Patent ID: 8111066

Claim:
A device for measuring the mass of magnetic material present in an analysis medium, the device comprising: a generator of an excitation magnetic field for exciting the magnetic material, the magnetic field comprising at least one low-frequency component and one high-frequency component, the low-frequency and high-frequency components corresponding to power peaks in the power spectrum of the excitation magnetic field respectively at frequencies f LF and f HF , the frequency f HF being strictly greater than the frequency f LF , a sensor suitable for transforming the magnetic field induced in the magnetic material in response to the excitation magnetic field into a measurement signal, a filter suitable for isolating the amplitude of a sinusoidal component of the measurement signal at a frequency mf HF ±nf LF , where m and n are nonzero integers, the filter isolating a new value of the amplitude at each measurement period T m , the temporal succession of the amplitudes isolated by the filter forming an amplitude signal, and an estimator of the mass of magnetic material present in the analysis medium on the basis of the amplitude signal and of a reference signal which is obtained on the basis of a gauge mass of the same magnetic material measured under the same conditions, characterized in that: the generator comprises a modulator of the phase of the high-frequency and/or low-frequency component with a modulation signal whose value is modified with a frequency f mod less than or equal to 1/(T m ), and the device comprises a demodulator suitable for demodulating the amplitude of the amplitude signal on the basis of the modulation signal, the demodulator being linked up to the output of the filter and to the input of the estimator.