GB2253734A - Alarm container - Google Patents

Description

2253734 1 ALARM SYSTEM This invention relates to an alarm system,

particularly a siren system intended to be mounted on an exterior wall of a building so that it can be activated from within the building to produce an audio alarm. The siren must be mounted in a secure container so that it cannot be easily disabled in its position exterior of the building.

In general a siren system will comprise a back plate secured to the exterior wall by fastening means only accessible from within the container and with an electrical connection passing through the wall and back plate into the container. A mounting plate is mounted on the back plate and carries the electronics, loud speaker(s), backup battery, switches, etc., for producing the audio signal. An inner cover member is secured to the mounting plate to form therewith an inner container/housing around the audio system and an outer cover member is secured to the back plate to form therewith an outer container/housing.

It is known for potential intruders to the building to try to disable such an alarm siren system on the exterior of the building before intrusion within the building. This has been done by cutting through the cover members with drills or cutters, cutting through or otherwise damaging the cover members with blow torches or other fire, cutting through the fastening members securing the cover members, hammering or otherwise abusing the containers with an attempt to crush the electronics or batteries or otherwise gain access to the electronics to disable them and/or injecting the foam under pressure to disable the alarm or dampen any sound produced. British Standard BS7042 sets the criteria which must be met to produce a siren alarm system capable of resisting to a degree an allerting a disablement attempt. In particular it is a requirement that the alarm is triggered if an electrical connection is made between the inner and outer cover members for example by penetration by a drill, the alarm is triggered if the fastening members securing the 2 outer cover to the back plate are removed, and the alarm is triggered if the container is attacked by fire.

One object of the present invention is to provide an alarm siren system which has the above features but additionally includes other features which make it more secure and less susceptible to successful disablement. The system according to the invention includes a plurality of new features any of which may be claimed independently or in any combination. In another aspect, the invention also extends to a new form of visual light arrangement particularly suitable for use with an alarm system but which may be claimed or used independently of an alarm system.

In a further aspect, the invention also extends to a foam or fire detector system suitable for an alarm but which may be claimed independently.

Particular novel features of the alarm siren system comprise the following:- a) The incorporation, mounted on the outer cover member of the system and/or on the inner cover member of the system, of a mercury tilt switch arranged to trigger the alarm if it detects tilting of the cover member or mounting plate by more than eg five degrees or if it is subjected to shock for example resulting from a hammer blow. The switch, for example, may be triggered by a blow of greater than 2G and the electrical system is designed to latch in the on position once the switch has activated it.

b) The back plate has forwardly and inwardly projecting edges and the inner cover plate has backwardly and outwardly projecting edges extending at substantially the same angle and dimensioned to fit within and against the edges of the back plate. The arrangement is such that if the front surface of the inner cover plate is subjected to damaging blows, the outer edges will expand outwardly sufficiently to lock it within the mounting plate edges.

C) The mounting plate (or back plate) incorporates forwardly extending walls around the electronic and/or 1 l.

3 battery, which walls extend to within a short distance e.g. 2 to 3 millimetres, of the back surface of the inner cover member. These walls protect against crushing of the operating circuit as a result of hammer blows to the inner cover member.

d) The outer cover member contains no openings (apart from holes receiving fastening members for fastening it to the back plate). All openings for the escape of sound and to allow ambient air to circulate within the container are in the back plate which is spaced f rom the wall e.g. by about 5 to 7 millimetres. Loud Speaker(s) (siren sounders) are arranged adjacent such openings in the back plate. The openings are preferably covered by a woven cloth material which allows breathing and access of air to the interior of the container, but prevents entry of foam if this is injected into the space between the wall and the back plate. Having no louvres in the outer cover member prevents the insertion of any tool which could be used to damage the working parts and having the apertures for the escape of sound covered by woven material prevents the entry of foam if this is injected between the wall and the back plate. I have found that if such foam is injected it merely wets the surface of the material and this wetting as it sets assists in creating it own barrier to foam entry.

e) A foam and fire detection unit comprising at least one thermistor which detects changed conditions if it surrounded and insulated by foam. preferably this unit is formed by two thermistors one exposed to the exterior of the container and the other located inside the inner container, the thermistors being linearly coupled and arranged to trigger the alarm if they detect temperatures which are different from one another by a preset amount. The alarm signal will not be triggered if they are at substantially the same temperature, normally ambient, and will preferably be triggered if the exterior thermister exceeds the temperature of the internal thermistor by a f irst value eg f ive degrees C 4 and if the internal thermistor exceeds the temperature of the external thermistor by a larger value e.g. 10 degrees C. This ensures that the alarm will not be triggered under normal conditions when the thermistor in the container may heat up more than the exterior thermistor because the container is receiving the sun's rays while the external thermistor is screened between the wall and the back plate. However, it will be triggered if the appliance is subjected to a blow torch or other fire. Since both thermistors are active and therefore generating heat which is normally lost to the ambient, if foam is injected behind the back plate it will surround and insulate the external thermistor and cause it to rise in temperature relative to the internal theremistor sufficient to trigger the alarm. Conventional foam detectors are placed only inside the container and work on optical detection of the foam. It is known for these to be triggered by accident by insects.

