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Homework Help: Control System: Find the Transfer Function From Block Diagram

  1. Dec 7, 2017 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    To find Ca / Rb we take Ra = 0 --- is this right?
    I used mason's formula
    P1 = -G2 G1 H1
    Loop = G1, G2, -H1, -H2
    Using Mason's Gain we get:
    Delta1 = 1
    Delta = 1 - G1G2H1H2
    Using Mason's Gain
    TF = -G1G2H1 Divided by ( 1 - G1G2H1H2)
    But substituting the values I don't get the answer that matches any options.

    3. The attempt at a solution
    Substituting I get:
    This gives answer in cube as second term of numerator will go in cube for s. None of options have s cube.

    Second Question:
    I think the options are wrong.
    For left TF we get C(s)/R(s) = 10/11
    For Right we get C(s)/R(s) = 5/3.5
    Multiplying them doesn't give the answer

    Attached Files:

  2. jcsd
  3. Dec 7, 2017 #2


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    It's been awhile since I've done these, but I got the same result as you, for the second one: C/R = 100/77. I haven't worked through the first one, yet.
  4. Dec 7, 2017 #3


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    I got the same thing as you for the second problem.

    In problem number one you can dive both the top and bottom side by s...
  5. Dec 9, 2017 #4
    Not sure if that helps.
    I'm getting: Ca/Rb = -G2 H1 G1 divided by (1 + ( -G2 H1 G1 H2 ) )
    And that's not reducing to any of the options.
  6. Dec 9, 2017 #5


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    Sounds like the problem might be "hosed":eek:
  7. Dec 11, 2017 #6
    Could be. Even I think the question has some typo.
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