GB2296763A - Improvements in and relating to smoke detectors - Google Patents

Abstract

A smoke detector 1, is formed of two or more units; the first unit 3 has a sub unit 13, 15 and a base 4 latched together; the first unit is adapted to be permanently fixed to a surface such as a ceiling; the first unit contains electronic control circuitry 7 to process a signal from one or more sensors 57 in the detector: a second unit 5 which has a smoke chamber 17 is detachable from the first unit so that the smoke chamber and or any other parts affected by smoke can be detached from the fixed parts including the electronic circuitry for cleaning or replacement with clean parts. <IMAGE>

Description

Improvements in and relations to smoke detectors The present invention relates to a smoke detector for providing early detection of a fire in a building.

Smoke detectors are frequently formed as self contained assemblies consisting of sensors to detect the presence of smoke or other products of combustion or the increasing temperature resulting from the fire, electronic circuits to process the signals from the sensors, and a sounder to provide audible warning of a fire. They are normally positioned on a ceiling sometimes at a high level and are exposed to the atmosphere in the building. The atmosphere in most buildings is contaminated with dust particles, and possibly also grease vapours which will deposit on all surfaces, including those of the smoke detector.

Contamination with dust or grease will affect the performance of the detector, such that eventually it will fail to operate correctly. Most detectors are designed to fail safe, such that in the event of contamination affecting the performance, the detector will fail to an alarm situation. Hence it is necessary to ensure that detectors are maintained in a clean condition.

Conventionally this may involve removing the complete detector or detector less the base from the ceiling to clean it. In the case of serious contamination, replacement may be the only alternative, which is expensive as the complete contaminated smoke detector has to be discarded and replaced with a new smoke detector. Most smoke detectors include a combustion products receiving chamber hereinafter referred to as a "smoke chamber" although some combustion products are not strictly in the form of smoke.

A smoke detector according to the invention comprises a first unit adapted for permanently fixing to a surface and a second unit removable from the first unit, wherein the first unit contains an electronic control circuit arranged to process a signal from one or more sensors in the detector, and wherein the second unit contains at least one smoke chamber.

The advantage of the invention is that the more expensive components of the detector remain permanently in place whilst those parts which are subject to contamination can be readily removed for cleaning or replacement.

In a first embodiment of the invention the first unit contains optical sensing means comprising a light source and a light receiver and the second unit contains a smoke chamber. In a second embodiment the second unit contains an ionisation chamber smoke detector.

Preferably the electronic control circuit is arranged to recognise and to distinguish between a gradual degradation of sensitivity of the sensor(s) due to contamination, an alarm state where the sensor has detected combustion products in a sufficient concentration, a normal state of readiness, and the state wherein the second unit has been removed.

Preferably where the detector includes optical sensing means, the smoke chamber in the second unit is provided with windows so arranged that the light source and receiver are separated from the smoke chamber and wherein the optical axes of the light source and receiver pass through the windows.

Preferably a distinctive electrical output is achieved by a contrast between a low level of light transmission through the smoke chamber and a high level of light transmission when the second unit is removed. In order to achieve this a reflector is preferably provided on the first unit in a location between the light source and light receiver.

Preferably the first unit of the detector further comprises a base with terminals connected to the control circuit of the first unit and is adapted to be permanently fixed to the surface and a sub-unit containing the control circuit which is arranged to plug into the base and to latch thereto.

The detector may be self contained, or be part of a larger system, where some of the information processing required to distinguish between the detection of a fire, the removal of the removable unit, and the degradation of performance caused by contamination is done by a central control unit rather than within the detector itself, hence the detector in this case will contain means to communicate with the central control unit.

