EP0939942A1 - Dispositif faisant partie de systemes d'alarme electronique qui generent des signaux de commande en vue de deplacer la frequence d'emission du systeme et d'eviter ainsi des perturbations - Google Patents

Dispositif faisant partie de systemes d'alarme electronique qui generent des signaux de commande en vue de deplacer la frequence d'emission du systeme et d'eviter ainsi des perturbations

Info

Publication number
EP0939942A1
EP0939942A1 EP97926322A EP97926322A EP0939942A1 EP 0939942 A1 EP0939942 A1 EP 0939942A1 EP 97926322 A EP97926322 A EP 97926322A EP 97926322 A EP97926322 A EP 97926322A EP 0939942 A1 EP0939942 A1 EP 0939942A1
Authority
EP
European Patent Office
Prior art keywords
frequency
transmitted
signal
transmitter
disturbing
Prior art date
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.)
Withdrawn
Application number
EP97926322A
Other languages
German (de)
English (en)
Inventor
Leif Asbrink
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Safeplus AB
Original Assignee
Asbrink Leif
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Asbrink Leif filed Critical Asbrink Leif
Publication of EP0939942A1 publication Critical patent/EP0939942A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL 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

Definitions

  • the present invention relates to an arrangement pertaining to electronic alarm systems of the kind used in goods monitoring systems.
  • Remote sensing is normally achieved by generating an alternating magnetic field in which the presence of an alarm element can be detected as a result of a change in the alternating field that is characteristic of the alarm element.
  • the alarm element may have the form of a long, narrow and thin strip of highly permeable material whose characteristic property is found in the transmission of high order harmonics when exposed to a magnetic alternating field.
  • This known basic principle enables the presence of narrow and inexpensive alarm elements to be detected with the aid of complicated and relatively expensive detection devices.
  • This type of alarm system is particularly suited for use in daily shopping complexes and is described in European Patent Specification EP 0 153 286, among others.
  • Known alarm elements can also consist of a simple electric resonance circuit.
  • the detector arrangement can therewith be made relatively simple and inexpensive, provided that the coil in the resonance circuit is made relatively large and that a relatively good Q-value can be easily obtained together with a large coupling to an external field. In this regard, the coil is placed in an alarm plate which is fastened to the goods to be protected, with the aid of some kind of locking device.
  • Such alarm systems may be constructed in a manner in which the detector arrangement includes two mutually spaced alarm arched coils that delimit the sensing zone. Several such alarm arches may be placed parallel with one another so as to form two or more parallel sensing zones.
  • One known method of solving this problem is to synchronize the fields transmitted from the various systems so that the fields will be transmitted synchronously, by drawing cables between the different systems so as to synchronize the transmitters.
  • the different systems can also be synchronized by allowing each system to operate intermittently over short time intervals and to activate the systems successively so that only one system will operate at any one time. Synchronization of the systems is effected by means of a cable connection also in this case.
  • the present invention relates to an arrangement pertaining to electronic alarm systems of the kind used in goods monitoring systems, wherein the system includes an alarm element which is adapted to receive a magnetic alternating field that is transmitted from a transmitter by means of a transmitter coil and the frequency of which is swept, wherein the alarm element is adapted to retransmit a magnetic alternating field, wherein a receiver that includes a receiver coil is adapted to receive and detect the retransmitted alternating field, wherein the electron ⁇ ic alarm system is characterized in that the system transmitter is adapted to vary the transmitted frequency; wherein the system receiver is adapted to receive and detect the presence of a signal deriving from a disturbing other system; wherein the system includes a control circuit that analyzes the frequency and phase position of a signal transmitted from a disturbing system relative to the frequency and phase position of the alternating field transmitted from the first-mentioned system; and wherein the control circuit is adapted to deliver a control signal to the transmitter of the first-mentioned system such as to displace its sweeping
  • Figure 1 is a block schematic illustrating an inventive arrangement.
  • the present invention relates to an arrangement pertaining to electronic alarm systems of the kind used in goods monitoring systems.
  • Such a system includes a known alarm element 1 that is adapted to receive a magnetic alternating field transmitted from a transmit ⁇ ter 2 by means of a transmitter coil 3.
  • the frequency of the transmitted alternating field is swept. For instance, there is transmitted an alternating field having a frequency of 8.2 MHz +/- 0.5 MHz.
  • the alarm element 1 is adapted to retransmit a magnetic alternating field.
  • a receiver 4 that includes a receiver coil 5 is adapted to receive and detect the retransmitted alternating field.
  • the transmitter 2 delivers the transmitted signal to the receiver 4 via a conductor 6 and the received signal is down-mixed in a known manner.
  • the system will include adapted circuits for the detection of the signal received by the receiver with respect to fields that are generat ⁇ ed by an alarm element. It can be said generally that known alarm elements retransmit a field periodically, i.e. at given time intervals contingent on the periodically sweeping field transmit- ted by the transmitter, thereby enabling the occurrence of such a periodically occurring signal to be detected.
  • the arrangement triggers an alarm signal when an alarm element is located in the monitoring zone.
