Classifications

• • 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
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
• • 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
  • G01N21/031—Multipass arrangements
  • G01N2021/0314—Double pass, autocollimated path
• • 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
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
  • G01N2021/3513—Open path with an instrumental source
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/08—Optical fibres; light guides
  • G01N2201/084—Fibres for remote transmission

Definitions

• the present invention relates to an apparatus for emitting and receiving light, said apparatus comprising an emitter with a spectrally broadband light source and a concave first mirror in the focus of which said light source is positioned, and a receiver which is adapted to receive light emitted from the light source and which is connected to an equipment for analysing the light received.
• This equip ⁇ ment is chiefly made up of a device for emitting light, a device for receiving the light emitted, a spectrometer, a multi-channel analyser, and a computer.
• the device for emitting light (in the following called the emitter) comprises a spectrally broadband light source and a con ⁇ cave mirror in the focus of which the light source is positioned.
• the device for receiving the light emitted comprises a concave mirror and an inclined plane mirror which is arranged in the vicinity of the focus of the concave mirror and which reflects the received light to the input optics of the spectrometer.
• Emitter and receiver should be spaced apart a distance of from 10 m to 10 km.
• a parallel light beam is emitted from the emitter to the receiver through the area in which the air pollution is to be measured.
• C is the concentration of a substance
• I' is the light intensity without any differential absorption
• I is the light intensity depending on the absorption of the substance
• ⁇ is the differential absorption cross-section of the substance, which is determined by calibra- tion
• L is the measuring distance
• the quotient (I'o/I) is determined by dividing the spectrum obtained from the spectrometer by a polynomial (first to fifth order) which is obtained by a least squares fit to the absorption spectrum.
• the apparatus described is in some respects inadequate.
• it can only by used for differential measurings, which means that only the concentration of substances which absorb light at one or a few distinct wavelengths or wavebands can be determined.
• concentrations of C1-, H-S and other substances which absorb light continuously or in broad wave length ranges cannot be determined by means of this equipment.
• total absorption measurings have to be effected.
• the receiver is difficult to mount because it has to be fixed in a highly exact position so that the light can be reflected to the plane mirror and further to the input optics of the spectrometer. In some weather conditions, the receiver may be dislocated and require adjustment.
• One object of the present invention is, therefore, to provide an apparatus for emitting and receiving light, which makes it possible to carry out not only differential measuring but also total absorption measuring.
• Another object of the invention is to provide an apparatus for emitting and receiving light, in which the difficulties associated with the mounting and position adjustment of the receiver have been reduced.
• a further object of the invention is to provide an apparatus for emitting and receiving light, in which only one power supply is needed.
• Yet another object of the invention is to provide an apparatus for emitting and receiving light, which requires less space for achieving a given measuring distance.
• the emitter and the receiver are mounted adjacent to one another, and a reflector unit is used for reflecting the emitted light towards the receiver.
• the position adjustment of the reflector unit is far less critical than that of the receiver described in the above article, since the reflector reflects the light in the same direction as it was received within a narrow range. Furthermore, the receiver is easily accessible for position adjustment, an operation which, furthermore, may be automated.
• the apparatus according to the invention is advan ⁇ tageous also in that the emitter/receiver can be movably mounted on a shaft, and a number of reflector units can be mounted in different directions so that the measuring can be carried out in different directions with only one equipment.
• the present invention will be illustrated below by means of an embodiment, reference being had to the accom ⁇ panying drawing which is a schematic longitudinal section of an apparatus 1 for emitting and receiving light, said apparatus being connected to an analysing equipment 3 which is only shown as a box.
• the apparatus 1 comprises a light source 5, a concave first mirror 7, a concave second mirror 9, a first shielding element 11, a second shielding element 13, all of which are mounted in a tube 15, and a retroreflector unit 17.
• the apparatus 1 is connected to the analysing equipment 3 by means of an optical fibre 19.
• the light source 5 consists of a spectrally broadband xenon lamp which is positioned in ⁇ the focus of the first mirror 7, the lamp and the mirror together forming the emitter.
• the diameter of the first mirror 7 is 100 mm, and its focal length is 60 cm.
• the second mirror 9, which forms the receiver, is mounted behind the first mirror 7, relative to the lamp 5.
• the focal length of the second mirror is 90 cm, its diame ⁇ ter is 150 mm, and one end of the optical fibre 19 is positioned in its focus.
• the mirrors may, of course, have other diameters and focal lengths than those stated above on condition that the periphery of the second mirror 9 is situated outwardl of the periphery of the first mirror 7 so as to be capabl of receiving the light from the reflector 17, and on con ⁇ dition that the focus of the second mirror 9 is located i front of the lamp.
• the first shielding element 11 is positioned between the lamp 5 and the optical fibre 19 so close to the lamp that it does not prevent the light reflected by the second mirror from reaching the optical fibre.
• the shielding element 11 comprises a shield which is mounted on a shaft and is movable from a first position in which the shield prevents the light emitted by the lamp from reaching the optical fibre directly, and a second position in which th shield is turned aside so that the light from the lamp ca be directly received by the optical fibre.
• a convex lens can be provided behind the first shielding element 11 for focussing the light from the lamp to the optical fibre 19 when the shield 11 is turned aside.
• the second shielding element 13 which is only shown schematically, is positioned between the optical fibre 19 and the front end of the tube 15.
• the second shielding element 13 consists of a shield which is mounted on a shaft and is movable between two positions. In the first position, the shield is turne aside so as to allow light to pass out of and into the tube 15. In the second position, the shield prevents the light from the retroreflector 17 from reaching the optical fibre.
• the second position is used when the reference spectrum of the lamp is to be established. Instead of having a shield which is made to block the tube, said tub may be turned away from the retroreflector unit.
• the retroreflector unit 17 comprises twelve to sixteen juxtaposed retroreflectors. Since these reflectors are already known and commercially available, they need not be described in detail.
• the apparatus operates as follows.
• differential measuring the light is emitted from the emitter 5, 7 towards the retroreflector unit 17 which reflects the light towards the receiver 9. Owing to dispersion, the light beam will have a larger diameter after having travelled the measuring distance from the emitter to the receiver, for which reason the light will impinge upon the second mirror 9 in the area outwardly of the periphery of the mirror 7. From there, the light is reflected towards the optical fibre 19 from which it is further conducted to the analysing equipment.
• the shielding element 11 is all the time maintained in the first position in which the direct light from the lamp is shielded off. Naturally enough, the second shielding element 13 is in the first position permitting the light to pass. The concentration is determined in the above manner.
• a reference spectrum for the lamp 5 is first established.
• the second shielding element 13 is moved to the second posi ⁇ tion in which it shuts off the light from the retroreflec tor unit, and the first shield element 11 is turned aside so that the optical fibre directly receives the light fro the lamp.
• the shielding elements are moved to their opposit positions and measuring is effected as in differential measuring.
• the Lambert-Beer law is, as before, used, but the quotien 1 ' 0 1 is replaced by the quotient of the reference spec ⁇ trum and the absorption spectrum obtained, while the differential absorption cross-section is replaced by the total absorption cross-section of the substance at issue.
• the described embodiment of the invention is only an example that can be varied within the scope of the appended claims.
• the description of the apparatus focusses on the determinatio of concentrations, the apparatus may, of course, also be used for determining other parameters.
• the apparatus is not restricted to measuring concentrations in air; it may also be used for measuring in other gases or in liquids.

