Talk:Nyquist stability criterion

Writing the Nyquist Criteria Artical
I'm currently an EE student, and I posted this page as I learned the information in class. I feel that considering the highly-graphical nature of the Nyquist technique, this artical would benefit highly from some illustrations. however, i have not been able to find any illustrations that are free from copyright that could be used.


 * Added a much needed image. Musically ut 03:28, 27 March 2007 (UTC)

Also, somebody posted a small blurb at the bottom when I had not yet completed the page. I certainly appreciate the help, but i worry that some of your information conflicts with my information, and that the quick change in terminology might cause too much confusion. either way, if i have something wrong let me know! -Wknight8111

Feel free to strip out my filler (It wasn't clear to me when you intended to return :-)) - it's many years since I used Nyquist. But isn't it a criteriON. And it's worth considering who is going to use the article - the present article is rather notationally heavy. Might be legit to assume that anyone reading is familar with the concept of or can find out about poles and zeroes of the transfer function? Just my 2p. Linuxlad 20:31, 21 Apr 2005 (UTC)

Good call linuxlad. This artical is a bit "notationally heavy", but I wanted to be complete. this is true, I suppose that people can find out about poles and zeros from the transfer function articals. I will need to do some research on the cross-references, and find out some better places to get the information. -Wknight8111

The article has either been edited by someone who doesn't know or care how to use the formula editor, or it's been hacked - could someone who is expert on these things please check out. Linuxlad 23:24, 10 May 2005 (UTC)

It might be a good idea for someone to discuss Nyquist with poles at the origin. I have an exam tomorrow, so it won't be me. On the lines of the last post, I was able to right click on the formula (red x) and hit "show picture" and the formulas came up. -guest user

Intro
Could someone (more knowledgable in this general field than me at least) please rewrite the intro?? It makes no sense to the non-technical. Thanks.

Zidel333 11:44, 21 March 2006 (UTC)

Nyquist Stability Criterion
I am a Student of EE. And there seems to be a mistake in the criterion mentioned. I am looking forward to discussing the statement of the criterion with someone.

The mistake, I believe is here - "Given a Nyquist contour Γs, let P be the number of poles of F(s) encircled by Γs, and Z be the number of zeros of F(s) encircled by Γs -- therefore the number of poles of enclosed by Γs. The resultant contour in the F(s)-plane, ΓF(s) shall, for a stable feedback system, encircle (clock-wise) the point (-1 + j0) N times such that N = Z − P."

For Stability Z,the number of closed loop poles, must be equal to zero. And N = -P. --Haditya 16:10, 26 January 2007 (UTC)


 * This is a great opportunity to site a reliable source, so we can check you. What source are you using? Dicklyon 16:55, 26 January 2007 (UTC)


 * The book i am using is Norman Nise, Control Systems Engineering.

Alternately any other book on the subject should provide the same info.

other authors are Ogata, Modern Control Engineering

Kuo, Automatic Control Systems

Haditya 16:52, 2 February 2007 (UTC)


 * So fix the article add the citation. Dicklyon 18:30, 2 February 2007 (UTC)

It was not incorrect, but it was confusing, as $${F}(s)$$ and $$\mathcal{F}(s)$$ sure look similar. I added a paragraph for clarity, and a reference to my controls book. Buffetrand (talk) 03:02, 23 July 2010 (UTC)

Nyquist Contour
The explanation seems complicated and is hard to visualise. Could anyone explain how the Nyquist contour relates say to the plot in the provided example image of a Nyquist plot ? Rod57 (talk) 11:58, 19 October 2008 (UTC)

Mathematical Derivation
I've added this section because I am taking the course now, and there doesn't seem to be any good source on this; even textbooks seem to say "Cauchy's argument principle" and wave their hands as if suddenly all of this means something. Sometimes, you just have to make your own sources.

I plan on enriching this page with some appropriate diagrams (probably matlab), maybe an example problem for good measure. Maybe a bit on how to do this in matlab, even. This page is going places. Sometimes, the best way to study for a midterm is to become an authority on the subject.

We'll see how this develops.

oooh, signature.Bengski68 (talk) 06:17, 4 April 2013 (UTC)

Trivia: the joke
Would it be a terribly silly idea to mention this?

Q: Why do Eastern European airlines fly half empty?

A: There must be no poles in the right half-plane

Sources and variations:

http://unclecj.blogspot.com/2009/02/two-very-nerdy-jokes.html

http://users.ox.ac.uk/~invar/links/jokes.html

http://forum.darwincentral.org/viewtopic.php?f=47&t=34992&start=0#p632962

http://scienceblogs.com/goodmath/2009/06/defining_dynamical_systems.php#comment-1701610

CarlJohanSveningsson (talk) 09:35, 31 May 2010 (UTC)