Patent ID: 6851318

Claim:
A motion detector according to the Ferraris principle, comprising: an excitation assembly including at least one primary excitation element for producing an inhomogeneous time-dependent alternating magnetic field having a fundamental frequency with a period, a movable electrically conducting induction element, with the inhomogeneous time-dependent alternating magnetic field applied to the induction element, wherein a motion of the movable induction element and the alternating magnetic field induce an eddy current in the induction element, with temporal changes of the eddy current depending on a velocity or an acceleration of the movable induction element, a sensor assembly with at least one primary sensor element adapted to measure at least one measurement signal which is proportional to the temporal changes of the eddy current, and a signal processing circuit including at least one demodulator which receives the measurement signal and a sinusoidal demodulation signal at the fundamental frequency and provides at least one useful signal as an output signal of the demodulator, wherein the at least one useful signal is proportional to the velocity or the acceleration of the movable induction element.