Patent ID: 8384557

Claim:
A proximity sensor arrangement comprising: a generator arrangement comprising a first antenna and an oscillator and operable to generate an electric field in a target region, the field oscillating at the frequency of the oscillator; a sensor arrangement comprising a second antenna and operable to sense the electric field; wherein the first and second antennas are mounted on an aperture closure member to define a target region at the perimeter of the closure member, and the arrangement further comprising control means operable to analyse the field strength sensed by the sensor arrangement, for changes indicative of a change in conditions in the target region, wherein the target region is a region through which the aperture closure member is movable, wherein the control means stores data representing an expected sensed field strength for a range of positions of the aperture closure member, for comparison with an actual sensed field strength to determine a change in conditions, and wherein an unacceptable change in conditions is determined by reference to at least one threshold change of sensed field strength and/or rate of change of sensed field strength, and wherein said at least one threshold is dependent on the current position of the closure member.