GB2169731A - Foam injection detector - Google Patents

Abstract

An enclosure for a security alarm (e.g. a bell housing) contains both a source of wave energy and a detector thereof, whereby attempts to disable the alarm by the injection of an interfering substance (such as foam) into the enclosure may be detected. In the case of a bell, the alarm may be energised before the substance has had the opportunity to cause disablement. <IMAGE>

Description

SPECIFICATION Foam injection detector This Invention refers to a component device of a security system (burglar alarm) In a security system, bells or similar sounding devices are mounted outside the building they protect in weatherproof enclosures. In recent times criminals have found a means of imobilising the sounding device by injecting polyurethane foam, or similar chemical preparations into a bell housing (weatherproof enclosure). When this foam sets and goes hard the bell or other sounding device cannot function or is so muffled that it is uselessly inaudiable, when this is done criminals may gain entry without the alarm being heard.

Acording to the invention I am submitting for patent, a means has been provided to detect the injection into the sounding device enclosure (bell housing), of any form of expanding foam or similar chemical preparation injected with the purpose of immobilising the sounding device. The detection of the injected chemical preparation will trigger the alarm system immediatly allowing the bell or other sounding device to function before the chemical preparation sets or hardens sufficiently to prevent its correct operation.

The device described is inteded to be mounted within the weatherproof enclosure adjacent to the alarm sounding device to be protected. The device will produce a beam of light (light meaning radiation within the range of the spectrum from invisible infra-red through to invisible ultra violet), the type of light at present in mind is invisible infra-red but the right is reserved to experiment with others should this prove neccesary. The beam of light will pass from a suitable source, either direct or by means of reflection, to a detecting device, when the foam or other chemical preparation is injected it will break the path of the light beam whitch will operate electronic circuitry to trigger the alarm system.

This device will form an integral part of the alarm system and will draw the supply to operate its electronic circuitry from power supplies already in existance within the alarm system.

Figure 1 shows a normal alarm bell enclosure being injected with foam.

Figure 2 shows the same enclosure after the foam has set preventing normal operation.

Figure 3 shows the alarm bell enclosure fitted with a "foam injection detector" Figure 4 shows the same alarm bell enclosure when an attempt is made to inject foam.

Figure 5 shows the foam injection detector with no foam present.

Figure 6 shows the "foam injection detector" with foam present.

Figure 7 shows an alternative means of detection with reflected light.

Refering to the drawings Fig. 1 shows a conventional alarm bell housing with polyurethane foam (or a similar chemical preparation) being injected in where 20 is the bell housing, 21 is the bell, or similar sounding device, 22 is the bell control circuitry, 23 is the foam aerosol, 24 is the injected foam.

Fig. 2 shows the same bell housing some time later when the foam has set where 30 is the bell housing 31 is the sounding device, 32 is the expanded and hardened foam immobilising the sounding device.

Fig. 3 shows the foam injection detector fitted to a bell housing, where 40 shows the bell housing, 41 shows the bell, 42 shows the bell control circuitry, 43 shows the "foam injection detector", 44 shows the uninterrupted light beam.

Fig. 4 shows an attempt being made to inject foam into the protected enclosure, where 50 is the bell housing, 51 is the sounding device, 52 is the bell control circuitry, 53 is the foam injection detector, 54 is the light beam broken by the foam and triggering the alarm before the foam fills the enclosure and sets, 55 is the foam partly filling the enclosure but insufficiently to prevent correct operation of the sounding device.

Fig. 5 shows the principal of the foam injection detector with no foam present where 60 is the light source, 61 is the light detector, 62 is the unbroken light beam (any components shown on the circuit board are purely for illustrative purposes and not representative) Fig. 6 shows the foam injection detector with foam present where 70 is the light source, 71 is the light detector, 72 is the interupted light beam, 73 is the foam.

Fig. 7 shows an alternative means of detection using reflected light, where 80 is the light source, 81 is the light detector, 82 is the reflecting surface, 83 is the unbroken light beam.

1. A device to be known as a "foam injection detector", comprising of electronic circuitry to produce a beam of light which will normally pass uninterupted to another circuit to detect its presence. When the beam is interupted by the presence of foam or any other chemical preparation this circuit will trigger the alarm. The circuit board carrying this device will be mounted within the bell housing (weatherproof enclosure), and when the foam is injected the light beam will be broken by its presence causing the bell to ring (or other device to sound), before the foam, or other chemical preparation sets preventing it from operating.

