GB2046971A - Security glazing units and signalling systems incorporating them - Google Patents

Abstract

A security glazing unit incorporates one or more optical fibres 5 attached to a transparent or translucent, toughened glass sheet 1, the fibre or fibres being firmly secured in a position fixed relative to one of the major surfaces of the glass sheet so that damage to the glass sheet results in damage to the fibre or fibres. The security glazing unit can be in the form of a laminated glass article. The fibre or fibres of one or more glazing units 12 can serve as a transmission 14 path coupling a light source 10 and receiver 11 together in a signalling system, the system being arranged so that damage to a fibre in any of the glazing units, gives rise to a condition in the signalling system which can be detected and/or indicated. <IMAGE>

Description

SPECIFICATION Improvements in or relating security glazing units and signalling systems incorporating them This invention relates to a security glazing unit and signalling systems incorporating such units.

The protection of buildings against intrudes by the provision of alarm systems which react to certain actions on the part of the intruder has been primarily based on the detection of either a break in an electrical conducting circuit, or the making or breaking of a contact in such an electrical circuit. Systems are also employed based on light beams, sound detection and detection of oscillations produced by movement near a detector. Electrical systems are vulnerable to bridging so that their detecting action is nullified. In addition, it is possible using sensitive flux meters to determine whether such systems are operating or not. In the case of light beams and sound detection, such systems are prone to false alarms, thus reducing the alertness of personnel meant to react to an alarm.

Vulnerable entrance points in many buildings are windows or doors made wholly or partially of transparent or translucent glass sheets. It is known to provide conducting electrical surfaces on such glass sheets so that if they are cut or broken an elecl;ical circuit is broken. However such a system is vulnerable to bridging either on the windows or at the leads or contacts external to the window. It is also feasible to detect when the system has been effectively bridged by checking that current is no longer passing in the conducting surface.

The present invention is directed to providing a glazing unit incorporating means for detecting breakage or cutting which means is not readily vulnerable to being bypassed and will only operate when the unit is cut or broken thus reducing the r ?;ibility of false alarms. Our invention is based on tne use of an optical glass fibre carrying a light signal rather than a system based on an electrical circuit. It is not possible to simply bridge an optical fibre as the fibre must be broken to interrupt the passage of a signal and the interruption is itself capable of detection. Also it is not possible to easily detect whether the system is in fact in use or not. Hence, if entry is based on achieving de-activation of an alarm system, the intruder has no means of checking that he has switched off all the systems.

According to the present invention there is pro ided a security glazing unit comprising at least one transparent or translucent toughened glass sheet and at least one optical fibre firmly secured in a position fixed relative to one of the major surfaces of the glass sheet so that damage to the glass sheet, or removal of it from the unit, will give rise to damage to the fibre such as to impair the optical transmission properties of the fibre.

By optical fibre is meant any fibre, such as a glass fibre capable of transmitting a light signal, which term is to be understood to include not only signals having frequencies in the visible light spectrum but also signals, or signals having components, having frequencies in the infra red or ultra violet spectra.

The transparent or translucent toughened glass sheet tends to rupture completely when any sufficient attempt is made to cut or break it, thus ensuring that only a single optical fibre firmly secured in a position fixed relative to one of the major surfaces of the glass sheet will be damaged, for example cut, kinked or broken, regardless of the point at which the sheet is initially cut or broken.

In a preferred embodiment of the presentinven- tion the transparent or translucent toughened glass sheet is included in a transparent or translucent laminate with the or each optical fibre firmly secured in a position fixed relative to a major surface of the glass sheet that does not form an external surface of the laminate. For example, the toughened glass sheet may be laminated in known manner together with a second transparent or translucent glass sheet and an interlayer of a suitable transparent plastics material such as polyvinylbutyral, the or each optical fibre being firmly secured in a position fixed relative to that surface of the first sheet which is in contact with the interlayer. The second glass sheet may be made of ordinary annealed glass ortouchened glass.