  • the system transmitter 2 is designed to be able to vary the transmitted frequency, i.e. the centre frequency about which the field sweeps.
  • the frequency at which the transmitted frequency sweeps is preferably synchronized with the frequency of the transmitted signal. This can be achieved, for instance, by generating the sweeping frequency by dividing the frequency 14 generated by the transmitter and applied to the amplifier 10. This causes the centre frequency to control the sweep frequency.
  • the system receiver 4 is adapted to receive and to detect the occurrence of a signal from a disturbing other system.
  • a control circuit 8 which functions to analyze the frequency and phase position of a signal transmitted from a disturbing system in relation to the frequency and phase position of the alternating field transmitted from the first- mentioned system.
  • the disturbing system may be a system of the same kind as the inventive system or of a kind different thereto.
  • the transmitted frequency of the disturbing system will interfere with the present system when the frequency lies so close to the transmitted frequency of the inventive system that reception of the disturbing frequency will cause the receiver amplifier to be over-driven and thereby prevent detection of an alarm system.
  • Detection of the disturbing frequency can be effected by includ ⁇ ing a quadrature detector 7 in the receiver.
  • the signals generat ⁇ ed in the quadrature detector can be delivered to a known control circuit 8 which functions to analyze the frequency and phase position of the received signal.
  • control circuit 8 also functions to deliver a control signal to the transmitter 2 of the first system and to displace the sweeping frequency of said transmitter so as to prevent the disturbing signal from disturbing the first- mentioned system.
  • control circuit 8 is adapted to deliver a control signal 9 to the transmitter 2 of the inventive system so as to cause the trans ⁇ mitter to transmit a frequency sweeping alternating field whose frequency and phase position coincide with the disturbing signal received at each moment in time.
  • the control circuit is suitably adapted to change the transmitted frequency so as to bring said frequency successively closer to the disturbing frequency.
  • the inventive system will adapt itself to transmit a field that is fully synchronous with the disturbing field.
  • the arrow 11 indicates the field transmitted by the inventive system and the arrow 12 indicates the disturbing signal.
  • both systems will individually adjust their phase position and frequency in accordance with the respective disturbing signal.
  • the two systems will thus finally transmit a frequency that lies somewhere between the original frequencies.
  • three or more mutually disturbing systems will also approach one another until they transmit on the same frequency.
  • all coordination systems are effected in a wireless fashion.
  • control circuit 8 is adapted to deliver to the transmitter 2 of the first-mentioned system a control signal which displaces its sweeping frequency so that said frequency will differ from the sweeping frequency of the disturbing signal by a difference frequency that is greater than the bandwidth of the signal that the first-mentioned system is intended to receive.
  • control circuit is conveniently adapted to change the transmitted frequency so as to bring said frequency successively closer to the disturbing frequency.
  • This second embodiment of the invention thus also causes the frequencies of two or more mutually disturbing systems to be displaced so that the systems will no longer disturb one another.
  • the different systems transmit frequencies that do not disturb one another at a given time point
  • one of the systems may be driven slowly in frequency so that the driving system will begin to disturb another system after a given period of time.
  • the respective control circuit of the mutually disturbing system may be adapted to displace respective frequen ⁇ cies directly upon the occurrence of disturbance, so that said disturbance will no longer occur.
  • the transmitter 2 includes a digital direct synthesis circuit to which the control signal 9 is delivered.
  • the digital circuit is adapted to generate digitally the frequency and its sweep to be transmitted.
  • the digital circuit is also adapted to transmit the frequency and its sweep in a phase position given by the control signal.
  • Such digital synthesis circuits, or chips are known and commercially available, as is also the simple logic required to effect a sweep that is correlated to the centre frequency. This can be achieved, for instance, with the aid of the clock that controls the digital direct synthesis circuit also counting in a frequency counter that controls the frequency generated by the digital direct synthesis circuit.
  • the signal generated by the digital direct synthesis circuit is thus amplified in an amplifi- er 10 and transmitted via the coil 3.
  • control circuit 8 includes a microprocessor that is adapted to carry out said analysis, preferably by means of a Fourier analysis and adapted to generate said control signal.
  • the frequency and phase position of a disturbing signal can be analyzed by a Fourier analysis.
  • the control circuit 8 is conveniently adapted to activate an alarm device 13 when the presence of an alarm element is detect ⁇ ed.
  • the digital direct synthesis circuit is constructed to enable the frequency of its internal oscillator to be influenced by the control signal. This enables the frequen ⁇ cy setting to be finely adjusted by slightly displacing the frequency of the internal oscillator, therewith displacing correspondingly the frequency generated by the digital direct synthesis circuit.
  • the control signal may, however, contain information that causes the digital direct synthesis circuit to generate the desired frequency while retaining the frequency of the internal oscilla ⁇ tor.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Computer Security & Cryptography (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Burglar Alarm Systems (AREA)

