Spectroscopic gas sensor

Abstract

A spectral gas sensor is described, comprising an absorption cell configured for gas exchange. The gas sensor includes a first concave reflector, at least one first planar reflector attached to the first concave reflector (10) and defining a first reflector plane (12), a light source (6) configured for emitting light, and a first detector (7) arranged for detecting light from the light source (6) after the light has been reflected at least once in the first concave reflector (10). The gas sensor (1) is configured such that light from the light source (6) is guided along a first principal direction (R1) before its first reflection in the first concave reflector (10) and along a second principal direction (R2) after its first reflection in the first concave reflector (10). The first reflector plane (12) is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the plane defined by the first and second principal directions. The planar reflector (11) and the first concave reflector (10) form an integrated reflector unit, and the first concave reflector (10) extends on both sides of the first reflector plane (12).

Description

Technical Field

[0001] This invention relates to a spectral gas sensor including an absorption cell. In particular, this invention relates to a spectral gas sensor with small external dimensions. Background Technology

[0002] Gas sensors are becoming increasingly common for various applications. One example is their use in monitoring ambient air pollution. In air pollution monitoring, the ability to simultaneously detect multiple different gases is desirable. Other application examples include detecting specific gases in industry, such as carbon dioxide. In breweries, carbon dioxide is used to carbonate beverages. Monitoring carbon dioxide concentration is crucial for accident prevention. Another example of an application is gas sensors for breath analysis, which can be used, for example, to detect hypoglycemia in diabetic patients. In many applications, handheld gas sensors are desirable. Optical gas sensors rely on the use of an absorption cell, in which light interacts with the gas to be analyzed. To miniaturize gas sensors for handheld use, minimizing the size of the absorption cell within the gas sensor is desirable.

[0003] WO 2020 / 263168 describes a gas sensor comprising a multi-pass absorption cell in which three reflective surfaces are arranged in a White cell configuration. This is an advantageous arrangement of the multi-pass cell because it allows the multi-channel gas sensor to provide long optical paths for some channels while keeping the housing of the multi-pass absorption cell relatively small.

[0004] US 6,016,203 describes a gas sensor designed to measure a gas sample enclosed in a cavity, the cavity having a bulk shape, wherein the walls or wall segments of the cavity exhibit high reflectivity to light. The cavity contains means for incident light and means for outgoing light. The cavity exhibits opposing surface segments designed and coordinated such that incident light is arranged—without reflection, or with minimal reflection in a plane (xz plane)—to pass through the cavity to a concave mirror surface oriented perpendicular to the plane; and such that the light is arranged to be reflected within the plane of the mirror surface, passing through the cavity to other surfaces, thereby forming a measurement path before the reflected beam is directed to the means for outgoing light. Summary of the Invention

[0005] The purpose of this invention is to provide a miniaturized spectral gas sensor.

[0006] Another object of the present invention is to provide a spectral gas sensor comprising a light source, a reflector and a detector, wherein light propagates substantially in a plane, and which is thinner in a direction perpendicular to the plane compared to gas sensors according to the prior art.

[0007] The above objective is achieved by the spectral gas sensor according to the independent claim.

[0008] The features of the dependent claims provide additional advantages.

[0009] According to a first aspect, a spectral gas sensor is provided, comprising an absorption cell configured for gas exchange. The gas sensor includes a first concave reflector, at least one first planar reflector attached to the first concave reflector and defining a plane of the first reflector, a light source configured to emit light, and a first detector arranged to detect light from the light source, the light having been reflected at least once in the first concave reflector. The gas sensor is configured such that light from the light source is guided along a first principal direction before its first reflection in the first concave reflector and along a second principal direction after its first reflection in the first concave reflector. The plane of the first reflector is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the plane defined by the first and second principal directions. The gas sensor is characterized in that the planar reflector and the first concave reflector form an integral reflector unit, and the first concave reflector extends on both sides of the plane of the first reflector.

[0010] The feature that the first reflector plane is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the plane defined by the first principal direction and the second principal direction can be expressed as light propagating substantially parallel to the first reflector plane.

[0011] A one-piece integrated reflector unit can be formed from a polymer material, for example, by molding. Having such an integrated reflector unit is advantageous because it facilitates the production and assembly of the gas sensor.

