| FR2379869A1 | 1978-09-01 | |||
| DE3128073A1 | 1983-02-03 | |||
| DE3152800A1 | 1983-08-25 | |||
| AU9031082A | 1983-05-19 | |||
| AU7611281A | 1982-04-22 | |||
| GB2038060A | 1980-07-16 | |||
| GB437205A | 1935-10-24 | |||
| US3742222A | 1973-06-26 |
| 1. | (1) A security system comprising a pane of translucent material having a light emitter sealed onto one edge thereof and a light detector sealed on an opposite edge thereof said pane providing a light path from emitter to detector, a power supply for said emitter (and detector) and an alarm system connected to the output of the detector to indicate breach of securit by breakage of said pane and interruption of said lig path, or by reducing the amount of light received by the detector. (2) A security system as defined in claim 1 wherein the arrangement is such that the path of light is defined by the critical angle reflections from the opposite surfaces of said pane. (3) A security system as defined in claim 1 wherein the light path is via one or more rods of similar but not identical refractive index to said pane, embedded therein. (4) A security system as defined in claims 1, 2 or 3 in w a narrow band of optical frequencies is transmitted t the detector which includes an optical filter whereby minimise interference from external light sources. (5) A security system as defined in claim 3 wherein the p is opaque to optical radiation and the rod or rods is or are transparent to optical radiation. (6) A system as claimed in claim 3 with optical fibres replacing the glass rods. "BU RE TE SHEET OMPI. |
This invention relates to a security alarm system which i off when an intruder attempts to enter the region secured said invention by cracking or breaking panes of glass set doors, windows and sky lights, transparent covers for val objects etc. consisting of panes of glass or plastic mate (herein after referred to simply as panes of glass) into may be embedded rods of glass (or rods of plastics and pl pane) of approximately the same refractive index through light from light emitting diodes or laser diodes sealed o the edge of said pane of glass propagates onto light dete sealed onto the said edge on the opposite side of said pa glass, optical rods to enhance the signal to noise ratio said detectors, power supplies to drive said light emitti diodes and optical detectors, interconnecting leads, cont unit and an alarm indicator. An alternative arrangement i one in which the light path from emitter to detector is vi a path of total internal reflection through the pane inste of via glass rods. The panes of glass used in this invention fit into windows doors and skylights as do prior art panes of glass, howeve the panes of glass of this invention, if cracked or broken by an intruder set off an alarm which is activated by the propagation path of the light within glass rods (or plasti rods in a plastic pane) embedded into the said pane of gla of approximately the same refractive index as said pane, being cracked or broken themselves in such a manner as to interfere with the level of light intensity detected by th optical detector monitoring the output of light from said In this invention, both the photo-emitting diodes and the optically filtered optical detectors are sealed onto the edges of the pane of glass on opposite ends of the embedde rods of glass so that a portion of the light emitted by th light emitting diode or laser diode, is propagated along t embedded rod via multiple reflections because being of slightly different refractive index from said pane of glas behaves as a core of an optical fibre whose cladding is th body of said pane of glass
OMPI
SUBSTITUTE SHEET A
Prior art intruder alarm systems have used electrical con¬ ducting tapes on panes of glass such that when said panes were broken the electrical units were also broken as the tapes broke. The false alarm rate of this invention is minimised both b using the light conducting rods embedded within the pane o glass and narrow band optical filters on the optical detec to block out a major portion of stray background light whi may accidentally enter the said pane of glass via its uncovered surfaces.
On the other hand if very intense ambient light was incide on the pane of glass and sufficient of this leaked through to activate the detectors momentarily, then the alarm elec ronics would not activate the alarm because the detectors would only respond to a decrease of light intensity as set by the light emitting diode transmitters. A further prote against false alarm is provided by my invention by modulat the photo emitting diode transmitter with a randomly gener code. It is an aim of this invention to provide a monitor of cracked or broken panes of glass as used in windows, doors and sky lights by reducing the transmission efficiency of light propagating within said pane of glass, said loss of intensity being detected via optically filtered, optical detectors which in turn trigger an alarm.
It is also an aim of this invention to propagate the monit oring light via critical angle reflections, which in the simplest, lowest false alarm threshold case is provided by the two surfaces of the said glass pane itself whilst in the highest false alarm threshold case is provided by em¬ bedding glass rods of slightly differing refractive index within the body of said pane of glass such that the former acts as the case of an optical fibre whilst the latter act as its cladding. It is a further aim of this invention to provide a securit alarm system comprising of panes of glass of standard dim¬ ensions so that they can readily fit into existing windows doors and skylights. ^ R UR
OM
SUBSTITUTE SHEET ;
It is yet further aim of this invention to provide a secu alarm system comprising light propagating paths which are very difficult to see via the naked eye due to the small differences of refractive indices between the various gla components.
Yet a further aim of this invention to use any light propagating media such as clear plastics and fused silica in addition to conventional glass.
It is also an aim of this invention to provide a security monitor in hazardous areas where multiple observation windows are used.
A better understanding of ' this invention may be obtained by consideration of the following figures which are not meant to limit the scope of this invention in any way. Figure 1 shows the high alarm threshold mode of this in¬ vention with the light emitting diode attached to one edg of the pane of glass so as to inject part of its output i the embedded glass rod which in turn propagates the said l onto the optical detector. via the narrow band optical fil Figure 2 shows the lower alarm threshold configuration of this invention where the light from the diode is transmit through the pane of glass via critical reflections from i surfaces. Figure 3 shows the overall configuration of thi invention with the transmitters and detectors sealed along the edge of the pane of glass and connected to power suppl control and alarm units.
In Figure 1, numeral 1 indicates the cross-section pane of glass whilst numeral 2 indicates the high conducting rod. Numeral 3 indicates the light emitting source, numeral 4 t optical detector whilst numeral 5 indicates the narrow ban optical filter. Light emitting source 3, optical detector and narrow band filter 5 are all sealed onto the edge of t pane of glass 1 by sealant indicated by numeral 6. Numera indicates the lead connecting the light emitting diode 3 t its power supply whilst number 8 indicates the lead connec optical detector 4 to its power supply. Numeral 9 indicat the lead connecting the optical detector 4 to the control alarm units.
SUBST I TUTE S HEET
In figure 2, numeral 10 indicates the path of light from light emitting source 3 to detector 4 via critical angle reflections between the surfaces of glass pane 1. The oth numerals indicate equivalent members to those indicated by the same numerals in Figure 1.
In Figure 3, numeral 11 indicates the complete glass windo pane and numeral 12 indicates the power supply for the lig emitting diodes 3. Numeral 13 indicates the control unit whilst numeral 14 indicates the alarm system. The other numerals indicate equivalent members to those indicated by the same numerals in Figure 1.
Several panes of glass can be connected up either in parallel or in series to control unit 14. This invention has applications in securing any enclosure which has windows, doors or skylights with panes of glass or light transmitting media such as plastics and crystals. This invention has application in securing buildings inclu ing banks, museums, houses, factories and offices. This invention also has application in transparent covers for valuable objects, and hazardous environments.
This invention can also incorporate a glass pane opaque to optical radiation with embedded rods of material transpare to optical radiation. Also the embedded rods may be repla with lengths of optical fibres, that is to say rods which already been clad.
SU E _OMP
SUBSTITUTE SHEET k. " W -A