GB2026219A - Security glazing alarm system - Google Patents

Abstract

A security glazing alarm system comprising a glazing panel VR, preferably a laminate, having at least one conductor, e.g. a uniform coating, extending across a major face thereof and connected to electrical circuit means (C2) arranged to deliver an electric pulse signal when the resistance of said conductor(s) changes and to pass such signal to an alarm circuit, preferably via an amplifier A, in order to activate a warning device WD. <IMAGE>

Description

SPECIFICATION Security glazing alarm system This invention relates to a security glazing alarm system.

Various security alarm glazing systems are well known. In one previous proposal which has been widely used, a conductive strip, for example a thin aluminium or lead foil adheres around the margin of the glazing unit, and the two ends of the strip are connected into an alarm circuit. When the strip is broken, an alarm is given, but the alarm system cannot then be reset without replacing the conductive strip and this generally involves replacement of the entire glazing unit. Such replacement is especially inconvenient during a holiday period.

Another disadvantage is that the strip must be broken, and this implies that any crack in the window must propagate to its edge. However this is not of itself sufficient. The broken ends of the strip must also separate.

Considering a glazing consisting of a single sheet of glass; if the glass is thermally tempered, there is a high probability that any crack will propagate to the edge, and because of the large number of fracture lines which are typical on breaking thermally tempered glass, it is also highly probable that a marginal conductive strip will be broken and that its broken ends will separate; in the case of an untempered sheet, it is by no means certain that any cracks will propagate to the edge of the sheet; in the case of a chemically tempered sheet, there is a high probability that cracks will propagate to its edge, but it is not so certain that a marginal conductive strip will both be broken and separated.When one of the above three types of glass sheet is incorporated in a laminated pane, as is preferred for added resistance to unauthorised entry, it is less certain that an alarm will be given, because the fragments of the broken glass sheet will be held together.

In one actual incident, a shot was fired at a laminated security glazing having such a marginal conductive strip adherent to a chemically tempered glass sheet, and although the area around the impact point was crazed, the cracks did not propagate to the edges of the sheet and the alarm was not set off.

A further disadvantage of this prior proposal is that it is not readily applicable to ordinary glass sheets orto plastics glazing sheets.

It is an object of the present invention to provide a security alarm glazing system which is more versatile.

According to the present invention there is provided a security alarm system including a glazing panel comprising at least one sheet of glazing material which carries at least one conductor extend ing across a major face thereof, characterised in that said conductor(s) is or are connected to electrical circuit means arranged to deliver an electric pulse signal when the resistance of said conductor(s) changes and to pass such signal to an alarm circuit.

It will be noted that it is not necessary for the or a said conductor to be broken before the electric signal is delivered, provided that its resistance is modified, though of course the circuit would react if the conductor or all of them were broken so that the resistance became substantially infinite. The security alarm glazing system is thus more versatile than the previous proposal outlined above, in that it does not require the glazing material to be thermally tempered glass for reliable operation.

Preferably, said circuit means is arranged to deliver a said pulse signal only when the rate of change of the resistance of said conductor(s) exceeds a predetermined value.

The reason for setting a threshold rate for resistance change is that the glazing panel may for example be installed in a jewelry store window where it may be subjected to marked temperature changes as between day and night and also during the course of a year, and this can often have a noticeable effect on the resistance of the conductor(s). The threshold rate can be set to take account of this so that the electrical circuit will not deliver any spurious alarm signals due to natural temperature changes.

For example when a said conductor is constituted by a tin oxide coating, the resistance thereof may alter at a rate of 1% per 6 hours due to diurnal temperature variations. It is undesirable to deliver a pulse signal to an alarm circuit when the conductor resistance changes for this reason, and indeed it would add to the expense of the system to construct a circuit which had the sensitivity to do so.On the other hand, if the glazing panel were to be attacked with a cutting torch, its resistance might alter at a rate of 1% per 5 minutes, and it would clearly be desirable to give an alarm signal in response to changes in the resistance which take place at that rate. Accordingly the threshold rate may be set at any desired value e.g. 1% per 10 minutes or 1% per hour, bearing in mind that the more sensitive the system is to slow changes the more expensive it is likely to be.

