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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/02—Details
  • G01J1/04—Optical or mechanical part supplementary adjustable parts
  • G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
  • G01J1/0411—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings using focussing or collimating elements, i.e. lenses or mirrors; Aberration correction
• • 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
  • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
  • G01N21/03—Cuvette constructions
  • G01N2021/0378—Shapes
  • G01N2021/0382—Frustoconical, tapered cell
• • 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
  • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
  • G01N21/03—Cuvette constructions
  • G01N21/05—Flow-through cuvettes
  • G01N2021/052—Tubular type; cavity type; multireflective
• • 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
  • G01N2021/4704—Angular selective
  • G01N2021/4707—Forward scatter; Low angle scatter
• • 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
  • G01N2021/4704—Angular selective
  • G01N2021/4711—Multiangle measurement
• • 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
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths

Definitions

• the present invention relates to detection and monitoring equipment for fluid pollution, including smoke and air pollution by light scatter techniques.
• Devices for the detection of smoke by light scatter techniques. Such devices include a light source configured to irradiate through a volume of air provided in a sampling region in which smoke, dust or like particles may be suspended. Light scattered off said particles is collected on a light detector means. The amplitude of the signal from said light detector is an indication of the quantity of particulates in the fluid.
• Particularly sensitive versions of such detectors are capable of monitoring low levels of fluid pollution and thus may be a useful tool for monitoring general atmospheric pollution.
• Such high sensitivity enables detection of fires at the earliest possible (incipient) stage, whereby the fire may be controlled by local personnel using portable extinguishers or by removal of the source of heat (e.g. by disconnection of electric current) before smoke levels become dangerous to life.
• Such detectors require a sensitivity as high as twenty microgra s of wood smoke per cubic metre for example, which is equivalent to a visual range of 40 kilometres.
• This prior apparatus can and does summon human intervention before smoke levels become dangerous to life or delicate equipment, it can cause an orderly shutdown of power supplies so that equipment overheating will subside (thereby preventing a fire), or it can operate automatic fire suppression and personnel evacuation systems.
• the prior art utilizes a sampling chamber as described in Australian Specification No. 31843/84 through which a representative sample of air within the zone to be monitored, is continuously drawn by an aspirator.
• the air sample is normally irradiated by an intense, wideband light pulse from a Xenon lamp.
• a miniscule proportion of the incident photons are scattered off airborne particles towards a very sensitive detector, to produce an analog signal which, after signal processing, represents the level of pollution (smoke) present in the air.
• the instrument is so sensitive that photons scattered off air molecules alone are detected. Therefore, minor pollution is readily detected as an increased signal.
• the rate of false alarms is much lower than for conventional smoke detectors (which are comparatively insensitive, by two or three orders of magnitude) .
• Photons scattered off air molecules are invisible to the naked eye, like faint starlight, whereas the incident light is of similar brilliance to sunlight (thus in the one instrument, the range of light levels spans "cosmic proportions").
• the task is to detect the equivalent of faint starlight in the presence of sunlight.
• This requires a chamber of advanced optical design, to separate the desired scattered light from the incident light, and advanced electronics to detect the miniscule scattered light component without resort to cryogenics or photomultipliers.
• the prior art has utilized a Xenon lamp as a suitable source of intense wideband light with low energy input.
• a fluid pollution monitoring apparatus including a fluid sampling chamber, means for projecting a coherent collimated light beam into said sampling chamber, means introducing sample air from an area to be monitored into said chamber to be exposed to said light beam, a light detector cell positioned at a location separated or shaded from the axis of said light beam, and means in said sampling chamber for directing any scattered light produced by the presence of airborne particles in the chamber towards said detector.
• the advantage of a coherent collimated light source is that light is not visible beyond the axis of the light beam, except as a result of light scattering off airborne particles. Therefore if a laser light beam is projected through the sampling chamber, its beam is invisible to the off-axis light detector cell.
• the introduction of airborne particles which scatter the light beam produces light capable of detection by said off-axis light detector cell.
• the incident light beam can be projected or reflected out through and beyond said chamber, such that it may be conveniently absorbed outside the said chamber and thereby readily separated from scattered light within the said chamber.
• the detector cell positioned within the chamber is responsive only to the scattered light component. Output from said detector cell varies in proportion to the level of scattered light, providing a measure of the concentration of particles within said chamber.
• said chamber is conveniently in the form of a highly reflective elliptical tube.
• the tube includes a flat wall at each end to confine the air sample, perpendicular to the axis of said light beam.
• the sampling tube preferably in the end walls contains an induction or exhaust port to enable the continuous renewal of the air sample.
• the laser beam is projected along one focus of said elliptical tube. Any particles present in the path of the said laser beam would cause light scattering in all directions, but the elliptical chamber design would cause much of the scattered light to pass through the second focus of said elliptical tube, after one reflection, and again after subsequent multiple reflections. This is especially so for light scattered at 90° to said light beam, as is often the predominant scattering direction in the case of gas molecules.
• the said second focus forms a line, parallel to the said laser beam.
• the detector cell should form the shape of a thin rod to collect light arriving in all directions, at all points along its length.
