WO1999044040A1 - Procede de mesure de la concentration d'un gaz a fonction de correction de derive et detecteur de gaz photo-acoustique - Google Patents

Procede de mesure de la concentration d'un gaz a fonction de correction de derive et detecteur de gaz photo-acoustique Download PDF

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Publication number
WO1999044040A1
WO1999044040A1 PCT/NO1999/000065 NO9900065W WO9944040A1 WO 1999044040 A1 WO1999044040 A1 WO 1999044040A1 NO 9900065 W NO9900065 W NO 9900065W WO 9944040 A1 WO9944040 A1 WO 9944040A1
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WO
WIPO (PCT)
Prior art keywords
gas
light
chamber
light source
measurement
Prior art date
Application number
PCT/NO1999/000065
Other languages
English (en)
Norwegian (no)
Inventor
Bjørn Erik SEEBERG
Martin Nese
Original Assignee
Presens As
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 Presens As filed Critical Presens As
Priority to AU32790/99A priority Critical patent/AU3279099A/en
Publication of WO1999044040A1 publication Critical patent/WO1999044040A1/fr
Priority to NO20004264A priority patent/NO327840B1/no

Links

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
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G01N21/274—Calibration, base line adjustment, drift 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
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • 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
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases

Definitions

  • the present invention relates generally to measurement or detection of gas in a room, and more particularly the invention relates to a photoacoustical gas sensor and a measuring method wherein measures have been taken to compensate for drift at measurement end or in a light source.
  • the gas in the chamber will then be heated/cooled intermittently at the same rate as the light pulses, and the chamber pressure will vary at the same rate, and to a degree that is a direct function of the concentration of the gas searched for in the "external" room.
  • the dynamic pressure variations that arise in the gas in the chamber can be sensed/measured by a dynamic pressure sensor.
  • the dynamic pressure sensor used in the above mentioned NO 1997.5447 is of a type having a diaphragm with a mechano-electric transducer.
  • the closed chamber is preferably divided in two by the diaphragm, and a narrow restriction or opening along parts of the diaphragm edge, makes sure that the gas is in both chamber parts, and that pressure equalization is achieved for sufficiently low sound frequencies, so that frequencies can only be measured above a certain "corner frequency", the position of which depends on chamber volume, restriction size and diaphragm volume displacement.
  • the gas sensor type mentioned hereabove may experience drift, i.e. that the measurement signal that is achieved, exhibits a slow variation over time due to e.g. collection of contamination deposits on sensitive surfaces, variation in the light source etc.
  • the goal of the present invention is to provide a solution to the drift problem for this type of gas sensor.
  • a solution is provided to the problem that has been sketched above.
  • a method for drift compensated detection or concentration measurement of a gas in a room where light is directed from at least one light source through at least part of the room toward and through a window constituting part of a wall surrounding a closed chamber containing the same gas as the one to be detected or measured, the light is pulsed in order to heat the gas in the chamber intermittently by absorption or scattering of light energy, at least one of the light sources emitting light having wavelengths matching the absorption line spectrum of the gas, and the chamber containing a diaphragm with a mechano-electric transducer for picking up sound generated by the gas through the above mentioned intermittent heating.
  • the method in characterized in that 5 - a special reference gas not expected to appear naturally in the room, and having a different absorption spectrum, however with lines in the same wavelength range as the gas to be detected or measured, is added in advance to the chamber together with the measurement gas, and that the light is sent into the closed chamber with two different values of at least ⁇ o one of the parameters spectral content, pulse frequency and phase, whereby measurement gas and reference gas will provide detectably different signal contributions from the transducer for the two different parameter values.
  • a photo- i5 acoustical sensor for drift compensated detection of a gas or measurement of concentration of gas in a room
  • said gas sensor comprising at least one pulsed light source for transmitting light through at least part of the room and through a window constituting part of a wall surrounding a closed chamber containing the same gas as the one to be detected or measured, and which chamber also 20 contains a diaphragm having a mechano-electric transducer for picking up sound generated by the contained gas when/if it is heated intermittently by absorption of light energy, the light source(s) emitting light having wavelengths covering the absorption line spectrum of the gas.
  • the gas sensor of the invention is characterized in that 25 - the chamber contains also a reference gas not expected to appear naturally in the room, and which reference gas has a different absorption spectrum, however with lines in the same wavelength range as the gas to be detected or measured, and that the light source(s), light path defining means and the closed chamber are 3o arranged in such a manner that at least one of the parameters spectral content, pulse frequency and phase can be provided with two different values, in order that measurement gas and reference gas in the chamber may provide detectably different signal contributions from the transducer for the two different parameter values.
  • figs. 1a, b, c show absorption spectra for carbon dioxide gas, methanol vapor and ethanol vapor respectively
  • fig. 2 shows an absorption spectrum of laughing gas ⁇ 2 O, which gas can be used for reference gas
  • fig. 3 shows schematically a measurement set-up that can be used in certain embodiments of the invention, using two light sources and one window in a measurement cell
  • fig. 4 shows schematically an alternative set-up of apparatus that can be used in another embodiment of the invention, using two light sources directing light toward respective parts of the measurement cell through separate windows; fig.
  • the invention relates to photoacoustical sensors, and in particular sensors having a gas in a closed chamber together with a microphone element, i.e. the same gas that it is interesting to detect in "the surroundings".
  • a gas in a closed chamber together with a microphone element, i.e. the same gas that it is interesting to detect in "the surroundings".
  • Such gas sensors will be subject to drift, in similarity with other types of gas sensors. Often some of the drift will be due to a deposit on the sensitive surfaces.
  • a solution to the two types of drift problem mentioned above, will be to provide a reference signal.
  • the idea of the invention is then to fill additional gas into the chamber.
  • This gas must have absorption lines in the same wavelength range as the gas that it is desirable to investigate. It is an important premise that the reference gas used as an additional gas in a chamber, does not appear in a natural manner in the measurement area where the sensor is mounted.
  • figs. 1a, b, c appear the most important absorption lines for carbon dioxide gas (CO 2 ), methanol vapor and ethanol vapor, respectively. In various connections it may be of importance to monitor these gases.
  • CO 2 carbon dioxide gas
  • methanol vapor methanol vapor
  • ethanol vapor ethanol vapor
  • the electronic signal processing unit that is used for processing signals from the microphone or transducer element in the measurement chamber must in some manner be able to distinguish between the signal from the measurement gas and from the reference gas (i.e. the additional gas).
  • the additional gas i.e. the additional gas.
  • the light vibration that is picked up e.g. with a frequency according to the flash frequency of this light, will provide a signal that is separable from the signal belonging to the light absorbed specially by the reference gas, and which is then flashed using another frequency.
  • signal amplitudes associated with the two flash frequencies/pitches that are picked up may be possible to distinguish.
  • fig. 3 appears schematically a measurement cell filled with measurement gas (M) and reference gas (R).
  • M measurement gas
  • R reference gas
  • the measurement ceil is in this case depicted as a two-part measurement cell wherein a diaphragm constitutes a partition dividing the cell in two chambers, while a restriction (a narrow opening) ensures that both chambers contain the same gas.
  • a diaphragm constitutes a partition dividing the cell in two chambers, while a restriction (a narrow opening) ensures that both chambers contain the same gas.
  • a transducer element or microphone
  • the light sources are provided with respective, specially adapted filters, and both light sources are flashed by switching on/off (i.e. pulsing of the light source itself), or by "chopping" using an electro-optical or mechanical chopper.
  • the filters are specially matched in order to absorb just those absorption lines that are of interest for the measurement gas and the reference gas, respectively, and the filters may then e.g. be constituted by light transmission cells containing just one respective of the two gases in question.
  • the light from the light source having an M filter i.e. a filter containing the measurement gas or a filter having corresponding abso ⁇ tion lines
  • R gas light from the light source having an R filter
  • the light from the source with an R filter will be able to respond (in an ordinary manner) to variable occurrence of M gas in the room, i.e. it will be attenuated according to the amount of M gas, and the light reaching the measurement cell will then be attenuated just at those wavelengths where the M gas inside the cell is able to absorb it. Less light will then be absorbed by the M gas inside the cell, i.e. a weaker sound signal will be produced at the frequency in question.
  • the two light sources are preferably flashed with different frequencies.
  • the flashing series of the two lamps can be run simultaneously, since the two different flash frequencies nevertheless provide characteristic and separate pitches inside the measurement cell simultaneously, which pitches can be distinguished through signal processing that there is no need to illuminate further here.
  • the two light sources must not necessarily flash at different frequencies.
  • One and the same frequency may also be used, but the flashing must then be made in such a manner that the two light pulse trains are in mutually opposite phases.
  • both pressure signals may possibly be equal in the measurement cell, i.e. the sensor unit will hardly detect any noticeable vibration at all, since both halves of a period will give the same amplitude. But when the gas searched for, appears, an imbalance will appear between the two period halves, which imbalance will give a clearly detectable difference.
  • the chopping/flashing is typically executed using frequencies in the range from about 1 Hz to about 10 kHz.
  • Another measurement arrangement is shown schematically in fig. 4, where the measurement cell is divided in two chambers by means of a diaphragm having a restriction, so that the same gases are present in both chambers. Additionally, the diaphragm has a mechano-electric transducer able to deliver electric signals in accordance with the movements of the diaphragm.
  • Each respective chamber has a window, and the two light sources are arranged in such a manner that they transmit light to respective chambers in the measurement cell.
  • the same technique is used as in the embodiment shown in fig. 3, with adapted M and R filters together with the light sources.
  • Both light paths toward the measurement cell pass through the room to be investigated/measured.
  • the two light sources may possibly be arranged close to each other, and transmit light beams rather close to each other, toward a not shown receiver unit that guides the light beams to the respective measurement cell windows by means of mirrors or possibly fiber optics.
  • the two light sources can be flashed at the same frequency and in phase with each other, or two different frequencies can be used. Also in this case, i.e. in the case with same frequency and phase for light toward the two chambers, it is so that a good resultant signal is achieved when an imbalance arises between the two pressure signals toward the diaphragm from two sides, when the measurement gas starts to appear in the measurement room, while when no measurement gas is present, a balance can be set up with equally strong pressure signals from both sides, i.e. a very low output signal from the sensor due to such a balance.
  • a microcontroller (not shown) controls the light frequency, and now and then it will change into another frequency than the normal frequency, in order to provide a reference signal.
  • the two frequencies that are used are adapted to the relaxation times of the two gases, i.e. the relaxation times associated with light excitation of certain excitation modi for the gas molecules. If e.g. CO 2 is the measurement gas, one such relaxation time of interest, is known to be about 8 ⁇ s.
  • Laughing gas ( ⁇ 2 O) may, as previously mentioned, be an interesting reference gas in connection with CO 2 , and a corresponding relaxation time for ⁇ 2 O is about 0,8 ⁇ s, which is lower by a factor of 10.
  • the two pulse frequencies selected may then typically exhibit the same ratio, i.e.
  • one frequency may be selected ten times as high as the other one.
  • Pulse frequencies of interest are generally situated preferably in the range of about 10 Hz to a few kilohertz, and the actual frequencies that are used, will depend on the dimensions and the gas pressure in the measurement cell. The different relaxation times of the measurement gas and the reference gas will then cause different ratios between the signals from the two flash frequencies.
  • This preferred method will be reasonable with regard to costs, and at the same time it will provide a possibility for letting a sensor calibrate itself, i.e. make an automatic resetting when information is submitted, e.g. by using a push button, to the effect that the measurement gas concentration is zero in the measurement room. Thereby, all drift can be compensated for completely.
  • the sensor will also be able to tell when it has become so dirty that it cannot be used any more (self test). This means that when the reference gas signal becomes very weak due to e.g. fouling, a special signal is produced which means that cleaning must be undertaken.

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  • Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)

Abstract

L'invention concerne un détecteur de gaz photo-acoustique comprenant au moins une source lumineuse émettant de la lumière 'hachée' dans une chambre où l'on souhaite détecter/mesurer un certain gaz, et une cellule de mesure présentant une fenêtre par laquelle passe la lumière. La cellule de mesure renferme le même gaz (gaz de mesure) que le gaz que l'on souhaite détecter/mesurer, et un détecteur de sons destinés à capter les sons produits dans le gaz à l'intérieur de la cellule. Afin de compenser la dérive due aux dépôts sur les fenêtres ou aux variations de la source lumineuse, la cellule renferme un gaz supplémentaire. Ce gaz supplémentaire possède un spectre d'absorption ayant des caractéristiques différentes de celles du spectre d'absorption du gaz de mesure.
PCT/NO1999/000065 1998-02-26 1999-02-26 Procede de mesure de la concentration d'un gaz a fonction de correction de derive et detecteur de gaz photo-acoustique WO1999044040A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU32790/99A AU3279099A (en) 1998-02-26 1999-02-26 A method for drift compensated measurement of gas concentration, and a photoacoustical gas sensor
NO20004264A NO327840B1 (no) 1998-02-26 2000-08-25 Fremgangsmate for drift-kompensert maling av gass-konsentrasjon, samt fotoakustisk gass-sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US7604598P 1998-02-26 1998-02-26
US60/076,045 1998-02-26

Publications (1)

Publication Number Publication Date
WO1999044040A1 true WO1999044040A1 (fr) 1999-09-02

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PCT/NO1999/000065 WO1999044040A1 (fr) 1998-02-26 1999-02-26 Procede de mesure de la concentration d'un gaz a fonction de correction de derive et detecteur de gaz photo-acoustique

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Country Link
AU (1) AU3279099A (fr)
NO (1) NO327840B1 (fr)
WO (1) WO1999044040A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004008112A1 (fr) * 2002-07-12 2004-01-22 Abb Research Ltd Spectrometre d'absorption a haute resolution et procede de mesure correspondant
WO2005093390A1 (fr) 2004-03-29 2005-10-06 Noveltech Solutions Oy Procede et systeme pour la detection d'un ou de plusieurs gaz ou melanges gazeux et/ou pour la mesure de la concentration d'un ou de plusieurs gaz ou melanges gazeux
DE102004034832A1 (de) * 2004-07-19 2006-03-16 Gerhart Schroff Verfahren und Anordnung zur Gasanalyse
US7595463B2 (en) * 2002-08-01 2009-09-29 Trumpf Werkzeugmaschinen Gmbh + Co. Kg Laser processing machine with monitoring of gas atmosphere and operating gases
DE102017130988A1 (de) * 2017-12-21 2019-06-27 Infineon Technologies Ag Vorrichtungen und verfahren zur nutzung des photoakustischen effekts

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0685728A1 (fr) * 1994-06-04 1995-12-06 Orbisphere Laboratories Neuchatel Sa Appareil et méthode d'analyse photoacoustique
WO1996031765A1 (fr) * 1995-04-05 1996-10-10 Nyfotek A/S Appareil de mesure photo-acoustique
WO1998029733A1 (fr) * 1996-12-31 1998-07-09 Honeywell Inc. Dispositif photo-acoustique et procede pour detecter des gaz multiples

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0685728A1 (fr) * 1994-06-04 1995-12-06 Orbisphere Laboratories Neuchatel Sa Appareil et méthode d'analyse photoacoustique
WO1996031765A1 (fr) * 1995-04-05 1996-10-10 Nyfotek A/S Appareil de mesure photo-acoustique
WO1998029733A1 (fr) * 1996-12-31 1998-07-09 Honeywell Inc. Dispositif photo-acoustique et procede pour detecter des gaz multiples

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004008112A1 (fr) * 2002-07-12 2004-01-22 Abb Research Ltd Spectrometre d'absorption a haute resolution et procede de mesure correspondant
US7595463B2 (en) * 2002-08-01 2009-09-29 Trumpf Werkzeugmaschinen Gmbh + Co. Kg Laser processing machine with monitoring of gas atmosphere and operating gases
WO2005093390A1 (fr) 2004-03-29 2005-10-06 Noveltech Solutions Oy Procede et systeme pour la detection d'un ou de plusieurs gaz ou melanges gazeux et/ou pour la mesure de la concentration d'un ou de plusieurs gaz ou melanges gazeux
CN1950693B (zh) * 2004-03-29 2010-05-05 伽泽拉有限公司 检测一种或多种气体或气体混合物和/或测量一种或多种气体或气体混合物浓度的方法和系统
US7797983B2 (en) 2004-03-29 2010-09-21 Gasera Ltd. Method and system for detecting one or more gases or gas mixtures and/or for measuring the concentration of one or more gases or gas mixtures
DE102004034832A1 (de) * 2004-07-19 2006-03-16 Gerhart Schroff Verfahren und Anordnung zur Gasanalyse
DE102004034832B4 (de) * 2004-07-19 2014-05-22 Gerhart Schroff Verfahren und Anordnung zur Gasanalyse
DE102017130988A1 (de) * 2017-12-21 2019-06-27 Infineon Technologies Ag Vorrichtungen und verfahren zur nutzung des photoakustischen effekts
CN109946234A (zh) * 2017-12-21 2019-06-28 英飞凌科技股份有限公司 利用光声效应的装置和方法
US10996201B2 (en) 2017-12-21 2021-05-04 Infineon Technologies Ag Photoacoustic measurement systems and methods using the photoacoustic effect to measure emission intensities, gas concentrations, and distances
CN109946234B (zh) * 2017-12-21 2021-05-25 英飞凌科技股份有限公司 利用光声效应的装置和方法
DE102017130988B4 (de) 2017-12-21 2022-07-07 Infineon Technologies Ag Vorrichtungen und verfahren zur nutzung des photoakustischen effekts

Also Published As

Publication number Publication date
NO327840B1 (no) 2009-10-05
AU3279099A (en) 1999-09-15
NO20004264L (no) 2000-08-25
NO20004264D0 (no) 2000-08-25

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