NL8304413A - Detection system protecting goods in shop from theft - uses two passive signals indicating passage through EM field and active signal also indicating unauthorised removal and discharged battery - Google Patents

Abstract

The detection system reacts in two different ways to the passage of an object through its electromagnetic field. Firstly, it produces a passive feedback message. Secondly, it responds in an active way by sending a second signal, pref. electromagnetic. The second signal is activated by the electromagnetic field from the system and is detected by a second receiver. An alarm is triggered by both this receiver and by the first detection arrangement. The second signal is also emitted if the detection system is interfered with by attempting to remove the detector from the goods being protected. The second signal is further emitted when the battery needs recharging. In this state optical and acoustic signals are also produced to alert the user.

Description

N.V. Ned. Nedap equipment factory in Groenlo.

The invention relates to a detection device, in particular a detection device to be used in conjunction with and in addition to electromagnetic detection systems, such as, for example, used to detect and prevent shoplifters. This particularly refers to anti-shoplifting systems as described in applicants NL. U.S. Nos. 7513348 and 7712500 / and in U.S. Patents 3/500/373 and 3/967/161.

Said anti-shoplifting systems are based on a cheaply to be manufactured detection plate or wafer, provided with a vibration circuit / consisting of a capacitor and a coil. The aim is always to use the detection plate in large quantities for securing clothing, etc. Because of the large numbers of plates that usually serve to secure an essential part of the goods stock in a department store, and because of the relationship between wafer and costs. to protect properly, the price of such a detection plate must be relatively low. The detection plate must therefore be of simple construction, which imposes limitations on both the electrical operation and the mechanical mounting options. The limitation in the electrical operation is expressed in that the detection plate can only emit a relatively weak and little specific signal. The result is a less good ratio between detection probability and false alarm probability. Interference signals can affect operation, so protections must be built into the system to prevent false alarms. The result of this is again that these systems have a detection probability below 100%, that is to say that goods with a detection plate can go out unnoticed without causing an alarm through the secured passage.

8304413 - · 9 \ - 2 - · -Also, such a detection plate is deliberately removed from a good by a thief, for example by forcing the lock, in order to be able to walk out with the merchandise without risk.

5 However, these risk factors are inherent in the use of a current generation anti-theft system. However, department stores that use such an anti-shoplifting system often also have departments where the more expensive items, such as fur, leather, etc. are sold. ; 10 People would like to provide extra security. Methods such as closed display cases and chains are experienced as laborious and not very friendly to the customer, since the goods cannot be viewed and fitted freely.

A partial solution to this problem has already been given in applicants NL. O.A. 7901218. This concerns a detection member, which contains a resonant circuit as in the usual detection plates for anti-theft theft systems, and which additionally has an electronic siren with a battery and an alarm lock built therein. The special thing about that alarm wafer is that the electronic siren gives an alarm, in case unauthorized persons try to open or sabotage the lock. The present invention, however, relates to a detection device which can activate an alarm remotely, for example via radio-graphic way. To this end, the detection member, also referred to as the universal alarm wafer, is provided with a low-power radio transmitter which can transmit an encoded signal.

The emission of the alarm signal can be started in three ways, viz .: 1) By activation via the resonant wafer coil, when passing through the passage of the originally present electromagnetic detection system. Thereby energy from the transmission field is absorbed in the passage and used to activate the transmitter present in the universal alarm wafer. Since energy from a * 8304413 - 3 - - - built-in battery is used when emitting the alarm signal, it will be clear to the skilled person that this enables a much greater sensitivity and thus a much higher chance of detection in the passage, than just the passive tuned coil. However, the in-5 built-in coil produces a field disturbance, so that this universal alarm wafer also reacts normally as a normal wafer in the passage, so without a battery-powered signal. Thus, the universal alarm wafer can actually be detected twice in the passage.

10 The resonant frequency of the passive circuit must of course be adapted to the system in which it is used.

2) By activation via the anti-tamper contact in the alarm lot as described in applicant NL mentioned above.

15 O.A. 7901218.

3) By activation via a built-in circuit, which detects a low battery voltage.

These three mentioned modes of activation, hereinafter also referred to as alarm causes, can be distinguished on the receiving side by modulating the alarm signal in such a way that three different codes are generated.

