DE102017205974A1 - Optical sensor device for measuring a fluid concentration and using the optical sensor device - Google Patents

Abstract

The present invention provides an optical sensor device for measuring fluid concentration and uses of the optical sensor device. The optical sensor device is formed with an at least partially closed sample space (PB) for receiving a fluid to be analyzed; a radiation source (Q) for emitting a measurement beam into the sample space (PB); and a detector device (D) for detecting the measuring beam after passing through the sample space (PB); and a movable controllable beam deflection device (MS) arranged between the radiation source (Q) and the detector device (D), by means of which the measuring beam can be deflected in such a way that it can traverse several different absorption paths (AS1, AS2) in the sample space (PB).

Description

The present invention relates to an optical sensor device for measuring a fluid concentration and a use of the optical sensor device.

State of the art

Optical sensor devices for measuring fluid concentrations, ie liquid or gas concentrations, e.g. The concentration of carbon dioxide gas, have a variety of applications, for example, to monitor the air quality or in safety technology. In optical spectroscopy, sensor devices are now available which can be realized in a very compact and cost-efficient manner.

6 shows a schematic cross-sectional view for explaining an exemplary optical sensor device.

In 6 Reference symbol Q designates a light source, for example a laser light source. The light beam emitted by the light source Q is guided through an absorption region A with a fluid to be detected and from the absorption region A through an optical filter F and subsequently to a detector device D, which is connected to a transmitter E. In the simplest case, the evaluation electronics E can determine a fluid concentration of the fluid to be detected in the absorption region A on the basis of the loss of intensity of the light emitted by the light source Q.

In this case, the absorption area A is a fixed optical path with a defined optical path length. This optical path length is designed in accordance with the respective application requirement with regard to the type and resolution of the fluids to be examined. If, for example, different substances with different concentrations have to be measured, then two different solid optical paths and corresponding sensor components are required.

Rigid optics with fixed optical paths only allow a conditional fine adjustment of the sensitivity (absorption parameter) of such an optical sensor device. Furthermore, a significantly larger space is typically required to realize multiple optical paths with associated optical components.

When such an optical sensor device is to be used in conjunction with a linear filter which is typically several square millimeters in size, using a wavelength-selective sensor array, the power of the optical source must be distributed over the entire area. This typically requires a source with a high aperture angle and high power, or multiple light sources are necessary to provide this necessary optical power across all the sensing pixels of the sensor array.

From the WO 2005/045404 A1 An infrared gas sensor is known which can measure a gas concentration by detecting infrared radiation propagated through an absorption path filled with the gas to be measured through a first filter by a first detection unit and through a second filter by a second detection unit is detected, wherein a concentration of the gas is measured by a difference of the intensities of the detected radiation.

The DE 10 2004 044 145 B3 discloses a reflector module for a photometric gas sensor having a radiation source, a first reflector for deflecting a radiation coming from the radiation source to a second reflector, a second reflector for deflecting the radiation coming from the first reflector to a detector.

Other optical sensor devices for measuring a fluid concentration with fixed optical paths using reflectors are known from US-A-5,439,791 DE 103 60 215 A1 and the DE 10 2015 212 870 A1 known.

Disclosure of the invention

The present invention discloses an optical sensor device for measuring a fluid concentration having the features of claim 1 and a uses of the optical sensor device having the features of claim 13.

Preferred developments are the subject of the respective subclaims.

Advantages of the invention

wobei k(λ) der wellenlängenabhängige Extensionskoeffizient des Fluids, C die Konzentration des Gases und I die Absorptionsstrecke ist. Aus diesem Zusammenhang wird ersichtlich, dass für den Fall, dass die Konzentration im zu detektierenden Fluid konstant bleibt, eine Änderung der Transmission durch die Änderung der Strecke im Fluid bewirkt werden kann. Damit kann die Auflösung der optischen Sensorvorrichtung an die Stoffkonzentration des Fluids angepasst werden.The idea underlying the present invention is based on the use of a movable micromirror, which is mounted in the absorption path of an optical sensor device in order to realize different optical paths or beam paths with different absorption lengths associated therewith. Due to the movement of the mirror, the effective path length in the fluid to be detected is varied by appropriate reflections at corresponding reflector surfaces in the beam path. This will be the Absorption or transmission behavior of the fluid varies. The absorption or transmission behavior is described in the simplest form by the Lambert-Beer-Bouguer law, which describes, for example for CO2 in the air, the following relationship for the path-dependent intensity: $$\text{I}\left(\text{x}\right)=\text{I}\left(0\right)\times {\text{e}}^{-\text{k}\left(\mathrm{\lambda }\right)\times \text{C}\times \text{I}}$$

