A control system is described by following differential equation:
\frac{3 d^2 y}{d t^2}+\frac{6 d y}{d t}+12 y=12 x
Determine the system time constant (in sec).
The given differential equation can be written as
\begin{aligned}& \frac{d^2 y}{d t^2}+\frac{2 d y}{d t}+4 y=4 x \\or \qquad\qquad & \frac{d^2 y}{d t^2}+\frac{2 d y}{d t}+(2)^2 y=(2)^2 x\end{aligned}
Comparing the above equation with the generalized second-order control system differential equation,
\frac{d^2 y}{d t^2}+2 \zeta \omega_n \frac{d y}{d t}+\omega_n^2 y=\omega_n^2 x
we get, 2ζω_n = and ω_n = 2 . The time constant is
\tau=\frac{1}{\zeta \omega_n}=\frac{1}{1}=1