[0012] When molding a one-piece reflector unit, it is difficult to obtain a perfectly sharp angle between the first concave reflector and the first planar reflector. Rounded corners are almost inevitable. Even if the first principal direction meets the first concave reflector at a certain distance from the first planar reflector, some portions of the light beam may still strike the first concave reflector near the first planar reflector. This is due to the extension of the light beam in a direction transverse to the beam direction. Using a gas sensor according to the first aspect, this problem is mitigated because the first concave reflector extends on both sides of the first reflector plane. This allows for the manufacture of a molded one-piece reflector unit without any rounded corners between the first concave reflector and the first planar reflector, and the light striking the first concave reflector near the first planar reflector is not interfered with by any rounded corners.

[0013] Using the gas sensor according to the first aspect, light can be guided to strike the first concave reflector at a position very close to the planar reflector, which in turn allows the first concave reflector to have a small extension in the direction perpendicular to the first planar reflector and allows the gas sensor to have a small volume.

[0014] The first concave reflector can be a cylindrical reflector, the center of curvature of which lies along a line perpendicular to the plane of the first reflector. Using such a cylindrical reflector, light incident on the first concave reflector in a manner not parallel to the first planar reflector will be reflected, causing the reflected light to continue traveling in the same direction relative to the first planar reflector. The reflected light will be focused only within the plane. Therefore, if light incident on the first concave reflector travels partially away from the first planar reflector, the reflected light will continue to travel partially away from the first planar reflector. If the angle is too large, the light may partially or completely miss the detector. Therefore, when the first concave reflector is such a cylindrical reflector, the direction of light incident on the first concave reflector should be substantially parallel to the first planar reflector.

[0015] A spectral gas sensor may include a second planar reflector that defines a second reflector plane and faces a first planar reflector. With such a second planar reflector, the direction of light incident on the first concave reflector is less critical because light at an excessively large angle to the first planar reflector will be reflected in the second planar reflector. This allows more light to reach the detector. However, due to losses in reflection, it is still preferable to keep the light substantially parallel to the first planar reflector.

[0016] The second reflector plane can be arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the first reflector plane. Using such an angle maximizes the amount of light emitted by the impact detector, thereby maximizing the efficiency of the gas sensor.

[0017] The first concave reflector may extend to both sides of the plane of the second reflector. This is advantageous for the same reasons described above for the extension to both sides of the plane of the first reflector.

[0018] The spectral gas sensor may include an assembly unit attached to a first planar reflector and a main reflector unit including a first concave reflector. The first concave reflector may be a double-curved concave reflector facing the assembly unit and partially facing the first reflector plane. An absorption cell may be configured such that light emitted from a light source is reflected and focused onto a light spot by the first concave reflector and the planar reflector, and a detector may be configured to detect light from the light spot. Using such a double-curved concave reflector, any deviation of the light direction from a direction parallel to the first planar reflector will be compensated for by the first concave reflector. This makes the efficiency of the gas sensor less sensitive to the direction of light incident on the first concave reflector.

[0019] The first concave reflector may have a first center of curvature, wherein the first center of curvature lies in the plane of the first reflector. This will cause the first planar reflector to image a virtual portion of the first planar reflector.

[0020] The component unit may include at least one component reflector, and the main reflector unit includes a double-curved second concave reflector facing the component unit and partially facing the first reflector plane. The second concave reflector may extend on both sides of the first reflector plane, having the same benefits as described for the first concave reflector. A first planar reflector may be attached to the first concave reflector, the second concave reflector, and the component unit. The absorption cell may be a multi-pass absorption cell configured such that light emitted from the light source is reflected and converged onto a spot on the component reflector by the first concave reflector and the planar reflector, and that light reflected from any spot at any location on the component reflector is reflected and converged to different locations by the main reflector unit and the planar reflector. Using such a multi-pass absorption cell, a long absorption path can be achieved with a small gas sensor size.

[0021] The first planar reflector, the first concave reflector, the component reflector, and the second concave reflector can form an integral reflector unit, having the same benefits as described above for an integral reflector unit.

[0022] The first concave reflector may have a first center of curvature and a first radius of curvature. The second concave reflector may have a second center of curvature and a second radius of curvature, and the component unit may define a concave double-curved surface having a third center of curvature and a third radius of curvature, wherein the first, second, and third centers of curvature are located in the same longitudinal plane of symmetry extending through the component unit and the main reflector unit, and wherein the first reflector plane deviates from the direction parallel to the plane of symmetry by no more than 10 degrees, preferably no more than 5 degrees. With such an arrangement, the quality of the light spot is high enough to allow the light to pass through the multi-pass absorption cell multiple times before impacting the detector, while simultaneously causing a large amount of emitted light to impact the detector.

