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System and method for detecting unauthorized removal of goods from protected premises, and magnet detecting apparatus suitable for use therein

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Publication number
US3919704A
US3919704A US31176772A US3919704A US 3919704 A US3919704 A US 3919704A US 31176772 A US31176772 A US 31176772A US 3919704 A US3919704 A US 3919704A
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Grant
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Prior art keywords
magnet
goods
clip
attendant
coils
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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Allan L Williams
Lyle D Heck
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CHECK MATE SYSTEMS Inc
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CHECK MATE SYSTEMS Inc
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
    • G08B13/2405Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used
    • G08B13/2408Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used using ferromagnetic tags
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
    • G08B13/2465Aspects related to the EAS system, e.g. system components other than tags
    • G08B13/2468Antenna in system and the related signal processing
    • G08B13/2474Antenna or antenna activator geometry, arrangement or layout
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
    • G08B13/2465Aspects related to the EAS system, e.g. system components other than tags
    • G08B13/2468Antenna in system and the related signal processing
    • G08B13/2477Antenna or antenna activator circuit

Abstract

An improvement in systems in which a clip containing a magnet is secured to goods in a store, and in which magnet-sensing means are provided at an exit from the store to give an alarm if one attempts to remove the goods through the exit with the magnetcontaining clip still attached; in an authorized removal of the goods, e.g. pursuant to a purchase, the goods with clip attached are taken to a check-out counter where the attendant removes the clip and magnet so the goods can be removed through the exit without sounding the alarm. The improvement comprises a mat-like array of loops of conductor coils disposed flat along a surface of the counter adjacent the attendant, over which array the goods are moved by the attendant in the course of the check-out procedure. If a magnet-containing clip is still attached to the goods, the motion of the magnet will induce currents in the coils to operate an indicator telling the attendant of this fact. If the attendant has failed to find and remove a clip from goods during the check-out procedure, the latter indications will so warn the attendant; upon observing the indication, the attendant then finds and removes the clip and magnet. This eliminates the possibility that the innocent purchaser may be embarassed by causing an alarm when he attempts to remove his purchases through the store exit. Preferably the coil array comprises at least two separate conductor loops of similar configuration, overlapping each other but spacially displaced in a horizontal plane, so that the moving magnet will induce currents in the loops; however the effects of simultaneous similar changes in magnetic flux through the two coils such as may be produced by changes in stray magnetic fields are cancelled out, and do not operate the indicator.

Description

United States Patent 1191 Williams et a1.

[ Nov. 11, 1975 1 1 SYSTEM AND METHOD FOR DETECTING UNAUTHORIZED REMOVAL OF GOODS FROM PROTECTED PREMISES, AND MAGNET DETECTING APPARATUS SUITABLE FOR USE THEREIN [75] Inventors: Allan L. Williams. Mt. Penn; Lyle D.

Heck. Reading. both of Pa.

[73] Assignee: Check Mate Systems. Inc., King of Prussia. Pa.

221 Filed; Dec.4.1972

211 App1.No.:3l1.767

[52] US. Cl. 340/280; 340/258 D; 343/65 SS;

343/872; 324/34 D [51] Int. Cl. GOSB 21/00 [58] Field of Search 340/280. 258 R. 258 C.

