WO2008139183A1

WO2008139183A1 - Detector

Info

Publication number: WO2008139183A1
Application number: PCT/GB2008/001650
Authority: WO
Inventors: Kieron Champman
Original assignee: Fircroft Consulting Ltd.
Priority date: 2007-05-14
Filing date: 2008-05-13
Publication date: 2008-11-20
Also published as: GB0709280D0; GB2449257B; GB2449257A

Abstract

A detector for detecting fires or smoke, the detector comprising: a housing defining a transducer receiving portion; a transducer received within the housing substantially adjacent the transducer receiving portion; a first reflector plate defining an aperture therethrough and spatially separated from the transducer so as to define a first acoustic cavity therebetween, a second reflector plate spatially separated from the first reflector plate and located distal to the transducer so as to define a second acoustic cavity between the first and second reflector plates, the housing defining one or more sound apertures therethrough in connection with the second acoustic cavity through which sound is emitted from the second acoustic cavity.

Description

DETECTOR

Background to the invention

The present invention relates to a fire or smoke detection device with an integral alarm signal. It is common practice for fire alarm systems to use detection devices on detection circuits and sounding devices on separate sounding circuits. However, this requires the installation of two cabled circuits, which requires considerably more work and expense and can increase the maintenance requirements of the system overall.

One solution is to provide sounding devices that fit between the detection device and the surface on which the detection device is mounted. Although this allows a single cable circuit to service both the detector and sounding device, the resultant larged combined unit is intrusive and aesthetically undesirable.

A further solution would be to integrate the sounding device into the detection device. However, the problem with this is that the main area available within the detection device which would be suitable for receiving a sounding device is typically reserved for the smoke detection chamber and the design of the detection device cannot usually be changed without affecting the detection device characteristics. The remaining space available for locating the sounding device is positioned behind the smoke detection chamber and is normally used for housing the electrical circuitry associated with the detection device. There are currently prior art detection devices which integrate a sounding device within this space. However, the available space is limited as this area is used for electronics, electrical terminal arrangements and in some cases installer configurable interfaces such as DIL switches. This makes the addition of a sounding device in this area a more complicated design solution which inevitably compromises the acoustic properties and/or cost of the product. Alternatively, a larger device may be fitted within the detector device, but at the expense of significant aesthetic impact and often accompanied by poor acoustic performance due to the incorporation of the sounding devices within the limited spaces within the detection devices, sometimes requiring an off-centre location thereby restricting even sound distribution. Thus, there is little or no space remaining with which to achieve reasonable acoustic performance of the sounding device within the detection device.

There is therefore a need for a detection device with an integral sounding device with improved acoustic qualities without an undesirable increase in the overall size of the detection device itself.

Summary of the Invention

Accordingly, a first aspect of the present invention provides a detector for detecting fires or smoke, the detector comprising a housing defining a transducer receiving portion, a transducer received within the housing substantially adjacent the transducer receiving portion, a first reflector plate defining an aperture therethrough and spatially separated from the transducer so as to define a first acoustic cavity therebetween, a second reflector plate spatially separated from the first reflector plate and located distal to the transducer so as to define a second acoustic cavity between the first and second reflector plates, the housing defining one or more sound apertures therethrough in connection with the second acoustic cavity through which sound is emitted from the second acoustic cavity.

In this way, sound may be produced by the transducer within a first acoustic cavity before being transmitted to the second acoustic cavity and subsequently emitted through the one or more sound apertures in the housing. This arrangement allows a small transducer to be incorporated within a detector without significantly compromising the frequency and sound pressure level capabilities of the transducer. This allows the provision of a detector unit which can emit an alarm signal of sufficient volume without compromising the aesthetic look of the detector device as the transducer is located within a small area of the overall device. A smoke or fire detection means is provided within the detector to detect the presence of smoke or heat. On detection of smoke or heat, sound generation is initiated via the transducer so as to provide an audible alarm to alert a user to the detection of smoke or heat.

In one embodiment, the aperture defined by the first reflector plate may be a centrally located aperture. However, it will be appreciated that the aperture need not be centrally located and may alternatively be located in an offset position relative to the centre of the first reflector plate.

The first and second reflector plates are preferably planar. However, it will be appreciated that one or both reflector plates need not be planar and may have an alternative profile including, but not limited to a curved, stepped or multi-faceted profile.

In one embodiment, the transducer receiving means comprises spatial separators positioned adjacent the first reflector plate in the periphery of the transducer itself. Such spatial separators may comprise a ledge or a plurality of ledge portions which support the transducer at a spatial separation from the first reflector plate, thereby defining the first acoustic cavity therebetween. The spatial separators and first reflector plate may be. co-moulded, thereby contributing to the increased ease of production with associated reduction in costs. Alternatively, the transducer receiving means may comprise abutments, recesses or any other suitable receiving means known to the skilled person.

In one embodiment, the detector may further comprise a smoke detection chamber, wherein the second reflector plate comprises at least a portion of the smoke detection chamber housing. For example, the wall of the smoke detection chamber housing distal to the surface on which a detector may be mounted may comprise the second reflector plate itself. Alternatively, it will be appreciated that the second reflector plate may be a separate surface to the walls of the smoke detection chamber housing itself.

