Experimental determination of the forward and backward-field torque in shaded-pole motors

An experimental method for determining the forward- and backward-field torque and the amplitude of a pulsating torque at twice the line frequency in shaded-pole motors is developed on the basis of revolving-field theory. These parameters are determined from the induced voltage in a measured winding by segregating a forward and backward fundamental component using a spectrum analyzer. This torque-measuring method has been tested for a shaded-pole motor with one shading coil, and a shaded-pole motor with two shading coils per pole. The forward-field torque minus the backward-field torque, as measured by the measuring winding, agreed with that measured by a Prony-brake torque meter with sufficient accuracy. The amplitude of the pulsating torque also agreed approximately with that measured with an accelerometer. Each torque can be determined more precisely in this experimental technique than in existing calculation techniques