EP1101210A1 - Smoke detectors - Google Patents

Smoke detectors

Info

Publication number
EP1101210A1
EP1101210A1 EP99937808A EP99937808A EP1101210A1 EP 1101210 A1 EP1101210 A1 EP 1101210A1 EP 99937808 A EP99937808 A EP 99937808A EP 99937808 A EP99937808 A EP 99937808A EP 1101210 A1 EP1101210 A1 EP 1101210A1
Authority
EP
European Patent Office
Prior art keywords
light
smoke
smoke detector
sources
light sources
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99937808A
Other languages
German (de)
French (fr)
Inventor
Dunstan Walter Runciman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GSBS Development Corp
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP1101210A1 publication Critical patent/EP1101210A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
    • G08B17/107—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device for detecting light-scattering due to smoke
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas
    • G08B17/113—Constructional details

Definitions

  • THIS INVENTION relates to smoke detectors.
  • Smoke detectors operate by detecting the scattering of light which occurs when there is smoke in the casing of the detector.
  • the detector includes a light source such as an LED or a laser which is activated at intervals to provide bursts of light.
  • a photosert tive device detects any light which is reflected off smoke particles in the casing.
  • an alarm condition is established at the control panel.
  • the pattern of the signal being received from the detector is taken into consideration instead of, or as well as, a threshold value. Pattern recognition is used to determine the probability that the received signal indicates a fire thereby to reduce the possibility of false alarms being generated. False alarms are one of the major problems encountered in fire alarm systems.
  • smoke detector which comprises a casing, two light sources for illuminating the
  • each light source producing light at a discrete wavelength
  • photosensitive means for determining discrete wavelengths being different to one another
  • the particles can be airborne smoke particles or particles which have
  • Said photosensitive means can detect forward scattered light, or back
  • both light sources and the photosensitive means are identical to each other. It is preferred that both light sources and the photosensitive means are identical to each other.
  • Said light sources can be LEDs of different colours.
  • the wave lengths of the LEDs should differ from one another by as much
  • infra red is to be deemed to be within the term "light" even though it is not visible to the human eye.
  • the light sources can be lasers emitting coherent light at different wavelengths.
  • one laser emits light at the blue / violet end of the spectrum and the other at the red / infrared end of the spectrum.
  • a method of detecting smoke particles which comprises illuminating the smoke particles using light at two discrete and different wavelengths and detecting the light which is scattered by the smoke particles.
  • the particles can be airborne smoke particles or particles, such as dust particles, which have settled on a surface.
  • smoke is illuminated alternately by light at a first wave length and by light at a second wave length.
  • the first wave length can be at the infra red end of the light spectrum and the second wave length at the blue or violet end of the light spectrum.
  • Figures 1 to 6 each diagrammatically illustrates the mode of operation of a smoke detector in accordance with the present invention
  • Figure 7 is an "exploded" view of a detector which operates in accordance with the mode of operation illustrated in Figure 4;
  • Figure 8 is a vertical, pictorial section through the detector of Figure 7; and Figure 9 is a vertical section through the assembled detector.
  • reference numerals 10 and 12 indicate two light sources which are mounted in the smoke detecting chamber of the smoke detector.
  • the chamber has a barrier 14 for shielding a photosensitive device 16 from the light sources.
  • the barrier 14 prevents light from the sources 10 and 12 travelling in a straight line to the device 16.
  • the device 16 can include a lens for concentrating reflected light onto the photosensitive surface.
  • the light sources 10 and 12 are preferably an LED emitting light at the blue / violet end of the light spectrum (about 430 nm) and an LED emitting light at the infrared end of the light spectrum (about 980 nm). This ensures that the difference between the wavelengths is as great as possible as this enhances discrimination.
  • the shaded area in Figure 1 indicates a concentration of smoke in the detecting chamber.
  • the chamber is bounded by the casing of the detector and the casing has a plurality of openings therein which permit smoke laden air to enter the chamber.
  • the detector of Figure 1 detects what is known as forward scatter. In other words it detects light which has been reflected off the smoke particles at an angle but has continued on, as shown by the arrows, in the same general direction rather than being reflected back. Some light is also transmitted through some particles due to their translucence. The angle is shown as being about a right angle but in practice it is far more obtuse. The size of smoke particles, and their shape, varies with the type of material that is burning. Because of the difference in light wave lengths, the interaction between the light from one source and the particles differs from the interaction between light from the other source and the particles.