where k (λ) is the wavelength-dependent coefficient of expansion of the fluid, C is the concentration of the gas and I is the absorption distance. From this connection it can be seen that in the event that the concentration in the fluid to be detected remains constant, a change in the transmission can be effected by the change of the distance in the fluid. Thus, the resolution of the optical sensor device can be adapted to the substance concentration of the fluid.

The variability of the beam path is realized according to the invention by one or more movable reflection or transmission elements in the beam path of the optical sensor device. These movable elements may allow adjustment of the optical length in the fluid either directly or in conjunction with other optical reflection or transmission surfaces. Many variations can be realized for the different applications.

In particular, the invention enables a flexible design of the optical path or optical path of an optical sensor device for measuring a fluid concentration, wherein an optical path with a movable element is sufficient to be able to implement different requirements for material type and measurement resolution.

The optical paths can also be changed dynamically and as required, wherein, for example, when using a linear filter, the wavelength can be selected by the corresponding position of the optical path.

Furthermore, self-diagnostic functions can be realized, which are not possible with fixed optical paths. For this purpose, the nonlinear relationship of the Lambert-Beer-Bouguer law is exploited. Thus, additional support points for the self-diagnosis can be created. Moving micromirrors can provide fast and accurate path changes for which there are respective path calibration options. By using partially reflecting or partially transmitting surfaces, a plurality of optical paths can be implemented simultaneously.

According to a preferred embodiment, a first fixed reflector device is arranged in the sample chamber, from the emitted from the radiation source measuring beam is reflected on the detector device and wherein the movable beam deflector is designed such that it the measuring beam to a plurality of different surface areas on the first fixed reflector device corresponding to the plurality can direct different absorption paths. Thus, continuous or discrete optical paths can be realized, whereby a very compact structure is made possible for the different paths.

According to a further preferred embodiment, the first fixed reflector device has a curved surface on which a reflection coating is arranged and which define the several different surface areas. This allows the optical paths to be varied continuously.

According to a further preferred embodiment, the curved surface is designed such that the measuring beam can be directed onto the detector device independently of the surface area. Thus, a compact detector device can be realized.

According to a further preferred embodiment, the first fixed reflector device has a curved surface with step-shaped recesses with intermediate curved sections on which the reflection coating is arranged and which define the several different surface regions. This allows the optical paths to be discreetly varied.

According to a further preferred embodiment, the first stationary reflector device has a cavity, wherein the measuring beam can be directed onto a surface region lying in the cavity such that a multiple reflection of the measuring beam occurs on further surface regions in the cavity before the measuring beam reaches the detector device. Thus, the optical path can be greatly increased.

In accordance with a further preferred embodiment, at least one second fixed reflector device is arranged in the sample space, wherein the measurement beam can be directed to the plurality of different surface regions such that a multiple reflection of the measurement beam occurs at the at least one second fixed reflector device and at at least one further surface region of the first stationary reflector device before the measuring beam reaches the detector device. This also increases the length of the optical path, wherein the compactness can be maintained.

According to a further preferred embodiment, the movable beam deflection device is seconded in the sample space, wherein the detector device has a detector array which can be scanned with the measurement beam by means of the movable beam deflection device corresponding to the several different absorption paths. Thus, a detector array can be implemented without the power of the measuring beam having to be increased.

