EP0242901A1 - Elektromagnetische Detektionsanlage mit Falschalarmunterdrückung - Google Patents

Elektromagnetische Detektionsanlage mit Falschalarmunterdrückung Download PDF

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Publication number
EP0242901A1
EP0242901A1 EP87200534A EP87200534A EP0242901A1 EP 0242901 A1 EP0242901 A1 EP 0242901A1 EP 87200534 A EP87200534 A EP 87200534A EP 87200534 A EP87200534 A EP 87200534A EP 0242901 A1 EP0242901 A1 EP 0242901A1
Authority
EP
European Patent Office
Prior art keywords
channel
detection system
pulse
responder
output
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.)
Granted
Application number
EP87200534A
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English (en)
French (fr)
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EP0242901B1 (de
Inventor
Tallienco Wieand Harm Fockens
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.)
Nederlandsche Apparatenfabriek NEDAP NV
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Nederlandsche Apparatenfabriek NEDAP NV
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Publication of EP0242901A1 publication Critical patent/EP0242901A1/de
Application granted granted Critical
Publication of EP0242901B1 publication Critical patent/EP0242901B1/de
Expired legal-status Critical Current

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    • 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
    • G08B13/2405—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 characterised by the tag technology used
    • G08B13/2414—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 characterised by the tag technology used using inductive tags
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
    • G08B29/18—Prevention or correction of operating errors
    • G08B29/20—Calibration, including self-calibrating arrangements
    • G08B29/24—Self-calibration, e.g. compensating for environmental drift or ageing of components

