With modern processes in manufacturing, we need to know and control the speed, position and velocity of electric motors. With this precision comes the need for feedback in these areas. Servo, closed loop vector, brushless DC, standard DC motors and standard three-phase AC motors use feedback devices such as encoders and resolvers. Many AC and DC motors have the feedback device mounted on the exterior of the opposite drive endbell, mechanically attached to the rotating shaft. Servo, vector and brushless DC motors usually have an encoder or resolver mounted inside the endbell as an integral part of the equipment. Three basic forms of feedback devices are resolvers, optical encoders and absolute encoders.