Electronic protection system,resonant circuit and method of passivating such resonant circuit

PATENT DESCRIPTION

150 494

REPUBLIC

POLAND

<img file="PL150494B1_D0001.tif" />

OFFICE

PATENT

Polish

Additional patent to patent no. Application: 84 07 27 / P. 248965 /

Priority -—

READING ROOM

AT^?* Patent Order * «►&gt; -» ·· ti iwn ,.

Int. Cl.^s G08B 13/24

The application was announced: 86 Ol 28

Patent description published: 1990 09 28

The inventor: George Jay Lichtblau

Patent holder: George Jay Lichtblau, Ridgefield / USA /

ELECTRONIC SECURITY SYSTEM

The subject of the invention is an electronic security system. Electronic security systems are known for detecting the removal of items from the supervised area without authorization. Such systems are used in particular in retail stores to protect items from shop theft and in libraries to prevent books from being stolen. Such electronic systems protection devices usually have an electromagnetic field, triggered in a controlled area through which articles must be moved when leaving protected premises · Objects have a marker resonance system attached to them and the presence of this marker system in the controlled area is tracked by the receiving system to notify about the removal of the article without authorization. The marker system is removed by authorized personnel from the article leaving the premises in a proper manner to pass this article through the controlled area without triggering an alarm ·

Another electronic security system is described in U.S. Patent No. 3,810 147, by the same author as the present invention, which uses a resonance system having two separate frequencies, one for detection and the other for passivation. In the passivation circuit a small flammable connector and a second capacitor are used to provide a separate resonant frequency of passivation.

The resonance system may have a resonant frequency which is within a certain range depending on manufacturing tolerances. The frequency of passivation is a constant value, so the resonance system cannot be tuned exactly to this fixed frequency of passivation. The series impedance with the inductive element and capacitor at the intended frequency of passivation must be as low as possible in order to allow the largest current to flow through the fusible switch to cause burn through the connector · So,

150 494

150 494 the capacitor capacity should be as large as possible * and the inductance of the induction element should be as small as possible · In the current design, the inductive element is made as a single coil * e the capacitor is created by the electrodes as large as possible * in accordance with the economic and physical constraints for the given marking system · Increasing the capacitor size increases the cost of 1 size of the entire resonance system ·

The purpose of the invention is to construct an electronic security system without the disadvantages of known systems * having a simple structure * very high sensitivity and small dimensions · The goal of the invention was achieved by constructing an electronic security system for detecting the resonance system * which is characterized by * that the passivation system activated by presence detection the resonance system includes a device for generating an electromagnetic field at a frequency 1 intensity to create an arc between the capacitor plates * suitable for creating in the dielectric material a lower resistance path with at least some predetermined sections to destroy the resonant properties of the resonance system * where the electromagnetic field generating device includes a voltage controlled oscillator supplying the antenna tracking the resonant system * converter analog-to-digital attached to antenna 1 providing digital representations of values current flowing in the antenna * electronic sensor system for indicating digital representations * electronic oscillator control circuit for step changes in the set frequency range for field generation, and electronic sensor system for determining the digital value corresponding to the resonant frequency of the resonant system and causing the passive system to be switched has passive components that cause a short circuit between the electrodes condenser * with elements of the passive system causing evaporation of the conductive areas of the resonance system to destroy its resonant properties ·

Preferably, the electronic security system includes means for indicating the presence of the resonant system being detected and elements for indicating the passivation of the resonant system resonance properties. Preferably, the passive system comprises a device for detecting an arc discharge between the capacitor electrodes of the resonance system and for providing a signal representing this detection and elements switched on in response to this signal to determine the period during which passive components work ·

The subject of the invention is shown in the embodiment in Fig. * In which Fig. 1 shows the electronic protection system according to the invention * in the block diagram * Fig. 2 - an electronic device for determining the resonant frequency of the resonant system passivated, fig. 3 and 4 - useful graphs for explaining the operation of the device in fig. 2 * fig. 5 - block diagram of the electronic passivation device * providing passivating energy in a controlled period. Fig. 1 shows a device for the passivation of resonant properties of marker systems · This device has an antenna 1 * tracking the presence of the marker resonance system 2 and attached to the system 3 tracking markers * which provides an output signal to the indicator 4 of the presence of markers 1 indicator 5 of the passivation of markers. The marker tracking system 3 also provides a control signal to the 6 marker passivation system * which has antenna 7. The passivating system of markers can also be manually activated by means of manual control 8. After detecting the presence of the resonance system 2 *, the tracer tracking system 3 activates the passivation system 6 * causing the antenna 7 to radiate energy at the resonant frequency of the marker system and with a power level sufficient to cause an electrical break at the breakdown point of the marker system and to create an electric arc. dual frequency * passivation system provides energy with the passivation frequency of this marker · Indicators of presence and passivation of the marker 4 and 5 may provide visual or other indications ·