The detector may be arranged such that the second unit is replaceable without affecting the performance of the detector. The benefit of this is that by replacing a relatively low cost part of the detector it may be restored to its original sensitivity without unfixing the first unit.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross section of a detector as seen from one side according to a first embodiment of the invention taken from one side on JJ as shown in Fig.2, Figure 2 is an underneath plan view of the detector of Fig. 1 as seen from H in Fig. 1, Figure 3 is an exploded cross section of a first unit of the detector shown in Fig. 1 less its base taken on section JKK as shown in Fig. 2, Figure 4 is an exploded cross section of a second unit of the detector shown in Fig. 1 taken on section JJ as shown in Fig. 2, Figure 5 is an enlarged plan view of the first unit of the detector of Fig. 1 as seen from LL in Fig. 3, Figure 6 is an enlarged plan view of the first unit of the detector of Fig. 1 with part of the second unit inserted as seen from MM in Fig. 4, Figure 7 is a plan view from below of the base of the detector of Fig. 1, Figure 8 is a cross section of the first unit of the detector of Fig. 1 taken on NN of Fig. 7, showing the interlocking of the first unit with the base of Fig. 7, Figure 9 is a block diagram of the electrical circuitry for the detector of Fig. 1, Figure 10 is an assembled diametric cross section of a detector according to a second embodiment of the invention less its base which is the same as that shown in Fig.s 1 and 7, Figure 11 is an exploded cross section of a first unit of the detector of Fig. 10 taken on the same cross section as Fig. 10, Figure 12 is an exploded cross section of a second unit of the detector of Fig. 10 taken on the same cross section as Fig. 10, and Figure 13 is a block diagram of the electrical circuitry for the detector of Fig. 10.

Figures 1 to 9 show a first embodiment of the invention which is an optical smoke detector generally shown at 1.

It comprises a first unit 3 which locks into a base 4 as will be described and which together are permanently fixed to a surface such as a ceiling. The detector further comprises a second unit 5 which can be readily detached and removed from the first unit as will be described. The first unit contains an electronic control circuit mounted on a printed circuit board (PCB) 7 and within spaces 9 and 11 between lower mounting plate 13 and circuit board 9 and upper plate 15 and circuit board 7 respectively. The second unit 5 contains a main smoke chamber 17 formed in an upper plate 19 and connected to ante chambers 21 above wire mesh 23 formed by smoke baffle member 25.

Returning to the first unit this comprises as previously indicated plates 13 and 15 which are locked together within a cylindrical cover 27 by catches 29, PCB 7 being latched to upper plate 15 by catches 31. Contacts 33 extend upwardly from PCB 7 through plate 15 so as to make contact with contacts 35 on base 4. The base contacts 35 connect with terminals L1, L2 and OV which are permanently wired to a central control box or control and indicating panel (not shown). The base 4 and upper plate 15 are retained together by lugs 39 on the interior of cover 27 which engages in circumferential slots 41 and by a 16.5 degree twist further engages in recesses 43 to be locked by a flexible resilient detent part 45 which springs in a recess 47 in the upper plate 15 (see Fig. 8).Base 4 then becomes a part of unit 3 and is essentially unremovable from the surface to which the base has been fixed. If the whole system has to be removed parts within the cover 27 and the cover itself can be taken apart from the base by means of an axially movable detent release member 49 which can be accessed by poking a probe into a hole 51 in plate 13.

When pressed upwards member 49 pushes detent 45 out of recess 47 so that the cover 27 can be twisted back to align lugs 39 with slots 41.

Mounted to lower plate 13 by guard support 53 and extending downwards is thermistor guard 55. These cover thermistor 57 which is connected to PCB 7. The thermistor 57 acts as a heat detector.

Also mounted to lower plate 13 as seen in Fig. 5 is an L.E.D light source 60 to one side of a smoke chamber receiving recess 62 and at the other side of recess a photoelectric receiver 64 is located. The optical axes 66 and 68 of the light source and receiver are angled to each other at an angle 0 of about 130 and are angled at an angle of about 5 in a plane at right angles to the plane of Fig. 5. Lenses 70 and 72 are mounted adjacent the source and receiver respectively to focus the light from and to these. On the outer side 74 of recess 62 there is fixed reflective material forming a curved mirror 76 which in the absence of the second unit and its smoke chamber reflects light from the source to the receiver.It will therefore be seen that the optical axis 66 of the source and axis 68 of the light receiver are angled to each other and intersect at a point 78 in a plane parallel to the fixing plane 80 of the smoke detector defined by the top surface of the base 44.

Further mounted to lower plate 13 is a piezo electric sounder 82 and a pair of L.E.D.s 84 and 85, 84 being a red light emitter which indicates the status of the detector, whilst 85 is an infra red emitter used for communicating information about the status of the detector to an infra red receiver.

