Measurements of the fluctuating magnetic field in a DC motor by a flat inductor sensor

Abstract

Abstract This paper describes, for the first time, a fluctuant phenomenon of the magnetic field in a DC motor. The magnetic field of the DC motor with 15 slots was simulated based on the mechanical and electrical parameters. From the simulation results, four key field positions in a commutation cycle were obtained, and the magnetic fields of the four positions represented the phenomenon of magnetic fluctuation. The flux densities of the magnetic fluctuation at three speeds ( 1418 r mi n − 1 , 1277 r mi n − 1 , and 1108 r mi n − 1 ) were calculated with the help of the simulation data. To verify the phenomenon of magnetic fluctuation, a flat and single-layer inductor sensor was fabricated on a PCB board with thickness 0.2 mm and embedded into the motor to measure the induced electromotive forces generated by the magnetic fluctuation. The maximum and minimum combined uncertainties of the measured fluctuation periods were 0.08 ms and 0.07 ms, respectively. Finally, the practical experiments of speed measurement from 700 r mi n − 1 to 1400 r min−1 were finished. The maximum and minimum relative errors between the set and measured speeds were 0.07% and 0.01%, respectively. The combined uncertainties of the measured speed were less than 0.09 r min−1, which represented the perfect accuracy of this method.