Preferably, said alarm circuit is arranged to deliver an alarm signal only in response to a change in said resistance which is greater than 0.05% of its initial value.

Advantageously said circuit means is responsive to successive modifications of the resistance of said conductor(s). Particular importance is attached to this feature. It sometimes happens that a burglar will make an attack on, say, a jewelry store window on a Saturday night or at the start of a holiday period with the aim of actuating the alarm system and in the knowledge that it will not be possible to replace the window until the next working day, so that there will be at least one night during which the alarm system for that window will be inoperable thus giving an opportunity for a burglary to be carried out via that window without the alarm being reactivated. The adoption of this feature enables this disadvantage to be overcome, since further modification to the resistance of said conductor(s) caused by such a successive attack can give rise to an alarm signal.

Preferably circuit means is provided which is adapted to supply DC potential across said conductor(s) and capacitor means is provided to deliver a said pulse signal in response to changes in such potential. This potential variation may be due to damage to the conductor(s), orto an attempt by a burglar to by-pass the conductor(s) using a jumplead.

The pulse signal from such a capacitor is suitably fed to an operational amplifier where it is amplified so that it can be used to trigger an alarm circuit.

In order that the panel may be effective as an alarm it is of course necessary that the resistance of the conductor(s) should be modified, and to ensure that this will happen when the panel is physically attacked, it is preferred that said conductor(s) should effectively cover substantially the whole area of the panel. For example the conductor may be a single thin wire or strip extending in zig-zag manner across the panel, or it may be a plurality of e.g. parallel wires or strips interconnecting bus bars at opposite margins of the panel which are in turn connected to said electrical circuit means. A wire spacing of say 1 to 5 cm effectively gives cover of substantially the whole area of the panel.

Preferably however said conductor is a transparent electrically conductive coating applied to substantially the whole of a major sheet face of the panel. Such a coating may for example be a transparent coating of a metal, e.g. gold, silver, copper or aluminium. Suitable thicknesses for such metal coatings usually lie in the range 50 to 500 .

A gold coating of 100 - 200 in thickness is very suitable. Such a coating eliminates the possibility that a small hole can be cut in the panel between separate conductors such as wires.

Advantageously, said transparent electrically conductive coating is a metal oxide coating. Among metal oxides which are suitable may be cited indium oxide, and tin oxide which is particularly advantageous in view of its abrasion resistance. Metal oxide coatings can be deposited in such a way that they are substantially indetectable by the naked eye which is an advantage in some circumstances.

Such an oxide coating may for example be 1200 A to 12000 in thickness, preferably between 7000 and 10000 A in thickness.

Preferably, a said metal oxide coating includes a doping agent since this enables convenient resistivity values to be achieved. Such doping agent may for example comprise chlorine and/orfluorine ions.

Antimony, arsenic, cadmium and tellurium have also been used as doping agents.

A said metal oxide coating may be applied to a sheet of glass in any convenient manner. For example a fluorine doped tin oxide coating can be obtained by the thermal decomposition of SnCl4 and NH4F.HF or a chlorine doped coating of indium oxide can be obtained by pyrolysis of InCI3.

Asaid conductive coating preferably extends between two metallised strips deposited along opposite margins of said major sheet face. Such metallised strips, which may conveniently be of copper, may be deposited on top of or beneath the conductive coating, and serve to permit the establishment of a uniform current flow across substantially the whole of the sheet while they themselves can be concealed in a frameforthe panel.

Preferably said sheet of glazing material which carries the conductor(s) is a sheet of glass.

Advantageously said panel is a laminate comprising at least two sheets of glass bonded together using one or more intervening layers of adhesive material such as polyvinyl butyral.

In the case of a laminate it is preferred that the sheet which carries the conductor(s) should form an outer face of the panel, and it is preferred that the conductor(s) should be located between the outer sheets of the panel so that it is or they are protected from accidentai damage such as scratching or deterioration due to weathering.

