WO2002093141A1 - Device for the optical analysis of gases - Google Patents

Device for the optical analysis of gases Download PDF

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Publication number
WO2002093141A1
WO2002093141A1 PCT/DE2002/001769 DE0201769W WO02093141A1 WO 2002093141 A1 WO2002093141 A1 WO 2002093141A1 DE 0201769 W DE0201769 W DE 0201769W WO 02093141 A1 WO02093141 A1 WO 02093141A1
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Prior art keywords
measuring chamber
light beam
mirror
mirror surfaces
ioe
Prior art date
Application number
PCT/DE2002/001769
Other languages
German (de)
French (fr)
Inventor
Hans Krause
Original Assignee
Emerson Process Management Manufacturing Gmbh & Co. Ohg
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 Emerson Process Management Manufacturing Gmbh & Co. Ohg filed Critical Emerson Process Management Manufacturing Gmbh & Co. Ohg
Priority to EP02742757A priority Critical patent/EP1390718A1/en
Publication of WO2002093141A1 publication Critical patent/WO2002093141A1/en

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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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/031—Multipass arrangements

Definitions

  • the invention relates to a device for the optical examination of gases with a light source producing a bundled light beam, a cuvette with a measuring chamber which receives the gas to be examined, has at least one window for the entry and exit of the bundled light beam and several hollow reflecting the light beam - Has a mirror, and with a detector that receives the light beam emerging from the measuring chamber and generates a measuring signal.
  • Devices of the specified type are used for the absorption spectrometric determination of one or more gases in a gas mixture.
  • the selective absorption of radiation of a certain wavelength by certain gases in the ultraviolet, visible and infrared is measured.
  • the design of the devices is determined by two conflicting requirements. In order to achieve a high sensitivity, on the one hand, the absorption length of the light beam should be as large as possible. On the other hand, efforts are made to keep the volume of the measuring chamber small so that the gas in the measuring chamber can be exchanged in the shortest possible time.
  • the measuring cells of these known devices have a large overall length and require a comparatively large chamber volume with a correspondingly long rinsing time.
  • the invention has for its object to provide a device of the type mentioned with a measuring chamber, which is characterized by compact dimensions and a small chamber volume with a correspondingly short rinsing time with a long absorption length.
  • this object is achieved by a device of the type mentioned at the outset, in which at least three concave mirrors with a spherical mirror surface are arranged in a rotationally symmetrical manner about a central axis in the measuring chamber, the spherical centers of the mirror surfaces lying on a common incircle touching the mirror surfaces Light beam entering the measuring chamber is directed onto a mirror surface in such a way that its reflection beam is focused in the center of a second mirror surface.
  • the light beam is alternately defocused and focused reflected on the mirror surfaces, the light beam crossing the measuring chamber between the entrance and exit once per mirror surface with an even number of mirrors and twice with an odd number of mirrors.
  • the mirror surfaces in the measuring cell according to the invention are arranged rotationally symmetrically, a comparatively large absorption length can thus be achieved with compact external dimensions.
  • the measuring chamber volume of the cuvette remains extremely small compared to the absorption length, so that short rinsing times can be achieved.
  • the cuvette according to the invention can be produced simply and inexpensively as a symmetrical body of revolution.
  • the cuvette can consist of simple molded parts that are made of glass as well as in injection molding. or plastic injection molding process inexpensively. If high resistance to aggressive gases is required, glassy carbon can also be used to manufacture the measuring chamber.
  • the cuvette is preferably designed so that the spherical centers of the mirror surfaces lie in the central plane of the measuring chamber.
  • the spherical centers of the mirror surfaces lie on a flat side wall delimiting the measuring chamber and the side wall has a second reflection surface lying in the plane mentioned, which extends radially inward from the mirror surfaces.
  • the number of reflection points of the light beam is greater in relation to the absorption length and thus the loss in intensity of the radiation, but there are structural advantages, for example in the design of measuring chambers for two-beam devices.
  • the input beam can be directed onto a mirror surface in such a way that the beam path runs only in a ring zone adjacent to the mirror surfaces and a core zone located within the ring zone is left out, the core zone being separated by a Ring wall delimiting the measuring chamber is separated therefrom.
  • the measuring chamber can be reduced by the volume of the core zone without disadvantage for the absorption length.
  • Openings can be provided either on one side or on opposite sides of the measuring chamber for supplying and removing the gas to be examined. If the openings in the center of the spherical zone lie opposite one another, a guide body for deflecting the gas flow can be arranged between the openings in the measuring chamber in order to ensure a good flow To flush the measuring chamber with the gas to be examined.
  • FIG. 1 shows a cross section of a cuvette according to the invention with five concave mirrors
  • FIG. 2 shows a longitudinal section of the cuvette according to FIG. 1,
  • Figure 3 is a schematic representation of the beam path in a cuvette according to the invention with nine concave mirrors and
  • Figure 4 shows a cross section of a cuvette according to the invention with two measuring chambers.