Definitions

  • This invention relates to an electromagnetic detection system which, by means of at least one transmission aerial coil, generates a sweeping-frequency interrogation field in a detection zone, which field can be disturbed by the presence in said zone of a responder equipped with a tuned circuit, there being provided detection means for detecting such disturbance and activating an alarm device.
  • Systems of this kind are known in various embodiments.
  • the disturbance takes place selectively, i.e. at a pre-determined frequency, or in a pre-determined frequency range, because the responder comprises a tuned circuit.
  • the field disturbance by a responder can be detected both by detecting the results of energy absorption by a responder at the transmission side of the system, and by detecting the signals sent out by a responder in reaction to the interrogation field, by means of a receiver.
  • the energy contents of the transmission circuit are modulated, which modulation can be detected by means of an envelope detector, which may consist of a simple diode.
  • This envelope detector produces a pulse in the form of the resonance curve of the tuned circuit of the responder. This form is known and the detected pulse can therefore be compared to the known form.
  • a pulse can be detected which has the form of the resonance curve.
  • the form of the detected pulse is also found back in the frequency spectrum contained in the pulse.
  • This frequency range has a lowest frequency f L and a highest frequency f ir . There are virtually no signal components above f H . In a practical system f L can be 2 kHz and f H 6 kHz.
  • Interference for example, noise from the system's own transceiver circuit, external radio signals, or crackling (caused by passing metal objects, such as perambulators) have a rather flat spectral distribution.
  • the receiver has a larger bandwidth than the responder pulse, e.g., a bandwidth of up to 25 kHz, frequencies of the spurious signals between 6 and 25 kHz are therefore also received.
  • spurious signals may in practice have the following cause.
  • the aerial coil may be placed in a, generally chromium-plated metallic tube which is electrically interrupted at one location.
  • This tube has both a mechanical carrier function and a screening function for electrical fields. As the tube is not hidden, it is possible to make electrical contact with the tube from the outside.
  • the tube By inductive coupling with the aerial coil; the tube carries a high-frequency voltage. Now, if the tube is touched by metallic articles, or human hands, a current will start to flow in it.
  • touching the screening tube only causes crackling interference in the frequency range of up to 6 kHz, i.e., only in the responder pulse band, and so may cause a false alarm.
  • an electromagnetic detection system of the kind described is characterized in that the detection means comprise aclanrelfor processing signals in a frequency band corresponding to the frequency band of a signal caused by a responder, and that a blanking circuit is connected to said channel for detecting the occurrence in said channel of signals exceeding a pre-determined threshold value, and, after detecting a first signal exceeding said threshold value, in response to one or more further signals exceeding said pre-determined threshold value, producing a blanking signal for a pre-determined time interval to prevent activation of said alarm device.
  • Fig. 1 shows, in line A,the variation of the frequency of the interrogation field of a sweeping-frequency detection system.
  • the frequency f of the interrogation field swings periodically relative to a frequency f r .
  • the frequency f may vary sinusoidally, as shown, but may also vary otherwise, e.g., in sawtooth form.
  • the frequency f corresponds to the resonant frequency of the responder.
  • the resonant frequency of the responder may be the average of the highest and lowest field frequency, as shown, but this is not strictly necessary.
  • Line B of Fig. 1 shows the moments when responder pulses occur.
  • the responder pulses occur at evey moment when the field frequency f passes the resonant frequency f r , provided indeed a responder is present in the interrogation field. Accordingly, in each sweep period of the field frequency a responder pulse occurs twice, and this at pre-determined points of time.
  • the responder pulses occur at intervals equal to half the period of the sweep frequency. In practice, as usual, a certain tolerance should be taken into account.
  • Line C in Fig. 1 shows these time slot pulses.
  • the time slot pulses are generated in the transmission section of the detection system and are high at the moments when responder pulses can be expected.
  • the time slot pulses open a responder pulse gating circuit at the times when the time slot pulses are high. This gating circuit then passes the responder pulses to the responder pulse detector.
  • Fig. 2 shows in a block diagram how this known technique is applied.
  • the high-frequency signal is rectified, whereafter the responder pulse is supplied to two parallel gates, namely, a responder pulse gate 2 and an interference gate 4.
  • the responder pulse gate 2 is opened by the time slot pulse p generated in the transmitter section. When no responder pulse is expected, the time slot pulse is low. The responder pulse gate 2 is then closed.
  • interference gate 4 is simultaneously switched open. Spurious signals can then be detected in interference detector 5, which subsequently blocks the responder pulse detector 3, if indeed a spurious signal is detected. During the reception of interference, therefore, this installation is completely blocked, and no alarm can be given.
  • the invention is predicated on the fact that the responder pulse itself occupies a limited period of time of the entire frequency sweep period, and that after the time interval of the first responder pulse a, generally longer, time interval follows in which a responder pulse is certain not to occur.
  • Fig. 3 shows a block diagram of an example of a circuit according to the invention forming part of an electromagnetic detection system.
  • Figs. 4 and 5 show associated time diagrams.
  • Fig. 3 shows diagrammatically the detection means of an electromagnetic detection system according to the invention.
  • a device 31 Connected to an aerial 30 is a device 31 which is capable of receiving signals caused by the presence of a responder.
  • the aerial 30 may be the same aerial as is used for generating the interrogation field or a separate aerial, depending on the fact whether the system works by the absorption principle or by the transmission principle.