Referring now to the second unit as shown in Fig. 4 and partly in Fig. 6, this comprises a cylindrical casing 87 having a closed bottom 89 in which is a hole 90 to view light from L.E.Ds 84 and 85 collected and channelled by light pipe 92 held in a recess 93 in smoke guide vane member 94. Smoke vane member 94 includes eight smoke vanes 96 shown in Fig. 4 and as broken lines in Fig. 6 which direct airflow from apertures 98 in casing 87 towards slots 100 in thermistor cover and spaces below and adjacent mesh 23 and into ante chamber 21 and main smoke chamber 17.

Immediately above smoke vane member 94 is the mesh 23 which is held between the smoke vane member and upper plate 19 and a smoke baffle member 102 which is pegged into upper plate 19 by three pegs 103. Baffle member 102 has two angled vertical baffle walls 104 and 105 each joining respective parallel vertical walls 106 and 107 shown in Fig. 4 and in broken lines in Fig. 6. Member 102 also has a further baffle wall 108 shown in broken lines in Fig. 4 and Fig. 6 angled at about 200 extending over the inner side of smoke chamber 17 to direct smoke from the mesh into the smoke chamber. The vertical walls 104-107 also direct smoke from the mesh above wall 108 into chamber 17.

The smoke chamber 17 formed in the upper walls of plate 19 has a central groove 110 facing and opposite intersection 78 of the optical axes 66 and 68 which are parallel to inner vertical sides 111 and 112 of the chamber. Side 111 has anti reflective teeth 113. The arcuate outer side 114 of the chamber also has anti reflective teeth 115. At the opposite ends of chamber 17 are clear plastic windows 117 and 118 which prevent smoke from impinging on lenses 72 and 70 respectively so that smoke or fumes are prevented from clinging to any parts of the first unit particularly the optical members 60, 70, 72 and 64. The top wall 120 and surfaces 121 of teeth 115 facing higher source 60 are given a textured finish to provide a surface. Teeth 115 are angled at 20 to the vertical on their surfaces facing the receiver 64.The material of plate 19 with chamber 17 and the baffle member 102 is typically black plastics having anti static properties.

Teeth 115 are radially between 80 and 9.50 from the vertical central axis 116 of the detector with their side surfaces 123 facing receiver 64 each aligned with the respective radius from the central axis 116.

The second unit fits into the first unit and locked thereto by partial rotation of casing 87 relative to casing 27, casing projections 130 fitted in grooves 132 to enter slots 134. Casing 87 is locked to plate 19 by means of similar projections 136 engaging by partial rotation behind slots 137, rotation being locked by latch 138 engaging with projection 139 (see Fig. 4).

In Figure 9 there is shown the circuitry 140 which is contained within the first unit 3. This comprises loop interface 141 connected to terminals L1 and L2 to power supply unit 142 and microprocessor 144. A remote central control unit 145 is connected to terminals L1 and L2.

Connected to the microprocessor is heat sensor 57, optical chamber interface 148 connected in turn to light source being L.E.D. 60 and receiver 64, and oscillator and sounder driver 150 connected in turn to sounder 82. Also connected to microprocessor 144 is L.E.D. driver 152 which causes L.E.D. 84 to illuminate steadily for a fault or to flash for a fire condition or L.E.D. 85 to transmit information to a receiver. The microprocessor 144 assembles and transmits values for assessment and controls the circuitry on the detector. The C.C.U. 145 is programmed to assess the level of optical signal received by receiver in order to determine whether: (a) the second unit is detached from the first unit, or (b) the detector has detected a particular type of test aerosol identified as an extremely thick smoke, or (c) the detector has detected smoke from a fire, or (d) there is a quiescent value with a clean optical chamber and no smoke or (e) the detector performance is degraded, or (f) the detector is disabled due to over degradation.

C.C.U. bits are allocated for situation (a) to (f) as follows: (a) 1-10 bits (second unit detached) (b) 11-29 bits (test) (c) 30-219 bits (normal detection range) (d) 220-239 bits (quiescence) (e) 240-244 bits (degradation warning) (f) 245-256 bits (unserviceable) A long term data drop below 210 bits will also be signalled as a warning of degraded performance due to contamination.

When the second unit is detached there is a high level of light transmission between L.E.D. 60 and receiver 64 by reflection of beam 66 off mirror 76 onto receiver 64, mirror 76 being of course covered by plate 19 when the units are fitted together. The microprocessor 144 is able to communicate the detection level in any one of situations (a) to (f) to a central unit which services a plurality of the detectors via loop interface 141. It should here be noted that the second unit can be replaced by any other unit of the same type without significant change in the sensitivity.