  • the cuvette 1 shown in FIGS. 1 and 2 has the shape of a hollow cylindrical disk, which is formed from an annular wall 2 and plates 3, 4 covering it on opposite sides and encloses a measuring chamber 5 for receiving the gas to be examined.
  • Inlet openings 6 in the plate 3 and a central outlet opening 7 in the plate 4 serve to supply and discharge the gas.
  • the ring wall 2 is composed of five mutually identical wall elements 8a, 8b, 8c, 8d, 8e, which are arranged rotationally symmetrically to the central axis 9 of the cuvette 1.
  • the sides of the wall elements 8a to 8e facing the measuring chamber 5 form five concave mirrors with spherical mirror surfaces 10a, 10b, 10c, 10d, IOe, the centers of which lie on an incircle 11 touching the mirror surfaces 10a to IOe, which lies in the middle plane between the plates 3 , 4 of the cuvette 1.
  • the diameter of the inscribed circle 11 is therefore equal to the radius of the mirror surfaces 10a to IOe.
  • a window 12 through which a light beam generated by a light source 13 and focused by means of a lens 14 can enter the measuring chamber 5 and can exit it again directed at a detector 15.
  • the surfaces 16, 17 of the plates 3, 4 delimiting the measuring chamber 5 have either a light-reflecting or a light-absorbing surface.
  • the incoming light beam is directed onto the center of the mirror surface 10c and focused onto the window opening in the mirror surface 10a, so that, according to the principle of the Rowland circle, the light beam reflected from the mirror surface 10c focuses on the center of the mirror surface IOe becomes.
  • the beam reflected by the mirror surface IOe strikes the mirror surface 10b in a defocused manner and is reflected by the latter in the center of the mirror surface 10d.
  • the mirror surface 10d reflects the beam defocused on the mirror surface 10a, whereby only a small proportion of the beam reaches the detector 15 through the window 12, but the rest of the light beam is reflected by the mirror surface 10a focused on the mirror surface 10c.
  • the light beam arrives at the mirror surfaces 10a to 10e in a focused manner and at an angle to the input beam into the window opening of the window 12, so that it can be received by the detector 15 located behind it.
  • the light beam has passed through the measuring chamber 5 a total of ten times in different directions, the absorption length corresponding to twice the length of the star-shaped central beam line 18. at With an inscribed diameter of 100 mm, the described cuvette achieves an absorption length of 950 mm.
  • FIG. 3 shows the beam path using the example of a cuvette with nine mirror surfaces 10a to 10i.
  • the input beam is directed defocused onto the mirror surface 10c and is reflected from it in a focused manner onto the mirror surface IOe.
  • the reflection continues, in that the light beam alternately defocuses and focuses on the next but one mirror surface until after 19 crossings it leaves the measuring chamber through the window on the mirror surface 10a.
  • the absorption length is 1157 mm.
  • the beam path runs exclusively in the outer ring zone of the measuring chamber, while the center of the measuring chamber remains unaffected by the beam path.
  • the measuring chamber can therefore be considerably reduced in size by means of an annular wall which spares the center, as a result of which the ratio of chamber volume to absorption length becomes even more favorable.
  • FIG. 4 shows a cuvette 19 which is divided into a measuring chamber 20 and a reference chamber 21.
  • Both chambers 20, 21 contain 7 spherical mirror surfaces 22, 23 which adjoin with their equator to a flat central wall 24 separating the chambers 20, 21 from each other.
  • the center points of the mirror surfaces 22, 23 are also arranged on an incircle touching the equator of the mirror surfaces.
  • the middle wall 24 is provided on both sides with a reflective surface.
  • a cylindrical body 25, 26 is arranged in the center of the chambers 20, 21, through which the chamber volume is reduced. Sample gas and reference gas are supplied or removed via connecting pieces 27, 28.
  • the light rays entering the chambers 20, 21 through windows 29, 30 are directed in the direction of the central wall 24 in such a way that they reflect on the spherical mirror surfaces 22 and 23, which are the next but one, by reflection on the mirror surfaces formed by the central wall 24 , The number of reflection points is therefore correspondingly higher.
  • the invention is not restricted to the exemplary embodiments described.
  • the concave mirrors can be designed as separate components which are produced separately from the wall elements or a differently designed cuvette wall and are inserted in the cuvette and aligned accordingly and fastened there.

Abstract

The invention relates to a device for the optical analysis of gases. Said device comprises a light source (13) that generates a focussed light beam, a cuvette (1) comprising a measuring chamber (5), which receives the gas to be analysed, at least one aperture (12) for the entry and exit of the focussed light beam, several concave mirrors that reflect the light beam and a detector (15), which captures the light beam that exits the measuring chamber (5) and generates a measurement signal. Several concave mirrors with spherical reflective surfaces (l0a to 10e) are arranged about a central axis (9) in a rotationally symmetric manner in the measuring chamber (5), with the spherical centres of the reflective surfaces (l0a to 10e) lying on a common inscribed circle (11) that touches said reflective surfaces (l0a to 10e), whereby the light beam that enters the measuring chamber is directed onto a reflective surface (10c) in such a way that its reflected beam is focussed in the centre of a second reflective surface (10e). A long absorption length can thus be achieved in comparison with the dimensions of the cuvette.

