WO1995031862A1 - An arrangement for preventing disturbances in electronic alarm systems - Google Patents
An arrangement for preventing disturbances in electronic alarm systems Download PDFInfo
- Publication number
- WO1995031862A1 WO1995031862A1 PCT/SE1995/000548 SE9500548W WO9531862A1 WO 1995031862 A1 WO1995031862 A1 WO 1995031862A1 SE 9500548 W SE9500548 W SE 9500548W WO 9531862 A1 WO9531862 A1 WO 9531862A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- coil
- conductors
- receiver
- conductor
- transmitter
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/24—Electrical actuation by interference with electromagnetic field distribution
- G08B13/2402—Electronic 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
- G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
- G08B13/2488—Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/24—Electrical actuation by interference with electromagnetic field distribution
- G08B13/2402—Electronic 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
- G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
- G08B13/2468—Antenna in system and the related signal processing
- G08B13/2474—Antenna or antenna activator geometry, arrangement or layout
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
- H01Q7/04—Screened antennas
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B15/00—Suppression or limitation of noise or interference
- H04B15/02—Reducing interference from electric apparatus by means located at or near the interfering apparatus
Definitions
- the present invention relates to an arrangement for prevent- ing disturbances in electronic alarm systems of the kind used in merchandise security systems.
- merchandise security alarm systems are described in the patent literature. These arrangements are intended to prevent merchandise from being removed from shops and stores without having been paid for. Normally, such merchandise security arrangements, or theft prevention systems, include some type of alarm element which is secured to the merchandise to be protected, and a detector device which is installed in the vicinity of the store exit and which delivers an alarm through the medium of remote detec ⁇ tion control when an alarm element is brought into the vicinity of the store exit.
- Remote detection of the alarm element is normally achieved by transmitting a magnetic alternating field, wherewith the presence of an alarm element can be detected through a change in the alternating field characteristic of the alarm element.
- the alarm element may have the form of an elongated, narrow thin strip of highly permeable material whose characteristic property is to transmit high order harmonics when subjected to the effect of a magnetic alternating field.
- This known basic principle enables small and inexpensive alarm elements to be detected with the aid of complicated and relatively expensive detection systems.
- This type of merchandise alarm is particularly well-suited for protecting everyday commodi ⁇ ties or merchandise and is described, inter alia, in European Patent Specification EP 0,153,286.
- alarm elements comprised of a simple electric resonance circuit.
- the detec- tion system can be made simple and inexpensive when the coil in the resonance circuit is relatively large, so that a good Q-value can be readily obtained at the same time as the coupling to external fields will be large.
- the coil is mounted in an alarm plate which is secured to the merchandise to be protected with the aid of some suitable fastener means.
- the detection systems which operate with this type of alarm can be made relatively uncomplicated at a relatively low cost, although it is difficult to avoid the problem of triggering false alarms, because the store environment will often include loops of conductive material which give rise to resonances similar to the resonances obtained from the alarm elements.
- Another problem resides in coupling of current in the receiver and transmitter coils and current on the alarm system cables that extend between the transmitter and receiver equipment and the detection system.
- current on conductors is meant that a net current flows in a pair of conductors between which an alternating voltage prevails, i.e. the current in one conductor of the conductor pair is greater than the current in the other conductor of said pair.
- Cable current means that the sum of the currents in all conductors of the cable differ from zero, when taking into account the direction of the current in each conductor.
- pairs of conductors is meant above and below, and also in the Claims, a pair which consists in two simple conductors and a cable including two or more conductors, of which one or more conductors can be comprised of a shield around one or more other conductors.
- a known solution which reduces, but does not eliminate, the problems of coupling between different disturbance source and the system is to balance transmitter and receiver to earth and to balance and screen the coils. This solution is described in Swedish Patent Specification SE 445,498.
- the present invention eliminates the problems of coupling between different units in the system and coupling between the system and external disturbance sources of different kinds.
