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EP1476741A1 - Procede de mesure spectroscopique rapide de la concentration, de la temperature et de la pression d'eau gazeuse - Google Patents

Procede de mesure spectroscopique rapide de la concentration, de la temperature et de la pression d'eau gazeuse

Info

Publication number
EP1476741A1
EP1476741A1 EP03706109A EP03706109A EP1476741A1 EP 1476741 A1 EP1476741 A1 EP 1476741A1 EP 03706109 A EP03706109 A EP 03706109A EP 03706109 A EP03706109 A EP 03706109A EP 1476741 A1 EP1476741 A1 EP 1476741A1
Authority
EP
European Patent Office
Prior art keywords
spectroscopic measurement
carried out
gas
temperature
pressure
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP03706109A
Other languages
German (de)
English (en)
Inventor
Franz Winter
Gerhard Totschnig
Maximilian Lackner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Innovationsagentur GmbH
Original Assignee
Innovationsagentur GmbH
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 Innovationsagentur GmbH filed Critical Innovationsagentur GmbH
Publication of EP1476741A1 publication Critical patent/EP1476741A1/fr
Withdrawn legal-status Critical Current

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
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers

Definitions

  • the exact water concentration in a hot, multi-phase measuring volume is often required for process optimization and control.
  • Spectroscopic methods are successfully used for the contactless, selective and sensitive concentration measurement of certain species.
  • Absorption spectroscopy using a tunable diode laser is a successfully used technique. Because of the tuning of the wavelength over a complete absorption feature, for example a single rotation line in the infrared spectral range, it is able to distinguish the absorption caused by the analyte from unspecific light attenuation (such as scattering). This gives a great advantage over methods that measure concentrations at a fixed wavelength (cf. Manfred Hesse, Herbert Meier, Bernd Zeeh: Spectroscopic Methods in Organic Chemistry, 4th Edition, Thieme, 1991, and Wolfgang Demtröder: Laser Spectroscopy. Basics and techniques, 4th edition, Springer, 2000).
  • the present invention has for its object to overcome the disadvantages of the prior art. This object is achieved with the inventive method according to claim 1. Preferred embodiments of the method according to the invention are specified in the subclaims.
  • the method presented solves in particular the illustrated problem of pressure limitation.
  • VCSEL Surface-emitting lasers
  • Detected, selective wavelengths for the detection of water in the range from 1.8 ⁇ m to 2.5 ⁇ m are approximately 1.80 ⁇ m, 1.87 ⁇ m, 1.97 ⁇ m, 1.98 ⁇ m, 1.99 ⁇ m, 2, 0 ⁇ m, 2.1 ⁇ m, 2.2 ⁇ m, 2.47 ⁇ m, 2.48 ⁇ m, and 2.50 ⁇ m.
  • Figure 1 is a schematic representation of a device for performing the method according to the invention
  • Figure 2 shows the basic scheme of a data evaluation
  • FIG. 3 shows the tuning behavior of a VCSEL (tuning range versus tuning frequency)
  • Figure 4 is a plot of the absorbance of the measurement signal for water
  • Figure 5 and Figure 6 absorption spectra of water at a pressure of 50 bar
  • Figure 7 Spectra of water at different pressure.
  • Surface-emitting lasers vertical cavity surface emitting lasers, VCSELs
  • VCSELs vertical cavity surface emitting lasers
  • edge emitters diode lasers of conventional design
  • the frequency with which the emission wavelength can be changed by varying the current is far above the bandwidth of the frequencies customary for absorption spectroscopy (a few hundred Hz to kHz).
  • Edge emitters can usually be tuned continuously over 1 cm "1 (ie a dominant mode, no mode jumps). In order to distinguish the absorption caused by the analyte from unspecific light attenuation, one has to tune the emission frequency of the laser to such an extent that a complete absorption characteristic is measured can.
  • the invention shown uses VCSEL for the spectroscopy of gases, in particular water, as shown for example in FIG. 1.
  • a suitable VCSEL (1) which is located in a block (2), is bundled by appropriate optics (3), mirrors (4), (5) through the measuring medium (13) and further directed via mirrors (6) and (7) to a detector (8) and to an evaluation device (12).
  • Diode lasers can be tuned with the current and the temperature. On the other hand, this means that the temperature at which the laser is located must be kept constant. This condition is not as strict for the VCSELs used in this procedure as for diode lasers of conventional construction (edge emitter). It is therefore not essential to control the temperature precisely.
  • the fastening of the VCSEL in a block (2), in an advantageous embodiment made of metal, is therefore sufficient in some cases.
  • the laser holder can also be thermostatted by water cooling or a thermoelectric cooler.
  • the detector (8) must be matched to the wavelength of the VCSEL, its bandwidth must be adapted to the desired tuning rate (see Nyquist sampling theorem, according to which the sampling frequency for signal reconstruction must be at least twice as high as the frequency of the signal itself).
  • the VCSEL (1) is operated either in series with an ohmic resistor (10) via a conventional laser driver (11) or via a function generator (9).
  • the laser driver (11) generates a current curve of any shape (symmetrical or asymmetrical triangle, sine, step, ...) typically of the order of magnitude 0-10 mA. It is not necessary to let the ramp start from 0 mA or from the current I th . It is possible and sometimes sensible to apply a current ramp to the laser, which begins at I> I t h.