340/258 D. 224'. 325/367. 369. 371'. 343/866. 872. 893. 6.5 SS. 324/34 R,

[56] References Cited UNITED STATES PATENTS 2.280.461 4/1942 Whisk 325/371 X 3.292.080 12/1966 Trikilis 324/41 3.423.674 1/1969 Goldsmith et a1...... 324/41 UX 3.665.448 5/1972 MCGlinchey 340/280 3.665.449 5/1972 Elder et a1 340/280 3.696.379 10/1972 Minasy 340/280 3.697.972 10/1972 Brown 340/258 C X 3.706.027 12/1972 Grice 324/34 R 3.711.848 1/1973 Martens 340/280 3.718.922 2/1973 Williams et a1. 340/280 3.747.086 7/1973 Peterson 340/280 3.754.226 8/1973 Fearon 340/280 3.763.424 10/1973 Bennett 324/41 Primary- E.\'aminerlohn W. Caldwell Assistant E.\'uminerWilliam M. Wannisky Attorney. Agent. or Firm-Howson and Howson [57] ABSTRACT An improvement in systems in which a clip containing a magnet is secured to goods in a store. and in which magnet-sensing means are provided at an exit from the store to give an alarm if one attempts to remove the goods through the exit with the magnebcontaining clip still attached; in an authorized removal of the goods. cg. pursuant to a purchase. the goods with clip attached are taken to a check-out counter where the attendant removes the clip and magnet so the goods can be removed through the exit without sounding the alarm. The improvement comprises a mat-like array of loops of conductor coils disposed flat along a surface of the counter adjacent the attendant. over which array the goods are moved by the attendant in the course of the check-out procedure. 1f a magnetcontaining clip is still attached to the goods. the motion of the magnet will induce currents in the coils to operate an indicator telling the attendant of this fact. 1f the attendant has failed to find and remove a clip from goods during the check-out procedure. the latter indications will so warn the attendant; upon observing the indication. the attendant then finds and removes the clip and magnet. This eliminates the possibility that the innocent purchaser may be embarassed by causing an alarm when he attempts to remove his purchases through the store exit. Preferably the coil array comprises at least two separate conductor loops of similar configuration, overlapping each other but spa cially displaced in a horizontal plane. so that the moving magnet will induce currents in the loops; however the eiTects of simultaneous similar changes in magnetic flux through the two coils such as may be produced by changes in stray magnetic fields are cancelled out, and do not operate the indicator.

1 Claim, 4 Drawing Figures SYSTEM AND METHOD FOR DETECTING UNAUTHORIZED REMOVAL OF GOODS FROM PROTECTED PREMISES, AND MAGNET DETECTING APPARATL'S SUITABLE FOR USE THEREIN BACKGROUND OF THE INVENTION Various systems have previously been proposed which use electrical and magnetic means for detecting the unauthorized removal of goods from protected premises, such as a retail store, as part of an effort to reduce serious financial losses due to theft. In certain of such systems, a magnet is secured to the goods in the store and a magnet-sensing device placed at the exit to the store to detect the presence of the magnet on the goods, Thus, an alarm is sounded when one attempts to conceal goods on or about his person and to remove them from the exit, so long as the magnet is still secured to the goods. When an authorized removal of goods (for example pursuant to a purchase) is to be made, the magnet member is normally removed as part of the purchase procedure, and the goods may be removed from the premises without causing the alarm to operate at the exit.

Such systems, and electrically releasable magnetcontaining clips to be secured to the goods, are disclosed and claimed in copending application Ser. No. H2355 of A. L. Williams and L. D. Heck, filed Feb. 3, l97l and now U.S. Pat. No. 3,718,922 issued Feb. 27, 1973', and in copending application Ser. No. 299,058, of A. L, Williams and T. A. Keifer, filed Oct. l9, 1972 now US. Pat. No. 3,806,910, issued Apr. 23, 1974. In such system, a hinged clip containing a permanent magnet is secured to the goods in a locked condition, and contains a bimetallic element which can be operated to open the clip only in response to an electrified key provided at the check-out counter and applied to the clip by the check-out attendant, Suitable magnetometer or like apparatus adjacent the store exit will detect the removal of unpurchased goods having the magnet'containing clip still secured thereto, and will sound an alarm indicating a theft.

One difficulty which can arise in such a system is that the check-out attendant may overlook removal of a clip, and an innocent purchaser carrying purchased goods through the exit may then cause an alarm to be given, which would not only require returning the goods to the check-out counter to remove the clip, but would also be embarassing to the customer. Failure to remove the clip can result from complete negligence by the attendant in forgetting to locate the clip on each piece of purchased merchandise, or can arise in situations in which not all goods are always provided with clips and the attendant believes thata particular piece of merchandise is ofa type not provided with a clip and hence does not search for the clip.