Abstract

L'invention concerne un dispositif faisant partie de systèmes d'alarme électronique du type de ceux utilisés dans les systèmes de contrôle de marchandises. Ce dispositif comprend un élément d'alarme (1) conçu pour recevoir un champ alternatif magnétique émis depuis un émetteur (2) par une bobine (3) et dont la fréquence est balayée. Cet élément d'alarme permet de retransmettre un champ alternatif magnétique. Le dispositif comporte également un récepteur (4) comprenant une bobine (5) adaptée pour recevoir et détecter le champ alternatif retransmis. Cette invention se caractérise en ce que l'émetteur (2) du système est conçu pour faire varier la fréquence transmise; et le récepteur (4) du système pour recevoir et détecter l'apparition d'un signal provenant d'un autre système perturbateur. L'invention comporte également un circuit de commande (8) destiné à analyser la fréquence et la position de phase d'un signal émis depuis un système perturbateur en relation avec la fréquence et la position de phase du champ alternatif émis depuis le premier système. Ce système de commande (8) envoie à l'émetteur (2) du premier système susmentionné un signal de commande qui déplace la fréquence émise de sorte que le premier système ne soit pas perturbé par le signal perturbateur.
EP97926322A 1996-05-31 1997-05-26 Dispositif faisant partie de systemes d'alarme electronique qui generent des signaux de commande en vue de deplacer la frequence d'emission du systeme et d'eviter ainsi des perturbations Withdrawn EP0939942A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9602147A SE506610C2 (sv) 1996-05-31 1996-05-31 Anordning vid elektroniskt larmsystem vilket avger styrsignaler för att förskjuta systemets utsända frekvens och därmed undvika störningar
SE9602147 1996-05-31
PCT/SE1997/000861 WO1997045819A1 (fr) 1996-05-31 1997-05-26 Dispositif faisant partie de systemes d'alarme electronique qui generent des signaux de commande en vue de deplacer la frequence d'emission du systeme et d'eviter ainsi des perturbations

Publications (1)

Publication Number Publication Date
EP0939942A1 true EP0939942A1 (fr) 1999-09-08

Family

ID=20402818

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97926322A Withdrawn EP0939942A1 (fr) 1996-05-31 1997-05-26 Dispositif faisant partie de systemes d'alarme electronique qui generent des signaux de commande en vue de deplacer la frequence d'emission du systeme et d'eviter ainsi des perturbations

Country Status (6)

Country Link
EP (1) EP0939942A1 (fr)
JP (1) JP2000511310A (fr)
AU (1) AU3111197A (fr)
CA (1) CA2256375A1 (fr)
SE (1) SE506610C2 (fr)
WO (1) WO1997045819A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2012202729B2 (en) * 2005-03-07 2015-04-09 Sensormatic Electronics Llc Adaptively transmitting a signal for activating a tag
CA2600445C (fr) 2005-03-07 2015-07-07 Sensormatic Electronics Corporation Transmission adaptative d'un signal pour l'activation d'une etiquette

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4667185A (en) * 1985-12-06 1987-05-19 Minnesota Mining And Manufacturing Company Wireless synchronization system for electronic article surveillance system
US5371490A (en) * 1989-03-22 1994-12-06 Actron Entwicklungs Ag System for electronic safeguarding against burglary using multiple transmitters and receivers
US5023600A (en) * 1990-04-10 1991-06-11 Sensormatic Electronics Corporation Electronic article surveillance system with adaptiveness for synchronization with companion systems

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9745819A1 *

Also Published As

Publication number Publication date
CA2256375A1 (fr) 1997-12-04
JP2000511310A (ja) 2000-08-29
AU3111197A (en) 1998-01-05
WO1997045819A1 (fr) 1997-12-04
SE9602147D0 (sv) 1996-05-31
SE9602147L (sv) 1997-12-01
SE506610C2 (sv) 1998-01-19

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