Fluxgate Vector Magnetometer 2024-10-31 07:00:00.0 0.1 Fluxgate magnetometers are active observing instruments sensitive to a magnetic field component aligned with the core axis. The sensors are nowadays built on linear or ring cores made of high permeability permalloy or mumetal around which two coils are wrapped. They constitute the drive and the reception circuits. The drive circuit drives the core with a frequency of the order of 100 kHz into fully symmetric saturation in alternating directions along the core axis. If an external quasi-stationary magnetic field (fully stationary or varying very slowly compared to the driver frequency) is imposed along the core axis the saturation symmetry is violated and higher even harmonics appear in the reception circuit. The amplitude of the second harmonic is usually exploited as a measure of the strength of the externally imposed magnetic field. Science quality magnetometers combine three cores to form an orthogonal three-axis system. They can thus measure the full magnetic field vector. The most sensitive science grade fluxgate magnetometers used in space and geoscience cover a dynamic range of up to six orders of magnitude (+/-50,000 nT full scale with 0.1 nT resolution) at 100 Hz sampling rate. Digitising the output would require a 20-bit AD converter. In order to relax this requirement the circuits of fixed location ground-based magnetometers for space science applications often employ mean geomagnetic field compensation circuits and return only the superimposed magnetic field variations.