In a preferred embodiment the or each optical fibre is firmly secured to the major surface of the toughened glass sheet by an adhesive. Conveniently the adhesive used is an epoxy type adhesive.

The glazing unit may for example be or form part of a door, a window or a partition or any similar structure. Where a door, window or partition has several glazing apertures, each aperture may be filled with a unit according to the present invention.

Preferably the optical fibre is a single filament as it is possible that with a fibre incorporating a bundle of filaments, one or more filaments may survive the damage to the bundle and provide a sufficient light transmission path.

The fibre may be provided with a thin protective layer of resin but should preferably not have an outer protective plastics sheath as is often provided on optical fibres, since this may prevent damage to the fibre when the glass breaks.

Normally, the fibre will extend beyond the edges of the sheet so as to facilitate its connection into a light transmission circuit.

Preferably, when the sheet is mounted in the glazing unit, the fibre is secured to or in a part or parts of the frame of the unit.

According to another aspect of the present invention a signalling system includes a source of light signals and a receiver for the same, and at least one transmission path coupling the source and the receiver, said path including the fibres of one or more glazing units in accordance with the invention and the system being arranged so that damage to a fibre in any of the glazing units, gives rise to a condition in the signalling system which can be detected and/or indicated.

An example of a glazing unit according to the invention and of a signalling system incorporating such units will now be described with reference to the drawing in which: Figure 1 shows a schematic front elevation of the unit, Figure 2 shows a section at A-A in Figure 1 and Figure 3 shows a schematic diagram of the system.

Referring first to Figures 1 and 2, the unit includes a laminate formed in conventional manner by two glass sheets 1 and 2 and an interlayer 3 of transparent polyvinyl butyral. The glass sheet 1 is ordinary annealed glass but the sheet 2 is of toughened glass, having been submitted in known manner either to thermal quenching or a chemical toughened process. The laminate is mounted in a frame 4 which is indicated only schematically in Figures 1 and 2.

An optical fibre 5 is secured to the inner major surface of the toughened glass sheet 2 having been stuck in position by means of an epoxy adhesive before the laminate was formed. The fibre 5 projects beyond the side edges of the laminate and on mounting of the latter in the frame 4, the free ends are passed through channels provided in the sides of the frame. Alternatively the free ends can be laid in grooves in the surface of the frame or otherwise secured to it, so that any attempt to remove the laminate as a whole from the frame 4 will give rise to damage to the fibre 5.

Figure 3 shows a schematic diagram of a simple signalling system according to the invention, for use for example as a burglar alarm system. The system includes a transmitter 10, a receiver 11, a series of glazing units 12 of which only three are shown in Figure 3, and a number of optical fibre connectors 13 of which only some are shown in Figure 3. A length of optical fibre 14 couples the output of the transmitter to a fibre connector 13 terminating one end of the fibre 5 in the first of the glazing units 12. Similarly a fibre 15 interconnects a connector 13 terminating the other end of the fibre 5 in the first of the units 12 and one end of the fibre 5 in the second unit 12.Other lengths of fibre 16, 17 and 18 are shown linking the second and third units 12, and as many more as it may be desirable to include, and finally in the case of timbre 18 coupling the connector 13 of the last unit 12 o tne receiver 11. The transmitter includes a suitable light source, such as a laser or a light emitting diode, which is coupled to the fibre 14 and transmits optical signals of predetermined frequency and form, for example either continuous or pulsed signals may be used and these may be modulated in any desired fashion.

If all the fibres 5 and 14 to 18 are intact and undamaged, the signals are received by the receiver 11 where they are detected and used to generate a predetermined condition, such as the energisation of a switch or an indicator, orthe actuation of a switching or logic circuit, corresponding to the correct and uninterrupted receipt of the signals. Any damage to any of the fibres 5 in the glazing units 12 or to any of the interconnecting fibres 14 to 18, such as may occur if any of the glazing units 12 is broken or cut, or if anyone attempts to tap them for short-circuiting purposes, or in any other way interferes with the transmission of the light through them, will lead to a change which may amount to interruption, in the signals received by the receiver 11.The latter is arranged to detect any such change and to produce a corresponding change from the condition indicating correct receipt of the signals to one indicating interruption of or interference with them. In a simple alarm system, interruption of or interference with the signals may give rise to the energisation of an audible alarm such as a bell or the energisation of alarm circuits providing remote indication of the alarm condition.

