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Desperate about Nyquist Diagrams

  1. Jan 7, 2013 #1
    Hi everyone! I searched all over the web and nobody/nothing gives a good explanation on how to plot nyquist diagrams... can somebody help with these ? I can't go forward in my study of control engineering without knowing these and i'm stucked...

    How are nyquist diagrams plotted starting from a transfer function or from bode diagrams?

    Can somebody explain in a detailed way or link me a site where it's explained step by step ?

    Thank you
  2. jcsd
  3. Jan 7, 2013 #2


    Staff: Mentor

  4. Jan 7, 2013 #3
    Already viewed, but it doesn't help...
  5. Jan 7, 2013 #4


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    How about this link:

    http://mmae.iit.edu/~mpeet/Classes/MMAE443/443Lecture23.pdf [Broken]
    Last edited by a moderator: May 6, 2017
  6. Jan 7, 2013 #5
    A nyquist plot is simply plotting the whole function G(jω).

    You have G(s) => G(jω), and then for each ω, you plot the resulting complex number in the complex plain. Normally this is done by using a polar plot, where instead of x and y (or Re and Im in the complex plain), we use r (the distance from origin to the point) and θ (the angle of the line from origin to that point, measured from the real axis of course, and counter-clockwise).

    Now for a complex number, the r is simply the magnitude of the number, and θ is the phase.

    So for the function G(jω), you simply plot each result as an r and θ. That is, you look at mag(G) and angle(G), and the you plot that.
  7. Jan 8, 2013 #6
    I already viewed even that link but cannot understand... ok i understand that i'm plotting G(jω) but what is the domain ? how much i havef to draw ? how can i know from which module to which module e from which fase to which fase ? Isn't there some place where this is well explained ?
  8. Jan 27, 2013 #7


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