Description

Gerät zur optischen Untersuchung von Gasen Device for the optical examination of gases
Die Erfindung betrifft ein Gerät zur optischen Untersuchung von Gasen mit einer einen gebündelten Lichtstrahl erzeugenden Lichtquelle, einer Kuvette mit einer Meßkammer, die das zu untersuchende Gas aufnimmt, wenigstens ein Fenster für den Ein- und Austritt des gebündelten Lichtstrahls aufweist und mehrere den Lichtstrahl reflektierende Hohl- Spiegel hat, und mit einem Detektor, der den aus der Meßkammer austretenden Lichtstrahl empfängt und ein Meßsignal erzeugt .The invention relates to a device for the optical examination of gases with a light source producing a bundled light beam, a cuvette with a measuring chamber which receives the gas to be examined, has at least one window for the entry and exit of the bundled light beam and several hollow reflecting the light beam - Has a mirror, and with a detector that receives the light beam emerging from the measuring chamber and generates a measuring signal.
Geräte der angegebenen Art dienen zur absorptionsspektrome- trischen Bestimmung eines oder mehrerer Gase in einem Gasgemisch. Hierbei wird die selektive Absorption von Strahlung einer bestimmten Wellenlänge durch bestimmte Gase im Ultravioletten, Sichtbaren und Infraroten gemessen. Die Gestaltung der Geräte wird von zwei gegensätzlichen Forde- rungen bestimmt. Um eine hohe Meßempfindlichkeit zu erzielen, soll einerseits die Absorptionslänge des Lichtstrahls möglichst groß sein. Andererseits ist man bestrebt, das Volumen der Meßkammer klein zu halten, damit das Gas in der Meßkammer in möglichst kurzer Zeit ausgetauscht werden kann.Devices of the specified type are used for the absorption spectrometric determination of one or more gases in a gas mixture. Here, the selective absorption of radiation of a certain wavelength by certain gases in the ultraviolet, visible and infrared is measured. The design of the devices is determined by two conflicting requirements. In order to achieve a high sensitivity, on the one hand, the absorption length of the light beam should be as large as possible. On the other hand, efforts are made to keep the volume of the measuring chamber small so that the gas in the measuring chamber can be exchanged in the shortest possible time.
Zur Erzielung großer Absorptionslängen sind Geräte mit einer mehrfach Reflexions- oder Langweg eßzelle bekannt. Hierbei wird mit in die Meßzelle eingebauten Hohlspiegeln, die einander gegenüberliegend angeordnet sind, ein auf den Eingangsspalt der Meßzelle fokussierter Eingangsstrahl mehrfach reflektiert, bevor er die Meßzelle durch einen Ausgangsspalt verläßt und auf den Detektor trifft. Die Meßzellen dieser bekannten Geräte haben eine große Baulänge und benötigen ein vergleichsweise großes Kammervolumen mit entsprechend langer Spülzeit. Der Erfindung liegt die Aufgabe zugrunde, ein Gerät der eingangs genannten Art mit einer Meßkammer zu schaffen, die sich bei großer Absorptionslänge durch kompakte Abmessungen und ein kleines Kammervolumen mit entsprechend kurzer Spülzeit auszeichnet.To achieve long absorption lengths, devices with a multiple reflection or long path measuring cell are known. Here, with concave mirrors installed in the measuring cell, which are arranged opposite one another, an input beam focused on the input slit of the measuring cell is repeatedly reflected before it leaves the measuring cell through an output slit and hits the detector. The measuring cells of these known devices have a large overall length and require a comparatively large chamber volume with a correspondingly long rinsing time. The invention has for its object to provide a device of the type mentioned with a measuring chamber, which is characterized by compact dimensions and a small chamber volume with a correspondingly short rinsing time with a long absorption length.
Erfindungsgemäß wird diese Aufgabe durch ein Gerät der eingangs genannten Art gelöst, bei welchem in der Meßkammer wenigstens drei Hohlspiegel mit sphärischer Spiegelfläche rotationssymmetrisch um eine Mittelachse angeordnet sind, wobei die Kugelmittelpunkte der Spiegelflächen auf einem gemeinsamen, die Spiegelflächen berührenden Inkreis liegen, wobei der in die Meßkammer eintretende Lichtstrahl derart auf eine Spiegelfläche gerichtet wird, daß sein Reflexionsstrahl im Zentrum einer zweiten Spiegelfläche fokussiert wird.According to the invention, this object is achieved by a device of the type mentioned at the outset, in which at least three concave mirrors with a spherical mirror surface are arranged in a rotationally symmetrical manner about a central axis in the measuring chamber, the spherical centers of the mirror surfaces lying on a common incircle touching the mirror surfaces Light beam entering the measuring chamber is directed onto a mirror surface in such a way that its reflection beam is focused in the center of a second mirror surface.
