Stability Analysis Using Nyquist Plot

There are a number of polar graph options for studying control systems including the nyquist, inverse polar plot and the nichols plot.  The nyquist open loop polar plot indicates the degree of stability, and the adjustments required and provides stability information for systems containing time delays.  Polar plots are not used exclusively because,without powerful computing facilities, they can be difficult to generate at a detailed level and they do not directly yield frequency values.

The Nyquist plot is obtained by simply plotting a locus of imaginary(G(j ω)) versus Real(G(j ω)) at the full range of frequencies from ( - ¥ to + ¥ ) It is very easy to produce nyquist plots by hand or by using proprietary software packages such as Matlab.   Links below show how bode and nyquist plots can be produced using Excel and using Mathcad.  The plots below have been produced in minutes using Mathcad..



The nyquist plot fundamentals are shown below....

Velocity Feedback control

Basic Circuit Equations and Laws

Ohm's and Joule's Laws

Diode

Diodes are semiconductor devices which might be described as passing current in one direction only. The latter part of that statement applies equally to vacuum tube diodes. Diodes however are far more versatile devices than that. They are extremely versatile in fact. It might pay you to review the topic of atom and electron theory.
Diodes can be used as voltage regulators, tuning devices in rf tuned circuits, frequency multiplying devices in rf circuits, mixing devices in rf circuits, switching applications or can be used to make logic decisions in digital circuits. There are also diodes which emit "light", of course these are known as light-emitting-diodes or LED's. As we say diodes are extremely versatile.