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Apparatus for detecting ferromagnetic objects at a protected doorway assembly

  • US 10,109,178 B2
  • Filed: 02/01/2018
  • Issued: 10/23/2018
  • Est. Priority Date: 10/24/2012
  • Status: Active Grant
First Claim
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1. Apparatus for protecting an entrance to a protected area comprising:

  • at least one magnetic sensor adapted to measure an ambient magnetic field or gradient within a localised 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 non-magnetic sensor means adapted to detect the presence of objects within a detection zone in the vicinity of the at least one magnetic sensor,a signal processing circuit arranged in communication with the at least one magnetic sensor and the non-magnetic sensor means, anda warning device operable by an output signal from the signal processing circuit, the warning device adapted to provide within the vicinity of the at least one magnetic sensor 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 the non-magnetic sensor means detects the presence of an object in the zones, and to cause the warning device to raise an alarm in the event that the correlation is indicative of the presence of a ferromagnetic object in the vicinity of the at least one magnetic sensor;

    and further comprising;

    a door position sensing means which is adapted to monitor the angular position of a door of the entrance,in which the signal processing circuit is adapted to modify the operation of the alarm in the event that output of the door position sensing means indicates that the door is moving, andthat includes a memory which stores historical data information about the change in ambient magnetic field in the zone of sensitivity of the magnetic sensor, and in the event that the output of the door position sensing means indicates that the door is moving at the same time that the non-magnetic sensor indicates the presence of an object in the first detection zone, the apparatus is arranged to cause an alarm to be raised if the stored historical data indicates that the ambient magnetic field was changing prior to the start of the movement of the door.

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