- the present invention thus relates to an arrangement for preventing disturbances in electronic alarm systems of the kind used in merchandise security systems, wherein the system includes an alarm element which is adapted to receive a magnetic alternating field transmitted from a transmitter and to retransmit a magnetic alternating field, wherein a receiver is adapted to receive and detect the retransmitted alternating field, wherein the arrangement is characterized in that there is provided in at least given pairs of electric conductors in the system between the electronics and the receiver coil of said system and alternatively also the transmitter coil of said system a resonance circuit which is tuned to the working frequency or working frequencies of the system such as to produce a high impedance on the pair of conductors for current directed in the same direction in said conductors and thereby markedly dampen disturbance sources that are coupled capacitively, inductively or resistively to the system.
- Figure 1 illustrates a first embodiment of the invention
- Figure 2 illustrates a second embodiment of the invention
- Figure 3 illustrates the use of the invention in a manner different to that shown in Figure or Figure 2
- Figure 4 illustrates a third embodiment of the invention.
- the present invention relates to an arrangement for prevent ⁇ ing disturbances in electronic alarm systems of the kind used in merchandise security systems, said systems including an alarm element which is adapted to receive a magnetic alter- nating field transmitted by a transmitter and also to retransmit a magnetic alternating field, wherein a receiver is adapted to receive and detect the retransmitted alternat ⁇ ing field.
- FIG. 1 shows a receiver coil 1. Also shown in the Figure is a receiver of a front-end circuit in the present type of alarm system, namely a differential amplifier 2. It is assumed that the coil is screened with a screen or shield 3 and that a two- conductor screened transmission conductor extends between the receiver coil 1 and the receiver 2. In the known technique this conductor is not wound in the form of a coil as shown in Figure 1.
- EMF electromotive force
- FIG. 1 One problem is that the receiver coils of existing systems are subjected to electrical disturbances which are coupled capacitively to the receiver coil.
- a disturbance source in the locality is referenced 4 and in the illustrated case has the form of an oscillator.
- This disturbance source is coupled capacitively to the screen 3 of the receiver coil 1.
- This capacitive coupling is illustrated with a capacitor corre ⁇ sponding to the capacitance CS that prevails between the disturbance source and the receiver coil.
- the current that arises in the screen 3 as a result of the capacitive coupling CS gives rise to a voltage on the receiver input through transformer output. This may cause the receiver to understand the signal as originating from an alarm element and to trigger an alarm.
- the current originating from the disturbance source 4 flows on the screen 3, clockwise on the screen 3, through the conductor 8, on the conductor 5 associated with the screen, and through the conductor 9 to earth.
- This current induces in the coil 1 an electromotive force which gives rise to a voltage difference between the positive terminal and the negative terminal of the amplifier 2.
- the resonance circuit is formed by winding the pair of conductors 5 concerned to provide a coil 6 of inductance L, and forming the capacitance in the resonance circuit from the stray capacitances C between the conductors in said coil, and optionally other stray capacitances.
- the stray capacitance is illustrated by a capacitor 7 shown in broken lines.
- the pair of conductors extend from the receiver coil, and alternative ⁇ ly also to the transmitter coil, in the form of solely one screened two-conductor cable which is wound to form a coil of inductance L and includes the stray capacitance C.
- This embodiment is illustrated in Figure 1.
- the impedance across the resonance circuit LC will be in the order of ten times the impedance across the capacitance CS.
- the bandwidth is then approximately +/- 10%. This means that the disturbing current originating from the disturbance source will be reduced by a factor of 10, whereby disturbance sensitivity will be reduced to the same extent.
- current originating from an alarm element will not be dampened to any appreciable extent. Higher damping effects can be obtained with narrower bandwidths.
- a capacitor is connected in parallel across each two-conductor screen, with respective connecting points located on respective sides of the coil, i.e. in the manner in which the broken-line capacitor of Figure 1 is connected.
- the total capacitance is comprised of the capacitor capacitance and the stray capacitance.
- each resonance circuit is a separate LC-circuit.
- a single resonance circuit is sufficient in other systems having only one working frequency.
- the capacitance C is preferably comprised of the stray capacitance of the coil 6 and optionally other stray capacitances.
- a pair of unscreened conductors 12, 13 extend from the receiver coil, and alternatively also to the transmitter coil, wherein the conductors are twisted around one another and in one twisted part are wound to form a coil 10 having the inductance L and including the stray capacitance C.