[0023] The module reflector can coincide with the double-curved surface of the module unit. Utilizing such a double-curved surface of the module reflector further improves the quality of the light spot.

[0024] Due to manufacturing tolerances, the plane of symmetry may not be perfectly aligned with the first planar reflector. To maintain the quality of the light spot and thus the efficiency of the gas sensor, the distance between the plane of symmetry and the first planar reflector is preferably no more than 10% of the first, second, or third radius of curvature, more preferably no more than 5%, and most preferably no more than 2%.

[0025] To maintain the quality of the light spot and thus the efficiency of the gas sensor, the first radius of curvature is preferably no more than 10% different from the second and third radii of curvature, more preferably no more than 5%, and most preferably no more than 2%.

[0026] To optimize the quality of the light spot and thus the efficiency of the gas sensor, the concave surface of the component unit preferably defines a spherical surface, and the first concave reflector and the second concave reflector are spherical reflectors.

[0027] Using the defined preferred shape and size, the resulting multi-pass absorption cell is, in principle, a White cell cut in half by the first planar reflector.

[0028] The spectral gas sensor may include at least one first recess located in a first planar reflector, the first recess extending along at least a portion of the first planar reflector at the first concave reflector, thereby providing extensions of the first concave reflector on both sides of the plane of the first reflector. If the gas sensor includes a second concave reflector, a corresponding first recess may be provided at the second concave reflector. The first recess is preferably located at least at the positions of light spots that appear during operation of the gas sensor.

[0029] As an alternative to or supplement to the first concave portion, the spectral gas sensor may include at least one aperture located in a first planar reflector, the aperture extending along at least a portion of the first planar reflector at the first concave reflector, thereby providing extensions of the first concave reflector to both sides of the plane of the first reflector. If the gas sensor includes a second concave reflector, a corresponding aperture may be provided at the second concave reflector. The aperture is preferably located at least at the positions of light spots that appear during operation of the gas sensor.

[0030] The first planar reflector may include a recess extending along the first planar reflector at a distance from it. When the reflector is a double-curved reflector, it is difficult to mold a one-piece reflector unit without using a mold consisting of two parts arranged with an expandable sliding gap. The mold components are placed in place before molding the concave reflector. After molding, at least one mold component is removed to allow the resulting one-piece component to be ejected from the jig. To avoid unwanted flanges on the planar reflector, it is preferable to provide a recess at the junction of the moving parts to hide any possible interference from the field of view of light passing through the cavity.

[0031] In the following description, embodiments of the present invention will be described with reference to the accompanying drawings. Attached Figure Description

[0032] Figure 1 A top view of a spectral gas sensor according to an embodiment is shown schematically.

[0033] Figure 2 A cross-section of a portion of a gas sensor according to another embodiment is shown in a side view.

[0034] Figure 3 Shown in top view Figure 2 The gas sensor part.

[0035] Figure 4 A top view shows a spectral gas sensor according to another embodiment.

[0036] Figure 5 Showing with Figure 4 The cross-section of a spectral gas sensor, similar to the implementation method, is viewed from the side.

[0037] Figure 6 Showing with Figure 4 The implementation method is similar to the arrangement of spectral gas sensors.

[0038] Figure 7 This is a top view of a cross-section of a gas sensor according to an alternative embodiment.

[0039] Figure 8 It is based on Figure 7 A side view of the cross-section of the gas sensor according to the embodiment. Detailed Implementation

[0040] In the following description of the embodiments, the same reference numerals will be used to denote corresponding features in different figures. The figures are not drawn to scale.