A second embodiment of the invention will now be described with reference to drawings 10 to 13 which shows an ionisation detector generally at 200. This detector has the same base 4 as previously described. Many other details and parts of detector 200 are the same as that of detector 1 that is the first embodiment. Where the parts of detector 200 are identically the same as those described in detector 1 they will be given the same reference number.

Thus detent release member 49 is the same in both embodiments and will not be further described. Other parts which are to all purposes identical but with minor unimportant details will be given similar reference numbers with 200 added. Thus upper plate 215 is virtually the same as plate 15 and will not be further described unless the details has a slight meaningful difference.

The detector 200 has as in detector 1 a first unit 202 which locks into base 4 by means of detent 45 and recess 47 as before with the same detent release member 49. A second unit 206 having the same casing 87 as before is locked and latched as before to the first unit 202. The control electronics are mounted on a printed circuit board (PCB) 207 and are between upper plate 215 and lower plate 212.

PCB 207 has mounted to it contacts 33 which go through upper plate 215 as in detector 1 for connection to the pattress 4. Also mounted to the PCB 207 and connected to the control electronics is a socket 214 with three contacts which connect with contacts on connector 216 which via a calibrating circuit connect with wire mesh 222 on electrode pin 224 and ion source 226. Mesh 222 encloses a smoke chamber formed as an ionisation chamber 232 which with ground plane 228 and cover plate 230 are retained in plate 218 of the second unit. Plate 230 is locked and latched into casing 87 as in the first detector 1.

Thus the disposable parts of the detector are all in the second unit 206 with the control electronics in the first unit 202. The disposability of the second unit is important since it should be returned to the manufacturers for disposal.

The electronic circuitry of the first unit is shown in Fig.

13. This is similar in some respects to that of the first embodiment having loop interface 141, power supply unit 142 and L.E.D. Driver 152 for L.E.D.s 84 and 85.

Microprocessor 344 is connected to ionisation chamber interface 350 which in turn is connected to electrode pin 224, ion source 226 and to mesh 22 via ground plane 228.

Claims (14)

1. A smoke detector comprising a first unit adapted for permanently fixing to a surface and a second unit removable from the first unit, wherein the first unit contains an electronic control circuit arranged to process a signal from one or more sensors in the detector, and wherein the second unit contains at least one smoke chamber.

2. A detector as claimed in claim 1 wherein the first unit contains as one of said sensors an optical sensing means comprising a light source and a light receiver and wherein the second unit contains a smoke chamber.

3. A detector as claimed in claim 1 or 2 wherein one of said sensors is a heat sensor.

4. A detector as claimed in claim 3 wherein the heat sensor is a thermistor mounted in the central axis of the detector within a cover.

5. A detector as claimed in any one of claims 1 to 4 wherein the electronic control circuit and an associated signal processor are such as to recognise and to distinguish between a gradual degradations of sensitivity of at least one said sensor, an alarm state, a quiescent state of readiness and a state wherein the second unit has been removed from the first unit.

6. A detector as dependent on claim 2 wherein the smoke chamber is provided with windows so arranged that the light source and receiver are separated from the smoke chamber and wherein the optical axes of the light source and receiver pass through the windows.

7. A detector as dependent on claim 2 wherein a distinctive electrical output is achieved by a contrast between a low level of light transmission through the smoke chamber and a high level of light transmission when the second unit is removed.

8. A detector as claimed in claim 7 wherein a reflector is provided on the first unit between the light source and light receiver.

9. A detector as claimed in claim 1 wherein the second unit contains an ionisation chamber smoke detector as one of said sensors in the smoke chamber.

10. A detector as claimed in any one of claims 1 to 9 wherein the first unit further comprises a base and a sub unit which is arranged to plug into the base and to latch thereto.

11. A detector as claimed in claim 10 wherein the base is provided with terminals connectable to the control circuit of the first unit.

12. A smoke detecting system including at least one smoke detector as claimed in any one of claims 1 to 11 and including a central control unit connected to the one or more said detectors.

13. A smoke detector substantially as described with reference to Figures 1 to 9 of the accompanying drawings.

14. A smoke detector substantially as described with reference to Figures 10 to 13 of the accompanying drawings.