f) The alarm system includes a strobe (flashing) light signalling means arranged to be triggered at the same time as the siren alarm which strobe unit is mounted on a separate mounting plate suspended from the back plate so that if the strobe light unit is attacked and damaged the siren alarm container is not necessarily also damaged.

g) A fluorescent strobe light generating tube, e.g. a xenon tube which builds up charge and discharges at breakdown voltage, is embedded within a solid sheet or block of strong transparent or translucent plastics material, e.g. acrylic, attached to the container of the alarm system. The means for operating the light generating tube to produce a strobe light are located within the container and connected to the tube such that no wiring is accessible for disablement. The plastics material is preferably multifaceted to transmit light in many directions. In another form the light generating tube may itself be within the container and the light transmitted to a solid piece of plastics material on the exterior of the container by reflection, refraction light tube or the like. Such a system is extremely indestructible and may be used and claimed independently of an alarm system.

One embodiment of alarm system will now be described, by way of example only, with reference to the accompanying drawings of which:- Figure 1 is a diagrammatic side view of the back plate of an alarm system attached to a wall with the mounting plate andinner and outer cover members of the system also shown adjacent.

Figure 2 is an exploded view of the housing parts of the system on a larger scale, Figure is a plan view of. the front surface of the back plate, Figure 4 is plan view of the front side of the mounting plate with some parts shown only diagramatically, Figure 5 is a section on the line V-V of Figure 4, with parts shown only diagramatically and other members of the system indicated in broken line, Figure 6 is a view similar to that of Fig 1 showing an arrangement during setup, An alarm system has a metal back plate 12 having a base 13 formed with four depressions defining feet 14 adjacent its corners.

The back plate is secured to the exterior wall 15 of a building by screws 16 extending through screw holes 17 in the centres of the depressions and. with the feet abutting the wall so that the back surface 18 of the back plate is spaced from the wall by about 6 millimetres. The top, side and bottom edges, 20, 21 and 22 respectively are turned forwardly and are also turned inwardly at an angle of about 10 degrees. The bottom edges 22 defines two screw holes 23 for receiving screws 24 for securing an outer cover member 25 to the back plate. The outer cover member 25 has an inwardly turned lip 26 alon ts top qdge which engages over the top of the back 1 C-v.,-.r W 4MA%--r.

plate andlhas no openings therein except those for receiving 6 the screws 24. The back plate and outer cover member when fixed thereto and secured to the wall thus form an outer container/housing whose only openings face the wall.

The back plate has two series of apertures 26, each arranged in an annulus 27 corresponding with the outer rim of a respective loud speaker 28 for outlet of sound. The back plate also has an aperture 31, defined by a bush 32, for receiving an electrical cable 33 extending through the wall and has an aperture 34 for a foam detector to be described hereinafter. The back plate also has four mounting pegs or screws 35 surrounded by insultating members 36 by which a mounting plate 40 is mounted on the back plate. The apertures 26 are covered by sheets of woven cloth material, indicated at 37, stuck to the inner surface of the back plate, which sheets prevent entry of foam.

The mounting plate 40 is formed from sheet metal having forwardly turned edges at least the side edges 41 of which are also turned inwardly at an angle of about 10 degrees. The plate 40 is formed with four keyhole apertures 42 by which the plate is mounted on the back plate suspended from the pegs or screws 35, with the mounting plate insulated from the back plate. The mounting plate carries all the electronics, loud speakers and backup battery for operating the siren alarm. These may be of known form and will not be described in detail nor is the connecting wiring shown in the drawings as this does not form part of the inventive features. The mounting plate carries loud speakers 28 and is also formed with a series of apertures indicated at 43 arranged in two annuali and substantially aligned with the apertures 26 in the back plate. The electronic circuitry is mounted on a circuit board 44 slidably mounted between two spaced upstanding walls 45. A battery 46 is also mounted on the mounting plate and partly surrounded by an upstanding wall 47. Micro switches 48 of known form are arranged to be engaged by the screws 24 such that if the screws are removed the alarm is triggered.

7 An inner cover member 50 is made from sheet metal having a flat top 51 and sides 52 which slope outwardly at about 10 degrees and are dimensioned to be a close f it within the inner sloping edges of the mounting plate. The inner cover member 50 is secured to the mounting plate by screws 53 and 54 through the top and ha--k sides. When so mounted the tops of the walls 45 and 47 are spaced about 2 millimetres from the inner surface of the inner cover member. These walls help to prevent damage to the electronic circuitry or the battery if the inner cover member is subjected to damaging blows. If the top of the inner cover member is subjected to hammering or other battering the sides will spread outwards slightly and will jam and lock within the sloped sides 41 of the mounting plate to make it dif f icult to remove the inner cover member and gain access to the electronic components.