[0041] Figure 1 A schematic top view of a spectral gas sensor 1 according to an embodiment is shown. The gas sensor 1 includes an absorption cell 4 disposed within a housing 2 having an opening 3. The absorption cell 4 is configured for gas exchange through the opening 3. The absorption cell 4 includes an assembly unit 5, which in the illustrated embodiment includes a light source 6 configured to emit light, a detector 7 configured to detect light from the light source, and an optional optical filter 8. The absorption cell also includes a primary reflector unit 9, which includes a first concave reflector 10 facing the assembly unit 5. The concave reflector may have a cylindrical surface, the center of curvature of which is along a line perpendicular to the plane 12 of the first reflector. The multi-pass absorption cell 4 includes a first planar reflector 11 attached to the first concave reflector, the first planar reflector 11 defining a first reflector plane extending in the plane of the drawing and attached to the first concave reflector 10. The absorption cell 4 is configured such that light emitted from the light source 6 propagates in the form of a beam having a principal direction R1 toward the first reflector 10. Light from light source 6 is reflected by first reflector 10 and converged into a second beam along the second principal direction R2, which then enters light spot S1. Figure 1In this embodiment, the light spot S1 is located between the optical filter 8 and the detector 7. Figure 1 In one embodiment, the detector is configured to directly detect light from the light spot S1. However, as will be described below, the gas sensor can be configured to cause the light to undergo multiple reflections between the light source 6 and the detector 7. A first principal direction R1 and a second principal direction R2 define a plane. The first reflector plane defined by the first planar reflector 11 is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the plane defined by the first principal direction R1 and the second principal direction R2. In other words, the first principal direction R1 and the second principal direction are substantially parallel to the first planar reflector 11. Figure 1 In one embodiment, an aperture 13 is formed in the first planar reflector 11. The aperture 13 allows the first concave reflector 10 to extend on both sides of the plane defined by the planar reflector 11.

[0042] exist Figure 1 In this embodiment, the spectral characteristics of the gas sensor 1 are provided by an optical filter 8. The optical filter 8 transmits only a portion of the wavelength range of light from the light source 6. The transmitted light is detected by the detector 7. The light from the light source 6 illuminating the detector 7 has passed through the optical filter 8. Alternatively, the spectral characteristics can be provided by the light source 6 and / or the detector 7. For example, a narrowband light source can be used. The planar reflector and the first reflector form an integrated reflector unit. Such an integrated reflector unit can be formed, for example, by molding from a polymer material. When molding... Figure 1 When using the integrated reflector unit shown, it is difficult to obtain a completely sharp angle between the first concave reflector 10 and the first planar reflector. Rounded corners are almost inevitable. Even if the first principal direction R1 meets the first concave reflector at a certain distance from the first planar reflector 11, some portions of the beam may still strike the first concave reflector 10 near the first planar reflector 11. The extension of the beam is determined by... Figure 1 The thick line 14 is shown in the diagram. Figure 1 In this embodiment, light striking the first concave reflector 11 near the first planar reflector 11 is not affected by any rounded corners because the first concave reflector 10 extends on both sides of the plane defined by the planar reflector 11.

[0043] Figure 2 Shown in side view according to Figure 1 A cross-section of a portion of the gas sensor in the embodiment of the invention. Figure 3 View from above Figure 2 A partial view within the text. Figure 1 The view in the middle is viewed from below. Figure 2 The view. In Figure 2The diagram shows a second planar reflector 55. A first planar reflector 11 defines a first reflector plane 12. The second planar reflector 55 defines a second reflector plane 56 and faces the first planar reflector 11. The second reflector plane 56 is preferably parallel to the first reflector plane 12. If the second reflector plane 56 is not parallel to the first reflector plane 12, the angle between the first reflector plane 12 and the second reflector plane is less than 10°, preferably less than 5°, and most preferably less than 2°. Due to manufacturing processes, the second planar reflector 55 is preferably not part of a single reflector unit, but is attached to the first concave reflector 10. The first concave reflector 10 extends on both sides of the second reflector plane 56.

[0044] The first concave reflector 10 partially faces the first reflector plane 12. This means that the normals of at least some points on the first concave reflector intersect the first reflector plane 12. Figure 1 Light incident perpendicular to the first concave reflector 10 will not be directed to the first planar reflector 11 or the second planar reflector 55. However, if the light source is divergent, some light may strike the first concave reflector 10 at an angle less than 90°. If this angle is small enough, and / or if the distance from the point of incidence on the first concave reflector 10 to the first planar reflector 11 or the second planar reflector 55 is small enough, the light will be reflected to the first planar reflector 11 or the second planar reflector 55 before being reflected to the detector. This minimizes the loss of light from the gas sensor.