When using a laminated (or indeed any multisheet) glazing panel, it is desirable to orient the panel so that the sheet bearing the conductor(s) is as close as possible to the side which is most likely to be attacked, that is, to the outside of a jewelry store window, bank teller cage or display case and to the inside of a detention cell.

Advantageously the panel comprises at least one glass sheet which has been tempered, preferably chemically tempered in order to increase its resist anceto breaking and further to ensure that when it is cracked, such cracking will be-propagated over a greater area than would be the case if it were untempered, thus giving a greater chance of impairing any conductor carried by such a sheet.

Preferred embodiments of the invention will now be described with reference to the accompanying diagrammatic drawings in which: Figures 1 and 2 are plan views of two glazing panels for incorporation into a security alarm system according to the invention, Figure 3 is a cross section through a third such glazing panel, and Figure 4 illustrates an electrical circuit for use in conjunction with such a glazing unit to form a security alarm system according to the invention.

Figure 1 shows a glazing panel 1 comprising a first sheet to which has been applied a single conductor 2 connected between a pair of terminals 3, 4 located in one corner of the panel. The conductor 2 extends in zig zag manner across substantially the whole area of the panel 1. The first sheet is laminated to a adhesive material with the conductor 2 located between the sheets.

Figure 2 shows a glazing sheet 5 carrying bus bars 6,7 extending along opposite margins of one face.

The bus bars 6,7 are respectively provided with terminals 8, 9, and they are interconnected by a plurality of conductors 10. A second glazing sheet (not shown) is then laminated to the sheet 5 on top of the conductor system 6 to 10 to complete the panel.

Figure 3 illustrates a laminated glazing panel 11 comprising sheets 12,13, l4ofglasswhich are bonded together using intervening layers 15 of adhesive material. The upper glass sheet 12 carries a substantially uniform transparent conductive coating 17 on the face which is bonded to the adjacent layer 15 of plastics material. Bus bars 18,19 (which may be similar to the bus bars 6,7 of Figure 2) extend along opposite margins of the coated face of the sheet 12 and are respectively provided with terminals 20, 21 for connexion to an electrical alarm circuit.

The outer side of the lower glass sheet 14 bears an optional tinted coating 22 comprising oxides of iron, chromium and cobalt formed from a solution of the acetyl acetonates of those metals in dimethyl formamide. In a specific practical embodiment, this lower sheet 14 is of grey glass and the other two sheets 12, 13 are of colourless glass.

Such an alarm circuit is shown in Figure 4.

In Figure 4, a glazing panel VR (for example as described in any of Examples 1 to 12 hereinafter and/or as illustrated in one of Figures 1 to 3) variations in the resistance of which it is desired to monitor is connected to earth and to a D.C. potential source via a resistor R1. The resistor R1 may be a variable resistor so that the potential across the glazing panel can be altered if this is desired. In one arrangement, the resistor R1 is constituted by the conductor(s) of a second glazing panel installed for example in an adjacent window frame so that a single alarm circuit serves to monitor resistance changes in two conductive glazing panels.

A capacitor C1 serving as a high frequency noise filter is placed in parallel with the glazing panel VR, so that if the glazing panel should act as an aerial for broadcast radio signals, this will not give rise to spurious alarm signals.

The potential across the glazing panel VR is fed to a capacitor C2 which will accordingly emit a pulse signal when the resistance of the glazing panel VR varies, and the size of the pulse depending on the change in resistance. This pulse signal is fed via a resistor R2 to one input of an operational amplifier A whose other input is connected to earth via a resistor R3, and whose output is protected by a resistor R4. A capacitor C3 and resistor R5 in parallel with the amplifier A determine its gain.