Accordingly, it is an object of the invention to provide a new and useful system and method for preventing false indications of unauthorized removal of objects from protected premises.

Another object is to provide such method and apparatus which will permit detection of unauthorized removal of objects from protected premises by operating an appropriate alarm, but will prevent operation of such an alarm when such goods are removed with authorization, as after purchase for example,

It is also an object to provide a method and system of the type in which magnet means are secured to objects within protected premises and their removal through an exit in the premises is detected by sensing the presence of the magnet, in which assurance is provided that the magnet means has been removed from those goods which have been purchased, prior to their removal through the exit.

Another object is to provide a convenient, inconspic uous magnet detector at the checleout station which will sense movement near it of a magnet associated with goods and produce an indication of the presence of the magnet.

A further object is to provide such magnet-detecting apparatus which is sensitive to the magnet on the goods but insensitive to the effects of usual stray magnetic fields.

It is also an object to provide such a magnet detector which is simple. safe, economical, reliable and does not interfere with usual checlcout procedures.

SUMMARY OF THE lNVENTlON In accordance with the invention, there is provided a method and system in accordance with which magnetdetecting means is provided along the path of authorized removal of goods from protected premises at a position prior to the location of the magnet-sensing means used to detect unauthorized removal of goods from the premises. Preferably the first-mentioned magnet-detecting means is located at the check-out position for purchased goods, and is such that when any goods having a magnet associated therewith are moved near the magnet-detecting means, an indication is provided to warn that the magnet means should be found and removed before their passage through the exit causes a false alarm. Preferably, the magnet-detecting means at the check-out position is in the form of a matlike structure lying horizontally along the check-out countertop, where movement of the goods by the check-out attendant adjacent the magnet detector will provide indications to the attendant if a magnet is still present on the goods. Preferably also, the magnet de tector comprises at least two separate conductive loops so positioned and configured as to cause a net current in response to motion near them of a magnet, but so as to produce little or no net currents in response to changes in stray magnetic fieldsv In a preferred embodi ment, the at-least-two separate coils are of similar or the same configuration but displaced from each other horizontally, preferably in an overlapping but non-congruent position.

Should the attendant fail to remove a magnet from the goods, the motion of the goods over the mat-like magnet detector on the countertop will produce a warning indication and alert him to the failure to remove the magnet. In this way it is assured that the customer will not be embarassed by a false alarm at the exit due to the presence of a magnet on properly purchased goods.

BRIEF DESCRlPTlON OF FIGURES These and other objects and features of the invention will be more readily understood from a consideration of the following detailed description, taken with the accompanying drawings in which:

FIG, I is a plan view of protected premises using the apparatus and system of the invention;

FIG. 2 is a perspective view of a mat-like magnetdetecting coil array in accordance with the invention;

FIG. 3 is a perspective view of the electronics unit for the magnet detector. including the indicator therefor: and

FIG. 4 is an electrical schematic drawing for the magnet-detector apparatus of the invention DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring now to the embodiment of the invention illustrated in the figures, there are represented protec tive premises within building walls I provided with a customer entrance I2 and a customer exit 14. Entrance I2 leads to a goods storage area I6 for goods and merchandise on sale or display. On either side of the path leading to the exit are located magnetometer devices or the like which will sense the presence of a magnet adjacent to them and provide an alarm, typically an audible alarm. Secured to the goods on sale in the store are magnet-containing clips such as 24, which may be of one of the types disclosed and claimed in the aboveidentified copcnding applications. Each such clip contains a magnet. generally a permanent magnet, and the clip is secured to the goods in a locked condition. The clip is provided with hinged jaws which can only be opened when the clip is supplied with an electrical current from an electrified releasing wand such as 26. The releasing wand 26 is in this example positioned at the check-out stations such as 28, the check-out stations being positioned along the path taken by customers on their way to the exit 14. At each check-out station there is normally an attendant such as 30, and a cash register 32, in addition to the electric wand 26.

