A multi-sensor fire alarm device

Abstract

A multi-sensor fire alarm device has a core (9) with a base (20) for engaging a ceiling and having a longitudinal axis. A cover (2) surrounds some of the core, and has vents (4, 204, 5, 205) to allow flow of ambient air radially inwardly into a first level (AF1) closest to the base and to flow (AF2) into a second level above the first level. An optical smoke chamber (160) is mounted centrally in the first level, and there are only two thermal probes on diametrically opposed sides near the vents in the second level. Air entering the second level is either directly incident on a thermal probe (50) or is deflected circumferentially towards it by a deflector (55) in the second level, and so there is only need for two probes. Guides provide air flow paths (150, 151, 152) from the first level to the smoke chamber Vents (204) for the first level have an insect-blocking mesh(204(a)) and vents (205) for the second level do not have such a mesh so that there is an open space for inflowing air without obstructions to affect temperature of the air.

Description

[0001] “A Multi-sensor Fire Alarm Device”

[0002] Introduction

[0003] The present invention relates to a multi-sensor fire alarm device having an optical sensor for smoke detection and a thermal sensor for heat detection at least.

[0004] An optical sensor works on the basis of air with entrained smoke entering a chamber with a light emitter and a detector, and the smoke causes reflection of some emitted light and the detector detects some of this reflected light. It is important to ensure that there is a good flow of air into the smoke chamber while at the same time preventing ingress of ambient light. An early example of a smoke alarm with an optical chamber is described in GB2251067 (The E.I. Company Limited).

[0005] On the other hand, a thermal sensor typically comprises a probe which reacts to temperature of air that is incident on it. A challenge in achieving a fast response for heat detection is that thermal mass of the device reduces air temperature as it passes through. Therefore, targeted airflow directly to the thermal sensor, with minimal obstruction is critical for a fast response time.

[0006] Here, the primary concern is to ensure that ambient air which is heated by a fire is quickly incident on the sensor probe.

[0007] Baffles are utilised to direct airflow into an optical smoke chamber. Generally, this baffle arrangement hinders airflow to the thermal sensors and results in longer airflow paths and more interaction with surfaces, reducing air temperature and delaying response time.

[0008] It is known to externally mount a thermal sensor so that it is exposed from the main body of the unit directly into the air flow. However, this results in a higher profile of the device, and the thermal sensor is more likely to be damaged due to being exposed. In general, a lower profile and more compact alarm device is preferred.

[0009] Other examples of such devices are described in EP4080476 (Panasonic), in which a ring of six thermal probes is arranged around the circumference of the device. EP4270342 (Hochiki Cork.) describes a device in which radial air inflow moves towards the centre by way of radially arranged guides. US2006 / 0007009 (Siemens) describes a device for sensing by different parameters.The present invention addresses the problem of the conflicting requirements of optical sensors and thermal sensors in a single multi-sensor device. It is also particularly directed towards achieving this in a device which has bulky items such as a sounder.

[0010] Summary of the Invention

[0011] The invention provides a fire alarm device with at least a smoke sensor and a thermal sensor to a achieve fast response time. This is achieved at least in part because the thermal and smoke sensors are mounted at different levels relative to the base of the device (or in other terms different positions along a longitudinal axis of the device). The levels are preferably defined by partitions which are also parallel or close to parallel to the plane of the base. In general, the device has air guides, some of which partition between levels and others of which guide radially towards the smoke sensor.

[0012] The thermal sensors are located internally within the device housing and are in preferred examples closer to the periphery of the device than the smoke sensor. This allows the thermal sensors to come directly into contact with air as it enters the device, and it provides paths to the smoke sensor without requiring it to be near the periphery and hence ambient light ingress is minimised.

[0013] The levels are generally parallel to the base of the device. On one level, preferably a first level closer to the base, baffles direct airflow into a smoke sensor chamber. On a second level, preferably further from the base, airflow is incident on the thermal sensors with minimal disruption to airflow.

[0014] The temperature sensors may comprise thermistor probes, and such probes may be mounted close to the edge vents of the device in the same level, thus reducing or avoiding any requirement for airflow through the device for the purpose of temperature sensing. Only one or two thermal sensors are required because of the manner in which air is either directly incident on the probes or is directed within this level to the probes from other radial directions.

