Patent ID: 9514624
Filing Date: 2016-12-06
CPC Classification: G01R,G01V,G08B

Claim Text:
1. Apparatus for detecting a ferromagnetic object in the vicinity of a doorway, the apparatus comprising: a primary sensor apparatus comprising at least one first magnetic sensor, the primary sensor apparatus adapted to measure at least one of an ambient magnetic field and a gradient within a localized volume of space defined by a first zone of sensitivity of the at least one magnetic sensor, and to produce a corresponding measurement signal, a secondary non-magnetic sensor apparatus comprising at least first and second secondary sensors, each one being adapted to detect the presence of objects within a respective one of a first zone or a second zone each in the vicinity of the primary sensor apparatus, the first zone for the first secondary sensor being distinct from the second zone for the second secondary sensor, a signal processing circuit arranged in communication with the primary sensor apparatus and the secondary non-magnetic sensor apparatus, and a warning device operable by an output from the signal processing circuit, the warning device adapted to provide within the vicinity of said primary sensor apparatus at least one of an audible and a visible warning, wherein the signal processing circuit is configured to identify temporal variations in the measurement signal due to the movement of a ferromagnetic object within the ambient magnetic field and to correlate the identified temporal variations in the measurement signal with instances in which both sensors of the secondary, non-magnetic, sensor apparatus detect the presence of an object in their respective first and second zones, and to provide an output indicative of the presence of a ferromagnetic object in the vicinity of the primary sensor apparatus in the presence of a correlation there-between, and wherein, when a door in the doorway moves from fully closed to fully open, the moving door first passes entirely through the first zone for the first secondary sensor and subsequently enters the second zone for the second secondary sensor only after the presence of the door exits the first zone and remains within the second zone while moving to fully open.