The motors that are used in automatic system are called servo motors. The servo motors are used to convert an electric signal applied to them into an angular displacement of the shaft. There are varieties of servo motors available for control system applications. The features of servo motors are linear relationship between the speed & electric control signal, steady state stability, wide range of speed controls, linearity of mechanical characteristic through the entire speed range, low mechanical & electrical inertia and fast response. The servo motors are broadly classified into DC servo motors and AC servo motors. The DC servo motors are expensive than AC servo motors.