[0015] In one embodiment, two thermal sensors are placed at opposite sides of the device in the same level. Flowing air can be directly incident on at least one of the probes, and air from a different direction is incident after being internally deflected in this same level by a baffle with a surface at an angle to the plane of the level. Such baffles preferably surround the longitudinal axis of the device.

[0016] This has the major advantage in that airflow in the second level is directed away from the centreof the unit thus allowing for the location of tall components at the centre of the unit such as user indicators, sounder, LED other indicators which can reach the outer surface of the unit for user indication.

[0017] If there were only a single thermal sensor placed at the centre of the unit airflow must be possible to this sensor from all 360°. The invention solves this problem by providing that there is only need for one or two thermal sensors, and they can be located close to the edges, achieving a fast response time.

[0018] In the case of the smoke sensor, radial baffles can be used to direct smoke towards a smoke chamber within the volume of the device. The fact that these baffles prevent airflow across the volume of the device is not a problem because the thermal sensors have their own level which is not affected by the smoke chamber baffles.

[0019] By arranging for airflow in different levels for each type of sensor there is optimum detection. Moreover, for some radial inflow directions the sir is split between upper and lower level so that the same airflows cause activation of both types of sensor.

[0020] We describe in some examples a multi-sensor fire alarm device comprising:

[0021] a core comprising a base for engaging a substrate such as a ceiling and having a longitudinal axis extending distally from the base,

[0022] a cover surrounding at least part of the core,

[0023] vents to allow flow of ambient air radially inwardly towards the longitudinal axis, an optical smoke chamber,

[0024] at least one thermal probe, and

[0025] air guides.

[0026] In some examples, the air guides allow air which is directly incident on the thermal probe to also flow towards the chamber, and to allow other air to reach both the chamber and the probe.

[0027] In some preferred examples, the guides comprise a partition to fully or partially separate a first level closest to the base from a second level further from the base. Where the partition partially separates the levels the guides preferably provide air flow paths from the second level to the smoke chamber, and the temperature probe is mounted in at least the second level.In some preferred examples, the guides comprise openings to allow longitudinal air flow from the first level towards the smoke chamber. In some preferred examples, the smoke chamber is mounted at a location overlapping or close to the longitudinal axis. In some preferred examples, the partition is mounted to divide incoming air flow from at least one direction between the first and second levels. In some preferred examples, the partition does not extend fully circumferentially around the longitudinal axis.

[0028] In some preferred examples, there are two partitions at different circumferential positions about the longitudinal axis. In some preferred examples, the partitions are substantially diametrically opposed.

[0029] In some preferred examples, the thermal probe is located near a vent. In some preferred examples, the thermal probe is no more than 20 mm from the nearest vent. In some preferred examples, there are at least two thermal probes. In some preferred examples, there are two thermal probes mounted at substantially diametrically opposed sides of the longitudinal axis.

[0030] In some preferred examples, the guides comprise a deflector mounted to deflect some air which enters the vents into the second level in a circumferential direction towards the thermal probe. In some preferred examples, the deflector surrounds the longitudinal axis. In some preferred examples, the deflector is elongate with opposed apexes subtending greater than 90° and located circumferentially distant from a thermal probe.

[0031] In some preferred examples, the deflector has a major axis and a minor axis, and the major axis is substantially aligned with the thermal probe or probes.

[0032] We also describe a multi-sensor fire alarm device of any example in which optical components are mounted within the optical chamber, and the components and the chamber are independently mounted to a circuit substrate.

[0033] In other embodiments, the partition between the first and second levels blocks air passage between the levels. Where this is the case the cover vents are arranged to provide flow directly into both levels. It is preferred that the cover vents for the first level have a mesh to prevent insects from moving into the device and so they do not access the smoke chamber. This helps to preserve integrity of the smoke chamber. It is also preferred that there is no mesh on the vents for the second level, thus avoiding an element in the air flow which could conduct heat from the air and thusreduce the temperature of the air reaching the thermal probes. A mesh in the air flow towards a thermal probe would act as a heat-reducing baffle, and so by completely separating the first and second levels there is no need for a mesh on the vents for the thermal probe, but there can be one for the vents for the smoke chamber.