Where long lengths of fibre are included in a particular link it will be desirable to use a suitably low loss fibre for example one giving a transmission loss of less than 20 Db per km.

It will be appreciated that the system described above is a simple one and that glazing units according to the invention may be incorporated in more complex or sophisticated systems. For example, the fibres may form a loop joining a single combined transmitter/receiver unit, and the units may be split between different fibre links, or indeed may each be incorporated in an individual link, so that the alarm system can remain operative, at least partially, even if one or more links are already broken. If a number of parallel links are provided, the transmitter and/or the receiver may be arranged to scan them instead of keeping each link continuously in operation.In yet more complex systems, it may be arranged that breakage of the fibre 5 in a glazing unit is detected locally in some way and that local detection gives rise to change in the signals in a main optical link such that the identity of the unit at which breakage occurs is detectable at the receiver.

In such a sytem the main optical link could if desired be replaced by an electrical one.

Whilst the glazing units described with reference to Figures 1 and 2 are three layer laminates incorporating one toughened and one annealed glass sheet, and are shown having only one fibre on the surface of the toughened glass sheet, it will be appreciated that other constructions may be employed. The laminate may for example contain more components or may be reduced to a single toughened glass sheet.

To confuse would be tamperers, it may be useful to put some fibres on the surface of the sheet which are not in fact used for the transmission signals and such fibres need not in fact be high quality optical fibre provided they have the correct external appearance.

Claims (12)

1. A security glazing unit comprising at least one transparent or translucent, toughened glass sheet and at least one optical fibre firmly secured in a position fixed relative to one of the major surfaces of the glass sheet so that damage to the glass sheet, or removal of it from the unit, will give rise to damage to the fibre, such as to impair the optical transmission properties of the fibre.

2. A security glazing unit according to Claim 1, wherein the transparent or translucent, toughened glass sheet is included in a transparent ortranslu- cent laminate with the optical fibre firmly secured in a position fixed relative to the major surface of the glass sheet that does not form an external surface of the laminate.

3. A security glazing unit according to claim 2, wherein the transparent or translucent, toughened glass sheet and a second glass sheet together form a laminated glass article having an interlayer of transparent, plastics material between the pair of glass sheets, the fibre being firmly secured in a position fixed relative to the surface of the first sheet which is in contact with the interlayer.

4. A security glazing unit according to any one of the preceding claims, wherein the optical fibre is firmly secured to the major surface of the toughened glass sheet by an adhesive.

5. A security glazing unit according to Claim 4, wherein the adhesive is an epoxy-type adhesive.

6. A security glazing unit according to any one of the preceding claims, wherein the optical fibre is a single filament.

7. A security glazing unit according to any one of the preceding claims, wherein the optical fibre is provided with a thin protective layer of resin.

8. A security glazing unit according to any one of the preceding claims, wherein the optical fibre extends beyond the edges of the sheet so as to facilitate its connection into a light transmission circuit.

9. A security glazing unit as claimed in any one of the preceding claims, wherein the fibre is secured to or in a part or parts of a frame of the glazing unit.

10. A signalling system including a source of light signals and a receiver for receiving the light signals, and at least on transmission path coupling the source and the receiver, the transmission path including the fibres of one or more glazing units as claimed in any one of the preceding claims and the system being arranged so that damage to a fibre in any of the glazing units, gives rise to a condition in the signalling system which can be detected and/or indicated.

11. A security glazing unit substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2.

12. A signalling system substantially as hereinbefore described with reference to and as illustrated in Figure 3.