[0045] Figure 4 A spectral gas sensor according to another embodiment is shown. Figure 5 A slightly modified spectral gas sensor is shown in cross-section viewed from the side, such as... Figure 4 The eye in the image is shown in Figure 45. Figure 4 Implementation methods and Figure 5 The difference between the implementation methods is that, Figure 5 The component reflector 24 is a double-curved concave reflector with a third curvature center 29. Figure 5 The image shows a first planar reflector 11, while... Figure 4 Not shown in the image. Figure 4In this design, component unit 5 includes component reflector 24, and main reflector unit 9 includes a double-curved first concave reflector 10 and a double-curved second concave reflector 15. The first concave reflector 10 and the second concave reflector 15 face component unit 5 and partially face the first reflector plane 12. The first concave reflector 10 and the second concave reflector 15 are attached to each other as integral components and are arranged along a first plane A. Component reflector 24 is arranged along a second plane B. The first concave reflector 10 is arranged such that a first center of curvature 27 is close to the second plane B. The second concave reflector 15 is arranged such that a second center of curvature 28 is close to the second plane B. Ideally, the centers of curvature 27 of the first concave reflector 10 and the centers of curvature 29 of the second concave reflector 15 are both located in the second plane B. Component reflector 24 is shown as a planar reflector, but ideally, component reflector 24 is a double-curved concave reflector with a third center of curvature 29, such as... Figure 5 As shown. Figure 5 As shown, the planar reflector 11 is attached to the first concave reflector 10, the second concave reflector 15, and the component reflector 24. The absorption cell 4 is a multi-pass absorption cell and is configured such that light emitted from the light source is reflected by the first concave reflector 10 and the planar reflector and converges onto a first light spot S1 on the component reflector 24. Figure 4 In the illustrated embodiment, the first light spot S1 is reflected by the component reflector 24, the second concave reflector 15, and the planar reflector 11 onto the second light spot S2 on the optical filter 8. Figure 4 In one embodiment, a plano-convex lens 26 is positioned between the optical filter 8 and the detector 7. The plano-convex lens 26 focuses light from the second light spot S2 onto the detector 7. This allows for the use of a smaller detector 7 while still collecting most of the light from the second light spot. The optical filter 8 may be an interference filter. The plano-convex lens 26 may be attached to the planar reflector 11. In an alternative embodiment, the gas sensor may consist only of the first concave reflector 10, and the detector may be positioned at the first light spot S1. By using one or two double-curved concave reflectors, the second planar reflector 55 is unnecessary because light reflected in the first concave reflector 10 or the second concave reflector 15 will not be reflected away from the first planar reflector 11.

[0046] As described above and as Figure 4 As shown in the embodiment, the first curvature center 27 and the second curvature center 28 are preferably both located in the second plane B. The light source is not in... Figure 4 As shown in the text, but Figure 5 This illustrates how light is reflected in the first concave reflector 10. Figure 5As can be seen, the light source 6 is arranged below the first reflector plane 12. A first ray is emitted from the light source 6 towards the plane reflector 11 along the first principal direction R1 (shown as a dashed line). The first ray is reflected by the plane reflector 11 and the first concave reflector 10 into a second ray along the second principal direction R2 (shown as a dotted line), which then strikes the first light spot S1 (…). Figure 1 and Figure 4 The first light spot S1 is at the same distance from the plane reflector as the light source 6, but is located along plane B ( Figure 3 Different positions of ) In Figure 5 In the middle, the thick dashed line 39 shows the shape of the first reflector 10 if the planar reflector 11 is removed and the shape of the first concave reflector 10 continues above the first reflector plane 12.

[0047] The first curvature center 27, the second curvature center 28, and the third curvature center 29 are located in the same longitudinal symmetry plane 33, which extends through the component unit and the main reflector unit. The first reflector plane 12 deviates from the direction parallel to the symmetry plane 33 by no more than 10 degrees, preferably no more than 5 degrees. Figure 5 In this embodiment, a small distance D exists between the symmetry plane 33 and the first reflector plane 12, and this distance should be as small as possible. Preferably, the distance D does not exceed 10% of the first radius of curvature, the second radius of curvature, or the third radius of curvature; more preferably, it does not exceed 5%; and most preferably, it does not exceed 2%.