As described in the above-identified copending applications, if a customer attempts to leave the premises by way of exit 14 with goods from which the magnet-containing clip has not been removed, the magnet detecting system will sound an alarm indicating a theft. In the course of a normal purchase. the customer or the attendant will bring the goods to one of the check-out stations, the clip will be removed by means of the electrified wand, the financial transaction involved in the purchase will be completed and the goods without the clip are removed by the customer through the exit without any alarm being given, as desired.

However, should an innocent purchaser carry to the magnet-detecting apparatus 20 goods to which a magnet-containing clip is still attached, a false alarm will be given, with considerable embarassment to all parties.

In accordance with the invention in this embodiment. failure to remove a magnet-containing clip during the purchase procedure at the check-out station is detected and indicated to the attendant by means of a mat-like magnet detector 40 positioned adjacent the check-out station, in this example lying flat on the top of the check-out counter 41. The mat-like detector 40 is electrically connected to an associated electronics unit 42, which may be housed in the same cabinet as the electronics for the release wand. The electronics unit may be placed on top of, beneath, or in any convenient location with respect to, the check-out counter.

When goods to which a magnet-containing clip is secured are brought to the checlcout station and moved adjacent the detector mat 40, currents induced by such motion produce an indication on the electronics unit 42 of the presence of the magnetv This indication constitutes a warning to the attendant that the magnet-containing clip is still present. so that he may remove it by use of the electrified wandv Preferably the mat-like detector is placed within easy reach of the attendant, so that the above-mentioned motion of the magnet with respect to the mat is produced during the ordinary course of purchase and packaging, or the attendant can consciously move the goods, either before or after packaging, through the region above the mat-like detector as assurance that the clips have all been properly removed. Of course if an indication is obtained in this procedure, the attendant then searches for clips on the goods and removes them with the wand, until motion of the goods near the mat-like detector no longer produces an indication of the presence of a magnet. In this way it is assured that all magnet-containing clips have been removed before the innocent purchaser removes the goods to the exit 14, and hence false alarms by the magnet detector apparatus 20 are prevented.

The detector 40 contains at least one electrical conductor, and preferably a plurality of separate coils of conductors, each comp rising one or more loops. FIG. 2 illustrates one preferred form of the mat-like detector. A flat rectangular base 48, suitably of a hard plastic material, is machined to provide the various grooves such as 50 in the upper surface of the base, the grooves being sufficiently deep to accomodate the two-multiturn coils 52 and 54 which overlap each other and lie substantially in the same plane. A printed-circuit terminal strip 56 is cemented to the bottom of a recess in the base 48, the four leads from the two coils being connected to four corresponding tabs of the terminal strip. The terminal strip connects these found leads to three output leads from the coil array as shown in FIG. 2 and in the electrical diagram of FIG. 4.

As an example only, each coil may be in the form of a generally rectangular loop about l2 inches long and 8 inches across, each loop overlapping the other to about the center line of the other loop, the loops also being slightly displaced from each other in their lengthwise direction. A top cover 57 of plastic material similar to base 48 may be cemented over the top of the base to seal the coils in position and to protect them from damage or deterioration. The complete detector unit may typically be about 1 /2 feet long and 14 inches in width and about 1 inch in height.

FIG. 3 illustrates a typical form of the electronics unit for the detector, to which the three leads from the matlike detector are connected by the cable 59. On its front, facing the attendant, are mounted a line fuse 60, key-operated on/off power switch 62, and a pilot lamp 64; a buzzer alarm providing the indication of the pres ence of the magnet near the detector mat is contained within the cabinet of the electronics unit. Line power for operating the unit is supplied over line 65.