[0034] We also describe a multi-sensor fire alarm device comprising:

[0035] a core comprising a base for engaging a substrate such as a ceiling and having a longitudinal axis extending distally from the base,

[0036] a cover surrounding at least part of the core,

[0037] cover vents to allow flow of ambient air radially inwardly towards the longitudinal axis, an optical smoke chamber,

[0038] at least one thermal probe, and

[0039] air guides including a partition to partially or fully separate a first level closest to the base from a second level further from the base, and wherein:

[0040] the optical chamber is in the first level, and the thermal probe is in the second level, the cover vents include:

[0041] vents for flow of air radially into the device in the first level, and said vents have an insect-preventing mesh, and

[0042] vents for flow of air radially into the device in the second level, and the guides comprise openings to allow longitudinal air flow within the first level towards the smoke chamber.

[0043] In some examples, the thermal probe is no more than 20 mm from the nearest vent. In some examples, there are two thermal probes mounted at diametrically opposed sides of the longitudinal axis, preferably only two probes.

[0044] In some examples, the guides comprise a second level deflector mounted to deflect some air which enters the vents into the second level in a circumferential direction towards the thermal probe.

[0045] In some examples, the second level deflector surrounds the longitudinal axis.

[0046] In some examples, the second level deflector is elongate, having a major axis which is longer than an orthogonal minor axis and the minor axis passes through opposed apexes each subtending an angle greater than 90° and located circumferentially distant from a thermal probe, and the major axis is aligned with the thermal probe or probes and passes through apexes each of which subtendsan angle of less than 90°.

[0047] In some examples, the device comprises a sounder, and the second level deflector at least partly surrounds the sounder.

[0048] In some examples, the smoke chamber comprises optical components mounted within the chamber, and the components and the chamber are independently mounted to a circuit substrate.

[0049] In some examples, the optical chamber comprises a vent in a top wall which is in fluid communication with the first level vent.

[0050] In some examples, the chamber extends over the substrate and covers the optical components.

[0051] In some examples, the partition prevents air from flowing between the first and the second levels, the cover vents comprise vents which allow air flow radially into the first level and said vents include an insect-blocking mesh, and the cover vents comprise vents which allow air flow radially into the second level and said vents do not have an insect-blocking mesh.

[0052] In some examples, the partition is mounted to divide incoming air flow through a cover vent between the first and second levels, and to allow some air in the second level to flow onwards into the first level.

[0053] In some examples, the partition does not extend fully circumferentially around the longitudinal axis. In some examples, there are two partitions at different circumferential positions about the longitudinal axis. In some examples, the partitions are substantially diametrically opposed.

[0054] In other examples we describe a multi-sensor fire alarm device comprising:

[0055] a core comprising a base for engaging a substrate such as a ceiling and having a longitudinal axis extending distally from the base,

[0056] a cover surrounding at least part of the core,

[0057] cover vents to allow flow of ambient air radially inwardly towards the longitudinal axis, an optical smoke chamber,

[0058] at least one thermal probe, and

[0059] air guides including a partition to partially or fully separate a first level closest to the basefrom a second level further from the base, and wherein:

[0060] the optical chamber is in the first level, and the thermal probe is in the second level, the cover vents include:

[0061] vents for flow of air radially into the device in the first level, and said vents have an insect-preventing mesh, and

[0062] vents for flow of air radially into the device in the second level, and the guides comprise openings to allow longitudinal air flow within the first level towards the smoke chamber,

[0063] the guides comprise a second level deflector mounted to deflect some air which enters the vents into the second level in a circumferential direction towards the thermal probe,

[0064] the second level deflector surrounds the longitudinal axis,

[0065] the second level deflector is elongate, having a major axis which is longer than an orthogonal minor axis and the minor axis passes through opposed apexes each subtending an angle greater than 90° and located circumferentially distant from a thermal probe, and the major axis is aligned with the thermal probe or probes and passes through apexes each of which subtends an angle of less than 90°, and the device comprises a sounder, and the second level deflector at least partly surrounds the sounder.