[0048] The planar reflector, the first concave reflector 10, and the second reflector are preferably formed as a single reflector unit. Such a single reflector unit can be formed, for example, by molding from a polymer material. During molding... Figure 5 When using the integrated reflector unit shown, it is difficult to obtain perfectly sharp angles between the first concave reflector 10 and the first planar reflector 11, and between the second concave reflector 15 and the first planar reflector 11. Rounded corners are almost inevitable. Even if the first principal direction R1 meets the first concave reflector at a certain distance from the first planar reflector 11, some portions of the beam may still strike the first concave reflector 10 near the first planar reflector 11. Figure 5 In this embodiment, a first recess 38 is formed in the first planar reflector 11. The first recess 38 allows the first concave reflector 10 to extend on both sides of the first reflector plane 12. In this way, light striking the first concave reflector 10 near the first reflector plane 12 will not be affected by any rounded corners.

[0049] exist Figure 5In this embodiment, the first planar reflector 11 includes a second recess 40 that extends along the first planar reflector at a distance from the first concave reflector 10, the second concave reflector 15, and the component reflector 24. When the reflector is a double-curved reflector, it is difficult to mold a one-piece reflector unit without using a mold consisting of two parts arranged with an expandable sliding gap. The mold components are placed in place before molding the concave reflector. After molding, at least one mold component is removed so that the resulting one-piece component can be ejected from the jig. To avoid unwanted flanges on the planar reflector 11, it is preferable to provide the recess 40 at the junction of the moving parts to hide any possible interference outside the field of view of the light rays R1, R2 passing through the cavity.

[0050] Figure 6 Showing with Figure 3 and Figure 4 Similar to the implementation of the spectral gas sensor along Figure 4 The arrangement of the first reflector plane 12 is as follows. The first concave reflector 10 has a first center of curvature 27 and a first radius of curvature Rc1. The second concave reflector 15 has a second center of curvature 28 and a second radius of curvature Rc2. The component unit 5 defines a concave double-curved surface 42, which has a third center of curvature 29 and a third radius of curvature Rc3. The first center of curvature 27, the second center of curvature 28, and the third center of curvature 29 are located on the same longitudinal symmetry plane 33. Figure 5 In the diagram, the longitudinal symmetry plane 33 extends through component unit 5 and main reflector unit 9. (As shown...) Figure 6 As shown, component reflector 24 coincides with the double-curved surface 42 of component unit 5. A first curvature center 17 and a third curvature center 19 are spaced apart and define a first axis 21. A second curvature center 28 is arranged between the second curvature center 17 and the third curvature center 19 in a direction parallel to the first axis 21. The center of component reflector unit 5 and the third curvature center 19 define a line of symmetry 22.

[0051] Regarding the radius of curvature of the reflector, the difference between the first radius of curvature and the second and third radii of curvature is no more than 10%, preferably no more than 5%, and most preferably no more than 2%. Using such a radius of curvature, the second light spot S2 will become as small as possible, which is advantageous for detection because even if the detector is small, all light can be guided as an impact detector. To optimize the imaging of the reflector, the concave surface of the component unit preferably defines a sphere. Preferably, the first concave reflector 10, the component reflector 24, and the second concave reflector 15 are spherical reflectors. The component unit 5 having the component reflector 24, the first concave reflector 10, and the second concave reflector 15 is preferably arranged in a White pool configuration.

[0052] Figure 7 It is based on Figure 7 The sensor in the embodiment. Figure 8 It is based on Figure 7 A side view of the cross-section of the gas sensor according to the embodiment, as shown. Figure 7 The eye 45 is shown in the image. The gas sensor includes a printed circuit board 44 (PCB), in which a plane reflector 11 (…) Figure 8 A first concave reflector 10, a component reflector 24, and a second concave reflector 15 form an integrated reflector unit, which can be molded from plastic. The integrated reflector unit is attached to a PCB 44 and defines an absorption cell 4. The integrated reflector unit includes a plurality of openings 3. A light source 6 is an LED attached to the PCB, and a detector 7 is a photosensitive device attached to the PCB. Alternatively, the light source can be an incandescent bulb, a hot spot film, or a laser diode (LD). The integrated reflector unit includes a first collimator 46 configured to collimate the light from the light source 6 to a first light spot S1 on the first concave reflector 10. The detector 7 is disposed on the PCB 44. The integrated reflector unit includes a second collimator 47 attached to a planar reflector 11, configured to collimate the light illuminating the detector 7. The spectral characteristics of the gas sensor 1 can be provided in many different ways. The light source can be tuned to a wavelength band corresponding to the absorption peak of the gas to be detected. The detector can be sensitive in a wavelength band corresponding to the absorption peak of the gas to be detected. Optical filters (such as interference filters) may be arranged in front of the detector, such that light must pass through the interference filter to reach the detector 7. The interference filter may have a transmission band in the wavelength band corresponding to the absorption peak of the gas to be detected. PCB 44 includes a central processing unit 48, which is configured to control the light source 6 and receive detection signals from the detector 7.

