I have a magnitude (Z) -bode plot with frequency but I want to convert it into Nquist plot. Can anyone help me and show me how to convert this Magnitude bode plot into Nquist plot
Please help.
Many thanks
Hello. Here is how I can help you:
1. Please remind that in order to build a Nyquist plot you definitely need the complete complex values of the function you want to plot. This means not only the magnitude; you cannot correctly convert a magnitude plot to a Nyquist one unless you've got the phase Bode diagram, too.
2. Given this requirement, you can plot a the Nyquist diagram either by combining (as I'll explain soon) magnitude and phase functions or by using directly the complex function you want to plot.
3. Let's suppose you've got distinct functions, i.e. magnitude M(f) and phase P(f): plot the function M(f)*exp(-i*P(f)) with its real and imaginary parts being abscissa and ordinate, respectively. Ex. in matlab code
x=real(M.*exp(i*P));
y=imag(M.*exp(i*P));
plot(x,y)
4. If you have the complex function F(f) it's even easier; you only need to plot its real and imaginary parts being abscissa and ordinate, respectively. Similar ex.
x=real(F);
y=imag(F);
plot(x,y)
5. And remember that now the frequency f is no longer the independent variable, but a parameter of a parametric curve.
Please let me know whether I've been clear...
the problem is I have frequency and magnitude Z and I want a Nquist plot which is Z-real (x-axis) and Z-imaginary (y-axis). I dont have phase (theeta in radians) values otherwise i can use
Zreal= Z-magnitude * Cos (theeta)
Zimag= Z-magnitude * Sin (theeta)
I only have a graph of frequency vs Z magnitude
I'm afraid this is an issue. If you have no phase data you miss half of the information you need, since you want to build the plot of a complex function.
Is this Z representing something specific (like for instance the frequency response of a system with poles and zeros of which you might infer the position)?
The only workaround I can think of now is trying some phase estimation/retrieval (for instance, as I said, by knowing where the poles and zeros are), because without a phase of Z I see no way to proceed.
Sadly, you need phase information as well as the magnitude in order to plot the Nyquist. But you could perhaps assume linear phase. Then, take the magnitude values from the Bode at incremental frequencies; thne take the inverse log10 of each magnitude point and plot these values on an Argand diagram. You might need to normalise the values if you are interested in absolute values rather than relative ones.
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