OPTICAL MEASURING CELL

Abstract

An optical measuring cell designed and provided for the absorption spectroscopic determination of at least one chemical and/or physical parameter of a fluid. A light beam for the absorption spectroscopic analysis is coupled into an interior of a housing, together with the fluid to be analyzed, via a coupling-in element connected to the housing such that the coupled-in light beam runs in the interior of the housing in parallel to the optical main axis of the measuring cell or the housing. A coupling-out element connected to the housing couples a light beam striking the coupling-out element out of the housing in order to supply the light beam, after multiple passes through the interior, to a detector for the absorption spectroscopic determination of a chemical and/or physical parameter of the irradiated fluid.

Claims

1. An optical measuring cell for absorption spectroscopic determination of at least one chemical and/or physical parameter of a fluid, the optical measuring cell comprising: a housing having a tube, cover, and base; a coupling-in element connected to the housing, the coupling-in element couples a light beam into an interior of the housing such that the coupled-in light beam runs substantially in parallel to an optical main axis; deflecting elements connected to the cover and the base, the deflecting elements reflecting an incident light beam running substantially in parallel to the optical main axis laterally offset into the interior of the housing substantially in parallel to the optical main axis; a coupling-out element connected to the housing, the coupling-out element coupling out a striking light beam, wherein a fluid-filled interior of the housing is irradiated multiple times, and wherein n (n>1) deflecting elements designed as roof prisms are connected to the cover and/or to the base such that they are arranged on each second side of a regular 2n-gon.

2. The optical measuring cell according to claim 1, wherein the cover is connected to the n deflecting elements designed as roof prisms such that they are arranged on each second side of a regular 2n-gon, n=3 being selected, in particular, and wherein the base is connected to a deflecting element designed as a concave mirror or plano-convex lens, in particular having a parabolic cross-section.

3. The optical measuring cell according to claim 1, wherein the deflecting elements connected to the cover and the base are selected from roof prisms, plano-convex lenses, concave mirrors, conical mirrors, conical lenses, or retro-reflector optical units.

4. The optical measuring cell according to claim 1, wherein at least one deflecting element is designed such that the incident light beam and the reflected light beam run axisymmetrically to the optical main axis.

5. The optical measuring cell according to claim 1, wherein the coupling-in element and/or the coupling-out element is/are connected to the cover or the base.

6. The optical measuring cell according to claim 1, wherein the coupling-in element and/or the coupling-out element has/have an optical element, in particular a prism, connected to a roof prism.

7. The optical measuring cell according to claim 1, wherein the arrangement of the housing, including the tube, cover, and base as well as the deflecting elements, is designed to be rotationally symmetrical to the optical main axis.

8. The optical measuring cell according to claim 1, wherein a plano-convex lens is assigned to the cover and the base, which is connected to the deflecting elements, in particular by its planar side.

9. The optical measuring cell according to claim 8, wherein at least one plano-convex lens is connected by its planar side to at least one deflecting element via gluing.

10. The optical measuring cell according to claim 9, wherein the two plano-convex lenses exhibit a focal length, which is equal to half the length of the working distance between the two plano-convex lenses.

11. The optical measuring cell according to claim 1, wherein the surface of the tube facing the interior is at least partially designed as a light-absorbing and/or non-reflective surface.

12. The optical measuring cell according to claim 1, wherein the housing is designed to be gas- and/or pressure-tight and for a gaseous fluid as the substance to be measured.

13. The optical measuring cell according to claim 1, wherein a semiconductor light source, in particular a laser or an LED light source for generating the light beam, is assigned to the optical measuring cell.

14. The optical measuring cell according to claim 1, wherein at least one sensor assigned to the optical measuring cell, including a deflecting element, the coupling-in element, or the coupling-out element is designed as a single structural unit, and/or a light source assigned to the optical measuring cell, including the coupling-in element, are designed as individual structural units or jointly as a single common structural unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0045] FIG. 1 shows a schematic representation of an example of an optical measuring cell according to the invention in an oblique view from above;

[0046] FIG. 2 shows a schematic oblique view from above of the optical measuring cell from FIG. 1;

[0047] FIG. 3 shows a schematic representation of a cover of the optical measuring cell from FIG. 1;

[0048] FIG. 4 shows a schematic representation of a base of the optical measuring cell from FIG. 1;

[0049] FIG. 5 shows a schematic representation of the arrangement of roof prisms on the top surface of the cover from FIG. 3; and

[0050] FIG. 6 shows a schematic representation of a roof prism including a coupling-in element.

