This paper presents a compact current sensor for the measurement of ac and dc. The sensor consists of two toroidal magnetic cores. One core works in fluxgate principle to measure dc and low-frequency ac, and the other one is used as a current transformer for higher frequency application. The closed-loop configuration with a magnetic core and feedback winding in the sensor improved the sensitivity of the sensor, eliminated the offset and drift related to temperature, and greatly reduced the error caused by magnetic hysteresis phenomenon. It can measure currents up to 20 A, has an accuracy of 0.7% and ∼30-kHz bandwidth.Index Terms-Closed-loop, current sensor, fluxgate, toroidal magnetic cores. 0018-9464

As giant magneto resistive (GMR) effect based current sensors are susceptive to stray magnetic fields, this paper proposes a GMR current sensor with a magnetic shielding. Magnetic shielding effectiveness and magnetic gain coefficient of the shielding are analyzed by finite element method (FEM), and some concerned parameters affecting the shielding effects are also discussed. In order to achieve accurate measurement for ac and dc, this paper proposed two methods for providing bias magnetic field. One method is using a coil winding and the other is using permanent magnet. Based on theoretical analysis and simulation results, a prototype was designed. Hysteresis effects on the sensor, the sensitivity of the GMR current sensor, and relative error of the measurement of the current sensor with and without magnetic shielding were tested and compared. The two methods for producing bias magnetic field were also tested and discussed. The designed GMR current sensor has the advantages of high sensitivity and accuracy, low nonlinear error (0.8%). It can measure currents from dc up to 200 kHz with the nominal primary current value of 20 A.Index Terms-Bias magnetic field, current sensor, giant magneto-resistive (GMR), magnetic shielding.

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