A model of a fluxgate magnetometer based on the field interactions in
the fluxgate core has been derived. The non-linearity of the ringcore
sensors due to large uncompensated fields transverse to the measuring
axis are calculated and compared with measurements. Measurements of th
e non-linearity are made with a spectrum analyzer measuring the higher
harmonics of an applied sinusoidal field. For a sensor with a permall
oy ringcore of 1 in. in diameter the deviation from linearity is measu
red to about 15 nT(p-p) in the earth's held and the measurements are s
hown to fit well the calculations. Further, the measurements and the c
alculations are also compared with a calibration model of the fluxgate
sensor onboard the 'MAGSAT' satellite. The later has a deviation from
linearity of about 50 nT(p-p) but shows basically the same form of no
n-linearity as the measurements. (C) 1997 Elsevier Science S.A.