  • the sources 10 and 12 are illuminated out of phase with one another. It is preferred that the light sources are illuminated alternately.
  • the output of the photosensitive device 16 is fed to a control panel, and software in the control panel can be used to differentiate between the output which has resulted from the scattering of the blue light and the output which has resulted from the scattering of infra red light.
  • the software can be used to determine smoke particle size, smoke
  • Some forms of smoke detectors incorporate processing software.
  • back scatter refers to light which has been reflected back
  • the device 18 is located as close to the sources 10 and
  • the detector of Figure 3 has two infra red light sources 20 and 22 and
  • the device 28 detects forward scatter from the sources 20 and 24 and back
  • the photosensitive device 34 detects light at
  • the device 36 can include a blue pass filter which blocks other wavelengths.
  • devices 34 and 36 detect forward scatter.
  • the detector of Figure 5 is similar to that of Figure 4 but includes two
  • Figure 6 shows a detector which has two blue / violet light sources 42
  • the devices 50 and 52 detect back scatter from the light
  • the filter device includes
  • 50 can include a blue pass filter.
  • photosensitive device could be in one chamber and the infrared light source and
  • each chamber would contain one light source and two photosensitive devices.
  • each chamber would contain two light sources of the same colour and one photosensitive device. If the smoke detector does have two chambers then bursts of light of two colours can occur simultaneously.
  • Reflection off dust particles that have been deposited on the inside of the casing can be used for the purpose of calibrating the detector.
  • Information derived from the two light sources may also be usable for the purpose of compensating for contamination of any lenses that are used.
  • the smoke detector illustrated is designated 60 and comprises a frusto conical cover 62 the wall 64 of which has therein openings 66 which are covered by mesh 68 to prevent the ingress of insects and unwanted dust particles while permitting smoke to enter.
  • Internal walls 70 which are ribbed to inhibit light reflection, lie internally of the wall 64. Between the walls 70 are slit-like smoke entrances 72 to the smoke chamber which is within the cover 62. The openings 66 are staggered circumferentially with respect to the entrances 72 to prevent ambient light entering the detector.
  • the smaller end of the cover 62 is closed by an end wall 64.1 which has a central opening 65.
  • An internal reflector 74 has a knob 74.1 which passes through the opening 65 and attaches the reflector 74 to an external adjuster 76.
  • the cover is secured to a ring 78 by means of an array of six bayonet connections the parts of which are generally designated 80.1 , 80.2.
  • the ring 78 includes partitions 82 which extend inwardly from opposite sides thereof and have
  • the housing 86 is in two parts 88 and 90, the part 88 comprising a
  • the housing is in the form of a closure cap which can be ultrasonically welded to the
  • the device 108 preferably has a blue pass filter over it so that
  • the sources 102 and 104 are in a space 110
  • An inclined partition 1 14 separates the photosensitive devices 106
  • the bottom wall 98 of the space 1 10 is
  • a printed circuit board is diagrammatically shown at 1 16, the light
  • the entire detector illustrated clips onto a base (not shown) which is itself secured to a ceiling.
  • Mechanical calibration is effected by rotating the reflector 74 thereby varying the light which reaches the photosensitive devices even in the absence of smoke particles.
  • Lasers produce coherent light of narrow band width whereas the light from LEDs is not coherent and its band width is wider. Use of a red laser and a blue / violet laser is preferred thereby to obtain maximum separation of the frequencies.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Fire-Detection Mechanisms (AREA)

Abstract

A smoke detector is disclosed which includes a smoke chamber having an inlet through which smoke can enter the chamber. In the chamber there are two light sources, preferably LEDs, which radiate light at frequencies which are as widely spaced as possible. Blue and infrared LEDs are preferred as these have wavelengths of about 430 nm and 980 nm respectively. The chamber also has therein one or more photosensitive devices onto which light scattered by smoke particles in the chamber falls. There is a barrier between the light sources and the photosensitive device to prevent light travelling in a straight line from the sources to the photosensitive device. Embodiments are disclosed which have more than two light sources, more than one photosensitive device and more than one smoke chamber.

