Digital tachometer with air gap adjusting yoke insertable through holes in the tachometer housing

Claim 1

A digital tachometer adapted to be mounted on a shaft projecting from a machine housing comprising: (a) a generator wheel, having an axis, a circumference and a plurality of set and reset magnets distributed about the circumference, adapted to be coupled to a machine shaft; (b) a housing having a lower part adapted to be fastened to a machine housing from which the machine shaft projects and an upper part enclosing said generator wheel, said upper part having a planar front surface perpendicular to the axis of said generator wheel; (c) a structural unit comprising: i. a stiff circuit board; ii. a sensor cassette containing therein one or more wire pulse sensors, said sensor cassette extending over a part of the generator wheel circumference such that the wire pulse sensors therein are spaced from the circumference of said generator wheel by an air gap; and iii. means for electrically connecting and mechanically coupling said sensor cassette to said stiff circuit board; (d) means for mounting said structural unit to the planar front surface of said upper part within said housing such as to be adjustable in a plane parallel to said planar front surface; (e) two adjusting holes in said stiff circuit board, at the location of the air gap between said sensor cassette and said generator wheel, and two corresponding holes in said planar front surface of said upper part, whereby two legs of an adjusting yoke can be inserted through the holes in said planar front surface and the holes in said stiff circuit board to accurately establish a uniform air gap, whereupon said structural unit can be fixed relative to said planar front surface and said yoke then removed.