1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    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


    User Avatar
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    Sounds like the problem might be "hosed":eek:
  7. Dec 11, 2017 #6
    Could be. Even I think the question has some typo.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted