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WO1999041589A1 - Mesure d'absorption optique avec cavite d'integration de lumiere - Google Patents

Mesure d'absorption optique avec cavite d'integration de lumiere Download PDF

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Publication number
WO1999041589A1
WO1999041589A1 PCT/GB1999/000296 GB9900296W WO9941589A1 WO 1999041589 A1 WO1999041589 A1 WO 1999041589A1 GB 9900296 W GB9900296 W GB 9900296W WO 9941589 A1 WO9941589 A1 WO 9941589A1
Authority
WO
WIPO (PCT)
Prior art keywords
target
radiation
detection means
cavity
optical
Prior art date
Application number
PCT/GB1999/000296
Other languages
English (en)
Inventor
Mark Johnson
Original Assignee
United Utilities Plc
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 United Utilities Plc filed Critical United Utilities Plc
Priority to AU22905/99A priority Critical patent/AU2290599A/en
Publication of WO1999041589A1 publication Critical patent/WO1999041589A1/fr

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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
    • G01N21/255—Details, e.g. use of specially adapted sources, lighting or optical systems
    • 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
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path

Definitions

  • the present invention relates to an apparatus and method for monitoring characteristics of a sample by an optical measurement. Particularly, but not exclusively, the invention provides an apparatus and method which is capable of being used to monitor the characteristics of a liquid such as water.
  • optical techniques for physical and chemical analysis of liquids, including monitoring the quality of water.
  • a beam of light is shone into a sample of the liquid and transmitted or scattered components of the light are detected and analysed.
  • transmission of light through a sample is measured (particularly at a range of wave lengths) to obtain information on the make-up of the liquid, for example providing information on the presence and nature of pollutants in a water sample.
  • Such optical systems may monitor various different effects (not just transmission and absorption) to measure particular characteristics of a liquid, such as scattering, refractive index and polarisation properties.
  • the liquid sample is either placed in a transparent bottle (cuvette), or some other container having transparent windows which are in direct contact with the liquid. It is therefore important for the efficient and reliable operation of such systems (and in particular for repeatable measurements) that the cuvette windows must be of high optical quality and kept free from damage, fouling and condensation. This can be particularly problematical outside a laboratory environment. Degradation of the optical quality of such windows is a fundamental problem encountered with practical industrial measurement systems where the reliability of measurement may be dominated by chemical and biological fouling.
  • a water stream of simple circular cross section is more stable than a rectangular section stream, but correcting for optical aberrations, and arranging for a stable optical transmission measurement to be made on the stream, is also difficult.
  • a fundamental disadvantage of such known falling stream optical measurement systems is that it is not possible to differentiate between absorbed and scattered light from a simple transmission measurement. That is, with a simple transmission measurement it is not possible to determine whether light which has failed to reach a detector has been absorbed by the sample or scattered from scattering particles in the sample.
  • an apparatus for performing an optical measurement on a foulable target substance comprising detection means arranged to define an optical cavity, a path defined through the optical cavity, means for delivering an unsupported flow of the target substance to the cavity and directing it to flow along said path and radiation emitting means arranged for irradiating the target as it flows through the cavity along said path, the detection means being arranged to detect radiation emerging from the target in a plurality of directions within the optical cavity.
  • the optical cavity is provided by a reflective surface.
  • the optical cavity may be based on a conventional optical device known as an "integrating sphere". Integrating spheres are discussed further below. It should be noted, however, that the optical cavity need not be spherical but could be any shape, such as cubic for instance. The more reflective the surface of the cavity the more accurate and consistent results will be and thus it is envisaged that in most practical situations the reflective material will be 95% reflective of the radiation used.
  • the radiation emitting means and detection means may comprise respective means disposed within the optical cavity, for instance on the wall of the cavity, or may be remote from the cavity and optically connected thereto by, for instance, optical fibres (which may terminate in the wall of the cavity exposed to the inside of the cavity).
  • the apparatus according to the present invention is suitable particularly, but not exclusively, for performing optical measurements on moving liquid targets.
  • the target may be a stream or jet of a liquid such as water.
  • the liquid may be propelled as a jet in any direction through the optical cavity.
  • the liquid may be delivered to the optical cavity from a source immediately above the cavity, so that the liquid simply falls through the cavity under force of gravity (and as such the invention will provide an improved falling stream optical measurement system of the general type discussed in the introduction to the this specification).
  • the apparatus may comprise an optical cavity defined by a diffusely reflective surface (for instance provided by a conventional integrating sphere) which is provided with inlet and outlet apertures positioned vertically one above the other, at least one radiation emitter (for instance a single emitter emitting, for example, visible wavelength light), at least one radiation detector sensitive to the radiation emitted by said at least one emitter, and means for delivering an unsupported stream of target liquid to the optical cavity inlet so that the stream falls through the cavity via the inlet and outlet under force of gravity.
  • a diffusely reflective surface for instance provided by a conventional integrating sphere
  • at least one radiation emitter for instance a single emitter emitting, for example, visible wavelength light
  • at least one radiation detector sensitive to the radiation emitted by said at least one emitter
  • a method for performing an optical measurement on a flowing target substance comprising causing the target to flow unsupported along a predetermined path, irradiating the target with radiation that is at least partially transmissive through the target material as the target flows along said path, and detecting radiation emerging from the target in a plurality of directions around the target.
  • the method may, for example, be performed using apparatus in accordance with the first aspect of the present invention discussed above.
  • Fig. 1 is a schematic illustration of a first embodiment of the present invention.
  • Fig. 2 is a schematic illustration of a second embodiment of the present invention.
  • the illustrated embodiment of the invention is adapted for monitoring the characteristics of a liquid sample, such as water.
  • Water is introduced into a header tank 1 through an inlet 2.
  • the header tank 1 is provided with an aperture 3 in its base through which water falls in the form of a substantially continuous stream 4. From the header tank 1 the water stream 4 falls through an integrating sphere 5, and then to waste.
  • the integrating sphere 5 is essentially a known instrument, comprising a sphere of suitable material with a highly diffusely reflective (typically 0.99 power reflectivity) internal surface defining a spherical optical cavity 6.
  • a single light source 7, which may be a simple LED of appropriate wavelength, and a single detector 8, which may for instance be a simple "pin" photo detector, are mounted within the sphere and exposed to the cavity 6.
  • Integrating spheres are conventionally used for measuring absorption of samples supported within the optical cavity.
  • integrating spheres are well known for measuring levels of absorption of optical fibres, irregular shaped objects (such as gem stones) and also of liquids which may either be contained within a transparent bottle or which may fill the integrating sphere directly. Since integrating spheres are well known instruments, their properties will only be discussed briefly here. Because the internal surface of the sphere defining the optical cavity is highly and diffusely reflecting, almost any input light distribution (including that from a single small collimated laser beam) is converted after only a few reflections to a highly uniform optical flux with little angular dependence.
  • a small detector positioned at a location in the wall of the sphere can measure the irradiance at that location due to the optical flux present within the sphere. Provided the sphere is uniform, the irradiance measured will be independent of the position of the detector within the sphere.
  • any absorbing medium placed within the cavity will reduce the irradiance within the cavity as a whole, which can therefore be measured by the detector. Moreover, only light which is absorbed will be removed from the flux detected by the detector. Thus light which is scattered by the sample (e.g. water stream 4) will contribute to the flux within the cavity regardless of the scattering angle, and thus will be detected at the detector. Accordingly, the measurement made at the detector will be substantially independent of scattering, since no matter what angle light is scattered at it will contribute to the flux within the cavity which is measured by the detector. Thus the cavity with a single detector effectively operates as a continuous spherical detecting means.
  • the cavity with a single located source will behave effectively as a continuous spherical source. Therefore, although changes in the surface of the sample (e.g. water stream 4) may vary the refraction of light, they will not substantially effect the measured irradiance.
  • the absorbed light as measured by the detector 8 is proportional only to the amount of water present within the sphere 5 at any given time and the amount of absorption by the water, and not on details of the shape of the water stream 4 or scattering properties of the water. It is therefore only necessary to measure the optical power detected at the detector 8, integrated over time, and the weight of water integrated over the same period of time.
  • a fixed water volumetric flow equivalently fixes the average volume of water in the sphere. Since shape stability of the water stream 4 is not necessary, use of the integrating sphere 5 obviates problems associated with existing water thread optical measurement systems.
  • the water stream 4 is not required to have a good optical quality, and could for instance be a broken stream of falling droplets, or a stream made up of several smaller streams in, for instance, a rosette configuration.
  • the apparatus can readily be calibrated by setting the "zero" absorption level as either that level measured by the detector with no liquid falling through the sphere, or with a pure sample of the liquid falling through the sphere.
  • the inner surface of the integrating sphere 5 should be highly and diffusely reflective to ensure that scattering independent results are obtained.
  • Known integrating spheres comprise inner surfaces coated with a reflective coating such as barium sulphate. More recently, integrating spheres have been manufactured by the US company Labsphere from a machineable polymer called Spectralon (trade mark).
  • a 100mm diameter integrating sphere was fabricated from Spectralon.
  • the light source was a green LED of wavelength 555nm, and the detector was a 6mm square silicon "pin" photodetector.
  • the water stream was produced from a 5mm diameter aperture.
  • source and detector may be used.
  • a source which is capable of producing a range of wavelengths of light could be mounted within the sphere used, or alternatively more than one source could be used each producing a different wavelength of light.
  • FIG. 2 A second embodiment of the present invention which incorporates an alternative to a conventional integrating sphere to provide the optical cavity around a falling water stream 4 is illustrated in Fig. 2.
  • the apparatus of Fig. 2 corresponds with that of figure 1, except that the integrating sphere is replaced by a spherical array of multiple light sources 9 and detectors 10.
  • the conventional integrating sphere effectively behaves both as a continuous spherical light source and also as a continuous spherical detector.
  • this structure is approximated by the cavity 6 defined by the spherical array of sources 9 and detectors 10 (the outputs of which may be combined).
  • the scattering independence of measured results is improved by increasing the number and distribution of detectors so as to detect light scattered in as many directions as possible.
  • increasing the number and distribution of light sources surrounding the sample will minimise the effect on the absorption measurement of the variations in the refracting shape of the water stream.
  • the light sources could be simple LED's in one or more colours or any other suitable light source such as an optical fibre leading in from an external source.
  • the detectors could be any suitable detector including localised detectors or remote detectors connected by optical fibres to locations around the sample.
  • the surface within which the detectors and sources are mounted need not be a highly reflecting surface, and could even be a black body surface.
  • the cavity may be defined by an array of detectors and only one light source.
  • the use of multiple detectors will maintain scattering independence, and the reduction in the number of light sources needed may enable further detectors to be incorporated in the apparatus.
  • the optical measurement methods described above are scattering-independent absorption measurements. However, as mentioned in the introduction to this specification other measurements may be desirable to yield other information as to the nature of the sample. For instance, it might be desirable to measure the turbidity (scattering properties) of the sample, rather than, or in addition to, the absorption properties.
  • the above described embodiments of the present invention can readily be modified to provide for a sensitive scattering measurement only by irradiating the sample from a single light source (which may be external to the optical cavity). The necessary light (or other radiation) may be coupled into the sample stream from above or below so that it will be guided along the stream by total internal reflection. Such an arrangement is, for instance, described in the PCT patent specification number WO96/16326 mentioned above.
  • the nature of the liquid stream must be controlled so that the stream is continuous.
  • the existing light sources could be disabled for a scattering measurement, or could be omitted entirely (and could be replaced by further detectors)
  • the invention has been described above with particular reference to the use of the invention to monitor the condition of water. It will, however, be appreciated that the method and apparatus in accordance with the present invention can be used to monitor the condition of a wide variety of liquids such as may be found in the pharmaceutical, brewing, paper, water and other industries. Furthermore, the invention is not limited to performing measurements on liquids. The invention could, for instance, be used to monitor the condition of other readily flowable materials, such as viscous fluids or streams of solid parti culate matter.
  • the method and apparatus in accordance with the present invention has an advantage over existing measurement methods utilising integrating spheres in that it is not necessary to support the sample being monitored so that the sample does not need to come into contact with any surface which might contaminate the sample.
  • the invention is not limited to operation at visible light wavelengths.
  • the invention may be operated at any desired electromagnetic radiation wavelength at which measurements are required (e.g. x- rays).
  • the inner surface of the integrating sphere 5 must, however, be sufficiently reflective of the radiation wavelength used.
  • the apparatus could be arranged so that the flow path of the sample through the optical cavity is not vertical, and a force other than gravity could be used to propel the target sample through the cavity.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention porte sur un appareil et un procédé permettant de réaliser une mesure optique sur une cible mouvante telle qu'une chute d'eau (4). L'appareil comprend un détecteur (5, 8) formant une cavité optique (6) par laquelle s'écoule la cible. Un émetteur (7) de rayonnements irradie la cible au moment où elle s'écoule dans la cavité (6). Le détecteur (8) détecte les rayonnements émergeant de la cible dans une pluralité de directions à l'intérieur de la cavité optique. Cet appareil et ce procédé peuvent être utilisés pour effectuer des mesures sur l'absorption, pratiquement exemptes de phénomènes de dispersion.
PCT/GB1999/000296 1998-02-13 1999-01-28 Mesure d'absorption optique avec cavite d'integration de lumiere WO1999041589A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU22905/99A AU2290599A (en) 1998-02-13 1999-01-28 Optical absorption measurement with light integrating cavity

