Transfer Function Problem 1.6

Ask

The open loop transfer function with unity feed back are given below for different systems. The unstable system is

(a)${2 \over (s+2)}$

(b)${2 \over s^{2}(s+2)}$

(c)${2 \over s(s+2)}$

(d)${2(s+1)\over s(s+2)}$

Answer is ( b )

Concept

Stability can be seen from Characteristic Equation:If in the polynomial equation there is a discontinuity of powers(exponent) of the variable, then the System is Considered UNSTABLE

In Option (b) this is evident $s^3+2s^2+2=0$