Bei der erfindungsgemäßen Meßzelle wird der Lichtstrahl an den Spiegelflächen im Wechsel defokussiert und fokussiert reflektiert, wobei der Lichtstrahl die Meßkammer zwischen Eingang und Ausgang bei geradzahliger Spiegelflächenzahl einmal und bei ungeradzahliger Spiegelflächenzahl zweimal pro Spiegelfläche quert . Bei einer Meßkammer mit drei Spie- gelflächen ergeben sich somit sechs Strahldurchgänge durch die Meßkammer, bei einer mit fünf Spiegelflächen zehn usw.. Da die Spiegelflächen bei der erfindungsgemäßen Meßzelle rotationssymmetrisch angeordnet sind, läßt sich somit bei kompakten äußeren Abmessungen eine vergleichsweise große Absorptionslänge erzielen. Das Meßkammervolumen der Kuvette bleibt hierbei im Vergleich zur Absorptionslänge außerordentlich klein, so daß sich kurze Spülzeiten erreichen lassen. Die erfindungsgemäße Kuvette läßt sich als symmetrischer Rotationskörper einfach und kostengünstig herstellen. Beispielsweise kann die Kuvette aus einfachen Formteilen bestehen, die sich sowohl aus Glas als auch im Spritzgieß- oder Spritzpreßverfahren aus Kunststoff kostengünstig herstellen lassen. Ist hohe Beständigkeit gegen aggressive Gase gefordert, so kann zur Herstellung der Meßkammer auch Glaskohlenstoff verwendet werden.In the measuring cell according to the invention, the light beam is alternately defocused and focused reflected on the mirror surfaces, the light beam crossing the measuring chamber between the entrance and exit once per mirror surface with an even number of mirrors and twice with an odd number of mirrors. In the case of a measuring chamber with three mirror surfaces, there are therefore six beam passes through the measuring chamber, in one with five mirror surfaces ten, etc. Since the mirror surfaces in the measuring cell according to the invention are arranged rotationally symmetrically, a comparatively large absorption length can thus be achieved with compact external dimensions. The measuring chamber volume of the cuvette remains extremely small compared to the absorption length, so that short rinsing times can be achieved. The cuvette according to the invention can be produced simply and inexpensively as a symmetrical body of revolution. For example, the cuvette can consist of simple molded parts that are made of glass as well as in injection molding. or plastic injection molding process inexpensively. If high resistance to aggressive gases is required, glassy carbon can also be used to manufacture the measuring chamber.
Vorzugsweise ist die Kuvette so gestaltet, daß die Kugelmittelpunkte der Spiegelflächen in der Mittelebene der Meßkammer liegen. Für manche Anwendungen kann es hingegen auch vorteilhaft sein, wenn die Kugelmittelpunkte der Spie- gelflächen auf einer die Meßkammer begrenzenden ebenen Seitenwand liegen und die Seitenwand eine zweite in der genannten Ebene liegende Reflexionsfläche aufweist, die sich von den Spiegelflächen radial nach innen erstreckt. Bei dieser Ausgestaltung ist die Zahl der Reflexionsstellen des Lichtstrahls bezogen auf die Absorptionslänge und damit der Intensitätsverlust der Strahlung größer, es ergeben sich aber bauliche Vorteile, zum Beispiel bei der Gestaltung von Meßkammern für Zweistrahlgeräte.The cuvette is preferably designed so that the spherical centers of the mirror surfaces lie in the central plane of the measuring chamber. For some applications, on the other hand, it can also be advantageous if the spherical centers of the mirror surfaces lie on a flat side wall delimiting the measuring chamber and the side wall has a second reflection surface lying in the plane mentioned, which extends radially inward from the mirror surfaces. In this embodiment, the number of reflection points of the light beam is greater in relation to the absorption length and thus the loss in intensity of the radiation, but there are structural advantages, for example in the design of measuring chambers for two-beam devices.
Um das Meßkammervolumen und damit die Spülzeit noch weiter zu verringern, kann der Eingangsstrahl so auf eine Spiegelfläche gerichtet sein, daß der Strahlengang nur in einer an die Spiegelflächen angrenzenden Ringzone verläuft und eine innerhalb der Ringzone befindliche Kernzone ausgespart bleibt, wobei die Kernzone durch eine die Meßkammer begrenzende Ringwand von dieser abgetrennt ist. Durch diese Gestaltung kann die Meßkammer um das Volumen der Kernzone ohne Nachteil für die Absorptionslänge verkleinert werden.In order to further reduce the measuring chamber volume and thus the rinsing time, the input beam can be directed onto a mirror surface in such a way that the beam path runs only in a ring zone adjacent to the mirror surfaces and a core zone located within the ring zone is left out, the core zone being separated by a Ring wall delimiting the measuring chamber is separated therefrom. With this design, the measuring chamber can be reduced by the volume of the core zone without disadvantage for the absorption length.