The outer cover member 25 is formed from sheet metal having a top 60 and sides 61 which are outwardly sloped at an angle of about 10 degrees. When the outer cover is secured to the back plate it is spaced from the inner cover. Mounted on the outer cover member between the inner and outer cover members is a mercury tilt. switch 63 of form known for other uses but not previously known in such an alarm system. The switch is arranged to activate the alarm if the outer cover member is tilted more than a predetermined amount for example 5 degrees or is subjected to a shock above a predetermined level for example 2 G. A similar mercury tilt switch 64 is mounted on the inner cover member.

The whole system has a depth when assembled between the front surface of the outer cover member and the back surface of the back plate which is only fifty millimetres.

A foam and fire detection unit 70 is mounted on the mounting plate under the circuit board 44. The unit comprises a circuit board 71 having first and second thermistors 72,73 projecting from opposite sides of the board and linearly coupled together. The board is mounted on a hollow member 74 8 secured in an aperture 75 in the mounting plate so that the first thermistor 72 is exposed to the exterior of the outer container through aperture 34 and the second thermistor is located in the inner container formed by the mounting plate and inner cover member 50. The circuitry on the board 71 is arranged to trigger the alarm if the temperature of the first or second thermistor exceeds that of the second or first thermistor respectively by more than five or ten degrees C respectively.

Figure 6 shows the outer cover member 25 being used as a tray and the inner cover being used as a hood during connection of the system to a wall. Alternatively the outer cover member is arranged to be supporteb at the side of the back plate during assembly.

A strobe fluorescent light is often mounted on a conventional outer cover of a siren alarm unit. As seen in Fig 3, 1 propose to mount such a unit 76 on a separate mounting plate 77 attached to the back plate by fasteners 78 only accessible from the interior of the unit. In an alternative arrangement, shown in Fig 5, a fluorescent light tube 80 is embedded in a sheet or block 81 of transparent or translucent plastics material mounted on the bottom edge of the cover member 50 and connected by wiring 82, also inaccessible, to the interior of the container. The light could be transmitted from a light source in the interior to the block of plastics by reflection or the like.

9

Claims (13)

1. An alarm container comprising a back plate for mounting to a wall or the like, the back plate having edges projecting forwardly and inwardly therefrom and an inner cover having edges projecting backwardly and outwardly therefrom and extending at substantially the same angle as the edges of the back plate, the edges of the inner cover fAl 1 10 being dimensioned to fit within and against thetof the back plate, the inner cover and the back plate together providing a substantially closed container.

2. A container according to Claim 1 including an outer cover dimensioned to fit over the inner cover and spaced therefrom and to be secured to the back plate to provide therewith a substantially closed outer container.

3. A container according to Claim 2 in which the outer cover, apart from screw holes for securing it to the back plate, has no openings therein.

4. A container according to Claim 3 in which the back plate has opening adjacent loud speakers which are located in the inner container, such openings being covered by a woven cloth material.

5. An alarm system comprising a container according to any of Claims 1 to 4 and including one or more mercury tilt switches mounted on the inner and/or the outer cover and arranged to set off the alarm when the associated cover is tilted more than a predetermined amount or subjected to more than a predetermined shock.

6. An alarm system compriing a container according to any of Claims 1 to 5 including a mounting plate on which a siren/loud speaker system with its electronics is mounted, the mounting plate being mounted to the back plate in an insulated manner.

7. An alarm system including a container according to Claim 6 together with Claim 2 in which the mounting plate or back plate includes forwardly projecting walls projecting to within a small distance of the front wall of the inner cover.

8. An alarm system including a container according to any of Claims 1 to 7 and including a foam and fire detection unit comprising at least one thermistor which is arranged to detect changed conditions if it is surrounded and insulated by foam.

9. An alarm system including a container according to Claim 8 in which the unit comprises a pair of thermistors one located exterior of the outer container and the other located inside the inner container, the thermigters being linearly coupled and arranged to trigger the alarm if they detect temperatures which are different from one another by a preset amount.

10. A system according to Claim 9 in which the alarm is arranged to be triggered if the exterior thermister exceeds the temperature of the internal thermister by a first value and if the internal thermister exceeds the temperature of the external thermister by a second larger value.

11. An alarm system including a container according to any of Claims 1 to 10 and including a strobe light signalling means arranged to be triggered at the same time as the alarm, which strobe means is mounted on a separate mounting plate suspended from the back plate.

12. An alarm system including a container according to any of Claims 1 to 10 and including a fluorescent strobe light generating tube embedded within a solid sheet or block of strong transparent or translucent plastics material attached to the exterior of the outer container and operating means for operating the light generating tube to produce a strobe light, the operating means being located within the container and connected to the tube so that no wiring is accessible for disablement.

13. An alarm system substantially as described herein, with reference to or as illustrated in the accompanying drawings.