Referring now to FIG. 4 showing the electronic cir cuitry of the magnet detector apparatus, as shown the two coil terminal leads 66 and 67 from the left-hand sides of the two coils 54 and 52 are connected together and to a common ground. The lead 70 from the righthand side of coil 54 is connected through a resistor 72 to the non-inverting input terminal 3 of the solid-state differential amplifier 74, while the lead 75 from the right-hand side of coil 52 is connected through resistor 76 to the inverting input terminal 2 of the differential amplifier.

Differential amplifier 74 may comprise, for example, the industry type-number 301 differential amplifier which produces at its output connection 6 an amplified version of the difference between the signals supplied to its inverting and non-inverting input terminals. Resistors 76, 82 and 84 constitute the gain-determining resistors for the inverting input 2, while resistors 72, 86 and 88 determine in part the gain for signals supplied to the non-inverting input terminal 3; preferably resistors 72. 86 and 88 are respectively equal in value to resistors 76, 82 and 84. In addition, the connection from junction point 89 between resistors 82 and 84, to the junction point 90 between resistors 86 and 88, by way of the variable resistance 92, provides additional feedback for increasing the gain of the amplifier. Resistor 92 is normally set to provide the maximum feedback and maximum gain possible without rendering the amplifier inoperative by causing it to be held in one of its extreme conduction states. A conventional bandwidth control circuit comprising capacitor 94 and resistor 96 limits the bandwidth of the amplifier to a few cycles per second, thereby reducing sensitivity to high-frequency noise or interference, including stray oil-cycle fields. In addition, the connection of resistor 98 to ground through the variable resistance 99 constitutes a conventional offset node adjustment to balance the amplifier so that it produces zero output when the input sig nals to its inverting and non-inverting terminals are ex actly equal. The amplifier output connection 6 is con nected to the remainder of the circuit through the AC coupling capacitor 100, to avoid drift problems sometimes encountered when DC coupling is utilized.

The signal passed through capacitor 100 is supplied to input terminals 3 and 2, respectively of amplifying comparators 101 and 102, which again may be standard solid-state devices, such as the industry type-num her 741. Each of these devices has the property that its output signal begins to exceed zero in the positive direction only when the voltage applied to its terminal 3 first exceeds the voltage applied to its input terminal 2. The output terminals 6 of comparators 101 and 102 are supplied, respectively, through diode rectifier 104 and resistor 106, and through diode rectifier 108 and resistor 110, to the base 112 of an NPN transistor 114. The polarity of connection of the two diode rectifiers 104 and 108 is such that each passes a positive signal to transistor base 112 to turn on transistor 114 only when the output of its corresponding comparator is positive.

Input terminal 2 of comparator 101 is biased positively by the bias voltage supplied thereto through fixed resistor 115 and adjustable divider 115A; input terminal 3 of comparator 102 is biased negatively by the bias supplied thereto through fixed resistor 1 l6 and divider 116A. Accordingly, when the signal through capacitor 100 is zero or small, neither comparator produces a positive output; when the signal through capacitor 100 becomes more positive than a value established by the position of the tap on divider llSA, comparator l0l produces a positive output; and. when the signal through capacitor 100 becomes more negative than a value established by the position of the tap on divider 116A, comparator 102 produces a positive output. Small signals due to noise or interference are thus prevented from turning on transistor 114.