Description

SMOKE DETECTORS
FIELD OF THE INVENTION
THIS INVENTION relates to smoke detectors.
BACKGROUND TO THE INVENTION Smoke detectors operate by detecting the scattering of light which occurs when there is smoke in the casing of the detector. The detector includes a light source such as an LED or a laser which is activated at intervals to provide bursts of light. A photosert tive device detects any light which is reflected off smoke particles in the casing. In older types of detector, once the output of the photosensitive device reaches a predetermined level, an alarm condition is established at the control panel. In newer types of detectors the pattern of the signal being received from the detector is taken into consideration instead of, or as well as, a threshold value. Pattern recognition is used to determine the probability that the received signal indicates a fire thereby to reduce the possibility of false alarms being generated. False alarms are one of the major problems encountered in fire alarm systems.
Such smoke detectors, to the best of Applicant's knowledge, whilst able to detect low levels of smoke concentration, reveal nothing about the type of smoke. BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the present invention there is provided a
smoke detector which comprises a casing, two light sources for illuminating the
interior of said casing, each light source producing light at a discrete wavelength, the
discrete wavelengths being different to one another, and photosensitive means for
detecting light from said sources after it has been scattered by particles in said
casing.
The particles can be airborne smoke particles or particles which have
adhered to inner surfaces of the casing.
Said photosensitive means can detect forward scattered light, or back
scattered light, or both forward and back scattered light. Thus the smoke detector
may include one or two photosensitive means.
It is preferred that both light sources and the photosensitive means are
in the same chamber as one another. However, it is possible to provide one or more
light sources and one or more photosensitive means in each of two or more
chambers into which the interior of the casing is divided.
Said light sources can be LEDs of different colours. For discrimination purposes the wave lengths of the LEDs should differ from one another by as much
as possible. Thus it is preferred to use an LED at the violet or blue end of the light spectrum and an infra red LED which is at the opposite end of the light spectrum. For the purposes of the present specification infra red is to be deemed to be within the term "light" even though it is not visible to the human eye.
The light sources can be lasers emitting coherent light at different wavelengths.
Preferably one laser emits light at the blue / violet end of the spectrum and the other at the red / infrared end of the spectrum.
According to a further aspect of the present invention there is provided a method of detecting smoke particles which comprises illuminating the smoke particles using light at two discrete and different wavelengths and detecting the light which is scattered by the smoke particles.
The particles can be airborne smoke particles or particles, such as dust particles, which have settled on a surface.
In the preferred form smoke is illuminated alternately by light at a first wave length and by light at a second wave length. The first wave length can be at the infra red end of the light spectrum and the second wave length at the blue or violet end of the light spectrum. BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:-
Figures 1 to 6 each diagrammatically illustrates the mode of operation of a smoke detector in accordance with the present invention;
Figure 7 is an "exploded" view of a detector which operates in accordance with the mode of operation illustrated in Figure 4;
Figure 8 is a vertical, pictorial section through the detector of Figure 7; and Figure 9 is a vertical section through the assembled detector.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring firstly to Figure 1 , reference numerals 10 and 12 indicate two light sources which are mounted in the smoke detecting chamber of the smoke detector. The chamber has a barrier 14 for shielding a photosensitive device 16 from the light sources. The barrier 14 prevents light from the sources 10 and 12 travelling in a straight line to the device 16. The device 16 can include a lens for concentrating reflected light onto the photosensitive surface.
The light sources 10 and 12 are preferably an LED emitting light at the blue / violet end of the light spectrum (about 430 nm) and an LED emitting light at the infrared end of the light spectrum (about 980 nm). This ensures that the difference between the wavelengths is as great as possible as this enhances discrimination.
The shaded area in Figure 1 indicates a concentration of smoke in the detecting chamber. The chamber is bounded by the casing of the detector and the casing has a plurality of openings therein which permit smoke laden air to enter the chamber.
The detector of Figure 1 detects what is known as forward scatter. In other words it detects light which has been reflected off the smoke particles at an angle but has continued on, as shown by the arrows, in the same general direction rather than being reflected back. Some light is also transmitted through some particles due to their translucence. The angle is shown as being about a right angle but in practice it is far more obtuse. The size of smoke particles, and their shape, varies with the type of material that is burning. Because of the difference in light wave lengths, the interaction between the light from one source and the particles differs from the interaction between light from the other source and the particles.
The sources 10 and 12 are illuminated out of phase with one another. It is preferred that the light sources are illuminated alternately. The output of the photosensitive device 16 is fed to a control panel, and software in the control panel can be used to differentiate between the output which has resulted from the scattering of the blue light and the output which has resulted from the scattering of infra red light. The software can be used to determine smoke particle size, smoke
