PCB sensors in fluxgate magnetometer with controlled excitation

A miniature fluxgate sensor with amorphous race-track core manufactured with printed circuit board (PCB) technology is presented in this paper. The number of PCB layers was increased to five; this allowed for increasing the number of turns of pickup/compensating winding (68), resulting in the compensation current in the feedback loop below 15 mA for a 50 μT measured field. The sensor was characterized using pulse excitation (10 kHz, 10% duty); the maximum sensitivity was found to be 615 V/T for 650 mA p–p excitation current with nonlinearity below 0.5% of full scale. In order to improve the long-term and temperature stability of the sensor, a closed-loop regulation of the excitation current amplitude was designed. A three-axial portable magnetometer using gated integrators and pulse excitation was constructed with these sensors. Feedback-loop operation allowed suppressing the nonlinearity below 100 ppm of ±50 μT full-scale, and the sensitivity increased to 120,000 V/T. Long-term stability was found to be 1 nT in 9-h period, and the temperature coefficient of sensitivity decreased to 50 ppm, which was a direct result of controlling the excitation current.