  • Commercially available laser drivers have bandwidths up to a few 100 kHz.
  • a function generator (9) is used to generate a saving curve of any shape (symmetrical or asymmetrical triangle, sine, step, ...), typically of about 0-10V , to create.
  • a series resistor (10) of approximately 2000 ohms must be connected in series with the VCSEL in order to limit the current that is passed through (VCSELs are sensitive to voltage and current peaks).
  • the current is typically 0 to 5 mA in a current-controlled manner. This makes it possible to tune the VCSEL very quickly (up to MHz).
  • a current curve corresponding to the economy curve now ensures the change in the laser emission frequency. It has been found that the tuning range of a VCSEL decreases with the tuning frequency. This results in a limit for the method at about 20 MHz.
  • a single measurement is possible during each ramp.
  • the signal is evaluated according to the Lambert Beer law (see below for the theory).
  • A ln (In / ⁇ )
  • the absorbance A gives one of the concentration of the water directly proportional size.
  • I 0 is the intensity of the incident laser light (depending on the wavelength), I that of the transmitted light, also depending on the wavelength.
  • the intensity IQ the baseline to a certain extent, can be determined by measuring the laser intensity as a function of the wavelength without absorbing water in the beam path. It is also possible to determine this mathematically.
  • FIG. 2 shows the basic diagram of the data evaluation.
  • a current ramp is shown with which the VCSEL is operated.
  • the second field shows the corresponding detector signal.
  • the laser output power increases linearly in the first approximation.
  • the wavelength changes, also approximately linear. If there is an absorbing molecule (e.g. water) in the beam path, the signal is weakened at the correct wavelength. This is illustrated by the indentation of the curve in the third drawing.
  • the partial picture on the right shows the absorbance, calculated from ln (output intensity / transmitted intensity) as a function of the wavelength. The absorbance is directly proportional to the concentration of the absorbing molecule.
  • the measured absorbance depends on the temperature. For a constant concentration of the absorbing water, the temperature of the water can therefore be determined in situ from the value of the absorbance.
  • 4 shows a plot of the absorbance (standardized) of the measurement signal for water with a partial pressure of 5 bar at a total pressure of 50 bar over a path length of 1 cm depending on the temperature for two absorption lines (1.92 and 2.02 ⁇ m). The range examined extends from 300K to 1500K.
  • the method presented allows the temperature of the absorbing gas (here: water) to be determined by comparing the signal strength for two lines.
  • one of the lines is strong at low temperature, while the other is more pronounced at high temperature. This is advantageously done by evaluating the Quotients of the absorbances with two absorption lines. One of these should be strong at a higher temperature, the other at a lower temperature.
  • multiplexing can be used.
  • time division multiplexing is used. This means that two VCSELs are used, each of which measures one of the two lines.
  • the laser beams run in parallel and hit the same detector.
  • the lasers are now controlled alternately, making quasi-simultaneous measurement possible.
  • Multiplexing is not just limited to temperature measurements. This principle can also be used for concentration measurement.
  • Fig. 7 shows spectra of water (100%) at 800K and different pressure (5 bar, 50 bar, 100 atm). It can be seen that at higher pressures, individual lines merge into a broad peak shape. Conventional diode lasers cannot be fully tuned across such wide formations. The procedure presented here is able to do this.
  • the method according to the invention is also suitable for use in a two-beam experiment.
  • the output beam is split; one of the two partial beams passes through the measuring volume and experiences specific absorption, the other, called the reference beam, is guided past it.
  • the reference beam can be called I 0 in analogy to the previous one, the measuring beam I.
  • the measuring beam passing through the measuring volume and the reference beam are of the same size.
  • Two detectors record the signals.
  • the reference beam is used to obtain a baseline for calculating the absorption.
  • the combination with an auto balancing technique allows significant noise suppression if the quotient of I 0 / I is formed before the signal amplification of the individual signals I and I 0 . If both signals are first amplified and then divided and logarithmized, they contain uncorrelated noise.
  • Wavelength modulation or frequency modulation enable an improved detection limit compared to simple absorption.
  • the method is therefore also suitable for determining the concentration of the gas to be detected (in particular water) only in order to infer the concentration of other species.
  • Fiber coupling is particularly useful when using the described method in sensors and measuring systems.
  • the optical fibers enable easier handling of a system constructed according to the method for field measurements.
  • the fibers can be made of quartz, for example.
  • the very fast tuning capability enables quick measurements or high time resolution
  • the very wide tunability also allows the investigation at high pressures.
  • the process is inexpensive.

