# Questions tagged [nyquist-plot]

For questions about Nyquist plots, often used to assess the stability of an electrical circuit which includes feedback. Consider also using the "frequency-response" tag, and "stability" tag if your question is about the stability of an electrical circuit.

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### How to check for stability for non-constant controller using Nyquist plots?

Let's say I have a unitary feedback system with one unstable (RHP) pole. Now if my $G_c$ is a constant, say $K$, I know that in order to have stability I should have a single counterclockwise ...
266 views

### Recording aliased tones on purpose

For research purposes, I am trying to transmit a tone and record it using sub-Nyquist sampling. Via the PC microphone, for instance, I would expect to see the aliasing effect somewhere in the ...
166 views

### Nyquist Criterion: Encirclement around origin

I am studying the Nyquist stability criterion and I am stuck on the following problem. The open-loop transfer function with unity feedback is $\small\mathrm{ G(s)=\large\frac{1}{s-3}}$. Following is ...
1 vote
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### How to determine difference between LHP poles and zeroes by observing Nyquist plot?

I am solving practice problems on Nyquist Plot and I got stuck at a problem having a solution which I do not get at all. Here it is: Which of the following is the transfer function of a system having ...
213 views

### Confused regarding gain margin and stability

I plotted the bode plots of the transfer function: G(s)= 2.123×10^6 ((0.105s+1.01))/(s^2 (s+12566.37) ) It is as follows: As can be seen, it shows the gain margin as negative infinity, however loop ...
1 vote
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323 views

### Nyquist Plot from Bode Plot

How do I know the value at which the Nyquist plot crosses -180 degrees from looking at the Phase plot from the Bode?
1 vote
863 views

### Gain margin and phase margin in Nyquist plots

Finding gain and phase margins from Nyquist plots is basically finding the margin of change in gain and phase beyond which the plot encircles -1, respectively, with the assumption that the Nyquist ...
69 views

### What is this functions Phase crossover frequency?

OLTF loop gain My approach What I have done wrong?
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### How to find Phase crossover frequency?

I make the imaginary part of $loop \ gain=0$ to find phase crossover frequency. But in one video, the person told that this method can only be applied when Polar plot crosses the real axis and ...
213 views

### Questions on Bode Plot and Nyquist Plot

Bode Plot 1) Why the gain plot |G(jw)| drops and then increases for conjugate zeroes ? 2) Why the gain plot |G(jw)| increases and then drops for conjugate poles ? Nyqust Plot 3) For Figure 9-18(B),...
1 vote
563 views

### Stability and Positive/Negative feedback

I often read that positive feedback is used to get oscillators (since the output of the circuit is summed up to its input signal and so leads to instability), while negative feedback to get amplifiers ...
1 vote
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### Why "-1 + 0j" is critical point on Nyquist plot?

I am reading about Nyquist plot from this (http://www.cds.caltech.edu/~murray/books/AM08/pdf/fbs-loopanal_11Nov18.pdf) chapter. On page no. 10-2 its mentioned that "-1 + 0j" is critical point on ...
2k views

### Is the book wrong about the Nyquist Sampling Criterion?

Is the following statement from a book wrong? I thought sampling with twice the signal's highest frequency component would be adequate to completely recover the signal. But above it says sampling ...
2k views

### How does a time delay affect the Gain and Phase Margin?

How does a time delay affect the gain and phase margin. Answers using nyquist plots would be helpful I know that a time delay of t corresponds to gain multiplying by 1 and phase subtracting omega*T . ...
442 views

### According to the Nyquist criterion this system is stable but when I apply an impulse I get an unstable response, why?

I have this open loop transfer function and I have to study the stability of the closed loop transfer function using the Nyquist criterion. What I got is that the characteristic equation 1+GH(s)=0 has ...
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### Nyquist Stability Criteria

Find the stability where: Find the stability: $G(s)= \frac{(s+3)(s+5)}{(s-2)(s-4)};$ $H(s)= 1;$ I run this code in matlab: ...
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### Why isn't Nyquist taught like this?

When I learnt how to do a Nyquist plot I was taught a really long-winded method that I don't understand to this day. I realised by myself that if you are given a system like below where $s=j\omega$ \$...
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### Cole-cole plot curve collapses when trying to alter the valule of horisontal axis

I am a beginner and trying to simulate a cole-cole plot of a simple parallel circuit having two R, one coil and a capacitor. Image attaced, LTspice version is XVII, pc is windows7. I've read this Q-A;...
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### Sampling rate understanding for ADC requirement

So I have this voltage plot. These are voltages corresponding to a current changes on a wire. I am trying to understand the rate of transmission for choosing a ADC to read these analog values. The ...
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### Is the Nyquist plot useful in actual electrical engineering?

I am currently doing a course on linear control theory, and we are covering Nyquist Plot to study phase and gain margin. I find myself unable to appreciate this concept. One, the proof of the Nyquist ...
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### What are the connection between bandwidth, Nyquist criteria and quantization?

I am trying to solve the below problem and I was not able to find the relation between bandwidth, Nyquist criteria and quantization. Can you please provide some hint? Imagine that the possible ...
I was given the system defined by the open-loop transfer function: $L(s)=\frac{5(s^2+1.4s+1)}{(s-1)^2}$ I was told to use the Nyquist criterion to determine stability. Examining the Nyquist plot ...