According to a further preferred embodiment, a wavelength-selective filter, in particular a linearly variable filter, is applied to the detector array. In this case, the movable micromirror can solve the problem of power distribution over the surface of a linear wavelength-selective filter. In this case, the micromirror is used to scan the area of the filter and thus distribute the power selectively as needed, without having to apply the same power to the entire surface. Furthermore, this scanning can improve the optical parameters of the system and allow new options in the detection of multiple properties of the fluid to be detected.

According to a further preferred embodiment, a second fixed reflector device is arranged between the radiation source and the movable beam deflection device, which bundles the measuring beam emitted by the radiation source on the movable beam deflection device. This allows the measuring beam to be bundled efficiently.

According to a further preferred embodiment, the movable beam deflection device is a MEMS micromirror device. This makes it possible to realize a very compact movable beam deflection device.

According to a further preferred embodiment, the radiation source and the detector device are arranged in a carrier substrate which is separated from the sample space by an optical window. Thus, the radiation source and the detector device are protected from the fluid to be analyzed.

list of figures

• 1a), b) schematische Querschnittsansichten zur Erläuterung einer optischen Sensorvorrichtung gemäß einer ersten Ausführungsform der vorliegenden Erfindung;
• 2 eine schematische Querschnittsansicht zur Erläuterung einer optischen Sensorvorrichtung gemäß einer zweiten Ausführungsform der vorliegenden Erfindung;
• 3 eine schematische Querschnittsansicht zur Erläuterung einer optischen Sensorvorrichtung gemäß einer dritten Ausführungsform der vorliegenden Erfindung;
• 4 eine schematische Querschnittsansicht zur Erläuterung einer optischen Sensorvorrichtung gemäß einer vierten Ausführungsform der vorliegenden Erfindung;
• 5 eine schematische Querschnittsansicht zur Erläuterung einer optischen Sensorvorrichtung gemäß einer fünften Ausführungsform der vorliegenden Erfindung; und
• 6 eine schematische Querschnittsansicht zur Erläuterung einer beispielhaften optischen Sensorvorrichtung.

Show it:

• 1a b) are schematic cross-sectional views for explaining an optical sensor device according to a first embodiment of the present invention;
• 2 a schematic cross-sectional view for explaining an optical sensor device according to a second embodiment of the present invention;
• 3 a schematic cross-sectional view for explaining an optical sensor device according to a third embodiment of the present invention;
• 4 a schematic cross-sectional view for explaining an optical sensor device according to a fourth embodiment of the present invention;
• 5 a schematic cross-sectional view for explaining an optical sensor device according to a fifth embodiment of the present invention; and
• 6 a schematic cross-sectional view for explaining an exemplary optical sensor device.

In all figures, the same or functionally identical elements and devices - unless otherwise stated - provided with the same reference numerals.

Description of the embodiments

1a ), b) are schematic cross sectional views for explaining an optical sensor device according to a first embodiment of the present invention, showing various settings of the movable controllable beam deflecting device.

In 1a ), b) denotes reference numerals 1 in general, an optical sensor device for measuring a fluid concentration, for example, a CO ₂ gas concentration. The fluid to be analyzed, here CO ₂ gas, is located in an at least partially closed sample space PB, which is indicated by a dashed line.

A radiation source Q, for example a laser radiation source, and a detector device D are arranged in a carrier substrate S, which is separated from the sample space PB by an optical window F.

The radiation source Q is used to emit a measurement beam into the sample space PB, and the detector device D is used to detect the measurement beam after passing through the sample space PB.

Between the radiation source Q and a movable beam deflection device MS in the form of a MEMS micromirror is a reflector device in the form of a rigid mirror S1 arranged, which bundles the emitted from the radiation source Q measuring beam to the movable beam deflection device MS. Also provided in the substrate S is the movable, controllable by a drive device MA beam deflection device MS, through which the measuring beam is deflected through an entrance region EF of the optical window F in the sample chamber PB. A fixed reflector device R, from which the measuring beam can be reflected onto the detector device D, is located in the sample space PB, the measuring beam leaving the sample space through an exit area AF of the optical window.