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

Abstract

La présente invention concerne un procédé de spectroscopie par absorption laser mis en oeuvre sur des gaz. Le procédé de l'invention se caractérise en ce qu'un gaz qui a au moins une caractéristique d'absorption dans une plage de longueurs d'onde de 5 ñm à 15 ñm est détecté, et que la mesure spectroscopique est réalisée dans cette plage de longueurs d'onde au moyen d'au moins un laser à diode à émission par la surface (VCSEL).
EP03706109A 2002-02-11 2003-02-11 Procede de mesure spectroscopique rapide de la concentration, de la temperature et de la pression d'eau gazeuse Withdrawn EP1476741A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
AT2102002 2002-02-11
AT2102002A AT500543B1 (de) 2002-02-11 2002-02-11 Verfahren zur raschen spektroskopischen konzentrations-, temperatur- und druckmessung von gasförmigem wasser
PCT/AT2003/000040 WO2003069316A1 (fr) 2002-02-11 2003-02-11 Procede de mesure spectroscopique rapide de la concentration, de la temperature et de la pression d'eau gazeuse

Publications (1)

Publication Number Publication Date
EP1476741A1 true EP1476741A1 (fr) 2004-11-17

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EP03706109A Withdrawn EP1476741A1 (fr) 2002-02-11 2003-02-11 Procede de mesure spectroscopique rapide de la concentration, de la temperature et de la pression d'eau gazeuse

Country Status (4)

Country Link
EP (1) EP1476741A1 (fr)
AT (1) AT500543B1 (fr)
AU (1) AU2003208157A1 (fr)
WO (1) WO2003069316A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108732113A (zh) * 2018-01-22 2018-11-02 复旦大学 一种水体中no的测定系统及方法

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Publication number Priority date Publication date Assignee Title
AU2007338957B2 (en) * 2006-12-22 2014-05-22 Photonic Innovations Limited Gas detector
CN101504367B (zh) * 2009-03-10 2011-07-20 哈尔滨工业大学 同时监测一氧化碳和二氧化碳浓度的装置
US8945936B2 (en) 2011-04-06 2015-02-03 Fresenius Medical Care Holdings, Inc. Measuring chemical properties of a sample fluid in dialysis systems
CN102269698A (zh) * 2011-07-04 2011-12-07 中国科学院合肥物质科学研究院 一种基于红外吸收光谱的氧化亚氮检测装置
CN102269699B (zh) * 2011-07-25 2013-12-25 北京农业智能装备技术研究中心 禽舍硫化氢气体浓度检测方法
CN102967580B (zh) * 2012-11-09 2015-03-11 山东微感光电子有限公司 一种基于vcsel的低功耗气体检测方法及装置
DE202013103647U1 (de) 2013-08-12 2013-09-02 Aspect Imaging Ltd. Ein System zum Online-Messen und Steuern von O2-Fraktion, CO-Fraktion und CO2-Fraktion
CN107884427B (zh) * 2017-11-09 2019-12-31 北京理工大学 一种基于循环水洞的通气空泡泡内气体含量测量系统

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US5570697A (en) * 1994-07-15 1996-11-05 Vixel Corporation Sensor for analyzing molecular species
US6091504A (en) * 1998-05-21 2000-07-18 Square One Technology, Inc. Method and apparatus for measuring gas concentration using a semiconductor laser
DE19840345B4 (de) * 1998-09-04 2004-09-30 Dräger Medical AG & Co. KGaA Verfahren und Vorrichtung zum quantitativen Aufspüren eines vorgegebenen Gases

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108732113A (zh) * 2018-01-22 2018-11-02 复旦大学 一种水体中no的测定系统及方法
CN108732113B (zh) * 2018-01-22 2021-03-23 复旦大学 一种水体中no的测定系统及方法

Also Published As

Publication number Publication date
AT500543B1 (de) 2006-11-15
AT500543A1 (de) 2006-01-15
WO2003069316A1 (fr) 2003-08-21
AU2003208157A1 (en) 2003-09-04

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