Capacitive article removal alarm

摘要

The alarm system comprises a sensing circuit 12 which includes two electrical conductors 10, 11 spaced from but adjacent each other and adjacent to the predetermined position to be occupied by at least one item when in use. The sensing circuit includes a signal generator responsive to the capacitance present between the two conductors to provide a first output condition indicative of a substantially constant capacitance value present between the electrodes due to the undisturbed presence of the item and to provide a second output condition indicative of a change in capacitance value due to the disturbance of the item or items present. The output of the sensing circuit is received by an alarm actuating circuit 13 which causes actuation of an alarm element when the output condition from the sensing circuit changes significantly to cause the actuating circuit to trigger due to the movement of the item from its predetermined position.