US 5,210,524 AGranted

Electro-magnetic desensitizer

AssigneeMinnesota Mining and Manufacturing Company

InventorsWerner Schwarz, Josef Graessle

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Abstract

The invention is related to a process of deactivating a magnetic security marker of an article surveillance system, wherein the security marker is detected by simulating conditions normally present in such a system, e.g., by creating between a transmitter and a receiver a sinewave electromagnetic field and the deactivating the security marker by means of the electronically switchable magnetizing apparatus in response to the detection of the magnetic field which corresponds to the magnetization of the security marker in the surveillance zone. It is the object of the invention to enable the magnetic security marker to be deactivated using any alternating power line. To this end, the magnetic system is automatically connected to a power line without circuit change when the security marker is detected. The magnetizing apparatus gradually builds up a magnetic field by rectifying the flow current, monitoring it by a current sensor and increasing it at each change of phase until the current reaches a level to which the sensor is set as effecting deactivation. Thereafter, the magnetizing apparatus is electronically disconnected from the power line.

Claims11

Dependent claims

A method for magnetizing a magnetically responsive marker of an electronic article surveillance system in which an alternating magnetic field is produced within an interrogation zone for interrogating a said marker and a characteristic response produced by an activated marker in said zone is detected and used to produce an appropriate alarm signal, said marker comprising at least one magnetizable element which, when magnetized, causes a different response to be produced than that resulting when the magnetizable element is unmagnetized, said method comprising the steps of

a) positioning a said marker proximate to a coil and thus within a first magnetic field produced by said coil which corresponds to that produced by said system for interrogating a said marker, detecting the response from the marker and producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal,
b) applying a second magnetic field identified by its flux density to said magnetizable element to change the magnetic state thereof, thereby altering said response, and
c) applying said first magnetic field to said marker, detecting the response therefrom and producing a deactivated marker signal when said altered response is detected,
said method being characterized by the steps of responding to a said active marker signal by automatically closing a switch so as to apply a source of alternating electrical current via a rectifier to said coil to gradually build up said second magnetic field, which is directionally constant,
sensing said current and using said sensed current to drive electronic control means to increase said current until a current level is reached corresponding to a magnetic field intensity level at which said characteristic response will be altered, and
automatically opening said switch to disconnect the current from the coil when said current level is reached.

3 more elements

A deactivating apparatus for magnetizing a magnetically responsive marker of an electronic article surveillance system, said system comprising means for producing within an interrogation zone an alternating magnetic field for interrogating a said marker and means for producing an appropriate alarm signal when a characteristic response produced by an activated marker in said zone is detected, said marker comprising at least one magnetizable element which, when magnetized, causes a different response to be produced than that resulting when the magnetizable element is unmagnetized, said deactivating apparatus comprising

a) electronic article surveillance system simulation means comprising a wave generatior (1), a coil (2) for generating a first magnetic field corresponding to that produced by said system for interrogating said marker, within which first field said marker may be positioned, means (8, 16) for detecting the response from the marker and for producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal,
b) means (3) for generating within said coil a second magnetic field identified by its flux density, and for applying said second field to said magnetizable element to change the magnetic state thereof, thereby altering said response, and
c) means (9) for applying a said first magnetic field to said marker, detecting the response therefrom and means (20) for producing a deactivated marker signal when said altered response is detected, said apparatus being characterized by
electronic switch means (13, 15) responsive to said active marker signal for automatically and gradually applying current through a rectifier means (12) directly from a source of alternating electrical power to said coil to gradually build up said second magnetic field, which is directionally constant,
means (14) for sensing the current in said coil,
electronic evaluator means (17) for responding when said sensed current reaches a current level at which the intensity of said second magnetic field corresponds to that level at which said characteristic response will be altered, and
electronic control means (18) for automatically opening said switch means (13, 15) to disconnect the source of alternating electrical power from the coil when the intensity of said second magnetic field is sufficient to alter said response.

4 more elements

Dependencies are inferred from the claim text.