If the designator system is a single resonance system * the designator tracking system 3 determines the resonant frequency of a given tracer 2 and provides the passive system 6 with a control signal representative of the measured resonant frequency of the designator. In response to the control signal, the passivating system 6 produces radiation at this resonant frequency and causes this radiation to be fed to the marker system in order to destroy the resonance properties of this system. The marker tracking system 3 may include a device for determining the approximate resonance frequency of the system

150 494 tracer · Voltage controlled oscillator 9 powers the antenna 1 tracking the mark !, with the oscillator 9 jaat controlled by the microprocessor output signal via a digital-to-analog converter 10 frequencies · Antenna signal is fed to the analog-to-digital converter 10, whose output digital signal is fed to the microprocessor storing such digital signals.Alternatively, after detecting the marker resonant system 2, the marker tracking system 3 may cause the passive circuit 5 to supply antenna 7 with a relatively high power signal, whose frequency is slowly changed passing through the resonant frequency of the marker · The device can be adapted to alternately track the presence of the marker and switch on the passive field in a cyclic way until the marker is passivated · Here, the operator can be notified by means of appropriate signaling if the marker is not passivation ·

When a two-frequency marker system is used, the marker tracking system 3 is adapted to detect the resonant frequency of the marker detection, while passivation system 6 is adapted to supply energy at the resonant frequency of the marker passivation. A device suitable for passivation and tracking of two-frequency markers is described in US Patent No. 3,938,044. The marker tracking system 3 may include the device for determining approximate resonant frequency of the marker system · The voltage controlled oscillator 9 powers the tracking antenna 1 reference number, whereby the oscillator is controlled by the output signal of the microprocessor 11 via the digital-to-analog converter 10. The microprocessor stores digital values, which after conversion to the analog form by the converter 10 control the oscillator 9, causing a step change in frequency. The antenna signal is fed to the analog-to-digital converter 12, whose output digital signal is fed to the microprocessor 11, which stores such digital signals

Operation of the device of FIG. 2 will be explained in connection with the waveforms of FIGS. 3 and 4. The output signal of the voltage controlled oscillator 9 is shown in FIG. 3 and includes frequency jumps, with each jump occurring for the respective time interval or jump number. Fig. 4 shows the current flowing in antenna 1 as a function of time. In the absence of any resonance system, the current in the antenna decreases with increasing frequency in the oscillator, which is illustrated by the straight-line part of the waveform in Fig. 4. When there is a resonant system 2 near the antenna 1, the impedance of the resonance system is transferred to the antenna and causes a steep decrease in antenna current, as shown in Fig. 4. The current flowing through the antenna is converted to digital values ​​by the converter 12 and these digital values ​​are stored in the memory of the microprocessor 11. The stroke number corresponding to the minimum value among the stored current values ​​corresponds to the approximate resonance frequency of the marker system resonance system 2.

Passivation energy is supplied over a set period according to the time required for passivation of the marker. After passivation, the marker tracking system 3 tracks the presence of the marker and if the marker has been passivated, indicator 5 is energized to confirm that the passivation has occurred. If the tracer tracked by system 3 is still active at its resonance frequency, the passivation system 6 is switched back on to the next passivation cycle. The passivation cycle is repeated a number of times until passivation is carried out. If after a certain number of cycles passivation does not occur, the siren may be turned on to draw attention to the operator that the given marker has not been passivated. The operator can then manually activate the passivation system in order to passivate this marker or take other actions to passivate or destroy the marker.

The passivating system 6 can be controlled as shown in Fig. 5. Marker tracking system 3 provides a marker signal in response to a signal with an altered radio frequency passing through the resonant frequency of the marker system

150 494 this tag signal is fed to a high-pass filter 13 with a steep transition band · This filter 13 filters out the modulation components 1 essentially all components of the tag signal spectrum · When an arc is generated between the capacitor electrodes, a relatively large and sudden change in the velocity flowing in antenna 1 takes place this signal passes through the high-pass filter 13 to the threshold detector 14, which activates the timer. 15, determining the time interval, during which works a passive system of 6 markers · The work cycle can be repeated if it is necessary to passivate the resonant properties of the marker system ·