Reference symbol AS1 denotes an absorption path which lies between the inlet region EF and the outlet region AF, within which the fluid to be analyzed can absorb energy of the measuring beam. The absorption path AS1 corresponds to a first position of the movable controllable beam deflection device MS. In 1b ), a second setting of the movable controllable beam deflecting device MS is shown, wherein the measuring beam passes through the inlet region EF 'in the sample space PB and after reflection at the fixed reflector means R through the exit area AF' reaches the detector device D.

The fixed reflector device R has a curved surface on which a reflection coating RB is arranged. The movable controllable beam deflection device MS can scan the curved surface with the reflection coating RB, wherein the absorption path is variable by the curvature of the surface, shown here schematically by the absorption path AS1 in FIG 1a ) and the absorption path AS1 'in 1b ).

In particular, the measuring beam according to 1a ) on a first surface area O1 of the reflection coating RB, whereas the measuring beam according to FIG 1b ) on a second surface area 02 the reflection coating RB hits.

The curvature of the surface of the reflector device R is designed such that the measuring beam can be directed onto the detector device D independently of the surface region O1, O2.

How out 1a ) and 1b), the absorption path AS1 is longer than the absorption path AS1 '. This first embodiment is particularly suitable when using a MEMS radiator or a laser as the radiation source Q, wherein the opening angle is typically less than 20 °.

The curvature of the fixed reflector device S1 and the movable controllable beam deflection device MS can be chosen such that the optical power of the measuring beam is bundled as efficiently as possible.

The operation of the optical sensor device 1 can be done either statically at different discrete measuring points or dynamically by a continuous scanning of the curved surface, for example in resonance mode of the movable controllable beam deflecting device MS in the form of the micromirror.

The evaluation of the absorption behavior is carried out either in an evaluation device (not shown), which comprises e.g. is provided in the detector device or which is a separate component.

2 FIG. 12 is a schematic cross-sectional view for explaining an optical sensor device according to a second embodiment of the present invention. FIG.

The second embodiment differs from the first embodiment by a different configuration of the fixed reflector device R 'within the sample space PB. The optical sensor device is denoted by reference numeral la.

The fixed reflector device R 'in the second embodiment has a curved surface with four stepped recesses A1, A2, A3, A4, wherein curved portions lie between each two recesses. At least on the curved portions, the reflection coating RB is provided. The curved sections define the surface areas O1 ', O2', O3 ', O4' to which the measuring beam can be directed by the movable controllable beam deflection device MS in the form of the MEMS micromirror. This results in several different absorption paths AS2, AS2 ', AS2 "and AS2"', which are quasi separated. If the measuring beam strikes a region of the recess A1, A2, A3, A4, it is not reflected, or at least not reflected, on the detector device D, as indicated here by a schematically indicated error beam FS.

Thus, the second embodiment of the optical sensor device 1a according to 2 preferably operated in quasi-static operation and not in the scan mode.

As with the first embodiment, it is therefore possible to define absorption paths AS2, AS2 ', AS2 ", AS2'", which have a different length.

3 is a schematic cross-sectional view for explaining an optical Sensor device according to a third embodiment of the present invention.

The third embodiment, in which the optical sensor device with reference numerals 1b is again different from the first or second embodiment by the structure of the fixed reflector device R ".

In this embodiment, the measuring beam can be directed, on the one hand, at the curved sections as in the second embodiment and, on the other hand, at a surface area located in a cavity H of the reflector device R " 02 " ,

A curved region corresponding to a first absorption path AS3 is designated by reference O1 ".

The absorption path AS3 'extends over the surface area lying in the cavity H. 02 " , Starting from the surface area 02 " a multiple reflection of the measuring beam at further surface areas 02 "a, 02" b, 02 "c takes place in the cavity H before the measuring beam passes through the exit area AF 'to the detector device D.

In this embodiment, a combination of short absorption paths AS3 and long absorption paths AS3 'can be realized. This combination is advantageous in gas sensors to measure and resolve high and low gas concentrations with high accuracy. This function is necessary, among other things, for a CO2 gas sensor, which is suitable both for safety functions such as leak or fire detection (measuring range up to 100% CO2) and at the same time for a comfort function (measuring range 0 to 0.2% CO2) should be used.