[0066] Detailed Description of the Invention

[0067] The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:

[0068] Fig. l is a perspective view from above of a multi-sensor alarm device of the invention,

[0069] Fig. 2 is a perspective view from above of the device with the top cover removed, showing components otherwise hidden by the device cover,

[0070] Fig. 3 is a perspective view from above showing parts of the device underneath partition plates and a deflector,

[0071] Fig. 4(a) is top view showing the lines for a cross-sectional view shown of Fig. 4(b) of the device,Figs. 5, 6, and 7 are perspective views illustrating paths for air flows which enter the circumferential vents of the device for optimum access to both thermal sensors and an optical chamber,

[0072] Fig. 8 is a perspective view showing potential air paths underneath the partition plates,

[0073] Figs. 9 is a perspective cut-away view and Fig. 10 is a perspective view of the optical chamber with many of the surrounding components removed to illustrate air flows towards the smoke chamber,

[0074] Fig. 11 is an elevational view of an alternative device, in this case having vents without a mesh for the second level,

[0075] Fig. 12 is a perspective view from above of the device of Fig. 11 with the top cover removed, in this case the partition completely separating the levels and the second level vents not having any mesh, and

[0076] Fig. 13 is a perspective view, showing air flows into the levels of the device of Figs. 11 and 12.

[0077] The invention provides a fire alarm device with at least a smoke sensor and a thermal sensor to a achieve fast response time. This is achieved at least in part because the thermal and smoke sensors are mounted at different levels relative to the base of the device (or in other terms different positions along a longitudinal axis of the device). The levels are preferably defined by partitions which are also parallel or close to parallel to the plane of the base. In some examples, the device has air guides, some of which partition incoming air between levels and others of which guide radially towards the smoke sensor.

[0078] The thermal sensors are located internally within the device housing and are in preferred examples closer to the periphery of the device than the smoke sensor. This allows the thermal sensors to come directly into contact with air as it enters the device from some angles, and it provides paths to the smoke sensor without requiring it to be near the periphery and hence ambient light ingress is minimised.The levels are generally parallel to the base of the device. On one level, preferably a first level closer to the base, baffles direct airflow into a smoke sensor chamber. On a second level, preferably further from the base, airflow is incident on the thermal sensors with minimal disruption to airflow.

[0079] The temperature sensors comprise thermistor probes mounted close to (within 20 mm, preferably less than 10 mm) the edge vents of the device in the same level, thus reducing or avoiding any requirement for airflow through the device for the purpose of temperature sensing. Only one or two thermal sensors are required because of the manner in which air is either directly incident on the probes or is directed circumferentially within this level to the probes.

[0080] In one embodiment, two thermal sensors are placed at opposite sides of the device in the same level. Flowing air can be directly incident on at least one of the probes, and air from a different direction is incident after being internally deflected in a generally circumferential direction in this same level by a baffle with a surface at an angle to the plane of the level. Such baffles preferably surround the longitudinal axis of the device.

[0081] This has the major advantage in that airflow in the second level is directed away from the centre of the unit thus allowing for the location of tall components at the centre of the unit such as user indicators, sounder, LED other indicators which can reach the outer surface of the unit for user indication.

[0082] If there were only a single thermal sensor placed at the centre of the unit airflow must be possible to this sensor from all 360°. The invention solves this problem by providing that there is only need for one or two thermal sensors, and they can be located close to the edges, achieving a fast response time.

[0083] In the case of the smoke sensor, radial baffles direct smoke towards a smoke chamber within the volume of the device. The fact that these baffles prevent airflow across the volume of the device is not a problem because the thermal sensors have their own level which is not affected by the smoke chamber baffles.

[0084] By arranging for airflow in different levels for each type of sensor there is optimum detection. Moreover, in some examples for some radial inflow directions the air is split between upper and lower level so that the same airflows cause activation of both types of sensor.Device of Figs. 1 to 10

[0085] Referring to the drawings, a multi-sensor alarm device 1 comprises an outer housing 2 which covers and partly surrounds a device core 9. The housing 2 has an outer (relative to a base of the device) portion surrounding a sounder wall 8 with openings for emission of sound, and the sounder 25 is symmetrically mounted about a longitudinal axis of the device. A rim 3 has two circumferential series of openings forming vents, a first (closest to the base) ring of vents 4 and a second or upper (furthest from the base) ring of vents 5. Each of the vents 4 and 5 has pillars 11 arranged at circumferential spacings, and the vents in some examples include meshes between the pillars 11 to prevent entry of insects.