The alarm signal must be received in an appropriate receiving device. The distance to be bridged can vary, for example, between one and thirty meters. The receiver will receive not only the alarm signal from the universal alarm wafer to the receiving antenna, but also interference signals, such as external radio signals and interference pulses, from the electricity network. Without additional measures, these signals can cause false alarms. The universal alarm wafer must therefore emit such a specific signal that the receiver can detect this signal in an unambiguous and secure manner, without false alarms occurring.

A common solution is to provide the signal to be detected with a characteristic modulation, 8304413 m -4--. -----.

for example, the impulse that arises in a field-disturbance anti-shoplifting system when the frequency of a transmitting electromagnetic field passes the resonant frequency of the wafer. Another possibility is to use the modulation 5 which is already present in the transmit signal and which is converted by the detection element into a similar modulation on the returned signal. The transmitter side determines the times at which the pulses occur, or the phase of the signal that forms the modulation. As a result, a reference signal can be obtained from the transmitter, by means of which the received and demodulated signal, further referred to as identification signal, is detected in a synchronous detection circuit, time or phase synchronous. Figure 1 shows this principle in a block-15 scheme. Block 1 is the transmitter part of the detection system, with block 3 as the high-frequency and modulation part.

Block 2 is the source of the signal with which the transmit signal is modulated. This modulation can be, for example: broadband FM ("wobbling"), such as is used in the field disturbance detection systems; narrow band FM; or amplitude modulation.

Detector 5 receives the transmit signal and transmits its own signal further to receiver 7. This signal from the detector contains information from the modulation of the transmitter signal (the pulse when the wafer resonance frequency passes through the current frequency of the transmitter signal in the field disturbance systems; the original modulation in the other systems). The modulation on the signal from the detecting member is recovered in the demodulation circuit in block 8 and then compared as an identification signal in synchronous detector 9 with a reference signal, which is involved in the transmitter via interconnection 11. The invention is based on an independently operating transmitter in the detection member, so that a fixed connection for the reference signal is not possible.

8304413 -5-- -.-.-

Therefore, part of the invention is the principle of transmitting the reference signal in the transmitting signal of the detection member. This can be done by modulating the reference signal on the transmission signal in such a way that this modulation is completely independent of the modulation of the identification signal. Accordingly, the receiver should include two independent demodulators: one for the identification signal and one for the reference signal. In a subsequent synchronous detection circuit, both demodulated signals are compared with each other. Another solution for transmitting the reference signal is to use the carrier as a reference signal. For this purpose, the source for the identification signal consists of a frequency divider, which divides the carrier frequency by a fixed number N. This sub-process has now created a link between the reference signal (carrier wave) and the identification signal. In the receiver, the carrier frequency of the received signal, originating from the detection element, is again divided by a divider circuit by the same number N, so that a derived reference signal is now formed with the same frequency as that of the identification signal. This identification signal is recovered by demodulation. Detection then takes place in the next synchronous detection circuit, where the identification signal is compared with the derived reference signal.

Figure 2 shows the block diagram of the invention. Herein block 2 in the first solution is the source, which modulates the transmitter part 3 in two ways (the reference signal 30 via connection 11).

In the second solution, block 2 mainly consists of a frequency divider with dividend N, which receives the carrier wave signal via connection 11 and modulates transmitter part 3 with the output signal of the divider.

In the receiver, block 8 in the first solution contains two demodulators, which respectively recover the identification signal and the reference signal from the received 8304413 t * 'τ 6 τ ·. ··· ·: ..

signal from the detector. In the second solution, block 8 includes a demodulator for obtaining the identification signal and a frequency divider with dividend N for generating the derived reference signal from the received signal by dividing the carrier in frequency. Block 9 contains the synchronous detector in both solutions, while alarm member 10 gives an acoustic or optical alarm.

The further; describe circuit is an example of the second solution. Figure 3 shows the schematic diagram of this detector, the universal alarm wafer. With the aid of oscillator 21 a high-frequency signal is generated with a frequency of, for example, 3 MHz.