The emitter of transistor [14 is grounded and its collector is connected through relay coil 118 and resistor 120 to positive supply potential. A conventional transient-suppressing diode rectifier 122 is connected in parallel with the relay coil. Relay coil H8 operates upon its associated contact arms 124 and 126, and causes them to move from the normal positions thereof shown in the drawing to their opposite positions when a current is passed through the relay coil. In the absence of signal from the comparators 101, 102, the base of transistor 114 is open-circuited and the transistor substantially cut off, so that no current flows through relay coil I18 and the contact arms 124 and 126 remain in the positions shown.

hi the normal condition shown, the contact arm 126 connects a resistor I30 in parallel with a timing capacitor 132, the opposite upper end of resistor 130 being connected to the positive supply potential; resistor 130 then serves to maintain capacitor 132 normally discharged. However, when relay contact arm I26 is changed to its opposite position, it connects to capacitor 132 in series between the positive supply voltage and the base 1 12 of transistor 114, by way of the series resistor 136. This causes a positive voltage to be applied to transistor base 112, holding the transistor in conduction. until capacitor 132 becomes charged up by the positive supply. Thus if either of the comparators 101 and 102 supplies only a momentary positive voltage to transistor 114, turning it on for only a short interval, the action of relay contact arm 126 and capacitor 132 is to maintain the transistor 114 conductive for a predetermined interval, typically a few seconds, even though the positive signal from the comparator has already disappeared. Accordingly. even a momentary output from one of the comparators will cause the tran- I sistor 114 to remain turned on for at least a few seconds. Also, when current flows through relay coil 118 contact arm 124 is operated to its opposite position, and an alarm such as a buzzer is connected in circuit with an alternating voltage source supplied over lines 144 and M6. Therefore, whenever a positive signal is applied to the base 2 of transistor 114 the buzzer will be sounded which will persist for the time required for capacitor 132 to charge.

To provide operating supply voltages for the circuit. an alternating-voltage supply source 148, such as a standard 1 lO-volt AC wall socket, is provided, one side of the line from source 148 being connected through the fuse 60 and the on/off power switch 62; pilot lamp 64 is connected between the opposite sides of the alternating voltage supply line, following the fuse and on/off switch, to provide an indication that the switch has been closed. The alternating supply voltage is then supplied to a conventional direct-current power supply 160, the output of which provides the direct voltages required for operating the circuit. In this example, the DC supply voltages are ground, +15 volts, 15 volts, +30 volts and 3() Volts.

In the operation of the circuitry shown. when there is no magnet moving near the sensing coils 52, 54 there will be no input voltage to, or output voltage from. the differential amplifier 74; transistor [14 will be nonconductive; there will be no current through relay coil 118; and the relay contacts 124 and 126 will be in the normal position shown. Accordingly, the alarm [40 will not receive operating voltage and the buzzer will not be operated. If there should be a simultaneous change in the magnetic field affecting both sensing coils equally. for example due to changes in the earths magnetic field or due to changes in other stray magnetic fields. the same current will be induced in both coils, there will be no difference in the inputs supplied to the differential amplifier. and accordingly there will be no output therefrom and the alarm again will not be operated. However, if a magnetcontaining clip is moved over the sensing coils, for example within about one foot thereof, the motion of the magnet relative to the conductors in the coils will induce currents in the coils which, in general. will be unequal in strength. For example, if the magnet is moved from left to right across the sensing coils, first a pulse of current of a given polarity will occur in leads 70, then a pulse of current of the same polarity will occur in lead 75, next a pulse of current of opposite polarity will occur in lead 70, and then a pulse of opposite polarity will occur in lead 75. Each of these pulses represent an unbalanced input to the differential amplifier which will at least momentarily turn on transistor I14, and timing capacitor [32 will hold that transistor on for at least a few seconds, during which time the alarm is given to the attendant, indicating a magnet-containing clip is near the detector mat. The attendant then searches for and removes the clip so that the customer may leave with the goods without sounding the alarm at the exit of the premises. Of course, the magnet need not be moved from left to right as described above, any substantial motion of the magnet near the coils generally producing an unbalanced signal to the differential amplifier.