Zum Zuführen und Abführen des zu untersuchenden Gases können entweder auf einer Seite oder auf gegenüberliegenden Seiten der Meßkammer Öffnungen vorgesehen sein. Liegen die Öffnungen in der Mitte der Kugelzone einander gegenüber, so kann zwischen den Öffnungen in der Meßkammer ein Leitkörper zum Umlenken des Gasstroms angeordnet sein, um eine gute Durchspülung der Meßkammer mit dem zu untersuchenden Gas zu erreichen.Openings can be provided either on one side or on opposite sides of the measuring chamber for supplying and removing the gas to be examined. If the openings in the center of the spherical zone lie opposite one another, a guide body for deflecting the gas flow can be arranged between the openings in the measuring chamber in order to ensure a good flow To flush the measuring chamber with the gas to be examined.
Die Erfindung wird nachfolgend anhand eines Ausführungsbei- spiels näher erläutert, das in der Zeichnung dargestellt ist. Es zeigenThe invention is explained in more detail below on the basis of an exemplary embodiment which is illustrated in the drawing. Show it
Figur 1 einen Querschnitt einer erfindungsgemäßen Kuvette mit fünf Hohlspiegeln,FIG. 1 shows a cross section of a cuvette according to the invention with five concave mirrors,
Figur 2 einen Längsschnitt der Kuvette gemäß Figur 1,FIG. 2 shows a longitudinal section of the cuvette according to FIG. 1,
Figur 3 eine schematische Darstellung des Strahlengangs bei einer erfindungsgemäßen Kuvette mit neun Hohlspiegeln undFigure 3 is a schematic representation of the beam path in a cuvette according to the invention with nine concave mirrors and
Figur 4 einen Querschnitt einer erfindungsgemäßen Kuvette mit zwei Meßkammern.Figure 4 shows a cross section of a cuvette according to the invention with two measuring chambers.
Die in den Figuren 1 und 2 dargestellte Kuvette 1 hat die Form einer hohlen zylindrischen Scheibe, die aus einer Ringwand 2 und diese auf gegenüberliegenden Seiten bedeckenden Platten 3, 4 gebildet ist und eine Meßkammer 5 zur Aufnahme des zu untersuchenden Gases umschließt. Eintritts- Öffnungen 6 in der Platte 3 und eine zentrale Austrittsöffnung 7 in der Platte 4 dienen zur Zu- und Abfuhr des Gases. Die Ringwand 2 ist aus fünf einander gleichenden Wandelementen 8a, 8b, 8c, 8d, 8e zusammengesetzt, die rotationssymmetrisch zur Mittelachse 9 der Kuvette 1 angeordnet sind. Die der Meßkammer 5 zugekehrten Seiten der Wandelemente 8a bis 8e bilden fünf Hohlspiegel mit sphärischen Spiegelflächen 10a, 10b, 10c, lOd, IOe, deren Mittelpunkte auf einem die Spiegelflächen 10a bis IOe berührenden Inkreis 11 liegen, der sich in der Mittelebene zwischen den Platten 3, 4 der Kuvette 1 befindet. Der Durchmesser des Inkreises 11 ist somit gleich dem Radius der Spiegelflächen 10a bis IOe. In der Mitte des Wandelements 8 befindet sich ein Fenster 12, durch das ein von einer Lichtquelle 13 erzeugter und mittels einer Linse 14 fokussierter Lichtstrahl in die Meßkammer 5 eintreten und auf einen Detektor 15 gerichtet diese wieder verlassen kann. Die die Meßkammer 5 begrenzenden Flächen 16, 17 der Platten 3, 4 haben entweder eine Licht reflektierende oder eine Licht absorbierende Oberfläche .The cuvette 1 shown in FIGS. 1 and 2 has the shape of a hollow cylindrical disk, which is formed from an annular wall 2 and plates 3, 4 covering it on opposite sides and encloses a measuring chamber 5 for receiving the gas to be examined. Inlet openings 6 in the plate 3 and a central outlet opening 7 in the plate 4 serve to supply and discharge the gas. The ring wall 2 is composed of five mutually identical wall elements 8a, 8b, 8c, 8d, 8e, which are arranged rotationally symmetrically to the central axis 9 of the cuvette 1. The sides of the wall elements 8a to 8e facing the measuring chamber 5 form five concave mirrors with spherical mirror surfaces 10a, 10b, 10c, 10d, IOe, the centers of which lie on an incircle 11 touching the mirror surfaces 10a to IOe, which lies in the middle plane between the plates 3 , 4 of the cuvette 1. The diameter of the inscribed circle 11 is therefore equal to the radius of the mirror surfaces 10a to IOe. In the middle of the wall element 8 there is a window 12 through which a light beam generated by a light source 13 and focused by means of a lens 14 can enter the measuring chamber 5 and can exit it again directed at a detector 15. The surfaces 16, 17 of the plates 3, 4 delimiting the measuring chamber 5 have either a light-reflecting or a light-absorbing surface.