[0086] The core 9 is shown in more detail in Figs. 2 to 4. It comprises a base 20 which is configured to engage a substrate such as a ceiling or wall, or to be mounted to a mounting plate, in turn mounted to a ceiling or wall. These details are not important to the invention, the important features being that the base 20 supports condition sensors, data processing circuits, a sounder 25 and LEDs.

[0087] The core 9 supports two diametrically opposed thermal probes, in this case thermistors, 50 mounted in a second level and close to the edge of the base 20, near the vents 5 (within 20 mm). In general terms it is preferred that the thermistors are no more than 20 mm from the closest vent, and in this case the distance from the vent is 9 mm. The second level comprises the thermistors 50 and a deflector 55 which encloses a volume of the second (top) level and is generally oblong in shape with a major (longer) axis extending through the thermistors 50. The deflector 55 has an apex 57 at one end and an apex 58 at the opposed end. The distance between each apex 57, 58 and the nearest thermistor 50 is in this case 6 mm and in general it is preferred that this distance is in the range of 4 mm to 15 mm. The angle defined by each apex 57, 58 is 80°, and in general it is preferred that the angle is in the range of 60° to 90°. In this case the apex 58 has a tubular upstanding housing 58(a) to accommodate light guides 58(b) to direct light from the circuit to lenses in the cover 2. It is not essential that light guides pass at this location, and they play no function in the air-deflecting function of the guide 55.

[0088] The deflector 55 has a curvature with a larger radius on the minor axis apexes 56, forming a shallow apex at each side. The radius of curvature at each minor axis apex 56 provides an angle in this case of 100°, and in general it is preferred that the radius be in the range of 90° (preferably 95°) to 120°, and that it be greater than the angle of the apexes 57, 58 on the major axis. The wide angle on the minor axis provides for very smooth laminar flow as air changes from a radial direction through the vents and turns either left or right to encounter one of the probes 50.The deflector 55 extends upwardly from radially extending partition plates 80 and 81 which are substantially parallel to the plane of the base and serve to partially separate the first (bottom) and second (top) levels. Air entering below a plate 80 or 81 moves generally radially and can enter an optical smoke chamber 160 which is mounted centrally, beneath the sounder 25.

[0089] Fig. 2 shows a surface 90 parallel to the partition plates 80 and 81 and the space between the surface 90 and these plates is in the first level and that above the plates 80 / 81 is the second level.

[0090] Fig. 3 shows particular detail of the first level, with axial openings 150, 151, and 152 allowing ingress of air in the first level towards the smoke chamber 160 affixed to the base 20 of the core 9. In this level air is guided radially by radial guides 155 and 156 and this contributes to flow towards the openings 150, 151, and 152. This (first) level is very important as it has vents 4 which allow air directly into the level and guides such as 155 which direct this air radially. This allows the smoke chamber 160 to be mounted in a central region (possibly overlapping the longitudinal axis) on the base 20 underneath the level of the sounder 8. Smoke alarm devices (as opposed or just detectors) require a sounder for the audible alarm and these need to be large and are best mounted centrally. The first level arrangement allows the smoke chamber 160 to be on the base, at a low level, despite the presence of the sounder, and this central and low location minimises ingress of ambient light to smoke chamber.

