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Desperate about Nyquist Diagrams 
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#1
Jan713, 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 


#2
Jan713, 03:03 PM

P: 2,928

These two references may help:
http://en.wikipedia.org/wiki/Nyquist_plot and http://www.facstaff.bucknell.edu/mas...req/Freq6.html 


#3
Jan713, 03:23 PM

P: 133

Already viewed, but it doesn't help...



#4
Jan713, 03:55 PM

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Desperate about Nyquist Diagrams



#5
Jan713, 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 counterclockwise). 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. 


#6
Jan813, 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 ?



#7
Jan2713, 07:02 AM

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The domain goes from f=0 Hz to f=∞ Hz, you make your own judgement on how many points to plot and their spacing.
http://www.facstaff.bucknell.edu/mas...req/Freq6.html Oops. Someone has already posted that link. 


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