- This embodiment is illustrated in Figure 2.
- the stray capacitance may be essentially smaller than the capacitance CS, therewith providing highly effective damping of disturbances.
- the screen 3 around the receiver coil may be removed to no great detriment, therewith reducing the cost of the receiver coil.
- the second embodiment may also include a capacitor 29 which is connected in parallel across one of the two conductors of said conductor pair, with its connection point on respective sides of the coil, as illustrated in broken lines in Figure 2.
- the coil 6; 10 is wound around a ferrite core 11 so as to increase the inductance of the coil.
- Figure 3 illustrates a third embodiment of the invention which includes a receiver coil 1 and a transmitter coil 14.
- This exemplifying embodiment also includes adjacent the transmitter coil 14 an electric contact unit 15 for connec ⁇ tion of an electronic unit 16 to the transmitter coil, via a conductor 21.
- the electronic unit 16 includes a voltage unit, oscillators for generating the magnetic alternating fields to be transmitted, a receiver for receiving an alternating field in the receiver coil, a microprocessor for processing a received signal, etc.
- the electronic unit is connected to mains voltage via a conductor 17 and is provided with an output 18 on which an alarm signal is delivered.
- An electric contact unit 19 for connecting conductors to the receiver coil 1 is also provided adjacent the receiver coil 1.
- the electrical contact unit may include certain electronic components.
- a conductor 20 extends between the receiver coil contact unit 19 and the transmitter coil contact unit 15.
- the receiver coil is thus connected to the electronic unit 16 via the contact unit 15 of the transmitter coil.
- Each of the conductors 20, 21 may include a plurality of electric conductors, depending on the construction of the receiver coil among other things.
- the component referred to as a receiver coil may, in fact, consist in a plurality of different, mutually separated coils.
- each of the conductors 20, 21 is wound to form a coil form around a ferrite core 22, 23, thereby to avoid net currents in the conductors.
- the conductors 20, 21 are either screened or twisted in the aforesaid manner.
- the stray capacitances of the formed coils are used as capacitance C in the resonance circuits.
- it is important that the resonance circuits are placed so that the stray capacitances, which determine the resonance frequency, will not vary appreciably with normal variations in the positioning of the conductors 20, 21.
- the inventive arrangement also prevents problems arising due to inductive coupling between coil 1 or the coil 14 in a set- up according to Figure 3 and a conductor belonging to the alarm system.
- Figure 4 illustrates an inventive arrangement which is advantageous in practice and which includes a receiver coil or transmitter coil.
- the conductors leading to the coil of the Figure 4 embodiment are two twisted single-conductors 25, 26 which have been wound to form a coil 27 along one twisted part thereof.
- the conductors 25, 26 are connected to a coaxial cable 28, with one of the conductors connected to the cable screen.
- the sensitivity of the system, or system response, in indicating an alarm is such that net currents that have been dampened by means of the resonance circuit will have, subsequent to being dampened, an amplitude which is too low to have an unfavourable affect on the function of the system.
- the resonance circuit or circuits is/are dimensioned to achieve sufficiently high damping of occurrent disturbances, i.e. net current, while the damping of a signal will be small when the net current is zero.