4 FIG. 12 is a schematic cross-sectional view for explaining an optical sensor device according to a fourth embodiment of the present invention. FIG.

In the fourth embodiment, in which the sensor device is generally denoted by reference numerals 1c is designated, corresponds to the fixed reflector means R '"in their construction of the fixed reflector means R' of the second embodiment, however, the beam guidance of the measuring beam is different.

In the fourth embodiment, a further fixed reflector device in the form of two planar mirrors S2, S3 is provided in the optical window F between the carrier substrate S and the sample space PB. The measuring beam can be directed onto the surface areas O1 ", O2 '" etc. of the fixed reflector device R' "such that a multiple reflection of the measuring beam at the stationary reflector device S2, S3 in the form of the mirrors and at at least one further surface region O1" 'a or 02 "'a occurs before the measuring beam passes through the exit region AF or AF' to the detector device D.

The absorption paths of different length AS4 and AS4 'correspond to the surface areas O1 "' and O2 '" of the fixed reflector device R'. "In this third embodiment, the absorption path can be formed more effectively by the multiple reflection, for example, the distance between detector device D and radiation source Q are used better, in addition to the entire dimensions of the sensor device 1c can be reduced. Furthermore, these additional reflector devices Sl, S2 can be used to improve the optical beam guidance. For this purpose, these reflector devices Sl, S2 can be designed according to size, curvature, facets, etc., in order to correct any optical errors.

5 FIG. 12 is a schematic cross-sectional view for explaining an optical sensor device according to a fifth embodiment of the present invention. FIG.

In the fifth embodiment, wherein the optical sensor device with reference numerals 1b is designated, the movable beam deflecting means MS 'in the form of the micromirror with the associated drive means MA' is mounted in the sample space to a base SR. Here, the measuring beam passes directly through the entrance region EF of the optical window F from the source to the movable beam deflecting device MF 'and is directed from there to the detector device D' depending on the setting of the movable beam deflecting device MS '. The detector device D 'here has a detector array with a plurality of detection pixels, which enable a spatially resolving detection. AS5 denotes a first absorption path according to a first setting of the movable beam deflection device MS ', and AS5' denotes a second absorption path according to a further adjustment of the movable beam deflection device AS '. A wavelength-selective filter F, in particular a variable filter, is mounted on the detector array, thereby enabling not only spatial resolution but also wavelength resolution. With this optical sensor device 1d For example, a fluid property can be measured dynamically and as needed. Here, the power of the radiation source Q is distributed only to the selected limited area and not static over the entire detector array.

In addition, in this embodiment, options for self-diagnosis can be realized be, for example, referencing to a wavelength by selecting a specific reference range in which a particular point of the detector array or filter F is driven.

Although the present invention has been fully described above with reference to preferred embodiments, it is not limited thereto but is modifiable in a variety of ways.

Although in the embodiments described above, the radiation source and the detector device have been shown in the carrier substrate, in appropriate applications, these or all components can also be arranged within the sample space.

Although the above embodiments have been described in terms of a CO ₂ gas sensor, the invention is not limited thereto, but suitable for any fluid or multi-fluid sensors. Fluids may also be liquids. It is also conceivable use with solid additives, which can be measured in transmission methods.

The geometry of the reflector device is only exemplary and arbitrarily variable, as well as the number and design of possible other beam components.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005/045404 A1 [0008]
• DE 102004044145 B3 [0009]
• DE 10360215 A1 [0010]
• DE 102015212870 A1 [0010]

Claims (15)