DETAILED DESCRIPTION

[0051] An optical measuring cell 1 for the absorption spectroscopic determination of at least one chemical and/or physical parameter of a fluid is shown in FIG. 1 and FIG. 2, which includes a housing 2 having a tube 3, cover 4, and base 5 made from metal, in particular high-grade steel. Housing 2 is designed as a gas-tight housing 2 and encloses the interior of housing 2 with cover 4, base 5, and tube 3 situated between base 5 and cover 4. The interior is filled with the fluid to be analyzed, in particular the gas to be analyzed.

[0052] With the aid of this optical measuring cell 1 according to the invention, it is possible to determine chemical and/or physical parameters of a fluid, for example the concentration of a gas component in a gas mixture, the moisture in an, in particular, gaseous fluid, the temperature and/or also the dew point of the fluid. For this purpose, a laser beam 7 is applied to the fluid-filled interior of optical measuring cell 1, and after passing multiple times, in particular 6 times, through the interior having a length of approximately 60 cm and a diameter of approximately 6 cm, this laser beam 7 is compared with original laser beam 7 with the aid of an optical sensor 41, 42, which is not illustrated in FIGS. 1 and 2, and the chemical and/or physical parameter of the fluid is/are determined therefrom. This is made possible in a very precise and robust way by illustrated optical measuring cell 1, since the construction of optical measuring cell 1 supports this to a special extent with the specially designed beam path in housing 2, by passing through interior 6 of housing 2 multiple times, and thus by the fluid to be analyzed.

[0053] Tube 3 is screwed gas-tight to cover 4 at one end and to base 5 at the other end. Cover 4 exhibits a circular region in the extension of interior 6 of tube 3, which is provided with a gas-tight end face 8, on which multiple roof prisms 9 are arranged. Base 5 likewise exhibits a circular region in the extension of interior 6 of tube 3, which is provided with a gas-tight end face 8, which is designed to be gas-tight with the aid of an aspherical lens 21. Aspherical lens 21 is assembled from a spherical lens 10, 22 having a parabolic cross-section, and a plano-convex lens 23, these being fixedly connected by their planar surface by means of gluing. Spherical lens 22 having the parabolic cross-section as part of aspherical lens 21 is apparent in FIG. 2.

[0054] The schematic representation of the optical element, which seals the circular region in cover 4 gas-tight is illustrated in a side view in FIG. 3.

[0055] A laser beam 7, which is supplied to optical measuring cell 1, for example from a tunable laser as light source 40 for laser beam 7, may be received via a coupling in/out element 11, which is designed as a prism having an orthogonal, triangular cross-section, and deflected in such a way that laser beam 7 is deflected in the direction of interior 6 via a side surface 13 of roof prism 9, after leaving the deflecting element designed as roof prism 9, laser beam 7 having a direction which is oriented in parallel to optical main axis 34 of measuring cell 1 or housing 2 and thus optical measuring cell 1. Coupling-in/out element 11 is fixedly connected to roof prism 9 by gluing and forms a common structural unit which, on the one hand, ensures that no air gap is present between coupling-in/out element 11 and roof prism 9 and, on the other hand, that the structural unit as a whole may be positioned or replaced as needed, thereby ensuring a very secure and maintenance-friendly operation. Coupling-in/out element 11 may furthermore be connected to roof prism 9, and thus also to cover 4, in a fixed and thus statically defined manner.