A transmit antenna 15 consisting of capacitor 23, air coil 24 and capacitor 25 is driven via amplifier / buffer circuit 22. If desired, an electrical antenna 26 can be added, which consists of a plate of conductive material or of a loose piece of wire, and which is intended to generate an electric high-frequency field.n.

The coil 24 generates a high-frequency magnetic field.

The high-frequency signal from 22 also controls the divider 27, which divides the frequency by a number Nj.

Nj_ is chosen such that the output signal has a relatively low frequency; for example, Nj = 25 * 0, where the frequency of the signal at the divider's output is 2.93 KHz at an oscillator frequency of 3 MHz. The circuits 21, 22 and 27 can be combined in a standard integrated circuit, for example the HEF 4060. The low-frequency signal from divider 27, which has the form of a square wave, is converted into a triangular signal in the low-pass filter 28. Control and encoding circuit 29 transmits this triangular signal via a switch to the modulation input 30 of oscillator 21. The generated oscillator signal is hereby modulated in frequency.

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Thus, a transmit signal has now been obtained, which is modulated in frequency 8304413 with a signal, the frequency of which is derived from the transmit frequency by division by Nj. This coupling between transmission frequency and modulation frequency offers the possibility of applying synchronous detection on the receive side to the demodulated signal, in which a reference signal is derived from the received transmission signal, by dividing that transmission signal also by N]. . In this way, reliable detection is possible, in which, even in the presence of 10 interference signals, the chance of false alarms is minimal.

The control and coding circuit 29 switches the transmitter circuit on and off on behalf of the three activation circuits, n.1. the wafer circuit 33, the alarm lock 32, and the battery 34. 29 also encodes the alarm signal to be transmitted by periodically switching the frequency modulation on and off and / or periodically switching the 3 MHz oscillator on and off, depending on of the. activation. The following coding is an example of implementation: 1) Alarm passage. The wafer circuit receives a transmission signal from the passage. Code: The carrier wave and the modulation are switched on continuously.

2) Tamper alarm. The contact in the alarm lock closes. The code is then transmitted: 3 MHz oscillator (carrier) continuously on and the frequency modulation is switched on and off with a duty cycle of 50%.

3) The voltage of battery 34 drops below the minimum allowable level. That is detected in circuit 29 and this does both the carrier wave and the modulation with a low duty cycle. At the same time, an LED 35 flashes with it, which is mounted in the housing of the universal alarm wafer. This LED makes it possible to quickly find the one between the collection of wafers, which contains an exhausted battery. Another way of encoding is possible by making the frequency 35 of the signal with which the oscillator 21 is modulated in frequency dependent on the activation. The number N must then become variable 8304413 - 8 - .. ·. . - gemaakt ^ made. See figure 4. A simple solution is possible with the CMOS circuit HEF 4060 »which contains the circuits 21» 22 »27» 36 and 37.

As an example we take Nj 212 for the dividend and 5 for N2 and N3 2. At an oscillator frequency of 3 MHz, we then get modulation frequencies = 732 Hz, f2 »366 Hz and f3 = 183 Hz.

Control and encoding circuit 29 selects one of the "three frequencies in switching circuit. 38. Circuit 29 controls »10 as in the circuit of Figure 3, the oscillator and an LED for the battery indication, and is controlled by the alarm lock 32 or wafer circuit 33 and it also controls the voltage of battery 34.

In a third form of coding, a combination of the above methods is used. For example, with pass-through and tamper alarm, two different modulation frequencies are selected, for example, 732 Hz and 183 Hz, and with battery alarm, the carrier wave and modulation are pulsed enabled, as in the first method. Figure 5 shows the associated block diagram.

The receiver

The basic principle of the receiver is given in Figure 6. In this amplifier 51 amplifies the alarm signal received from the receiving antenna 50 with carrier frequency 25 q q. In circuit 52, that signal is limited and then applied to the FM demodulator 53 and the divider 54.

In 53, the signal of frequency f j (the identification signal) is recovered, with which the oscillator in the α-arm wafer was originally frequency-modulated.

Divider 54 divides the frequency of the received signal (carrier) by N, so that its output signal, which serves as a derived reference signal for the synchronous detector 55, has the frequency fo: Ni. If the frequency £ \ and the frequency fo: Nj are the same, which is the case with an alarm signal from the universal alarm wafer 8304413 «- 9 -. - # «xs (provided that the dividend is also Nj ^), then alarm 57 is activated. The interleaved integrator 56 thereby suppresses alarms due to interference pulses.