Wie in Figur 1 gezeigt, wird der eintretende Lichtstrahl auf die Mitte der Spiegelfläche 10c gerichtet und auf die Fensteröffnung in der Spiegelfläche 10a fokussiert, so daß nach dem Prinzip des Rowland-Kreises der von der Spiegelfläche 10c reflektierte Lichtstrahl auf das Zentrum der Spiegelfläche IOe fokussiert wird. Der von der Spiegelfläche IOe reflektierte Strahl trifft defokussiert auf die Spiegelfläche 10b und wird von dieser fokussiert ins Zentrum der Spiegelfläche lOd reflektiert. Die Spiegelfläche lOd reflektiert den Strahl defokussiert auf die Spiegelflä- ehe 10a, wobei nur ein geringer Anteil des Strahls durch das Fenster 12 den Detektor 15 erreicht, der Lichtstrahl im übrigen aber von der Spiegelfläche 10a fokussiert auf die Spiegelfläche 10c reflektiert wird. Es folgt nun eine zweite Reflexion des Lichtstrahls an den Spiegelflächen 10b bis IOe entsprechend der sternförmig verlaufenden Mittelstrahllinie 18, wobei der Fokus jedoch jeweils auf den Spiegelflächen liegt, die den Lichtstrahl bei der ersten Reflexion defokussiert empfangen haben. Entsprechend gelangt der Lichtstrahl nach insgesamt 9-facher Reflexion an den Spiegelflächen 10a bis IOe fokussiert und in einem Winkel zum Eingangsstrahl in die Fensteröffnung des Fensters 12, so daß er von dem dahinter liegenden Detektor 15 empfangen werden kann. Der Lichtstrahl hat hierbei die Meßkammer 5 in unterschiedlichen Richtungen insgesamt zehnmal durchquert, wobei die Absorptionslänge der doppelten Länge der sternförmigen Mittelstrahllinie 18 entspricht. Bei einem Inkreisdurchmesser von 100 mm wird mit der beschriebenen Kuvette eine Absorptionslänge von 950 mm erreicht.As shown in FIG. 1, the incoming light beam is directed onto the center of the mirror surface 10c and focused onto the window opening in the mirror surface 10a, so that, according to the principle of the Rowland circle, the light beam reflected from the mirror surface 10c focuses on the center of the mirror surface IOe becomes. The beam reflected by the mirror surface IOe strikes the mirror surface 10b in a defocused manner and is reflected by the latter in the center of the mirror surface 10d. The mirror surface 10d reflects the beam defocused on the mirror surface 10a, whereby only a small proportion of the beam reaches the detector 15 through the window 12, but the rest of the light beam is reflected by the mirror surface 10a focused on the mirror surface 10c. There now follows a second reflection of the light beam on the mirror surfaces 10b to IOe corresponding to the star-shaped central beam line 18, the focus, however, in each case on the mirror surfaces which received the light beam defocused during the first reflection. Accordingly, after a total of 9-fold reflection, the light beam arrives at the mirror surfaces 10a to 10e in a focused manner and at an angle to the input beam into the window opening of the window 12, so that it can be received by the detector 15 located behind it. The light beam has passed through the measuring chamber 5 a total of ten times in different directions, the absorption length corresponding to twice the length of the star-shaped central beam line 18. at With an inscribed diameter of 100 mm, the described cuvette achieves an absorption length of 950 mm.
Wie das beschriebene Beispiel zeigt, quert bei den erfin- dungsgemäß gestalteten Küvetten der Lichtstrahl die Meßkammer mit einer dem zweifachen der vorhandenen Spiegelflächen entsprechenden Zahl. Durch Erhöhung der Anzahl der Hohlspiegel kann somit bei gleichen Außenabmessungen der Meßkammer die Absorptionslänge erhöht werden. Figur 3 zeigt den Strahlengang am Beispiel einer Kuvette mit neun Spiegelflächen 10a bis lOi. Aus Gründen der einfacheren Darstellung wurde in der Zeichnung die von dem Inkreis abweichende Krümmung der Spiegelflächen ignoriert. Der Eingangsstrahl wird bei dem dargestellten Beispiel defokussiert auf die Spiegelfläche 10c gerichtet und von dieser auf die Spiegelfläche IOe fokussiert reflektiert. Die Reflexion setzt sich fort, indem der Lichtstrahl im Wechsel defokussiert und fokussiert die jeweils übernächste Spiegelfläche trifft, bis er nach 19 Querungen die Meßkammer durch das Fenster an der Spiegelfläche 10a wieder verläßt. Bei einem Inkreis von 100 mm ergibt sich hierbei eine Absorptionslänge von 1157 mm. Wie die Darstellung zeigt, verläuft bei dieser Lenkung des Lichtstrahls der Strahlengang ausschließlich in der äußeren Ringzone der Meßkammer, während das Zentrum der Meßkammer vom Strahlengang unberührt bleibt. Die Meßkammer kann daher durch eine das Zentrum aussparende Ringwand erheblich verkleinert werden, wodurch das Verhältnis von Kammervolumen zu Absorptionslänge noch günstiger wird.As the example described shows, in the case of the cuvettes designed according to the invention, the light beam crosses the measuring chamber with a number which corresponds to twice the number of mirror surfaces present. By increasing the number of concave mirrors, the absorption length can thus be increased with the same external dimensions of the measuring chamber. FIG. 3 shows the beam path using the example of a cuvette with nine mirror surfaces 10a to 10i. For reasons of simplicity of illustration, the curvature of the mirror surfaces deviating from the incircle was ignored in the drawing. In the example shown, the input beam is directed defocused onto the mirror surface 10c and is reflected from it in a focused manner onto the mirror surface IOe. The reflection continues, in that the light beam alternately defocuses and focuses on the next but one mirror surface until after 19 crossings it leaves the measuring chamber through the window on the mirror surface 10a. With an incircle of 100 mm, the absorption length is 1157 mm. As the illustration shows, in this direction of the light beam the beam path runs exclusively in the outer ring zone of the measuring chamber, while the center of the measuring chamber remains unaffected by the beam path. The measuring chamber can therefore be considerably reduced in size by means of an annular wall which spares the center, as a result of which the ratio of chamber volume to absorption length becomes even more favorable.