Negative going pulses from the protected output of the amplifier A go to earth via a diode D1. Such negative going pulses will follow from an effective decrease in the resistance across the glazing panel VR and may be due to various causes. For example the resistance of a tin oxide coating decreases with increase in temperature, so that such reduction in resistance may be due to diurnal temperature variations or to an attack by a cutting torch. Another possible reason for a reduction in the effective resistance of the glazing panel VR would be an attempt by a burglarto short out the glazing panel in order to render the alarm ineffective.

If it is desired to give an alarm in response to a negative going pulse, then additional circuit means (not shown) can be connected to the diode D1 in a manner which is analogous to that which will now be described for the giving of an alarm for positive going output pulses.

Positive going output pulses from the amplifier A are passed to the base of a transistor T1 via a second diode D2 and to earth via a resistor R6. A capacitor C4 connected between the base of the transistor T1 and earth serves as a by-pass filter. The emitter of the transistor T1 is connected to earth via a trigger circuit for a thyristor Thl which trigger circuit comprises a resistor R7 and a capacitor C5.

The potential between the emitter of the transistor T1 and the resistor R7 and capacitor C5 is applied to the gate of a thyristor Th 1 which is thus arranged on increase of the resistance of the glazing panel VR to set off a multivibrator M1 comprising transistors T2, T3 and capacitors C6, C7 connected to the thyristor Thl by parallel resistors R8, R9, R10, Rl 1. The output of the multivibrator is passed to an amplifier comprising transistors T4 and T5 which generates the alarm signal as such powering a warning device WD which gives an audible and/or visible warning signal.

Alternatively, or in addition it may be arranged to give a radio warning signal for a remote receiver, or even to activate a camera to photograph the scene of the glazing panel.

Such a circuit can react to a change in the resistance of the conductive glazing panel VR of 0.3% within 10 milliseconds.

It will be appreciated that the electrical circuit above described is only one of many which may be used in a security glazing alarm system according to the present invention.

The use of a circuit such as the one described with reference to Figure 4 has the advantage that once the resistance of the conductive glazing panel VR has been modified from a first value to a second value so that the alarm is set off, the alarm can simply be reset by pressing a reset button RB whereupon the system will again be sensitive to changes in resistance from that second value to a third value.

Various examples of glazing panel for incorporation into an alarm system according to the invention (or example as described with reference to Figure 4) will now be described.

Example 1 (Figure 1} Athin stainless steel wire 2 having a total resistance of 10P was adhesively secured in zig-zag manner to the face of a glass sheet which was 4mm in thickness and has a face area of 60 cm by 90 cm.

The various runs of the wire across the major dimension of the sheet face were approximately 5 cm apart.

A second similar glass sheet was laminated on top of the wire on the first sheet using a layer of polyvinyl butyral 0.38mm in thickness to form the glazing panel.

In a variant, each glass sheet was tempered.

In a second variant, the panel 1 comprised only a single sheet.

In a third variant, the conductor 2 was applied to a transparent polycarbonate sheet 10mm in thickness.

Example2 (Figure 2) A glass sheet measuring 750mm x 400mm x 5mm was taken and a conductive grid comprising marginal busbars 6,7 which are interconnected by eleven conductive strips 10 as shown in Figure 2 was applied thereto by a serigraphic process.

The manufacturing technique was as follows: Firstly, a photo-sensitive composition was applied onto both faces of a "Nytal" (Trade Mark) screen marketed by Schweiz Seiten Gaze Fabrik, CH 9424 Thal St. Gallen, Switzerland. It is equally suitable to use a polyester screen of type 110D manufactured by the same firm.

The photo-sensitive composition was "Tamisol Red" marketed by Publivenor, 87-91 rue de l'Eglise St. Pierre, 1090 Bruxelles-Jette, Belgium.

The screen covered by the photo-sensitive composition was exposed for about half an hour to a light source through a diapositive image of the intended pattern of conductive strips. The diapositive was constituted by a sheet of glass covered by self-adhesive opaque sheets along the strip zones.

The latent image on the screen was then developed by soaking the screen in water at about 50do, which caused removal of the photo-sensitive composition along the strip zones. This development was followed by rinsing in water and firing at about 100"C for about 30 minutes. The screen was then ready for use in the manufacture of the glazing panel.

