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5  Other responses

5.1  Nyquist plot

Nyquist plot of the open loop plant G(s) can be seen by clicking on ``Response ®Nyquist''. The gain and phase margin is displayed on the plot. If you find that your plot is too coarse or cluttered, you can change the minimum and maximum frequency in ``Settings ®Nyquist-Nichols plot''. The units for frequency can be changed in the ``Options'' menu of the Nyquist plot window. You must close this window to return to the main rltool window.

5.2  Nichols plot

Nichols plot for G(s) is obtained by selecting ``Response ®Nichols''. If the grid (in the main menu) is set to ``on'' you will see the logarithmic grid superimposed on the Nichols plot. Here too, you can select the desired frequency units. You must close this window to return to the main rltool window.

5.3  Popov plot

The Popov plot can be used to predict the stability of the closed loop system with a sector bound nonlinearity in loop. We plot real part of G(iw) on the real axis and w Imaginary   G(iw) on the imaginary axis. A simple construction then gives the range of the ``Popov sector'' and the ``multiplier''. Please see any standard text on nonlinear systems for more details on the Popov plot.


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