Abstract: A magnetic field sensor is employed to determine a rotational velocity of an element by sensing frequency variations in a magnetic flux during rotation of the element. The magnetic field sensor includes a sensor face provided with obstacles, such as a series of spaced, substantially parallel grooves arranged perpendicular to a direction in which contamination tends to move across the face during operation of the sensor. The obstacles inhibit movement of contamination across the face such that the contamination does not cause false variations in the magnetic flux which would degrade sensor signals.

Abstract: A magnetic field sensor is employed to determine a rotational velocity of an element by sensing frequency variations in a magnetic flux during rotation of the element. The magnetic field sensor includes a sensor face provided with obstacles, such as a series of spaced, substantially parallel grooves arranged perpendicular to a direction in which contamination tends to move across the face during operation of the sensor. The obstacles inhibit movement of contamination across the face such that the contamination does not cause false variations in the magnetic flux which would degrade sensor signals.