  • the apparatus 31 may comprise means for eliminating so-called out-band signals, i.e., spurious signals having a frequency outside the sweep frequency band.
  • the apparatus 31 does not by itself form part of the invention, and will therefore not be described in any detail herein.
  • the output of apparatus 31 is connected to an amplifier 32 with automatic gain control (AGC).
  • AGC automatic gain control
  • the output signals of the amplifier consist of noise and of signals resulting from signals received by the detection means and having a frequency within the sweep frequency band.
  • the output signals from amplifier 32 are supplied to a discriminator filter device comprising two channels and serving to take so-called in-band spurious signals into account in actuating an alarm device.
  • the discriminator filter device comprises a low-freqency channel including a low-pass filter 33, an amplifier 34 and a diode detector or rectifier 35.
  • the low-frequency channel can process signals having a frequency between f L and fii, i.e., signals having a frequency corresponding to the frequency of responder pulse signals.
  • the cut-off frequency of the low-pass filter 33 may be at 6 kHz.
  • the discriminator filter device further comprises a high-frequency channel including a high-pass filter 36, an (adjustable) amplifier 37 and a diode detector or rectifier 38.
  • the high-frequency channel can process output signals from amplifier 32 having frequencies higher than f H .
  • the high-frequency channel can process (spurious) signals having frequencies of between 6 kHz and, e.g., 25 kHz.
  • the output of the low-frequency channel is connected to a positive input of a summator 39, and the output of the high-frequency channel is connected to a negative input of summator 39.
  • the output of summator 39 is in turn connected to an integrator 40.
  • an output signal from the high-frequency channel causes a decrease of the output signal from the integrator, whereas an output signal from the low-frequency channel causes an increase of the output signal from the integrator.
  • an (adjustable) AGC-detector 41 which controls the gain of the amplifier 32 in such a manner that the tops of the signal pulses at the output of amplifier 34 keep a substantially constant level.
  • Summator 39 is arranged so that the negative input is more sensitive than the positive input, so that, at rest, when the discriminator filter device only passes broad-band noise (2-25 kHz) the output signal from integrator 40 is low and no alarm signal can be given.
  • circuitry 12 will be elucidated with reference to Figs. 4 and 5.
  • a pulse detector 8 connected to the output of amplifier 34 in the responder pulse channel forms a pulse P 1 so long as the (negative) top of a responder pulse R (see Fig. 4, line 1) exceeds a pre-determined detection threshold D (line 2) recorded in pulse detector 8.
  • This pulse causes a timer pulse Pt (line 4) to start at the leading edge in a delay circuit 9 connected to pulse detector 8.
  • the trailing edge of pulse Pt activates a time slot generator 10, which generates a time slot pulse Pe (line 5).
  • the output of the time slot generator is connected to an input of an AND gating device 11.
  • the other input of the AND gating device 11 is connected to the output of pulse detector 8. Furthermore, the output of gating device 11 is connected to a negative input 14, which is separate in this example of the summator.
  • a pulse which passes gate 11 (blocking pulse Pb, see line 6; Fig. 5), does causes the integrator output to be immediately decreased to zero, independently of the other input voltages of a summator and thus blocking alarm signals.
  • Fig. 4 shows that responder pulses R do not give rise to blocking pulses in gate 11 (see line 6), while Fig. 5 shows that (pulse) interference S of an irregular pattern does cause blocking pulses Pb in gate 11, so that alarm signals are blocked.
  • Fig. 5 shows similarly to Fig. 4 signals occurring in the blanking circuitry, but now for the case that a spurious pulse signal S appears at the output of amplifier 34 and hence at the input of pulse detector 8.
  • a spurious pulse signal S appears at the output of amplifier 34 and hence at the input of pulse detector 8.
  • a responder pulse R such a signal will generally comprise a number of closely-spaced successive peaks, which with a correct selection of the detection threshold of pulse detector 8 will exceed this threshold, as indicated in Fig. 5 for the negative peaks S 1 -S 9 .
  • peak S 1 gives rise to an output pulse P 1 of the pulse detector 8, and the output pulse P 1 in turn causes a timer pulse Pt, which again results in a time slot pulse Pe.
  • Peak S 2 falls within the duration of pulse Pt and thus has no effect.
  • Peak S 3 falls within time slot pulse Pe and is thus, just as peaks S 4 , S 5' S 7 , S 8 and S 9 (in part), passed by gate 11 in the form of pulses Pb, Pb' and Pb" (see line 6 of Fig. 5).
  • the duration of pulses Pt i.e., the delay caused by delay circuitry 9, may be, e.g., 0.25 msec. This delay should be chosen so that any width of a responder pulse R which occurs in practice at the level of detection threshold D leads to a pulse P 1 which lasts no longer than Pt.
  • the time slot pulse Pe may, in a practical apparatus, last e.g. 2 msec.
  • the pulse detector may be arranged to react to positive peaks exceeding a positive pre-determined threshold.
  • pulse detector 8 could be combined with the delay device 9.
  • summator 39 and integrator 40 could be combined to form,a single integrator with a positive and a negative input and an additional negative input 14 or a reset input.
  • the normal negative input of the summator is more sensitive than the positive input, a good suppression of spurious signals can in certain situations also be obtained if the output of gate 11 is connected to the (normal) negative input of the summator.
  • the blanking circuit 12 can even be applied fully independently of the way in which signals in the frequency band associated with the frequency band of the responder pulses are obtained and further processed separately from the signals outside that band.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Electromagnetism (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Burglar Alarm Systems (AREA)
EP19870200534 1986-03-24 1987-03-24 Elektromagnetische Detektionsanlage mit Falschalarmunterdrückung Expired EP0242901B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL8600738A NL8600738A (nl) 1986-03-24 1986-03-24 Onderdrukking van valse alarmen als gevolg van aanraken.
NL8600738 1986-03-24