[0091] In more detail, it is evident from Fig. 4(b) that the device 1 needs to contain a number of components such as the sounder 25, the smoke chamber 160 centrally, a PCB 161 with circuits, a battery among others as is known in the art. However, the air guiding features of the device ensure optimum access of ambient air where it is needed for sensing. Fig. 4(b) shows that the smoke chamber 160 is in a location that is central and close to the base 20 of the core 9. Fig. 4(b) also shows that the chamber 160 is positioned on a PCB 161. Optical transmitter and receiver components 165 and 166 are also mounted to the PCB, the PCB providing an accurate structure for relative positions of the chamber and the optical components. The chamber 160 has “wings”, side extensions, 167 and 168 for accommodating the optical components to shield them from ambient light. However, the chamber also includes vents (not shown in this view, refer to Figs. 9 and 10) for ingress of air. Fig. 4(b) in particular demonstrates the advantages of the air guiding aspects of the invention for ensuring that sufficient air is guided to the low and central chamber location in addition to the thermal probes. As illustrated in Fig. 4(a) this view of Fig. 4(b) does not include the sounder, but as shown in the other drawings the sounder needs to be large to generatesufficient alarming sound, and it is best located centrally because of the vibrational symmetry which is preferred, particularly where the device housing is circular in plan. The arrangement allows the sounder to be centrally located in the second level, furthest from the base 20 / 9 and most exposed but not affecting access of air for sensing. The second level air guiding features allow there to be only two thermal probes, as radially incoming air is directly incident on a probe 50 or is quickly and smoothly guided to a probe 50 by the shallow angles on the minor axis of the guide 55. The deflector surrounds the sounder for at least part of its longitudinal dimension, providing very effective guidance of air towards the probes, irrespective of circumferential position of entry through the cover vents, and allowing presence of the bulky sounder.

[0092] Fig. 4(b) also shows hooks 170 extending from the base for engagement with a mounting plate.

[0093] In this embodiment, each partition plate 80 and 81 does not extend fully circumferentially around the longitudinal axis. The plate 80 has side edges 80(a) and (b) and the plate 81 has side edges 81(a) and (b) which allow air flows at the second level to partially enter the first level for access to the smoke chamber 160.

[0094] As shown by the air-flow arrows AF in Figs. 5 to 8 air which flows radially through the vents is categorised in two major flows as follows.

[0095] A first flow is where the air enters through the vents 4 or 5 in circumferential positions between the probes 50. This air is split by the partition plate 80 or 81 into a first level flow towards the optical chamber and a second level flow which is deflected by a shallow minor axis apex 56 towards one or both thermistors 50. Hence such air reaches both the optical chamber 160 via the first level and a thermistor 50 via the second level despite the fact that the optical chamber is centrally mounted near the base 20 (thereby well positioned for minimal ingress of ambient light) and the thermistors are near the edge.

[0096] A second flow which enters at or circumferentially near one of the thermistors 50 is immediately incident on the relevant thermistor 50, but some also flows onwards beneath at least one of the partitions 80 and 81 to be guided towards the optical chamber.

[0097] Fig. 5 in particular shows air flows AF in one side between the two probes 50. It reaches the probes 50 after deflection by the deflector 55 and circumferential flow, and some enters into the first level to reach the smoke chamber. A small portion can pass over the deflector to reach a volume within the deflector to move generally axially to reach the smoke chamber. The deflector 55 being oblong (having a larger major axis than minor axis) is important, as the large angle at the apexes of theminor axis provide for gradual guided movement towards the thermal probes 50 located at the narrower angled apexes of the major, longer, axis.

[0098] Fig. 6 shows that air flows AF also reach these destinations when it flows into the device from the opposite side.

[0099] Fig. 7 shows air flows AF which are akin to those of Fig. 5, with emphasis on how they are separated between the first and second levels. Some air flows directly into the first level only.

[0100] Fig. 8 shows how air which flows from any angle will reach the smoke chamber via the first level via the various axial openings 150, 151, and 152.

[0101] Figs. 9 and Fig. 10 show the optical chamber with many of the surrounding components removed to illustrate air flows towards the smoke chamber, after they have been guided as shown in Figs.

[0102] 5 to 8 within the first level towards the smoke chamber. These views show the smoke chamber in more detail, particularly a vent 169 in its top wall which is in fluid communication with the first level vents shown in Fig. 8. Also, Fig. 9 shows in more detail the chamber wings 167 and 168 over the PCB 61 and covering the optical components 165 and 166. Fig. 10 shows that there is air ingress parallel to the levels, normal to the longitudinal axis. This drawing also shows the sounder 171, which is of necessity large, and so the invention is particularly important at ensuring that air flows around this component towards the vents in the chamber 160.

[0103] As shown in Figs. 9 and 10 both the optical components 165 and 166 and the chamber 160 are independently mounted to the PCB substrate 162. This helps to ensure that there is excellent accuracy in the relative positions of the components and the chamber.

