A New Method for Speed Measurement/Control of DC Motors

A new approach to the speed measurement of small dc shunt/permanent magnet motors is presented. It is based on the measurement of the back EMF of the motor, with the addition of a sensing resistor in series with the armature and associated simple electronic circuitry. This can replace the conventional speed measuring transducers like tacho-generator and magnetic-optical pickups, offering a low weight, compact and reliable system and eliminating the mechanical coupling between the motor and the transducers. The experimental results and the steady-state response of the control scheme are also presented.