[0053] Figure 7 and Figure 8 The gas sensor in the image is a multi-pass gas sensor, where light from the light source 6 is reflected four times in the main reflector unit 9. The light routes through the absorption cell 4 are schematically shown by arrows 51, 52, 53, and 54. The light route from the light source 6 to the first light spot S1 is shown by solid arrow 31. The light route from the first light spot S1 to the second light spot S2 is shown by dashed arrow 32. The light route from the second light spot to the third light spot S3 is shown by dotted-dashed arrow 33. The light route from the third light spot to the detector is shown by double-dashed arrow 34. Dashed lines 35 and 36 show the curvatures of the first concave reflector 10 and the second concave reflector 15, respectively. Dashed line 37 shows the curvature of the component reflector 24.

[0054] By configuring the first concave reflector 10, the second concave reflector 15, and the component reflector 24 as spherical reflectors, reflectors 10, 15, and 24 can provide a high-quality image of the light source 6 at the detector 7. The detector 7 can be at least as small as the light source 6 and still collect all the light directed to the detector 7. However, in order to collect all the light directed to the detector, the detector must be correctly aligned relative to the reflectors 10, 15, and 24. The arrangement of the reflectors 10, 15, and 24 relative to the printed circuit board requires precise positioning to achieve correct alignment. The reflectors 10, 15, and 24 can be configured such that the light source 6 and the detector 7 are slightly out of focus when the reflectors are arranged on the printed circuit board. This facilitates the positioning of the reflectors 10, 15, and 24 relative to the printed circuit board 44, at the cost of a slightly lower signal from the detector 7, since only a portion of the light falls on the detector 7.

[0055] A recess 38 is disposed between the reflector unit 9 and the first planar reflector 11. The recess 38 has the effect of extending the first concave reflector 10 and the second concave reflector 15 on both sides of the first reflector plane 12. The advantage of extending the first concave reflector 10 and the second concave reflector 15 on both sides of the first reflector plane 12 is that the corner between the first concave reflector 10 and the second concave reflector 15 is difficult to manufacture with a very small curvature.

[0056] The effect of the recess 38 can also be achieved by making the recess 38 deep enough to completely penetrate the body material of the reflector 11, which forms an opening 13 in front of the spherical reflectors 10, 15 and 24, such as Figure 2 and Figure 3 As shown. If the width of the aperture 13 remains small compared to the height of the optical cell, any signal loss due to the presence of these apertures 13 will be negligible, since most of the light rays in the optical cell propagate nearly parallel to the planar reflector 11. Such apertures 13 will simplify mold design for mass production of integrated reflector units.

[0057] The described embodiments can be modified in many ways without departing from the scope of the invention, which is defined only by the appended claims.

Claims

1. A spectral gas sensor (1), comprising: - Configure an absorption cell (4) for gas exchange, wherein the gas sensor includes - First concave reflector (10). - At least one first planar reflector (11) attached to the first concave reflector (10) and defining the first reflector plane (12). - A light source configured to emit light (6), and - A first detector (7) is arranged to detect light from the light source (6) that has been reflected at least once in the first concave reflector (10). The gas sensor (1) is configured such that light from the light source (6) is guided along a first principal direction (R1) before the first reflection in the first concave reflector (10) and along a second principal direction (R2) after the first reflection in the first concave reflector (10), and wherein the first reflector plane (12) is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the plane defined by the first principal direction and the second principal direction, characterized in that the planar reflector (11) and the first concave reflector (10) form an integral reflector unit, and the first concave reflector (10) extends on both sides of the first reflector plane (12).

2. The spectral gas sensor (1) according to claim 1, wherein, The first concave reflector (10) is a cylindrical reflector, and the center of curvature of the cylindrical reflector is along a line perpendicular to the plane (12) of the first reflector.

3. The spectral gas sensor (1) according to claim 1 or 2, comprising a second planar reflector (55) defining a second reflector plane (56) and facing the first planar reflector.

4. The spectral gas sensor (1) according to claim 3, wherein, The second reflector plane (56) is arranged at an angle of less than 10°, preferably less than 5°, and most preferably less than 2° to the first reflector plane (12).