- the person skilled in this art will be quite capable of dimensioning the capacitance C and the inductance L of the resonance circuit to correspond to relevant working frequencies in each individual case.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP95919726A EP0772915A1 (en) | 1994-05-16 | 1995-05-16 | An arrangement for preventing disturbances in electronic alarm systems |
US08/737,730 US5883574A (en) | 1994-05-16 | 1995-05-16 | Arrangement for preventing disturbances in electronic alarm systems |
AU25426/95A AU2542695A (en) | 1994-05-16 | 1995-05-16 | An arrangement for preventing disturbances in electronic alarm systems |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9401676-3 | 1994-05-16 | ||
SE9401676A SE504899C2 (en) | 1994-05-16 | 1994-05-16 | Device for preventing interference in electronic alarm systems |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1995031862A1 true WO1995031862A1 (en) | 1995-11-23 |
Family
ID=20394013
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE1995/000548 WO1995031862A1 (en) | 1994-05-16 | 1995-05-16 | An arrangement for preventing disturbances in electronic alarm systems |
Country Status (5)
Country | Link |
---|---|
US (1) | US5883574A (en) |
EP (1) | EP0772915A1 (en) |
AU (1) | AU2542695A (en) |
SE (1) | SE504899C2 (en) |
WO (1) | WO1995031862A1 (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3835420B2 (en) * | 2003-03-19 | 2006-10-18 | ソニー株式会社 | Antenna device and method for manufacturing antenna device |
US7162264B2 (en) * | 2003-08-07 | 2007-01-09 | Sony Ericsson Mobile Communications Ab | Tunable parasitic resonators |
US7298260B1 (en) | 2005-03-09 | 2007-11-20 | Cossette Harold J | Tesla coil security system |
US8786439B2 (en) * | 2005-09-02 | 2014-07-22 | Wg Security Products | Active antenna |
US8450997B2 (en) * | 2009-04-28 | 2013-05-28 | Brown University | Electromagnetic position and orientation sensing system |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3810147A (en) * | 1971-12-30 | 1974-05-07 | G Lichtblau | Electronic security system |
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 |
US4751500A (en) * | 1987-02-10 | 1988-06-14 | Knogo Corporation | Detection of unauthorized removal of theft detection target devices |
WO1988008181A1 (en) * | 1987-04-13 | 1988-10-20 | Lichtblau G J | Continuously armed high reliability pulse train processor |
US5103209A (en) * | 1989-01-09 | 1992-04-07 | Checkpoint Systems, Inc. | Electronic article surveillance system with improved differentiation |
US5111186A (en) * | 1990-11-29 | 1992-05-05 | Sensormatic Electronics Corporation | LC-type electronic article surveillance tag with voltage dependent capacitor |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5285191A (en) * | 1981-10-30 | 1994-02-08 | Reeb Max E | LC marker construction useful as an electromagnetically interrogatable transponder means |
US4598276A (en) * | 1983-11-16 | 1986-07-01 | Minnesota Mining And Manufacturing Company | Distributed capacitance LC resonant circuit |
ATE53675T1 (en) * | 1984-02-15 | 1990-06-15 | Esselte Meto Eas Int Ab | METHOD AND ARRANGEMENT FOR DETECTING AN INDICATOR. |
US5309147A (en) * | 1992-05-21 | 1994-05-03 | Intelectron Products Company | Motion detector with improved signal discrimination |
-
1994
- 1994-05-16 SE SE9401676A patent/SE504899C2/en unknown
-
1995
- 1995-05-16 US US08/737,730 patent/US5883574A/en not_active Expired - Fee Related
- 1995-05-16 AU AU25426/95A patent/AU2542695A/en not_active Abandoned
- 1995-05-16 EP EP95919726A patent/EP0772915A1/en not_active Withdrawn
- 1995-05-16 WO PCT/SE1995/000548 patent/WO1995031862A1/en not_active Application Discontinuation
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3810147A (en) * | 1971-12-30 | 1974-05-07 | G Lichtblau | Electronic security system |
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 |
US4751500A (en) * | 1987-02-10 | 1988-06-14 | Knogo Corporation | Detection of unauthorized removal of theft detection target devices |
WO1988008181A1 (en) * | 1987-04-13 | 1988-10-20 | Lichtblau G J | Continuously armed high reliability pulse train processor |
US5103209A (en) * | 1989-01-09 | 1992-04-07 | Checkpoint Systems, Inc. | Electronic article surveillance system with improved differentiation |
US5111186A (en) * | 1990-11-29 | 1992-05-05 | Sensormatic Electronics Corporation | LC-type electronic article surveillance tag with voltage dependent capacitor |
Also Published As
Publication number | Publication date |
---|---|
SE9401676L (en) | 1995-11-17 |
SE504899C2 (en) | 1997-05-26 |
US5883574A (en) | 1999-03-16 |
SE9401676D0 (en) | 1994-05-16 |
EP0772915A1 (en) | 1997-05-14 |
AU2542695A (en) | 1995-12-05 |
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