[0056] Laser beam 7 coupled in via coupling-in/out element 11 is deflected in the direction of the focal point of plano-convex lens 23 with the aid of plano-convex lens 23 connected to roof prism 9 by gluing, which forms an end face 8 for sealing the interior of optical measuring cell 1. Plano-convex lens 10 is connected in each case with its planar side to base surfaces of the three roof prisms 9 by gluing in a fixed and optically neutral manner. The connecting surface of roof prisms 9 and plano-convex lens 23 together form end face 8, which seals the circular region of cover 4 gas-tight. Plano-convex lens 23, roof prisms 9, and the adhesive for gluing are preferably selected in such a way that they have the same or nearly the same refractive index.

[0057] Coupling-in/out element 11 furthermore has the task of coupling out a laser beam 7, which is supplied via roof prism 9 and enters roof prism 9 having coupling-in/out element 11 after irradiating gas-filled interior 6 of housing 2 multiple times, out of optical measuring cell 1 and thereby makes it possible to compare coupled-out laser beam 7 with original laser beam 7 to be coupled in, using one or multiple optical sensors 41, 42, and thereby makes it possible to determine the desired chemical or physical parameter of the gaseous fluid in interior 6, and thereby allows optical measuring cell 1 to act as part of an optical measuring arrangement according to the absorption spectroscopic method.

[0058] As schematically illustrated in FIG. 5 in connection with FIG. 6, the three roof prisms 9 shown in FIG. 3 are arranged above three sides 33 of a regular hexagon 31, a not completely covered, empty side 33 being present between each of roof prisms 9. End face 8 illustrated in FIG. 5 corresponds to the planar surface of plano-convex lens 23, which is connected to base surfaces 12 of roof prisms 9. Roof prisms 9 are selected in such a way that side surfaces 13 of roof prisms 9 are situated above vertex points 32 of regular hexagon 31 and thereby ensure that a laser beam 7 incident upon the region of a vertex 32 from the direction of interior 6 in parallel to optical main axis 34 is deflected by side surfaces 13 in such a way that laser beam 7 continues to run in roof prism 9 in parallel to base surface 12 and leaves roof prism 9 in the direction of interior 6 on the other side surface 13 of roof prism 9 in the direction of other vertex 32, over which latter side surface 13 is arranged, and thus in parallel to optical main axis 34 and offset with respect to incident laser beam 7. This roof prism 9 thus forms a deflecting element according to the invention.

[0059] Due to the arrangement of the three roof prisms 9 on the three non-adjacent sides 33 of regular hexagon 31, a rotationally symmetrical design of cover 4, including the deflecting elements designed as biprisms 9 arranged thereon, is given. The rotation point of the rotationally symmetrical design forms center point 35 of hexagon 31 and simultaneously the point at which optical main axis 34 penetrates end face 8.

[0060] FIG. 4 shows a side view of a biconvex, aspherical lens 21, which is made up of a plano-convex lens 23 and a spherical lens 22 having a parabolic cross-section, these lenses 22, 23 being fixedly connected to each other with their planar surfaces by gluing. Lenses 22, 23 and the adhesive are selected in such a way that their refractive index is the same or largely the same. End face 8, which seals the interior of optical measuring cell 1 gas-tight and in which the laser beams oriented in the direction of the interior or out of the interior run in parallel to optical main axis 34, is situated in the connecting region between plano-convex lens 23 and spherical lens 22.

[0061] Alternatively, it has proven to be successful to form biconvex, aspherical lens 21 as a single piece with a plano-convex lens part 23 and a spherical lens part 22 having a parabolic cross-section.

[0062] Spherical lens 22 having a parabolic cross-section is designed in such a way that it forms a deflecting element and thereby reflects an incident laser beam 7 running in parallel to optical main axis 34 of housing 2 laterally offset n the direction of interior 6 of housing 2 in parallel to optical main axis 34. Plano-convex lens 23 is connected with the aid of its planar side to the planar surface of spherical lens 22. This connecting surface forms end face 8, which seals the circular region of base 5 gas-tight.

[0063] Plano-convex lens 23 of base 5 and plano-convex lens 10 of cover 4 exhibit the same focal length f and are arranged in tube 3 in the particular end region in such a way that their distance from each other corresponds to twice the focal length f, and they have a common focal point in the center of tube 3.