The receiver can be made selective for the coded alarms with individually identifiable alarm causes by: le In the first encoding method (switched modulation), place a circuit behind the integrator circuit 56, which selects according to the duty cycle of the received identification signal; 2nd In the second coding method (frequency of the i-dentification signal), the divisor of divider 54 can be set: 3rd In the third method, a combination of the above 15 solutions.

8304413

Claims (10)

A detection member, to be used in conjunction with an electromagnetic detection system, for example against shoplifting, characterized in that this member 5 reacts in two different ways to the passage through the electromagnetic field of the detection system. 1.. - firstly by giving the direct, passive feedback which is usual for the electromagnetic detection system, and - secondly by actively transmitting an additional signal, different from the one referred to above, for example also electromagnetic, which - 15 th signal is activated by the electromagnetic field of the electromagnetic detection system, and which last signal is an additional receiver can be detected such that. both via the first electromagnetic detection system and via the additional receiving device an alarm can be given with a significantly increased chance of detection of the passage of the detection member through the electromagnetic field of the detection system. A detection device according to claim 1, characterized in that the second signal is also emitted upon unauthorized removal of the detection device from the object to be protected, such that this second signal can be detected again in a suitable receiving device in order to obtain an alarm at an unauthorized removal of the detection device. A detection device according to claims 1 and 2, characterized in that the second signal is also emitted when the built-in power source required for this second signal, e.g. a dry battery, is almost exhausted, such that this second signal can be detected in a proprietary receiver to obtain a signal for depletion of the power source in one of the present detecting means. A detecting member according to claim 3, characterized in that the almost exhausted state of the power source not only causes a second signal to be emitted, but also activates an acoustic or light signal on the detector itself, such that in a collection of detection organs, in which already dmv the second signal has been signaled that there is in this case an instance with an almost exhausted power source, it is indicated which instance contains an almost exhausted power source. A detection device according to claims 1 to 4, characterized in that the second signal can again occur in itself in 15 forms which can be distinguished from each other, any form specific to the associated cause, viz. - passage through the passage of the electromagnetic detection device, - unauthorized removal of the detection device 20 from the object to be protected, - depletion of the built-in power source, such that the cause of the alarm can be distinguished via one or more appropriate receiving devices. 6. A detection element according to claim 5, characterized in that the cause distinction of the second signal is applied by causing a different transmission frequency to be generated for the second signal, per cause. A detection device according to claims 1 to 4, characterized in that the second signal contains a modulation such that an identification signal and a reference signal are emitted simultaneously and independently of each other, such that the second signal is so specific. , that a suitable receiver, who is dmv the modulation of the received second signal and phase-35 sensitive comparison of the recovered identification signal with the recovered reference signal, 8304413 * - 12 -. · .·· (h V * unambiguous and sure that second signal can detect 'in the presence of external interfering signals and therefore! Trigger a reliable alarm. 8. A detection device according to claim 7, characterized in that the carrier wave of the second signal forms the reference signal, which additionally comprises the identification signal by means of frequency division is derived from the carrier, and that this identification signal is modulated in frequency, phase, or amplitude on the carrier. 9. A detection device according to claims 5 and 8, characterized in that the cause distinction of the second signal is made by the magnitude of the part of the frequency division, with which the identification signal is derived from the carrier wave, can be selected differently for each cause, such that it can be determined in one or more appropriate receivers, that an alarm occurs and then the cause of that alarm can be indicated, or that only 20 signals the receiver intended for the particular alarm cause, with exception from other recipients. A detection element according to claims 5 and 8, characterized in that the cause distinction of the second signal is applied by switching the identification signal 25 on and off in one or more rhythms or not, whether or not combined with the switching the carrier on and off in one or more rhythms, whether or not in combination with varying the carrier frequency in one or more rhythms, such that it is possible to determine in one or more appropriate receivers that an alarm occurs, and then the cause of that alarm can be indicated, respectively, which signals only the receiver intended for the particular cause of the alarm, with the exception of other receivers. 8304413