How to draw Nyquist Plot for representing variation of impedance with frequency

[manishanand14]

Hello everyone!

How to draw Nyquist Plot for Impedance variation with frequency
**broken link removed**

 

[schmitt trigger]

This obviously requires a network analyzer with dedicated computer software.

You could roll your own and perform manual plots if you are only interested in the |Z| component, with a sinewave oscillator, a good (flat frequency response) audio amp, a wideband current probe (or sampling resistor) and a dual channel scope.

Stepping the frequency, take voltage/current readings, write them in an Excell spreadsheet and perform the conversions and perform the plot there.

If you are really resourceful and have the patience to do it, you could also measure the time delay between the reference voltage waveform and the current waveform. Convert it to electrical degrees by multiplying such delay by the test frequency and 360. Keep note whether the current's phase advances or delays with respect to the voltage waveform, and apply the proper polarity's signs to the phase readings.

Write everything down in your spreadsheet. There and using standard electrical calculations, you can get both the R and jX components of |Z|. Use Excell's plotting capabilities.

Very cumbersome, but it can be done.

 

[manishanand14]

I want to do Nyquist plot when i already have Z values corresponding to frequency values.

Just tell me how to do Nyquist plot with the available values. It is an R C circuit.

 

[FvM]

Nyquist diagram is just a plot of complex Z values (Z = R+ jX). For each frequency point, the R value is the horizontal and the X value the vertical coordinate.

So the question is, do you have complex Z values or only |Z| magnitudes?

You don't necessarily need a network analyzer and a computer software to measure and plot the Nyquist diagram of a device. A sine generator, a voltmeter and a reference resistor together with pencil and paper are sufficient (with some understanding of AC networks).

 

[manishanand14]

I have complex Z values

I need something like this

I also need to do bode plot of magnitude of Z.

Something like this

 

[FvM]

I have complex Z values

Good. Why you don't simply plot it?

I also need to do bode plot of magnitude of Z.

|Z| = √(R² + X²)

 

[manishanand14]

how will i get Nyquist plot.What about the frequency variation?

 

[manishanand14]

I know that we can take left to right or right to left as frequency increment direction but what about the scale of frequency variation?

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This is how I will calculate the real and imaginary part of the impedence if I can observe the current and voltage waveform and the phase difference.

Please verify it.

 

[FvM]

The number of frequency points is your choice.

If you connect the impedance points by straight lines, you get a fairly smooth curve. Doesn't it look like sufficient number of points? You may want to add more points in the low frequency range, but they probably don't represent more information.

 

[manishanand14]

So can i take linear frequency variation scale[equal frequency change in equal space] along x-axis
I will surely add more points in low frequency range as per suggestion.

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Also please verify my Impedence Re{Z} and Im{Z} calculations