A high accuracy fluxgate DC current sensor applicable to two-wire electric appliances

Abstract

This paper presents a novel high-precision low noise self-oscillating fluxgate DC current sensor that can be used for two-wire measurement. This new sensor mainly consists of an EE-type ferromagnetic core, an oscillator, an inverter, six windings, sampling resistors, a feedback compensation circuit and a potential collection circuit. Two primary coils are placed in the hollow hole of the middle arm to realize the condition of fluxgate effect. The sensor still satisfies the average current model even when considering the mutual inductance among the windings. It can reach the ampere-turn balance by feedback and compensation to eventually achieve zero-flux detection. A new scheme to suppress secondary modulation ripple has been proposed by designing magnetic path and arranging the windings. In addition, researches have been conducted to study some relevant factors of eliminating secondary modulation ripple in this new way. Some relevant factors influencing the elimination of noise are simulated. The outcomes show that sum of the secondary modulation ripple voltage in the feedback compensation windings reaches a peak value of about 0.7 mV when the parameters of both circuits and magnetic path in the sensor’s left and right parts are symmetrical. And the more asymmetrical these parameters are, the larger ratio of suppressing noise is. That makes the sensor better perform under the condition of temperature drifting and decreases the influence of the error of both electric components and during the process of measurement.