Although the form of coils shown is preferred, other arrangements thereof may also be utilized. As examples only, more loops (such as 4, 6 or 8 loops) may be employed if desired, half of them being connected in parallel with each other and the other half being separately connected in parallel with each other; each coil may itself be formed into several displaced loops if desired. Furthermore, although it is preferred to utilize coils having the same configuration, but spacially displaced from each other, it is possible to use two loops which are of different configurations but which respond in the same way to changes in uniform fields by selecting the number of turns of wire in each to produce the same output in response to the same flux changes. Also, the connections to the two coils may be reversed from that shown so that, instead of producing equal outputs in response to equal changes in uniform fields through them, they produce outputs of the same magnitude but opposite polarity. in this event, the electronic circuitry may be arranged to add algebraically the effects of the currents in the two loops, instead of effectively sub 8 tracting them. The coils may also be completely separated from each other, rather than overlapping. although this requires more space and has been found less effective.

While one preferred location for the detector mat is lying flat on the top of the counter, it may be mounted in the counter top, or below it if the counter top is of non-magnetic material such as wood or plastic, It may also, for example, be mounted vertically rather than horizontally, along one side of the counter where the attendant normally carries the goods, so that she may conveniently move the goods across the detector pad to determine if any clips are still on the goods. Also, while it is preferred to utilize an arrangement of coils and as sociated circuitry which cancels or nulls out the effects of similar simultaneous currents in the two coils, it is possible to use a single coil, or theoretically even a single straight conductor, although in the first case susceptibility to interference and false indications would be increased, and in the second case the sensitivity of the system would be greatly decreased.

Thus while the invention has been shown and described with particular reference to specific embodi ments thereof in the interest of definiteness, it may be embodied in a variety of forms diverse from those spe cifically shown and described, without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. Apparatus for detecting the presence of a magnet secured to goods adjacent a counter, comprising a matlike housing adapted to lie flat on said counter, at least a pair of similar partially-overlapping electrical conductor coils lying flat within said housing and conneeted so that current is induced in any of said conductors by said magnet only when said magnet is adjacent said conductors and in motion relative to said conductors, and indicator means connected to said at least pair of conductor coils for producing indications in response to currents induced in said conductors by adjacent movement of said magnet and non-responsive to the effects on said coils of extraneous magnetic fields from remote sources.

Claims (1)

1. Apparatus for detecting the presence of a magnet secured to goods adjacent a counter, comprising a mat-like housing adapted to lie flat on said counter, at least a pair of similar partially-overlapping electrical conductor coils lying flat within said housing and connected so that current is induced in any of said conductors by said magnet only when said magnet is adjacent said conductors and in motion relative to sAid conductors, and indicator means connected to said at least pair of conductor coils for producing indications in response to currents induced in said conductors by adjacent movement of said magnet and non-responsive to the effects on said coils of extraneous magnetic fields from remote sources.
US3919704A 1972-12-04 1972-12-04 System and method for detecting unauthorized removal of goods from protected premises, and magnet detecting apparatus suitable for use therein Expired - Lifetime US3919704A (en)

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Applications Claiming Priority (5)

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US3919704A US3919704A (en) 1972-12-04 1972-12-04 System and method for detecting unauthorized removal of goods from protected premises, and magnet detecting apparatus suitable for use therein
JP13643173A JPS49116998A (en) 1972-12-04 1973-12-03
GB5591673A GB1458977A (en) 1972-12-04 1973-12-03 System and method for detecting unauthorized removal of goods from protected premises and magnet detecting apparatus suitable for use therein
CA 187193 CA1017427A (en) 1972-12-04 1973-12-03 System and method for detecting removal of goods from protected premises, and magnet detecting apparatus suitable for use therein
DE19732360108 DE2360108A1 (en) 1972-12-04 1973-12-03 System and method for displaying the unauthorized removal of products from a sheltered grundstueck

