Apparatus for detecting ferromagnetic objects at a protected doorway assembly

• US 10,109,177 B2
• Filed: 02/01/2018
• Issued: 10/23/2018
• Est. Priority Date: 10/24/2012
• Status: Active Grant

• Current Assignee: Metrasens Incorporated
• Original Assignee: Metrasens Incorporated
• Inventors: Keene, Mark Nicholas, Horton, Thomas John
• Primary Examiner(s): Feild, Joseph
• Assistant Examiner(s): Akhter, Sharmin
• Application Number:
  US15/886,706
• Publication Number:
  US 20180158306A1
• Time in Patent Office: 264 Days
• Field of Search: 340551, 3405726, 3405731
• CPC Class Codes: G01V 11/00 Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00
• CPC Class Codes: G01V 11/002 Details, e.g. power supply systems for logging instruments, transmitting or recording data, specially adapted for well logging, also if the prospecting method is irrelevant means for transmitting well survey signals E21B47/12; signal transmission systems in general G08C; transmission in general H04B
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: G08B 21/18 Status alarms G08B21/02 takes precedence

Abstract

An apparatus for protecting an entrance to a protected area comprises a magnetic sensor to measure an ambient magnetic field or gradient within a first zone of sensitivity at a non-magnetic sensor means adapted to detect the presence of objects within a primary detection zone, a signal processing circuit arranged in communication with the magnetic sensor apparatus and nonmagnetic sensor apparatus, and a warning device operable by an output signal from the signal processing circuit, the warning device adapted to provide an alarm. The signal processing circuit identifies temporal variations due to the movement of a ferromagnetic object within the ambient magnetic field and correlates them with instances in which the non-magnetic sensor means detects the presence of an object in its detection zone, and causes the alarm to operate in the event that the correlation is indicative of the presence of a ferromagnetic object in the primary detection zone. It also determines the direction from which an object is approaching the using signals from the nonmagnetic sensor means and modifies the operation of the warning device dependent on the direction.

Claims

1. Apparatus for protecting an entrance to a protected area, the apparatus 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 primary detection zone in the vicinity of the at least one magnetic sensor,

an RF receiver which is adapted to receive an identity signal from a transducer when the transducer is within a detection zone,

a memory which stores one or more identity codes corresponding to respective identities of transducers,

a signal processing circuit arranged in communication with the at least one magnetic sensor, the non-magnetic sensor means, and the RF receiver, and

a warning device operable by an output signal from the signal processing circuit, the warning device adapted to provide within the vicinity of the apparatus at least one of an audible and a visible warning,

and further in which;

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 its detection zone, and in which the signal processing circuit is arranged to cause the alarm to operate in the event that the correlation is indicative of the presence of a ferromagnetic object in the primary detection zone but to modify the operation of the alarm in the additional event that the RF receiver detects a transducer which has an identity that is stored in the memory; and

which is adapted to suppress the alarm for a defined period of time sufficient to allow a person to move through the doorway or entering and then leaving the detection zone of the apparatus, in which the time of suppression is varied according to the identity of the RF tag that is detected.

2. Apparatus according to claim 1 in which the RF receiver comprises an RFID tag reader, and the transducer radio frequency identify tags (RFID tags).

3. Apparatus according to claim 2 in which the modification comprises suppressing the alarm if the presence of an RFID tag of a known identity is detected by the RFID receiver.

4. Apparatus according to claim 2 in which the modification comprises modifying the threshold at which an alarm is triggered as a function of the magnitude of the temporal variations in magnetic field detected by the magnetic sensor when a known RFID tag is detected.

5. Apparatus according to claim 4 in which the memory stores alongside each identity in the memory a value indicative of a ferromagnetic profile associated with an RFID tag, the profile being used by the apparatus to set the threshold level of change of magnetic field which may trigger an alarm.

6. Apparatus according to claim 2 which includes at least one RFID tag which can be allocated to person who is to pass through the entrance, or can be stuck to, embedded into or otherwise attached to an object that might move through the protected entrance.

7. Apparatus according to claim 3 in which modification to the alarm comprises suppressing the alarm completely, or partially.

8. Apparatus according to claim 7 in which the warning device is adapted to produce both visual and audible alarms and the modification comprises suppressing the audible but not the visible alarm.