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9802982.0A GB9802982D0 (en) 1998-02-13 1998-02-13 Optical measurement
GB9802982.0 1998-02-13

Publications (1)

Publication Number Publication Date
WO1999041589A1 true WO1999041589A1 (fr) 1999-08-19

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ID=10826872

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1999/000296 WO1999041589A1 (fr) 1998-02-13 1999-01-28 Mesure d'absorption optique avec cavite d'integration de lumiere

Country Status (3)

Country Link
AU (1) AU2290599A (fr)
GB (1) GB9802982D0 (fr)
WO (1) WO1999041589A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004046709A1 (fr) * 2002-11-20 2004-06-03 Richard Fritz Sauter Procede d'analyse de molecules pour le sequençage de molecules et spectrometre associe
RU2235991C1 (ru) * 2003-04-30 2004-09-10 Уфимский государственный авиационный технический университет Бесконтактный мутномер
RU2627561C1 (ru) * 2016-03-24 2017-08-08 Общество с ограниченной ответственностью "ЛЮМЭКС-АвтоХимКонтроль" Устройство для измерения концентрации светопоглощающих веществ
WO2024052821A1 (fr) * 2022-09-07 2024-03-14 Marama Labs Limited Dispositif de cavité d'intégration pour des mesures indépendantes de volume

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838926A (en) * 1972-02-23 1974-10-01 Fuji Photo Film Co Ltd Method of continuously determining the absorbance light of a chemical reaction mixture
GB2198551A (en) * 1984-10-05 1988-06-15 Spandrel Ets Integrating cavity
GB2287784A (en) * 1994-03-25 1995-09-27 Parascan Technologies Ltd Apparatus and method for optical inspection of objects
WO1997036167A1 (fr) * 1996-03-26 1997-10-02 United Utilities Plc Instrument optique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838926A (en) * 1972-02-23 1974-10-01 Fuji Photo Film Co Ltd Method of continuously determining the absorbance light of a chemical reaction mixture
GB2198551A (en) * 1984-10-05 1988-06-15 Spandrel Ets Integrating cavity
GB2287784A (en) * 1994-03-25 1995-09-27 Parascan Technologies Ltd Apparatus and method for optical inspection of objects
WO1997036167A1 (fr) * 1996-03-26 1997-10-02 United Utilities Plc Instrument optique

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004046709A1 (fr) * 2002-11-20 2004-06-03 Richard Fritz Sauter Procede d'analyse de molecules pour le sequençage de molecules et spectrometre associe
RU2235991C1 (ru) * 2003-04-30 2004-09-10 Уфимский государственный авиационный технический университет Бесконтактный мутномер
RU2627561C1 (ru) * 2016-03-24 2017-08-08 Общество с ограниченной ответственностью "ЛЮМЭКС-АвтоХимКонтроль" Устройство для измерения концентрации светопоглощающих веществ
WO2024052821A1 (fr) * 2022-09-07 2024-03-14 Marama Labs Limited Dispositif de cavité d'intégration pour des mesures indépendantes de volume

Also Published As

Publication number Publication date
AU2290599A (en) 1999-08-30
GB9802982D0 (en) 1998-04-08

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