[0064] This makes it possible for laser beams 7 running in parallel to optical main axis 34 from the deflecting elements to enter the two plano-convex lenses 10, 23 via the planar surfaces thereof and to be deflected thereby in the direction of the common focal point and enter the convex surface of opposite plano-convex lens 23, 10 and be reflected by this lens in parallel to laser beams 7 running in parallel to optical main axis 34, which enter, via the particular planar surfaces of plano-convex lenses 23, 10, assigned spherical lens 22 having a parabolic cross-section or roof prisms 9 and be laterally offset thereby and be reflected in the direction of interior 6 in parallel to optical main axis 34 to subsequently be focused again in the direction of common focal points 24 by connected, plano-convex lenses 23, 10.

[0065] A lateral offset along one side 33 or by the length of one side 33 of hexagon 31 is effectuated by the positioning and arrangement of roof prisms 9. Spherical lens 22 is designed in such a way that such an offset of reflected laser beam 7 takes place thereby, which runs axisymmetrically to optical main axis 34 of measuring cell 1 or housing 2 and thus optical measuring cell 1. A side change and thus a reflection of incident laser light 7 on the opposite side of the point of incidence is achieved thereby. The offset between the deflecting element of cover 4 having roof prism 9 and the offset of the deflecting element in base 5 having spherical lens 22 are fundamentally different from each other. The one offset takes place along the side lines of regular hexagon 31 arranged around the optical center line, while the other offset effectuates a lateral change with respect to optical center line 34. A multiple irradiation of interior 6 over common focal point 24 is effectuated by these differences in the offset between base 5 and cover 4, the coupling-in and coupling-out points of the deflecting elements changing regularly in roof prisms 9 or in spherical lens 22.

[0066] In optical measuring cell 1 illustrated in the figures, laser beam 7 is coupled in via a common coupling-in/out element 11, which is arranged on a side surface 13 of a roof prism 9, and, after the passage through all three roof prisms 9 and assigned vertices 32 with opposite base 5 and the particular oblique crossing of interior 6 of housing 2, it is again coupled-out of optical measuring cell 1.

[0067] Roof prism 9 having coupling-in/out element 11 is provided with two optical sensors 41, 42. Optical sensor 41 is arranged over a wide area without an air gap on side surface 13 of roof prism 9 for the purpose of measuring the optical properties there, in particular the intensity of incident laser light 7 from laser light source 40 during the first deflection in the direction of the interior of optical measuring cell 1 and thus in the coupling-in region. The other optical sensor 42 is arranged in the coupling-out region of laser light 7, in that it is arranged on the side surface of coupling-in/out element 11 in such a way that laser light 7 is measured during the coupling-out from measuring cell 1 with respect to the optical properties, in particular the intensity of laser light 7, after the multiple passage through the interior of measuring cell 1. The desired chemical or physical property of the fluid to be analyzed in the interior of measuring cell 1 may be determined by comparing the measured values of the two optical sensors 41, 42.

[0068] Due to this multiple passage through the interior having the gas to be analyzed, it is possible to make a very precise statement on the absorption properties of the gas and thus the chemical or physical parameters of the gas, for example the moisture content of a compressed air. This is especially applicable, since a highly robust and not very sensitive determination is made possible by this arrangement. It has been shown that this arrangement has also been proven to have little susceptibility to contaminants, in particular due to the introduced gas to be analyzed, which is achieved, in particular, by the use of plano-convex lenses 10, 23. By designing the inner wall of tube 3 as a blackened inner wall and thus as a non-reflective surface, it is also possible to minimize the influences of stray light, which is coupled into the optical path of laser beam 7 and corrupts the measurement result, and thereby further increase the achievable precision of optical measuring cell 1.

[0069] By designing this optical measuring cell 1 with screwed-on gas-tight cover 4 and screwed-on gas-tight base 5 and with tube 3 without optical elements, it is furthermore possible to particularly easily maintain and inspect optical measuring cell 1 or its housing 2. The quality of optical measuring cell 1 and thus the entire optical measuring arrangement may be kept particularly high thereby.

[0070] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.