particle shape, air velocity, concentration, colour and light absorption characteristics
at the specific wave lengths. It can also be used to distinguish between smoke and
dust particles. These abilities give information about the type of material that may
be burning.
Some forms of smoke detectors incorporate processing software. In
these forms the signal fed to the control panel has already been pre-processed and
less processing power is required at the panel.
In Figure 2 there is a further photosensitive device 18 which detects
back scatter. The term back scatter refers to light which has been reflected back
towards the light sources. The device 18 is located as close to the sources 10 and
12 as the physical sizes of the sources and device 18 will allow.
The detector of Figure 3 has two infra red light sources 20 and 22 and
two blue / violet light sources 24 and 26. It also has a single photosensitive device
28. The device 28 detects forward scatter from the sources 20 and 24 and back
scatter from the sources 22 and 26.
Only two light sources 30 and 32 are shown in Figure 4 but there are
two photosensitive devices 34 and 36. The photosensitive device 34 detects light at
long wavelengths, that is, at the red end of the spectrum and the device 36 detects light at short wavelengths, that is, at the blue / violet end of the spectrum. Both can
include lenses for concentrating reflected light onto the photosensitive surface, and
the device 36 can include a blue pass filter which blocks other wavelengths. The
devices 34 and 36 detect forward scatter.
The detector of Figure 5 is similar to that of Figure 4 but includes two
further devices 38 and 40 for detecting back scattered light at short wavelengths and
back scattered light at long wavelengths.
Figure 6 shows a detector which has two blue / violet light sources 42
and 44, two infra red light sources 46 and 48, a photosensitive device 50 for
detecting light at short wavelengths and a photosensitive device 52 for detecting
light at long wavelengths. The devices 50 and 52 detect back scatter from the light
sources 44 and 48 and forward scatter from the sources 42 and 46. The filter device
50 can include a blue pass filter.
In the embodiments of Figures 1 to 3, the structures are such that both
light sources and the photosensitive device or devices must be in the same chamber
as one another. In the embodiments of Figures 4 to 6 there can be more than one
smoke chamber. For example, in Figure 4 the blue light source and the associated
photosensitive device could be in one chamber and the infrared light source and
associated photosensitive device could be in a second chamber. In the form of
Figure 5 each chamber would contain one light source and two photosensitive devices. In the form of Figure 6 each chamber would contain two light sources of the same colour and one photosensitive device. If the smoke detector does have two chambers then bursts of light of two colours can occur simultaneously.
Reflection off dust particles that have been deposited on the inside of the casing can be used for the purpose of calibrating the detector. Information derived from the two light sources may also be usable for the purpose of compensating for contamination of any lenses that are used.
Referring now to Figures 7 to 9, the smoke detector illustrated is designated 60 and comprises a frusto conical cover 62 the wall 64 of which has therein openings 66 which are covered by mesh 68 to prevent the ingress of insects and unwanted dust particles while permitting smoke to enter. Internal walls 70, which are ribbed to inhibit light reflection, lie internally of the wall 64. Between the walls 70 are slit-like smoke entrances 72 to the smoke chamber which is within the cover 62. The openings 66 are staggered circumferentially with respect to the entrances 72 to prevent ambient light entering the detector. The smaller end of the cover 62 is closed by an end wall 64.1 which has a central opening 65. An internal reflector 74 has a knob 74.1 which passes through the opening 65 and attaches the reflector 74 to an external adjuster 76.
The cover is secured to a ring 78 by means of an array of six bayonet connections the parts of which are generally designated 80.1 , 80.2. The ring 78 includes partitions 82 which extend inwardly from opposite sides thereof and have
between them a gap 84 for receiving a housing designated 86.
The housing 86 is in two parts 88 and 90, the part 88 comprising a
vertical end wall 92, two side walls 94, 96 and a bottom wall 98. The other part 90 of
the housing is in the form of a closure cap which can be ultrasonically welded to the
part 88. Once the housing is in place clips 98 (only one of which is shown) are
pushed through slots 100 the wall 92 and in the other part 90 to secure the ring 78
and housing 86 together.
Two light sources 102 and 104 and two photosensitive devices 106
and 108 are shown. The device 108 preferably has a blue pass filter over it so that
all other light frequencies are blocked. The sources 102 and 104 are in a space 110
and the photosensitive devices in a space 112.
An inclined partition 1 14 separates the photosensitive devices 106,
108 from the light sources 102, 104 and prevents light travelling in a straight line
from a source to a photosensitive device. The bottom wall 98 of the space 1 10 is
ribbed, as is the partition 1 14, to inhibit light reflection as is well known in the art.
A printed circuit board is diagrammatically shown at 1 16, the light
sources 102 and 104, the photosensitive devices 106 and 108 and the circuitry of
the detector being mounted on this. The entire detector illustrated clips onto a base (not shown) which is itself secured to a ceiling.
Smoke particles in the smoke chamber bounded by the walls 70 and reflect light onto the photosensitive devices 106, 108 and the output of these is used to determine whether an alarm condition has arisen.
Mechanical calibration is effected by rotating the reflector 74 thereby varying the light which reaches the photosensitive devices even in the absence of smoke particles.
It is possible to use lasers instead of LEDs. Lasers produce coherent light of narrow band width whereas the light from LEDs is not coherent and its band width is wider. Use of a red laser and a blue / violet laser is preferred thereby to obtain maximum separation of the frequencies.