Landscapes

• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Biochemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Eye Examination Apparatus (AREA)
• Instruments For Viewing The Inside Of Hollow Bodies (AREA)
• Optical Couplings Of Light Guides (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20376004

Family Applications (1)

Country Status (8)

Cited By (1)

Families Citing this family (26)

Citations (4)

Family Cites Families (5)

• 1989
  • 1989-05-19 SE SE8901808A patent/SE462934B/sv not_active IP Right Cessation
• 1990
  • 1990-05-18 WO PCT/SE1990/000334 patent/WO1990014581A1/en active IP Right Grant
  • 1990-05-18 US US07/775,983 patent/US5255073A/en not_active Expired - Lifetime
  • 1990-05-18 CA CA002057891A patent/CA2057891C/en not_active Expired - Fee Related
  • 1990-05-18 DE DE69012557T patent/DE69012557T2/de not_active Expired - Fee Related
  • 1990-05-18 EP EP90908731A patent/EP0472637B1/en not_active Expired - Lifetime
  • 1990-05-18 ES ES90908731T patent/ES2058920T3/es not_active Expired - Lifetime
  • 1990-05-18 JP JP2508453A patent/JP2542124B2/ja not_active Expired - Fee Related

Patent Citations (4)

Also Published As

Similar Documents

Legal Events