Nyquist diagrams
6.1 Introduction
This chapter follows on from Chapter 5 and presents another method of considering the frequency response of systems and their stability. The method uses Nyquist diagrams; in these diagrams the gain and the phase of the open-loop transfer function, i.e. the product of the forward path and the feedback path transfer functions, are plotted as polar graphs for various values of frequency. With Cartesian graphs the points are plotted according to their x and y coordinates from the origin; with polar graph the points are plotted from the origin according to their radial distance from it and their angle to the reference axis (Figure 6.1).
Figure 6.1 (a) Cartesian graph with points specified by x and y values, ...
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