Bei der Anordnung von neun Spiegelflächen besteht auch die Möglichkeit, den Eingangsstrahl auf die Spiegelfläche lOd oder IOe zu richten. Da die Länge der einzelnen Strahlabschnitte zwischen zwei Spiegelflächen hierbei deutlich grö- ßer ist, ergibt sich auch eine entsprechend größere Absorptionslänge, wobei allerdings für eine Aussparung im Zentrum der Meßkammer kein nennenswerter Freiraum bestehen bleibt. Bei einem Inkreisdurchmesser von 100 mm lassen sich dann Absorptionslängen von 1577 mm bzw. 1775 mm erzielen.With the arrangement of nine mirror surfaces, it is also possible to direct the input beam onto the mirror surface 10d or 10e. Since the length of the individual beam sections between two mirror surfaces is significantly greater, there is also a correspondingly greater absorption length, although for a recess in the center there is no significant free space in the measuring chamber. With an incircle diameter of 100 mm, absorption lengths of 1577 mm or 1775 mm can be achieved.
Figur 4 zeigt eine Kuvette 19, die in eine Meßkammer 20 und eine Referenzkammer 21 unterteilt ist. Beide Kammern 20, 21 enthalten 7 sphärische Spiegelflächen 22, 23, die mit ihrem Äquator an eine die Kammern 20, 21 voneinander trennende ebene Mittelwand 24 angrenzen. Wie bei den vorangegangenen Beispielen sind auch hier die Mittelpunkte der Spiegelflächen 22, 23 auf einem den Äquator der Spiegelflächen berührenden Inkreis angeordnet. Die Mittelwand 24 ist auf beiden Seiten mit einer spiegelnden Oberfläche versehen. Im Zentrum der Kammern 20, 21 ist jeweils ein zylindrischer Kör- per 25, 26 angeordnet, durch den das Kammervolumen verkleinert wird. Meßgas und Referenzgas werden über Anschlußstutzen 27, 28 zu- bzw. abgeführt.FIG. 4 shows a cuvette 19 which is divided into a measuring chamber 20 and a reference chamber 21. Both chambers 20, 21 contain 7 spherical mirror surfaces 22, 23 which adjoin with their equator to a flat central wall 24 separating the chambers 20, 21 from each other. As in the previous examples, the center points of the mirror surfaces 22, 23 are also arranged on an incircle touching the equator of the mirror surfaces. The middle wall 24 is provided on both sides with a reflective surface. A cylindrical body 25, 26 is arranged in the center of the chambers 20, 21, through which the chamber volume is reduced. Sample gas and reference gas are supplied or removed via connecting pieces 27, 28.
Bei der Kuvette 19 werden die durch Fenster 29, 30 in die Kammern 20, 21 eintretenden Lichtstrahlen so in Richtung der Mittelwand 24 gelenkt, daß sie durch Reflexion an den von der Mittelwand 24 gebildeten Spiegelflächen auf die jeweils übernächste sphärische Spiegelfläche 22 bzw. 23 fallen. Die Zahl der Reflexionsstellen ist daher entspre- chend höher.In the case of the cuvette 19, the light rays entering the chambers 20, 21 through windows 29, 30 are directed in the direction of the central wall 24 in such a way that they reflect on the spherical mirror surfaces 22 and 23, which are the next but one, by reflection on the mirror surfaces formed by the central wall 24 , The number of reflection points is therefore correspondingly higher.
Die Erfindung ist nicht auf die beschriebenen Ausführungsbeispiele beschränkt. Insbesondere ist es auch möglich, den Lichtstrahl über seitliche, beispielsweise in den Platten 3, 4 angeordnete Fenster mit Hilfe von in der Meßkammer vorgesehenen Umlenkspiegeln ein oder auszukoppeln. Weiterhin können die Hohlspiegel als separate Bauelemente ausgeführt sein, die getrennt von den Wandelementen oder einer anders gestalteten Küvettenwand hergestellt werden und ent- sprechend ausgerichtet in die Kuvette eingesetzt und dort befestigt werden. The invention is not restricted to the exemplary embodiments described. In particular, it is also possible to couple the light beam in or out via lateral windows, for example arranged in the plates 3, 4, with the aid of deflecting mirrors provided in the measuring chamber. Furthermore, the concave mirrors can be designed as separate components which are produced separately from the wall elements or a differently designed cuvette wall and are inserted in the cuvette and aligned accordingly and fastened there.

