Active Wheatstone Bridge — A solution of tight speed dc motor control

Abstract

Very tight control of the speed of a d.c. motor drive may be achieved by incorporating the machine within a closed loop system. The employed feedback signal is proportional to the motor speed for comparison against a reference quantity. For armature-controlled d.c. motors the difference or error signal provides appropriate adjustment to the armature supply voltage. There are varieties of methods of achieving a feedback signal proportional to the speed of the motor. This paper describes a technical application in which the armature of a d.c. motor is connected as one of the arms of a Wheatstone bridge, now becoming an active Wheatstone bridge. By analyzing the operation of the active Wheatstone bridge, its transfer function is derived. The active Wheatstone bridge is incorporated in a feedback control system. Applying a variable torque to the motor proves the achievement of a very tight speed control. Experiments are performed on a motor with low rated power, although the implementation of active Wheatstone bridge can be applied for d.c. motors with high rated power as well.


(Botswana Journal of Technology: 2002 11(1): 1-8)