# Routh Hurwitz Criterion for 3 Real Poles

Cuthbert Nyack
This Applet shows the Routh Hurwitz criterion applied to a system with 3 real poles. They allow the effect of gain and pole locations on the stability of the system to be studied. The step response of the system is also shown.

The first Applet shows the variation of the elements in the first column of the RH array as a function of gain from 0 to K
The second shows the more conventional array with the step response added. When the system is oscillatory the frequency can be calculated from the auxiliary equation or measured from the step response.

some eg parameters and their stability are shown below:-

m can be used to amplify the b1 (green) line.

(10.0, 1.5, 0.5, 1.0, m = 5.0) unstable for K > 7.5
(10.0, 1.5, 1.5, -0.5, m = 6.0) unstable for K < 1.13 and > 3.0
(20.0, 1.0, 1.0, 2.0, m = 5.0) unstable for K > 18
(5.0, 1.0, 1.0, 0.0, m = 5.0) unstable for K > 2
(40.0, 0.5, 1.5, 2.5, m = 2.5) unstable for K > 24

Gif images below shows how applet should appear.