MAGNETIC VELOCITY SENSORS

There are two types of low-cost velocity sensors based on magnetic pri nciples, variable-reluctance sensors, and galvanomagnetic semiconducto r (Hall effect or magnetoresistive) sensors. Variable-reluctance devic es sense variations in flux linkage while semiconductors read variatio ns in local flux density. The paper shows how recognizing this fundame ntal difference leads to markedly different sensor design approaches, and proposes new configurations with improved performance. The analysi s of the sensors is based on a general theory specifically developed f or these sensors. The magnetic field computations use the finite-eleme nt method, which is particularly well suited to this problem involving complex airgap configurations and a need for the calculation of local flux densities and flux linkages. Experiments were carried out to val idate the models and confirm the predicted sensitivity improvements of the new sensor structures.