Driven shielding capacitive proximity sensor

Claim 1

A capacitive type proximity sensor having improved range and sensitivity between a machine and an intruding object in the immediate vicinity of the machine, comprising: an outer electrical conductor on said machine forming one electrode of a sensor capacitor, the other electrode comprising said object, said outer conductor comprising a first thin sheet of conductive material; an intermediate electrical conductor located between said outer conductor and said machine and being of a size substantially larger than said outer conductor to act as a shield for reducing the parasitic capacitance between said outer conductor and said machine, said intermediate conductor comprising a second thin sheet of conductive material substantially wider than said first conductor; said outer and intermediate conductors attached to a surface on said machine with no gap between the conductors and no gap between said surface and said intermediate conductor and said outer and intermediate conductors coplanar with each other and said surface of said machine, said surface of said machine acting as a ground plane; first circuit means for coupling in phase the instantaneous voltage at said outer electrical conductor to said intermediate electrical conductor; second circuit means coupled to said outer conductor and being responsive to the capacitance of said sensor capacitor for generating a control signal to said machine.