5. The spectral gas sensor (1) according to claim 3 or 4, wherein, The first concave reflector (10) extends on both sides of the second reflector plane (56).

6. The spectral gas sensor (1) according to claim 1 or 2, comprising a component unit (5) attached to the first planar reflector and a main reflector unit (9) including the first concave reflector (10), wherein, The first concave reflector (10) is a double-curved concave reflector facing the component unit (5) and partially facing the first reflector plane (12), wherein the absorption cell (4) is configured such that light emitted from the light source (6) is reflected by the first concave reflector (10) and the plane reflector (11) and converged to the light spot (S1), and wherein the detector (7) is configured to detect light from the light spot (S1).

7. The spectral gas sensor (1) according to claim 6, wherein, The first concave reflector (10) has a first curvature center (27), wherein the first curvature center (27) is located in the first reflector plane (12).

8. The spectral gas (1) sensor according to claim 6, wherein, The component unit (5) includes at least one component reflector (24), and the main reflector unit (9) includes a double-curved second concave reflector (15) facing the component unit (5) and partially facing the first reflector plane (12), wherein the second concave reflector extends on both sides of the first reflector plane (12), wherein the first planar reflector (11) is attached to the first concave reflector (10), the second concave reflector (15) and the component unit (5), and wherein the absorption cell (4) is a multi-pass absorption cell and is configured such that light emitted from the light source (6) is reflected by the first concave reflector (10) and the planar reflector (11) and converged to light spots (S1-S3) on the component reflector (24), and such that light reflected from any light spot (S1-S3) from any position on the component reflector (24) is reflected by the main reflector unit (9) and the planar reflector (11) and converged to different positions.

9. The spectral gas sensor (1) according to claim 8, wherein, The first planar reflector (11), the first concave reflector (10), the component reflector (24), and the second concave reflector (15) form an integrated reflector unit.

10. The spectral gas sensor (1) according to claim 8 or 9, wherein, The first concave reflector (10) has a first center of curvature (27) and a first radius of curvature (Rc1), the second concave reflector (15) has a second center of curvature (28) and a second radius of curvature (Rc2), and the component unit (5) defines a concave double-curved surface having a third center of curvature (29) and a third radius of curvature (Rc3), wherein the first center of curvature (27), the second center of curvature (28) and the third center of curvature (29) are located in the same longitudinal plane of symmetry (33) extending through the component unit (5) and the main reflector unit (9), and wherein the parallelism deviation between the first reflector plane (12) and the plane of symmetry (33) does not exceed 10 degrees, preferably not more than 5 degrees.

11. The spectral gas sensor (1) according to claim 10, wherein, The component reflector (24) coincides with the double-curved surface of the component unit (5).

12. The spectral gas sensor (1) according to claim 10 or 11, wherein, The distance between the symmetry plane (33) and the plane reflector (11) shall not exceed 10% of the first radius of curvature (Rc1), the second radius of curvature (Rc2) or the third radius of curvature (Rc3), preferably not more than 5%, and most preferably not more than 2%.

13. The spectral gas sensor (1) according to any one of claims 10, 11 or 12, wherein, The difference between the first radius of curvature (Rc1) and the second radius of curvature (Rc2) and the third radius of curvature (Rc3) does not exceed 10%, preferably not more than 5%, and most preferably not more than 2%.

14. The spectral gas sensor (1) according to any one of claims 6 to 10, wherein, The concave surface of the component unit (5) defines a spherical surface, and wherein the first concave reflector (10) and the second concave reflector (15) are spherical reflectors.

15. The spectral gas sensor (1) according to any one of the preceding claims includes at least one recess (38) in the first planar reflector (11), the recess (38) extending along at least a portion of the first planar reflector (11) at the first concave reflector (10), thereby providing the first concave reflector (10) to extend on both sides of the first reflector plane (12).

16. The spectral gas sensor (1) according to any one of the preceding claims includes at least one aperture (13) located in the first planar reflector (11), the at least one aperture (13) extending along at least a portion of the first planar reflector (11) at the first concave reflector (10), thereby providing the first concave reflector extension on both sides of the first reflector plane (12).

17. The spectral gas sensor (1) according to any one of claims 6 to 16, wherein, The first planar reflector (12) includes a second recess (40) that extends along the first planar reflector (12) at a distance from the first concave reflector (10).

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