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Desperate about Nyquist Diagrams

by nebbione
Tags: desperate, diagrams, nyquist
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Jan7-13, 02:52 PM
P: 133
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
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Jan7-13, 03:03 PM
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These two references may help:

Jan7-13, 03:23 PM
P: 133
Already viewed, but it doesn't help...

Jan7-13, 03:55 PM
Sci Advisor
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PF Gold
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Desperate about Nyquist Diagrams

How about this link:
Jan7-13, 03:56 PM
P: 140
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.
Jan8-13, 01:23 PM
P: 133
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 ?
Jan27-13, 07:02 AM
HW Helper
P: 5,243
The domain goes from f=0 Hz to f=∞ Hz, you make your own judgement on how many points to plot and their spacing.

Oops. Someone has already posted that link.

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