Claims

CLAIMS:
1. A smoke detector which comprises a casing, two light sources for illuminating the interior of said casing, each light source producing light at a discrete wavelength, the discrete wavelengths being different to one another, and photosensitive means for detecting light from said sources after it has been scattered by particles in said casing.
2. A smoke detector as claimed in claim 1 , wherein said photosensitive means detects forward scattered light.
3. A smoke detector as claimed in claim 1 , wherein said photosensitive means detects back scattered light.
4. A smoke detector as claimed in claim 1 and including two photosensitive means one for detecting back scattered light and one for detecting forward scattered light.
5. A smoke detector as claimed in claims 1 to 4, wherein both light sources and the photosensitive means are in the same chamber as one another.
6. A smoke detector as claimed in claims 1 , 2, 3 or 4 and including one or more light sources and one or more photosensitive means in each of two or more chambers into which the interior of the casing is divided.
7. A smoke detector as claimed in claim 1 , wherein said light sources are LEDs of different colours.
8. A smoke detector as claimed in claim 7, and including an LED which emits light at the blue / violet end of the light spectrum and an infra red LED which is at the other end of the light spectrum.
9. A smoke detector as claimed in claim 1 , wherein said light sources are lasers emitting coherent light at different wavelengths.
10. A smoke detector as claimed in claim 9, wherein one laser emits light at the blue / violet end of the spectrum and the other at the red / infrared end of the spectrum.
11. A smoke detector as claimed in claims 1 to 4 and including means for firing the light sources alternately.
12. A method of detecting smoke particles which comprises illuminating the smoke particles using light at two discrete and different wavelengths and detecting the light which is scattered by the particles.
13. A method as claimed in claim 12, wherein the smoke is illuminated alternately by light at a first wave length and by light at a second wave length.
14. A method as claimed in claim 12, wherein said first wave length is at the infrared end of the light spectrum and the second wave length is at the violet or blue end of the light spectrum.
15. A method as claimed in any one of claims 12 to 14 and including the step of triggering the light sources alternately.
EP99937808A 1998-07-31 1999-08-02 Smoke detectors Withdrawn EP1101210A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
ZA986865 1998-07-31
ZA9806865 1998-07-31
PCT/ZA1999/000059 WO2000007161A1 (en) 1998-07-31 1999-08-02 Smoke detectors

Publications (1)

Publication Number Publication Date
EP1101210A1 true EP1101210A1 (en) 2001-05-23

Family

ID=25587179

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99937808A Withdrawn EP1101210A1 (en) 1998-07-31 1999-08-02 Smoke detectors

Country Status (4)

Country Link
EP (1) EP1101210A1 (en)
AU (1) AU5256499A (en)
CA (1) CA2339170A1 (en)
WO (1) WO2000007161A1 (en)

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Also Published As

Publication number Publication date
WO2000007161A1 (en) 2000-02-10
CA2339170A1 (en) 2000-02-10
AU5256499A (en) 2000-02-21

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