Publications (2)

Publication Number Publication Date
EP0242901A1 true EP0242901A1 (de) 1987-10-28
EP0242901B1 EP0242901B1 (de) 1990-12-12

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ID=19847757

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Application Number Title Priority Date Filing Date
EP19870200534 Expired EP0242901B1 (de) 1986-03-24 1987-03-24 Elektromagnetische Detektionsanlage mit Falschalarmunterdrückung

Country Status (3)

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EP (1) EP0242901B1 (de)
DE (1) DE3766644D1 (de)
NL (1) NL8600738A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0373716A3 (de) * 1988-12-10 1991-06-19 Id Systems International B.V. Sabotagesicherungsvorrichtung
FR2704960A1 (fr) * 1993-05-03 1994-11-10 Diet Jean Paul Dispositif de détection de passage d'étiquettes.

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103925521A (zh) 2005-12-21 2014-07-16 科锐公司 照明装置

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3110007A (en) * 1959-10-14 1963-11-05 Gen Signal Corp Ultrasonic vehicle detector
US3868669A (en) * 1973-04-13 1975-02-25 Knogo Corp Reduction of false alarms in electronic theft detection systems
FR2384306A1 (fr) * 1977-03-14 1978-10-13 Lichtblau George Circuit d'elimination de frequences de battement pour dispositifs electroniques de securite
WO1983001331A1 (en) * 1981-10-08 1983-04-14 I D Engineering Inc Electronic security system with noise rejection
EP0100128A1 (de) * 1982-07-21 1984-02-08 N.V. Nederlandsche Apparatenfabriek NEDAP Absorbierungsdetektoranlage

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3110007A (en) * 1959-10-14 1963-11-05 Gen Signal Corp Ultrasonic vehicle detector
US3868669A (en) * 1973-04-13 1975-02-25 Knogo Corp Reduction of false alarms in electronic theft detection systems
FR2384306A1 (fr) * 1977-03-14 1978-10-13 Lichtblau George Circuit d'elimination de frequences de battement pour dispositifs electroniques de securite
WO1983001331A1 (en) * 1981-10-08 1983-04-14 I D Engineering Inc Electronic security system with noise rejection
EP0100128A1 (de) * 1982-07-21 1984-02-08 N.V. Nederlandsche Apparatenfabriek NEDAP Absorbierungsdetektoranlage

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0373716A3 (de) * 1988-12-10 1991-06-19 Id Systems International B.V. Sabotagesicherungsvorrichtung
FR2704960A1 (fr) * 1993-05-03 1994-11-10 Diet Jean Paul Dispositif de détection de passage d'étiquettes.

Also Published As

Publication number Publication date
NL8600738A (nl) 1987-10-16
EP0242901B1 (de) 1990-12-12
DE3766644D1 (de) 1991-01-24

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