Claims

Patentansprüche claims
1. Gerät zur optischen Untersuchung von Gasen mit einer einen gebündelten Lichtstrahl erzeugenden Lichtquelle, einer Kuvette mit einer Meßkammer, die das zu untersu- chende Gas aufnimmt, wenigstens ein Fenster für den Ein- und Austritt des gebündelten Lichtstrahls aufweist und mehrere den Lichtstrahl reflektierende Hohlspiegel hat, und mit einem Detektor, der den aus der Meßkammer austretenden Lichtstrahl empfängt und ein Meßsignal erzeugt, dadurch gekennzeichnet, daß in der Meßkammer (5) wenigstens drei Hohlspiegel mit sphärischer Spiegelfläche (10a bis IOe) rotationssymmetrisch um eine Mittelachse (9) angeordnet sind, wobei die Kugelmittelpunkte der Spiegelflächen (10a bis IOe) auf einem gemeinsamen, die Spiegelflächen (10a bis IOe) berührenden Inkreis (11) liegen und wobei der in die Meßkammer eintretende Lichtstrahl derart auf eine Spiegelfläche (10c) gerichtet wird, daß sein Reflexionsstrahl im Zentrum einer zweiten Spiegelfläche (IOe) fokussiert wird.1. Device for the optical examination of gases with a light source producing a bundled light beam, a cuvette with a measuring chamber which receives the gas to be examined, has at least one window for the entry and exit of the bundled light beam and several concave mirrors reflecting the light beam and with a detector that receives the light beam emerging from the measuring chamber and generates a measuring signal, characterized in that in the measuring chamber (5) at least three concave mirrors with a spherical mirror surface (10a to IOe) are arranged rotationally symmetrically about a central axis (9) , wherein the center of the spheres of the mirror surfaces (10a to IOe) lie on a common incircle (11) touching the mirror surfaces (10a to IOe) and the light beam entering the measuring chamber is directed onto a mirror surface (10c) in such a way that its reflection beam in Center of a second mirror surface (IOe) is focused.
Gerät nach Anspruch 1, dadurch gekennzeichnet, daß die Meßkammer eine aus Wandelementen (8a bis 8e) zusammengesetzte Ringwand aufweist, wobei jedes Wandelement (8a bis 8e) einen Hohlspiegel trägt.Device according to claim 1, characterized in that the measuring chamber has an annular wall composed of wall elements (8a to 8e), each wall element (8a to 8e) carrying a concave mirror.
Gerät nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß die Kugelmittelpunkte der Spiegelflächen (10a bis IOe) in der Mittelebene der Meßkammer (5) liegen. Device according to one of claims 1 or 2, characterized in that the spherical centers of the mirror surfaces (10a to IOe) lie in the central plane of the measuring chamber (5).
4. Gerät nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Kugelmittelpunkte der Spiegelflächen (22, 23) auf einer die Meßkammer (5) begrenzenden ebenen Seitenwand (24) liegen und die Seitenwand (24) eine zweite in der genannten Ebene liegende Reflexionsfläche aufweist, die sich von den Spiegelflächen (22, 23) radial nach innen erstreckt.4. Device according to one of the preceding claims, characterized in that the spherical centers of the mirror surfaces (22, 23) lie on a flat side wall (24) delimiting the measuring chamber (5) and the side wall (24) is a second reflection surface lying in said plane which extends radially inwards from the mirror surfaces (22, 23).
5. Gerät nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß der Eingangsstrahl so auf eine5. Device according to one of the preceding claims, characterized in that the input beam so on a
Spiegelfläche gerichtet sein, daß der Strahlengang nur in einer an die Spiegelflächen angrenzenden Ringzone verläuft und eine innerhalb der Ringzone befindliche Kernzone ausgespart bleibt, wobei die Kernzone durch eine die Meßkammer begrenzende Ringwand von dieser abgetrennt ist.Mirror surface be directed so that the beam path runs only in an annular zone adjacent to the mirror surfaces and a core zone located within the ring zone remains recessed, the core zone being separated from this by an annular wall delimiting the measuring chamber.
6. Gerät nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß der Lichtstahl durch ein im Zentrum einer Spiegelfläche angeordnetes Fenster (12) in die Meßkammer (5) eingekoppelt oder aus ihr ausgekoppelt wird.6. Device according to one of the preceding claims, characterized in that the light steel is coupled into or out of the measuring chamber (5) through a window (12) arranged in the center of a mirror surface.
7. Gerät nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß der Lichtstrahl mit Hilfe von7. Device according to one of the preceding claims, characterized in that the light beam with the aid of
Umlenkspiegeln quer zur Inkreisebene in die Meßkammer eingekoppelt oder aus ihr ausgekoppelt wird. Deflecting mirrors are coupled into or out of the measuring chamber transversely to the incircle plane.
PCT/DE2002/001769 2001-05-16 2002-05-16 Device for the optical analysis of gases WO2002093141A1 (en)

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