Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL 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 SYSTEMS, e.g. PERSONAL 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)

Applications Claiming Priority (3)

Publications (1)

Family

ID=25587179

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (27)

Family Cites Families (3)

• 1999
  • 1999-08-02 EP EP99937808A patent/EP1101210A1/de not_active Withdrawn
  • 1999-08-02 AU AU52564/99A patent/AU5256499A/en not_active Abandoned
  • 1999-08-02 WO PCT/ZA1999/000059 patent/WO2000007161A1/en not_active Ceased
  • 1999-08-02 CA CA002339170A patent/CA2339170A1/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events