Demagnetising factor and noise in the fluxgate ring-core sensor

A method for measuring the demagnetisation of fluxgate sensors is introduced and used to evaluate the demagnetising factors for four ring-core sensors having 5, 10, 15 and 20 wraps of magnetic core ribbon. The demagnetising factor is proportional to the number of wraps, and the noise is also proportional to the number of wraps except for the more noisy 5-wrap core. The estimated internal core noise was 1 pT RMS taking into consideration the demagnetising factor and the relative permeability of the core material.