Section 6–2 / Root-Locus Plots 289
Typical Pole–Zero Configurations and Corresponding Root Loci. In summa-
rizing, we show several open-loop pole–zero configurations and their corresponding
root loci in Table 6–1. The pattern of the root loci depends only on the relative separa-
tion of the open-loop poles and zeros. If the number of open-loop poles exceeds the
number of finite zeros by three or more, there is a value of the gain Kbeyond which root
loci enter the right-half splane, and thus the system can become unstable. A stable sys-
tem must have all its closed-loop poles in the left-half splane.
Table 6–1 Open-Loop Pole–Zero Configurations
and the Corresponding Root Loci
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