The developed screen was applied onto the glass sheet substrate, and electrically conductive coating composition in the form of a paste was forced through the open meshes of the screen. The paste adhered to the glass substrate.

The paste was obtained by mixing silver particles less than 5 microns in size with particles of two glasses of different compositions, the glass particles being less than 3 microns in size, and adding a liquid vehicle.

One of the glasses, which will hereafter be designated "the binder glass", and the softening point of which is lower than that of the other glass, has the following composition in percentages by weight: SiO2 25.95%, Na2O 1.49%, K2O 0.61%, CaO 1.02%, Al203 + TiO2 8.06%, NaO 0.41%, ZrO2 1.35%, PbO 48.03%, B20313.01 MgO 0.067%.

The other glass has the following composition in percentages by weight: SiO2 28.31%, Na2O 1.72%, K2O 0.73%, CaO 0.20%, Al203 + TiO211.41 Fe2O3 0.43%, BaO 0.23%, ZrO21.68%, PbO 47.08%, B203 5.06%, CdO 3.07% MgO 0.02%.

The paste comprised the specified different constituents in the following amounts: 852.4 g silver, 147.6 g of the binder glass, 200 g of the higher softening glass, and an organic liquid vehicle of conventional type in an amount of 15% by weight based on the total weight of the paste.

The conductive strips 10 each had a width of 1 mm, a thickness of 10 microns and a length of 730mm.

The areas of the bus bars 6 and 7 were than overcoated with layers formed by the local deposition of a paste composed of the same ingredients but in the following proportions: 800 g silver, 85 g binder glass, 115 g higher softening point glass and 15% of the liquid vehicle based on the total weight of the composition.

The thus coated substrate was then subjected to a thermal treatment in order to fire the coating composition.

During the firing of the applied electrically conductive composition the liquid vehicle in the paste evaporated and the binder glass was melted. This binder glass enveloped the particles of silver and of the higher softening point glass and adhered to the glass sheet substrate. The sheet was then slowly cooled.

The sheet possesses the advantage that one can easily solder electrically conductive wires or terminals to the thus deposited bus bars 6 and 7, e.g. as indicated at 8 and 9. Forthis purpose one can for example use a lead-tin-silver or lead-tin-cadmium or lead-tin-indium alloy.

The thus-coated sheet was then assembled into a laminate with a second, similarly sized glass sheet, in known manner.

Example 3 A glazing panel was manufactured using a serigraphic process as described in Example 2. The panel was in all respects similar to that manufactured in accordance with Example 2 except for the fact that after firing the applied electrically conductive coating compositions the glass substrate was cooled in a current of gas in order to effect thermal tempering thereof and render it more resistant to breakage. The second glass sheet was also thermally tempered.

Example4 (Figure 3) A laminated glazing panel measuring 1.5m by 2m was made for use as a shop window. This panel comprised three sheets of float glass 12,13,14 each 6mm in thickness bonded together by two intervening layers 15,16 of polyvinyl butyral each 3.04mm in thickness.

Prior to lamination the sheet 12 was given an electrically conductive coating 17 extending over one face thereof.

The coating used was of SnO2 doped with F-ions obtained by the thermal decomposition of SIC14 and MH4F.HF and was 7,500 thick so that it had a resistivity of 15 Q/2.

After coating, the shorter margins of the coated face were provided with metallised strips 18, 19 each 10 mm wide and 30 Rm thick. These strips were of copper tinned with solder, and terminal connexions 20,21 were then soldered to them. In fact the copper was 8 lim thick and the solder 22 Rm thick.

In a variant of this Example each glass sheet was chemically tempered.

In a second variant of this Example, the glass sheet 14 was of grey glass and was provided with a coating 22 between 600 and 750 A thick comprising oxides of iron, chromium and cobalt formed by spraying a solution of the acetyl acetonates of these metals in dimethyl formamide onto the (preheated) sheet.

In a further variant, at least one glass sheet is tempered.

