Sensor for optical analysis of a liquid

Abstract

The invention relates to a sensor (20) for the optical examination of a liquid, wherein the sensor (20) comprises a light source (23) and a light detector (24), wherein at least one first optical fiber (21) extends from the light source (23) to an examination chamber (25), wherein each of the at least one first optical fiber (21) is associated with a second optical fiber (22) which extends from the examination chamber (25) to the light detector (24), wherein a first and an associated second optical fiber (21; 22) are located opposite each other in the area of ​​the examination chamber (25). According to the invention, the sensor (20) comprises a base body (30) with a mounting section (33), wherein the base body (30) can be inserted into an associated opening (12) of a superior assembly (11), wherein it can be attached to the superior assembly (11) at the mounting section (33), wherein the mounting section (33) separates a first and a second side (31; 32) of the base body (30) from each other, wherein the base body (30) forms the examination space (25) on the first side (31), wherein the light source (23) and the light detector (24) are arranged on the second side (32), wherein the at least one first optical fiber (21) and the at least one second optical fiber (22) are arranged inside the base body (30), each passing through the mounting section (33).

Description

[0001] The invention relates to a sensor according to the preamble of claim 1, a sensor arrangement with such a sensor and a method for producing the sensor.

[0002] DE 10 2021 201 017 A1 discloses a measuring system for the optical examination of a hydraulic fluid in a line. The line has transparent sections through which light from a light source can be radiated into the interior of the line, whereby the light filtered by the fluid can exit the line through other transparent sections to the light detector. The transparent sections are comparatively large, thus achieving a high-quality examination result. Consequently, however, the measuring device is not suitable for use in lines carrying hydraulic high pressures of 100 bar or more. The comparatively large transparent glass sections cannot withstand this pressure.

[0003] Another measurement system for the optical analysis of a fluid is known from WO 2014 / 090309 A1. Here, light is guided into and out of the fluid using optical fibers. The ends of the optical fibers are spaced apart, with a fiber spacing that can be as small as 0.5 mm. The described system setup is more suitable for scientific investigations than for real hydraulic systems. In particular, the small fiber spacing of 0.5 mm is achieved by a circular channel, the carrier of which is arranged within a cup containing the fluid to be analyzed. The optical fibers are guided unprotected through the fluid. In a real hydraulic system, they would be destroyed after a short time. The problem of pressure-tight sealing of the optical fibers does not even arise with the cup used in the experimental setup.

[0004] One advantage of the sensor according to the invention is that it can be mounted as a whole in a single opening of a higher-level assembly in order to examine fluid flowing within the higher-level assembly. The optical fibers are protected from damage caused by high fluid pressure and / or high fluid flow velocity. No fluid can escape from the interior of the higher-level assembly into the environment of the higher-level assembly past the optical fibers. The distance between the first and second optical fibers in the examination area can be reduced even further compared to the prior art in order to improve the quality of the examination result, even when using a low-cost light source and a low-cost, and therefore usually less sensitive, light detector.The sensor according to the invention can be manufactured cost-effectively in large quantities and can be used in a wide variety of different higher-level assemblies without modification. It has only a minimal impact on the flow in the higher-level assembly. The sensor requires very little installation space and is very robust.

[0005] According to claim 1, it is proposed that the sensor comprises a base body with a fastening section, wherein the base body can be inserted into an associated opening of the higher-level assembly, wherein it can be fastened to the fastening section on the higher-level assembly, wherein the fastening section delimits a first and a second side of the base body from one another, wherein the base body forms the examination space on the first side, wherein the light source and the light detector are arranged on the second side, wherein the at least one first optical fiber and the at least one second optical fiber are arranged within the base body, each passing through the fastening section. The first side is accordingly arranged within the higher-level assembly, wherein the second side is arranged outside the higher-level assembly.The fastening section can be adapted to a separate union nut, which can be screwed onto an external thread surrounding the opening in the superordinate assembly, so that the base body can be fastened to the superordinate assembly by means of the union nut. The opening in the superordinate assembly is preferably circular, with the fastening section of the base body being adapted to the opening in such a way that the corresponding fixed connection can be sealed in a fluid-tight manner.

[0006] The light source and / or the light detector are preferably attached to the second side of the base body, most preferably directly attached. The said liquid is preferably oil, in particular hydraulic oil, for example HLP or HEES. The liquid can be under high pressure during the examination, which can be more than 100 bar, for example. The first and / or the second optical fiber are preferably each made of a crystalline material, although they can also be designed as hollow fibers made of glass (hollow silica waveguide). This allows them to guide the preferred infrared light particularly well. Simple glass or SiO2, on the other hand, strongly absorbs the preferred infrared light and is therefore not preferred. The first and / or the second optical fiber can also be made of transparent plastic.The higher-level assembly is preferably a pipeline, a valve block, a pump, a hydraulic motor, or a tank of a hydraulic circuit. The base body is preferably formed in one piece. It can be formed in multiple parts, particularly if the first wall distance is to be adjustable.

