Consider the transfer function
(F-13)
which corresponds to the characteristic equation
(F-14)
The pole-zero configuration of G(s)H(s) is shown in Fig. F-4. From the six properties of the root
loci discussed so far, the following information concerning the root loci of Eq. (F-14) when K varies
from to is obtained:
1. K 0: The points at which K 0 on the root loci are at the poles of G(s)H(s): s 0,
4, 1 j, and 1 j.
2. K : The points at which K on the root loci are at the zeros of G(s)H(s): s
1, , , and .
3. There are four root loci branches, since Eqs. (F-13) and (F-14) are of the fourth order.
4. The root loci are symmetrical to the real axis.
s1s 421s2 2s 22 K1s 12 0
G1s2H1s2
K1s 12
s1s 421s2 2s 22
s1
© real parts of poles of G1s2H1s2 © real parts of zeros of G1s2H1s2
n m
s1
© finite poles of G1s2H1s2 © finite zeros of G1s2H1s2
n m
n m 1.
ui
2i
0n m0 180° n m