10

CONSTANT M- AND N-CIRCLES AND NICHOLS CHART

10.1 Introduction

The frequency-response techniques discussed in the previous chapters are the open-loop frequency plots that have obtained the information about the closed-loop stability using the open-loop frequency response of the system. In these methods, the frequency response of the loop transfer function Eqn1 is plotted and information regarding the closed-loop stability is derived from the plot. In this chapter, constant M-circles (magnitude), ­constant N-circles (phase) and Nichols chart are discussed, which directly give the information regarding the closed-loop stability of the system.

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