Example 5 (Figure 3) A panel was made as described in Example 4 except for the following differences. The third glass sheet 14 and its adjacent layer 16 of polyvinyl butyral were omitted, the coating was deposited to a thickness of 7000 A (resistivity 191/n) and the metallised strips 18,19 were deposited along the longer margins of the coated face of the sheet 12.

Example 6 (Figure 3) Example 4 was repeated except that the coating 17 was 8000 thick of SnO2 doped with antimony ions formed by the pyrolysis of tin chloride and antimony chloride.

Example 7 (Figure 3) Example 4 was repeated except that the coating 17 was 9000 A thick of indium oxide doped with chlorine ions formed by pyrolysis of a solution of InCI3.

Example 8 (Figure 3) Example 5 was repeated except that the coating 17 was of gold 150 A thick.

Example 9 (Figure 3) Example 5 was repeated except that the coating 17 was of silver 100 Athick.

Example 10 (Figure 3) Example 5 was repeated except that the coating 17 was of aluminium 75 A thick.

Example ii (Figure 3) Example 5 was repeated except that the coating 17 was of copper 110 thick.

Example 12 (Figure 3) Example 4 was repeated except that the coating 17 was of In203 between 1300 and 1400 A thick formed by vacuum deposition.

Claims (19)

1. A security alarm system including a glazing panel comprising at least one sheet of glazing material which carries at least one conductor extending across a major face thereof, characterised in that said conductor(s) is or are connected to electrical circuit means arranged to deliver an electric pulse signal when the resistance of said conductor(s) changes and to pass such signal to an alarm circuit.

2. A security alarm system according to claim 1, characterised in that said circuit means is arranged to deliver a said pulse signal only when the rate of change of resistance of said conductor(s) exceeds a predetermined value.

3. A security alarm system according to claim 2, characterised in that said predetermined value of the rate of change of the resistance is 1% per 5 minutes.

4. A security alarm system according to any preceding claim, characterised in that said alarm circuit is arranged to deliver an alarm signal only in response to a change in said resistance which is greater than 0.05% of its initial value.

5. A security alarm system according to any preceding claim, characterised in that said circuit means is responsive to successive modifications to the resistance of said conductor(s).

6. A security alarm system according to any preceding claim, characterised in that circuit means is provided which is adapted to apply DC potential across said conductor(s) and capacitor means is provided to deliver a said pulse signal in response to changes in such potential.

7. A security alarm system according to any preceding claim, characterised in that said pulse signal is fed to said alarm circuit bia an amplifier.

8. A security alarm system according to any preceding claim, characterised in that said conductor is a transparent electrically conductive coating applied to substantially the whole of a major sheet face of the panel.

9. A security alarm system according to claim 8, characterised in that said coating is a metal oxide coating.

10. A security alarm system according to claim 9, characterised in that said coating comprises tin oxide.

11. A security alarm system according to claim 9 or 10, characterised in that said metal oxide coating includes a doping agent.

12. A security alarm system according to any of claims 8 to 11, characterised in that said conductive coating extends between two metallised strips deposited along opposite margins of said major sheet face.

13. A security alarm system according to any preceding claim, characterised in that said sheet of glazing material which carries the conductor(s) is a sheet of glass.

14. A security alarm system according to any preceding claim, characterised in that said glazing panel is a laminate comprising at least two glass sheets bonded together using one or more intervening layers of adhesive material.

15. A security alarm system according to claim 14, characterised in that the sheet which carries the conductor(s) forms an outer face of the panel.

16. A security alarm system according to claim 14 or 15, characterised in that the conductor(s) is or are located between the outer sheets of the panel.

17. A security alarm system according to any preceding claim, characterised in that the panel comprises at least one glass sheet which has been tempered.

18. A security alarm system according to claim 1 and incorporating a glazing panel substantially as herein described with reference to any of Figures 1 to 3 of the accompanying drawings.

19. A security alarm system substantially as herein described with reference to Figure 4 of the accompanying drawings.