[0104] It will be appreciated that the device 1 provides that any air flow will efficiently reach both the smoke chamber and at least one of the thermal probes. If it does not enter near a probe, it will be split by a partition plate into the first level to reach the chamber, and the second level to reach a thermal probe after deflection within the second level. If it enters near a thermal probe, it will be immediately incident on the thermal probe, and some will then flow on under a side edge of a partition plate to reach the smoke chamber.

[0105] Embodiment of Figs. 11 to 13

[0106] In an alternative embodiment the partition between the first and second level blocks air passagebetween the levels and each cover vents is dedicated to providing flow directly into both levels. It is preferred that the cover vents for the first level have a mesh to prevent insects from moving into the device and so they do not access the smoke chamber as this helps to preserve integrity of the smoke chamber. It is also preferred that there is no mesh on the vents for the second level, thus avoiding an obstacle in the air flow which could conduct heat from the air and thus reduce the temperature of the air reaching the thermal probes 50.

[0107] Referring to Figs. 11 to 13, a multi-sensor alarm device 200 of another embodiment comprises an outer housing 202 which covers and partly surrounds a device core 209. Parts which are similar to those of the device 1 are assigned the same reference numerals. Fig. 11 is an elevational view of the device 200, in this case having vents for the second level which do not have a mesh. Fig. 12 is a perspective view from above of the device 200 with the top cover removed, in this case the partition 280 completely separates the levels and the second level vents not having any mesh. Fig.

[0108] 13 is a perspective view, showing air flows into the levels of the device of Figs. 11 and 12, AF1 into the first level and AF2 into the second level.

[0109] The housing 202 has an outer (relative to a base of the device) portion surrounding the sounder 25 outer wall 8 with openings for emission of sound, and the sounder 8 is symmetrically mounted about a longitudinal axis of the device. A rim 203 has two circumferential series of openings forming vents. These are a first (closest to the base) ring of vents 204 and a second or upper (furthest from the base) ring of vents 205. Each of the vents 204 and 205 has pillars 211 arranged at circumferential spacings

[0110] The first vents 204 have a mesh 204(a) to prevent insects from accessing the first level within the cover 202. However, the second vents 205 do not have a mesh. This means that air entering the second level is unimpeded and so there is less risk of heat loss before it is incident on the thermal sensors. As for the device 1, there are thermal probes 50 in the same arrangement, mounted in the second level and close to the edge of the base 209, near the vents 205 (within 20 mm). Again, it is preferred that the thermistors are no more than 20 mm from the closest vent, and in this case the distance from the closest vent is 9 mm. The second level comprises the thermistors 50 and the deflector 55 which encloses a volume of the second (top) level and is generally oblong in shape with a major (longer) axis extending through the thermistors 50. The deflector 55 has the apex 57 at one end and the apex 58 at the opposed end. The distance between each apex 57, 58 and the nearest thermistor 50 is again 9 mm and in general it is preferred that this distance is in the range of 4 mm to 15 mm. The angle defined by each apex 57, 58 is also 80°, and in general it is preferredthat the angle is in the range of 60° to 90°. The description above of configuration and effect of the air guide 55 and the thermal probes 50 in the device 1 applies in this embodiment too.

[0111] Unlike the device 1, the partition 280 between the two levels extends fully circumferentially and does not allow an air passage between the levels (preventing any insects which enter via the mesh-free vents 205 from accessing the smoke chamber). Hence the vents 204 allow air into the first level via the mesh 204(a) and this air is directed to the smoke chamber 160 in the same way that air in the first level of the device 1 is. Air entering the second level vents 205 is solely for incidence on the thermal probes 50. As the second level vents 205 do not have meshes there is nothing in contact with the air as it flows radially into the device, thereby not risking reduction of temperature, the thermal probes 50 receiving more accurate readings. If insects enter through the vents 205 it does not matter as there is unlikely to be any effect on the thermal sensing.