2. A device as claimed in claim 1 where the light beam passes from the generating circuit, to the detection circuit not directly as in claim 1 but by indirect means such as reflection from a mirror or other reflective surface.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Foam injection detector This Invention refers to a component device of a security system (burglar alarm) In a security system, bells or similar sounding devices are mounted outside the building they protect in weatherproof enclosures. In recent times criminals have found a means of imobilising the sounding device by injecting polyurethane foam, or similar chemical preparations into a bell housing (weatherproof enclosure). When this foam sets and goes hard the bell or other sounding device cannot function or is so muffled that it is uselessly inaudiable, when this is done criminals may gain entry without the alarm being heard. Acording to the invention I am submitting for patent, a means has been provided to detect the injection into the sounding device enclosure (bell housing), of any form of expanding foam or similar chemical preparation injected with the purpose of immobilising the sounding device. The detection of the injected chemical preparation will trigger the alarm system immediatly allowing the bell or other sounding device to function before the chemical preparation sets or hardens sufficiently to prevent its correct operation. The device described is inteded to be mounted within the weatherproof enclosure adjacent to the alarm sounding device to be protected. The device will produce a beam of light (light meaning radiation within the range of the spectrum from invisible infra-red through to invisible ultra violet), the type of light at present in mind is invisible infra-red but the right is reserved to experiment with others should this prove neccesary. The beam of light will pass from a suitable source, either direct or by means of reflection, to a detecting device, when the foam or other chemical preparation is injected it will break the path of the light beam whitch will operate electronic circuitry to trigger the alarm system. This device will form an integral part of the alarm system and will draw the supply to operate its electronic circuitry from power supplies already in existance within the alarm system. Figure 1 shows a normal alarm bell enclosure being injected with foam. Figure 2 shows the same enclosure after the foam has set preventing normal operation. Figure 3 shows the alarm bell enclosure fitted with a "foam injection detector" Figure 4 shows the same alarm bell enclosure when an attempt is made to inject foam. Figure 5 shows the foam injection detector with no foam present. Figure 6 shows the "foam injection detector" with foam present. Figure 7 shows an alternative means of detection with reflected light. Refering to the drawings Fig. 1 shows a conventional alarm bell housing with polyurethane foam (or a similar chemical preparation) being injected in where 20 is the bell housing, 21 is the bell, or similar sounding device, 22 is the bell control circuitry, 23 is the foam aerosol, 24 is the injected foam. Fig. 2 shows the same bell housing some time later when the foam has set where 30 is the bell housing 31 is the sounding device, 32 is the expanded and hardened foam immobilising the sounding device. Fig. 3 shows the foam injection detector fitted to a bell housing, where 40 shows the bell housing, 41 shows the bell, 42 shows the bell control circuitry, 43 shows the "foam injection detector", 44 shows the uninterrupted light beam. Fig. 4 shows an attempt being made to inject foam into the protected enclosure, where 50 is the bell housing, 51 is the sounding device, 52 is the bell control circuitry, 53 is the foam injection detector, 54 is the light beam broken by the foam and triggering the alarm before the foam fills the enclosure and sets, 55 is the foam partly filling the enclosure but insufficiently to prevent correct operation of the sounding device. Fig. 5 shows the principal of the foam injection detector with no foam present where 60 is the light source, 61 is the light detector, 62 is the unbroken light beam (any components shown on the circuit board are purely for illustrative purposes and not representative) Fig. 6 shows the foam injection detector with foam present where 70 is the light source, 71 is the light detector, 72 is the interupted light beam, 73 is the foam. Fig. 7 shows an alternative means of detection using reflected light, where 80 is the light source, 81 is the light detector, 82 is the reflecting surface, 83 is the unbroken light beam. CLAIMS

1. A device to be known as a "foam injection detector", comprising of electronic circuitry to produce a beam of light which will normally pass uninterupted to another circuit to detect its presence. When the beam is interupted by the presence of foam or any other chemical preparation this circuit will trigger the alarm. The circuit board carrying this device will be mounted within the bell housing (weatherproof enclosure), and when the foam is injected the light beam will be broken by its presence causing the bell to ring (or other device to sound), before the foam, or other chemical preparation sets preventing it from operating.

2. A device as claimed in claim 1 where the light beam passes from the generating circuit, to the detection circuit not directly as in claim 1 but by indirect means such as reflection from a mirror or other reflective surface.

3. A device where the path of the light beam is normally interupted by the presence of a none reflective surface, and the light reflected from the foam or other chemical preparation completes the light path and then causes the alarm to trigger