It is more important for engineers to predict the response of servo system rapidly and easily by using appropriate approximation than to calculate it by solving the characteristic equation of servo system.
According to this demand, in this paper, after the method how to approximate high order servo system by second order servo system and dead time is considered, this approximated system is used in order to predict the response of high order servo system. In particular, as the approximated system has only three parameters, that is, gain, time constant and dead time, the effects that three parameters give to response can be investigated beforehand. Therefore, when the transfer function of high order servo system is given, the response of it can be easily defined by calculating the approximated system.
Furthermore it is very important that the approximated system can be determined by easy algebraic calculation.
