attachment and I got my answer, but it's different from the solution.

    My answer is

    Transfer function : K/(JS^2 + aS + K*Kf*s +K)

    But the answer from the solution is

    Transfer function : (K*Kf) / [JS^2 + (aS + K*Kf)s +K*Kf]

    As you noticed, there're Kf added on each.

    Am I wrong or is solution wrong. I've been struggling with this for 3 hours and can't see

    any problem from mine.

    (The way I solved this is, I considered the system as two separate closed-loop. Firstly, calculated the first closed-loop in the middle then multiplied by 1/s. Then calculated as a closed-loop again with it. )

    And another question is, I need to draw Nyquist plot with transfer function above.
    Normally the transfer function is given as a form of 'G(s)/[1 + G(s)H(s)], so I can draw the Nyquist plot with open-loop function G(s)H(s). But with the function above, I can't seem to seperate G(s)H(s). How can I do this?

    Could somebody help me with this matter?
    Thanks a lot for your time.
     
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  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I believe your answer is the correct one. At least that's the answer I derived.
     
  3. glorimda

    Thread Starter New Member

    Oct 12, 2011
    17
    0
    I got the same answer from others. Thanks.
     
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