399 16.3 E.t.eclback Systems unstable for all a Figure 16.9: Second-order plant with proportional control Figure 16.10: Root locris of the control circuit from Figure 16.9 for which the denominator polynoniial is a Hurwitz polynomial, if the constant K and hFzare clioscn so that bK2 > O and n f K l b > Ii’igure 16.11: Second-order plant with proptil‘tional-cilfferentialcontrol ( 16.33)