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JP (1) JPS49116998A (en)
CA (1) CA1017427A (en)
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US4326198A (en) * 1976-08-18 1982-04-20 Knogo Corporation Method and apparatus for the promotion of selected harmonic response signals in an article detection system
US4375289A (en) * 1977-07-19 1983-03-01 PRECITEC Gesellschaft fur Prazisionstechnik und Elektronik mbH & Co. Entwicklungs und Vertriebs-KG Apparatus for monitoring a boundary line
US4476459A (en) * 1981-10-23 1984-10-09 Knogo Corporation Theft detection method and apparatus in which the decay of a resonant circuit is detected
US4555696A (en) * 1983-06-08 1985-11-26 Brown Donald G Passageway selective detector mechanism and system
US4647917A (en) * 1984-03-26 1987-03-03 Allied Corporation Article control system having coded magnetomechanical marker
WO1987004283A1 (en) * 1986-01-10 1987-07-16 Checkpoint Systems, Inc. Security tag deactivation system
EP0273938A1 (en) * 1986-07-17 1988-07-13 Checkpoint Systems Inc Article security system.
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WO1997048990A1 (en) * 1996-06-19 1997-12-24 Flying Null Limited Magnetic reading devices
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US4326198A (en) * 1976-08-18 1982-04-20 Knogo Corporation Method and apparatus for the promotion of selected harmonic response signals in an article detection system
US4375289A (en) * 1977-07-19 1983-03-01 PRECITEC Gesellschaft fur Prazisionstechnik und Elektronik mbH & Co. Entwicklungs und Vertriebs-KG Apparatus for monitoring a boundary line
US4476459A (en) * 1981-10-23 1984-10-09 Knogo Corporation Theft detection method and apparatus in which the decay of a resonant circuit is detected
US4555696A (en) * 1983-06-08 1985-11-26 Brown Donald G Passageway selective detector mechanism and system
US4647917A (en) * 1984-03-26 1987-03-03 Allied Corporation Article control system having coded magnetomechanical marker
WO1987004283A1 (en) * 1986-01-10 1987-07-16 Checkpoint Systems, Inc. Security tag deactivation system
EP0252975A1 (en) * 1986-01-10 1988-01-20 Checkpoint Systems Inc Security tag deactivation system.
US4728938A (en) * 1986-01-10 1988-03-01 Checkpoint Systems, Inc. Security tag deactivation system
EP0252975A4 (en) * 1986-01-10 1988-12-15 Checkpoint Systems Inc Security tag deactivation system.
EP0273938A1 (en) * 1986-07-17 1988-07-13 Checkpoint Systems Inc Article security system.
EP0273938A4 (en) * 1986-07-17 1989-01-26 Checkpoint Systems Inc Article security system.
WO1992018958A1 (en) * 1991-04-10 1992-10-29 Esselte Meto International Produktions Gmbh Security system for articles
US5661470A (en) * 1994-03-04 1997-08-26 Karr; Gerald S. Object recognition system
WO1997048990A1 (en) * 1996-06-19 1997-12-24 Flying Null Limited Magnetic reading devices
US6230972B1 (en) 1996-06-19 2001-05-15 Flying Null Limited Magnetic reading devices
US7416117B1 (en) * 1998-12-21 2008-08-26 Ncr Corporation Method and apparatus for determining if a user walks away from a self-service checkout terminal during operation thereof
US6184846B1 (en) 2000-02-03 2001-02-06 Marconi Commerce Systems Inc. Loop conductor antenna for fuel dispenser
US6724311B1 (en) 2001-11-09 2004-04-20 B&G Plastics, Inc. Anti-theft hang tag
US20040069847A1 (en) * 2002-10-15 2004-04-15 Chester Kolton Electronic article surveillance marker assembly
US20150230436A1 (en) * 2014-02-14 2015-08-20 Elive Llc Magnetized mat for an aquarium

Also Published As

Publication number Publication date Type
JPS49116998A (en) 1974-11-08 application
DE2360108A1 (en) 1974-06-06 application
CA1017427A1 (en) grant
CA1017427A (en) 1977-09-13 grant
GB1458977A (en) 1976-12-22 application

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