The transducer may comprise any suitable transducer known to the skilled person and appropriate for the function, including, but not limited to piezo-based devices and electromagnetic transducers such as moving coil loud speakers and the like.

In one embodiment, the sound apertures are located transverse to the plane of the reflector plates. For example, the sound apertures may be located such that the sound travels from the first acoustic chamber through the second acoustic chamber to the exterior of the detector through apertures located in the side of the detector.

The dimensions of the acoustic cavities may be varied to alter the acoustic properties of the sound emitted from the detector. For example, it is preferred that the transducer is separated from the first reflector plate by around 3 mm or less, and more preferably by 1 mm or less. In one embodiment of a detector in accordance with the present invention, the transducer is separated from the first deflector plate by between around 0.5 mm and 1 mm to form the first acoustic cavity.

The first and second reflector plates are preferably separated by around 7 mm or less and more preferably by 4 mm or less. In one embodiment of a detector in accordance with the present invention, the first and second reflector plates are separated from one another by between around 2 and 4 mm to form the second acoustic cavity.

It is known to provide a detector housing where the surface furthermost from the detector base in a separate part. In one embodiment of the preferred invention, the transducer is located within the separate part. Optionally, the first reflector plate also forms part of the separate part.

In one embodiment, the method of assembly of the detector is facilitated by the provision of the housing in two separate portions, one portion incorporating the detector base and the other including a cover portion located distal to the detector base.

Brief Description of the Drawings An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a first embodiment of a detection device in accordance with a first aspect of the present invention.

Detailed Description of the Invention

Figure 1 shows a cross-sectional view of a first embodiment of a detection device 10. Detection device 10 comprises a housing 20, having a detector base 22 which in use is mounted on a substantially planer surface, such as a wall or a ceiling or the like. The housing 20 defines a smoke detection chamber 30. Located within housing 20 distal from detector base 22, a transducer, such as a piezo disc 40 is mounted on transducer receiving portions in the form of spatial separators 50. Facing piezo disc 40 is first reflector plate 60 which defines a central aperture 65 therethrough. Thus, first acoustic cavity 70 is defined by piezo disc 40, first reflector plate 60 and housing 20. Thus the sound emitting portion of detection device 10 can use first reflector plate 60 and the volume of air located between first reflector plate 60 and piezo disc 40 to produce better acoustic performance in a compact space. In the embodiment shown in figure 1, the piezo disc 40 is located 2 mm from the first reflector plate 60. Detection device 10 is further provided with a second acoustic cavity 80 defined by first reflector plate 60 and the portion of the housing of smoke detection chamber 30 located distal to detector base 22. Second acoustic cavity 80 is further defined by portions of housing 20 of detection device 10. Those portions of housing 20 defining second acoustic cavity 80 are further provided with sound apertures 90 extending in a direction transverse to the axis through central aperture 65, such that sound from piezo disc 40 is emitted into first acoustic cavity 70 transmitted through central aperture 65 into second acoustic cavity 80 before being emitted to the exterior of housing 20 of detection device 10 via sound apertures 90 located in the side of housing 20.

It will be appreciated that although one surface of second acoustic cavity 80 is formed by a portion of the housing defining smoke detection chamber 30, it is envisaged that in an alternative embodiment a separate reflector plate moulding could be provided within housing 20 to define one surface of second acoustic cavity 80. However, it will be appreciated that the embodiment shown in Figure 1 is more cost-effective to manufacture.

The volume of the rear acoustic cavity 100 has a lesser effect on the acoustic performance than the first and second acoustic cavities and hence can be of various dimensions without significantly affecting the acoustic performance of the detector. A small aperture may be provided in housing 20 to provide a passage from the rear acoustic cavity to the exterior of housing 20 for the purposes of pressure equalisation.

Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort.

Claims

1. A detector for detecting fires or smoke, the detector comprising: a housing defining a transducer receiving portion; a transducer received within the housing substantially adjacent the transducer receiving portion; a first reflector plate defining an aperture therethrough and spatially separated from the transducer so as to define a first acoustic cavity therebetween, a second reflector plate spatially separated from the first reflector plate and located distal to the transducer so as to define a second acoustic cavity between the first and second reflector plates, the housing defining one or more sound apertures therethrough in connection with the second acoustic cavity through which sound is emitted from the second acoustic cavity.

2. A detector according to Claim 1, wherein the transducer receiving means comprise spatial separators positioned adjacent the first reflector plate in the periphery of the transducer.

3. A detector according to Claim 1 or Claim 2, further comprising a smoke detection chamber, wherein the second reflector plate comprises at least a portion of the smoke detection chamber housing.

4. A detector according to any preceding Claim, wherein the transducer comprises a piezo disc.

5. A detector according to any preceding Claim, wherein the sound apertures are located transverse to the plane of the reflector plate.

6. A detector according to any preceding Claim, wherein the transducer is separated from the first reflector plate by less than 3 mm.

7. A detector according to Claim 6, wherein the transducer is separated from the first reflector plate by less than 1 mm.

8. A detector according to Claim 7, wherein the transducer is separated from the first reflector plate by between around 0.5 and 1 mm.

9. A detector according to any preceding Claim, wherein the housing comprises a removable cover, the transducer being located within the removable cover.

10. A detector substantially as hereinbefore described and with reference to the accompanying drawings.