[0112] Fig. 13 shows typical air flows, with air flows AF1 through the first level vents 204 entering the first level and accessing the smoke chamber in the same manner as illustrated above for the device 1. In this case air flows AF2 which enter the second level remain in the second level and encounter the thermal probes 50 either directly radially or after internal deflection at a wide-angle apex 56. The description of the air flows in the second level of the device 1 apply here, the only difference being that no air that enters the second level also migrates onwards into the first level.

[0113] Components of embodiments can be employed in other embodiments in a manner as would be understood by a person of ordinary skill in the art. The invention is not limited to the embodiments described but may be varied in construction and detail.

Claims

Claims1. A multi-sensor fire alarm device comprising:a core (9) comprising a base (20) for engaging a substrate such as a ceiling and having a longitudinal axis extending distally from the base,a cover (2) surrounding at least part of the core,cover vents (4, 204 5, 205) to allow flow of ambient air radially inwardly towards the longitudinal axis,an optical smoke chamber (160),at least one thermal probe (50), andair guides (55, 80, 81, 155,156) including a partition (80, 81, 280) to partially or fully separate a first level closest to the base from a second level further from the base, and wherein:the optical chamber (160) is in the first level, and the thermal probe is in the second level,the cover vents include:vents (4, 204) for flow of air radially into the device in the first level, and said vents have an insect-preventing mesh (204(a)), and vents (5, 205) for flow of air radially into the device in the second level, andthe guides comprise openings (150, 151, 152) to allow longitudinal air flow within the first level towards the smoke chamber.

2. A multi-sensor fire alarm device as claimed in claim 1, wherein the thermal probe (50) is no more than 20 mm from the nearest vent (4, 5).

3. A multi-sensor fire alarm device as claimed in claim 2, wherein there are two thermal probes (50, 51) mounted at diametrically opposed sides of the longitudinal axis, preferably only two probes.

4. A multi-sensor fire alarm device as claimed in any preceding claim, wherein the guides comprise a second level deflector (55) mounted to deflect some air which enters the vents (5, 205) into the second level in a circumferential direction towards the thermal probe (50).

5. A multi-sensor fire alarm device as claimed in claim 4, wherein the second level deflector (55) surrounds the longitudinal axis.

6. A multi-sensor fire alarm device as claimed in claim 5, wherein the second level deflector (55) is elongate, having a major axis which is longer than an orthogonal minor axis and the minor axis passes through opposed apexes (56) each subtending an angle greater than 90° and located circumferentially distant from a thermal probe, and the major axis is aligned with the thermal probe or probes and passes through apexes (57) each of which subtends an angle of less than 90°.

7. A multi-sensor fire alarm device as claimed in any of claims 4 to 6, wherein the device comprises a sounder (25), and the second level deflector (55) at least partly surrounds the sounder.

8. A multi-sensor fire alarm device as claimed in any preceding claim, wherein the smoke chamber comprises optical components (165, 166) mounted within the chamber (160), and the components and the chamber are independently mounted to a circuit substrate (161).

9. A multi-sensor fire alarm device as claimed in claim 8, wherein the optical chamber comprises a vent (169) in a top wall which is in fluid communication with the first level vent (4, 204).

10. A multi-sensor fire alarm device as claimed in claim 8 or claim 9, wherein the chamber extends (167, 168) over the substrate (161) and covers the optical components (165, 166).

11. A multi-sensor fire alarm device as claimed in any preceding claim , wherein the partition (280) prevents air from flowing between the first and the second levels, the cover vents comprise vents (204) which allow air flow radially into the first level and said vents include an insect-blocking mesh (204(a)), and the cover vents comprise vents (205) which allow air flow radially into the second level and said vents do not have an insect-blocking mesh.

12. A multi-sensor fire alarm device as claimed in any of claims 1 to 10, wherein the partition (80, 81) is mounted to divide incoming air flow through a cover vent (4, 5) between the first and second levels, and to allow some air in the second level to flow onwards into the first level.

13. A multi-sensor fire alarm device as claimed in claim 12, wherein the partition does not extend fully circumferentially around the longitudinal axis.

14. A multi-sensor fire alarm device as claimed in claim 12 or claim 13, wherein there are two partitions (80, 81) at different circumferential positions about the longitudinal axis.

15. A multi-sensor fire alarm device as claimed in claim 14, wherein the partitions (80, 81) are substantially diametrically opposed.

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