Optical sensor device (1; 1a; 1b; 1c; 1d) for measuring a fluid concentration with: an at least partially closed sample space (PB) for receiving a fluid to be analyzed; a radiation source (Q) for emitting a measurement beam into the sample space (PB); and a detector device (D; D ') for detecting the measurement beam after passing through the sample space (PB); and a movable controllable beam deflection device (MS; MS ') arranged between the radiation source (Q) and the detector device (D; D'), by means of which the measuring beam can be deflected in such a way that it has a plurality of different absorption paths (AS1, AS1 ', AS2-AS2'). "AS3, AS3", AS4, AS4 ', AS5, AS5') in the sample space (PB) can traverse. Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 1 , wherein in the sample space (PB) a first fixed reflector means (R; R '; R ";R'") is arranged, from which of the radiation source (Q) emitted measuring beam to the detector device (D) is reflected and wherein the movable beam deflecting device (MS) is designed such that it measures the measurement beam onto a plurality of different surface areas (O1, O2; O1'-O4 ', O1 ", O2"; O1 "', O2 '") on the first fixed reflector device (R) corresponding to FIG several different absorption paths (AS1, AS1 ', AS2-AS2'", AS3, AS3 ', AS4, AS4') can judge. Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 2 wherein the first fixed reflector means (R; R ') has a curved surface on which a reflection coating (RB) is arranged and which define the plurality of different surface areas (O1, 02). Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 3 , wherein the curved surface is designed in such a way that the measuring beam can be directed onto the detector device (D) independently of the surface region (O1, O2; O1'-O4 '; O1 "O2";O1'",O2"'). Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 3 wherein the first fixed reflector means (R ') has a curved surface with stepped recesses (A1-A4) with intermediate curved portions on which the reflection coating (RB) is arranged and which define the plurality of different surface areas (O1'-O4') , Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 3 or 5 wherein the first stationary reflector device (R ") has a cavity (H) and wherein the measuring beam can be directed onto a surface region (02") lying in the cavity (H) in such a way that a multiple reflection of the measurement beam at further surface regions (02 "a, 02 "b, 02" c) occurs in the cavity (H) before the measuring beam reaches the detector device (D). Optical sensor device (1; 1a; 1b; 1c; 1d) according to one of the Claims 3 . 6 or 7 , wherein in the sample space (PB) at least one second fixed reflector means (S2, S3) is arranged and wherein the measuring beam on such a plurality of different surface areas (O1 "', O2'") is directable that a multiple reflection of the measuring beam at the at least one second fixed reflector device (S2, S3) and at least one further surface region (O1 "'a, O2"' a) of the first stationary reflector device (R; R '; R ";R'") occurs before the measuring beam is directed to the detector device ( D) arrives. Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 1 , wherein the movable beam deflection device (MS ') is seconded in the sample space (PB) and the detector device (D') has a detector array which communicates with the measurement beam by means of the movable beam deflection device (MS; MS ') corresponding to the several different absorption paths (AS5, AS5 ') is scannable. Optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 8 , wherein a wavelength-selective filter (F), in particular a linearly variable filter, is applied to the detector array. An optical sensor device (1; 1a; 1b; 1c; 1d) according to one of the preceding claims, wherein a second stationary reflector device (S1) is arranged between the radiation source (Q) and the movable beam deflection device (MS), which device detects the radiation emitted by the radiation source (Q ) emitted measuring beam on the movable beam deflector (MS) bundles. An optical sensor device (1; 1a; 1b; 1c; 1d) according to any one of the preceding claims, wherein the movable beam deflector (MS; MS ') is a MEMS micro-mirror device. Optical sensor device (1; 1a; 1b; 1c; 1d) according to one of the preceding claims, wherein the radiation source (Q) and the detector device (D; D ') are arranged in a carrier substrate (S) which is guided through an optical window (F ) is separated from the sample space (PB). Use of an optical sensor device (1; 1a; 1b; 1c; 1d) according to one of the preceding claims, wherein the movable beam deflection device (MS; MS ') is controlled in such a way that the measuring beam is the several different ones Absorption paths (AS1, AS1 ', AS2-AS2'", AS3, AS3 ', AS4, AS4', AS5, AS5 ') in the sample space (PB) can pass dynamically. Use of an optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 13 wherein, as the movable beam deflection device (MS; MS '), a MEMS micromirror device is used, which is driven in a resonant manner. Use of an optical sensor device (1; 1a; 1b; 1c; 1d) according to Claim 13 or 14 in which the detector device (D ') is a detector array which is scanned with the measuring beam by means of the movable beam deflection device (MS; MS') corresponding to the several different absorption paths (AS5, AS5 ').

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