• One form of such a detector could be an optical fibre or preferably a long thin laser rod with a detector cell mounted at one end. This can be a difficult or costly requirement which can be simplified by the novel modification of tapering the said elliptical tube. Because the walls of said elliptical tube are not now parallel, then by multiple reflections most of the scattered light would be focussed at a line or point on an end wall. It should be noted that with a tapered tube, one end wall is larger than the other and focussing will occur at the second focus of the larger end wall.
• a comparatively simple detector cell is therefore placed at the second focus of the larger end wall.
• Said detector cell requires a wide reception angle, between a few degrees and approaching 90 degrees from its perpendicular, depending upon the length and taper of said elliptical chamber.
• a suitable light-collecting lens e.g. "fisheye"
• cone or prism may be used with the said detector cell.
• light may be predominantly scattered at 90° for gas molecules, in the case of larger particles, such as smoke, the majority of scattering occurs within 0° to 30° of the axis of said light beam.
• One method for detecting the light scattered at small angles to the axis of said light beam could be to position a very large detector cell at one end of said chamber such as a disc with a relatively small central.hole to permit the passage of said light beam.
• a very large detector cell at one end of said chamber such as a disc with a relatively small central.hole to permit the passage of said light beam.
• Such cells are not usually available with sufficient sensitivity and low noise, so a comparatively small cell must be used.
• a concave mirror or lens could be used.
• a light sensing device for use in a fluid pollution monitoring apparatus, including a fluid sampling chamber, means for providing or projecting a coherent collimated light beam into said sampling chamber, means introducing sample fluid from an area to be monitored into said chamber to be exposed to said light beam, a light detector cell positioned at a location separated or shaded from said light beam, reflecting means in said chamber focussing as much as possible the available scattered light towards said reflecting means onto said detector cell.
• said reflecting means is an axially disposed concave reflector,
• a further reflecting means is placed at the centre, and in front of said reflecting means, to reflect said light beam in a desired direction, such as back towards said source or towards a light absorbing means within or beyond said chamber.
• Said detector cell is mounted at the rear of said further reflecting means, and positioned to receive scattered light which has been collected and focussed by said concave reflector.
• the detector cell is prevented from detecting direct light from said laser beam but will receive a large proportion of the scattered light which is received by said further reflecting means.
• a combination of a reflective elliptical wall chamber and concave reflector to achieve a resultant combination of all sources of reflected light is also possible according to the present invention.
• Two detector cells may be used to indicate differing proportions of light scattered either at small angles or angles of up to 90° to the light beam axis respectively in response to incidence of particles of differing size.
• first mentioned version of the present invention utilizes a highly light-reflective chamber with a collimated coherent laser beam instead of a highly light-absorbing chamber with a wide-angle incoherent Xenon lamp.
• This improvement provides an opportunity for substantial improvement in the ratio of scattered light to remnant incident light, improving the "optical signal-to-noise ratio".
• the incident light intensity (required to produce a given scattered light intensity appropriately matched to the sensitivity of said detector cell), may be reduced. Therefore the energy consumption of the light source may be reduced.
• Use of a Xenon lamp in the prior art accounted for the majority of the power consumption of the entire instrument. Thus it is possible in the present invention to provide for a substantial reduction in power consumption.
• the laser beam may be pulsed or modulated.
• the modulation frequency may be synchronised with a digital filter means provided by a phase-locked loop or microprocessor circuit (not shown), to optimise the signal-to-noise ratio. This modification further reduces the required intensity of the laser beam, reducing the energy consumption of the overall instrument.
• Figure 1 shows a sectional view of a sampling chamber for a light sensing pollution detection device.
• Figure 2 shows a further embodiment of a sampling chamber.
• the two laser beams may be rendered colinear by use of a prism 12 or mirror system.
• a prism 12 or mirror system One embodiment of such a m - system would utilize the differing angle of refraction applicable to each wavelength.
• each laser beam would be projected at a differing incident angle such that the two beams emerge as a pair of colinear beams into the collimator 13.
• the laser beams are directed back towards said source, they strike said prism at an angle greater than the critical angle and may be totally reflected toward a light absorbing means.
• a light absorbing means may be employed within or without the chamber and thus allow
• each said laser could be pulsed alternately at a rate _ synchronised with a switched-gain amplifier means to compensate for said differing sensitivity. It is known that the light-scattering coefficient for any gas or aerosol is dependent upon the wavelength of the incident light. Rayleigh has found that for gases, this coefficient varies inversely with the fourth power of the wavelength employed. Larger airborne particules have a coefficient which varies inversely with an exponent less than four (possibly as low as zero).
• said compensation means could also be used to compensate for the differing light-scattering coefficients at the two said laser wavelengths.
• the whole instrument could be used to determine the said exponent for a known air/gas/particulate sample.
• a novel circular light absorbing device 22 is shown for receiving the unscattered light beam travelling through the chamber.
• the device is circular as shown with reflective walls so that received light is continually reflected around the walls as shown and prevented from returning into the sampling chamber. Scattered light is received by reflector 17 ( Figure
• the cell preferably has a finite dimension to enable receipt of more light without the necessity to focus the light to a sharp point.
• a lens or lens system (not shown) may be used as an alternative to the reflector.
• Port means 23 are provided for introducing sample air into and out of the chamber.

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

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• 1989
  • 1989-03-30 KR KR1019890702208A patent/KR900700871A/ko not_active Application Discontinuation
  • 1989-03-30 WO PCT/AU1989/000138 patent/WO1989009392A1/en not_active Application Discontinuation
  • 1989-03-30 EP EP19890903975 patent/EP0407429A4/en not_active Withdrawn

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