[0007] The at least one first and the at least one second optical fiber are preferably designed such that they can conduct infrared light with low loss. The liquid is preferably examined using infrared light because this allows the most meaningful measured values ​​to be achieved. Light with a wavelength between 2650 nm and 20,000 nm is preferably used in order to obtain particularly meaningful results. Accordingly, the optical fibers should conduct this light particularly well. This can be easily achieved by selecting suitable materials for the optical fibers. The at least one first optical fiber and the at least one second optical fiber are preferably arranged essentially entirely within the base body, wherein they can protrude into the light source or the light detector, respectively, wherein these are preferably directly adjacent to the base body.

[0008] Advantageous further developments and improvements of the invention are specified in the dependent claims.

[0009] It can be provided that the at least one first optical fiber and the at least one second optical fiber each run in a J-shape such that a first optical fiber and an associated second optical fiber together run in a U-shape, wherein the corresponding U-shape comprises a base and two legs, wherein the examination space is arranged in the region of the base, wherein the light source and the light detector are each arranged at a free end of an associated leg. This results in a particularly compact sensor. Excessively tight radii of curvature of the optical fibers can nevertheless be avoided. The two legs preferably pass through the fastening section and most preferably run straight.

[0010] It can be provided that the examination space is formed by an examination gap that has a constant first wall distance in sections, with the at least one first optical fiber and the at least one second optical fiber terminating in the region of the constant first wall distance. The constant wall distance can be easily established, yet can still be selected to be particularly small. This results in high evaluation quality.

[0011] It can be provided that the examination gap has a first side wall with a first flat section and a second side wall with a second flat section, wherein the first and the second section run parallel to one another with the first wall distance, wherein all first optical fibers terminate at the first flat section, wherein all second optical fibers terminate at the second flat section. Preferably, a first optical fiber ends exactly flush with the first flat section, wherein a second optical fiber ends exactly flush with the second section. It is understood that tolerance-related deviations from this ideal state can occur. The quality of the examination result primarily depends on the end-face fiber spacing between a first and an associated second optical fiber.This design allows for a very narrow examination chamber, which, thanks to minimal light attenuation, delivers the best possible examination results. Furthermore, the examination chamber creates a sufficiently extensive fluid film whose optical properties correspond to those of the fluid flowing freely around the sensor, so that the evaluation result is representative of the entire fluid in the superordinate assembly. This design is particularly cost-effective.

[0012] It can be provided that a second wall distance between the first and second side walls, which is measured away from the first and second planar sections, is greater than the first wall distance. This allows a tool, in particular a saw blade or an EDM wire, to be easily inserted into the base body for producing the first and second planar sections.

[0013] The inspection gap can be provided on the side of the base body facing away from the fastening section. This opening allows the tool to be easily inserted into the base body.

[0014] It can be provided that the first wall distance is selected such that a first and an associated second optical fiber are located opposite each other at a fiber distance that is between 30 µm and 300 µm, preferably between 50 µm and 200 µm. The said fiber distance can be 100 µm, for example. With such a narrow examination space, it can be achieved that particles in the fluid flow past the outside of the examination gap so that they do not interfere with the optical examination of the fluid. It should be noted here that a particle the size of a diameter of an optical fiber can shade all of the light emitted by a first optical fiber in such a way that it can essentially not reach the associated second optical fiber.

[0015] It can be provided that at least one first optical fiber and / or at least one second optical fiber are individually accommodated in a respective associated fiber channel in the base body, wherein each is glued to at least a portion of the fiber channel. Preferably, all first and all second optical fibers are accommodated in a respective associated fiber channel and glued there at least in sections. This achieves the desired compressive strength and the desired tightness of the sensor.

[0016] It can be provided that the at least one first optical fiber and / or the at least one second optical fiber each have a constant first cross-sectional shape over their entire length, wherein the associated fiber channel runs along a sealing length with a constant second cross-sectional shape which is adapted equidistantly to the first cross-sectional shape, so that an adhesive gap is produced between the first and the second cross-sectional shape, wherein the adhesive gap is filled with adhesive in such a way that, on the one hand, the respective first or the respective second optical fiber is firmly connected to the base body, wherein, on the other hand, the passage of liquid from within the higher-level assembly through the adhesive gap to outside the higher-level assembly is prevented.Preferably, all first and all second optical fibers have a constant cross-sectional shape over their entire length, wherein they are accommodated in a correspondingly adapted fiber channel. It should be noted that the first or second optical fiber is not necessarily glued centrally into the fiber channel. Due to manufacturing tolerances, the opposite is to be expected. However, this is not a disadvantage as long as the adhesive exerts its sealing effect. The fluid in the higher-level assembly can be under a pressure of 100 bar or more if the sensor is used in a hydraulic system. This high pressure can be reliably sealed in the manner described. The adhesive is preferably one that has a low viscosity in the uncured state, in particular an acrylate or epoxy resin adhesive.

[0017] The sealing length is preferably at least 50% of the diameter of the opening in the superordinate assembly. The adhesive gap is preferably filled with adhesive over at least 80% of the sealing length. This allows for reliable sealing even against high pressures in the superordinate assembly.

[0018] It can be provided that the fiber channel with the second cross-sectional shape opens out at the first or second side wall. The sealing length is accordingly measured starting from the first or second side wall. The base body with the first and second optical fibers is preferably produced by providing a blank of the base body without the examination gap, wherein for each pair of a first and an associated second optical fiber, a single common optical fiber is glued into a respective common fiber channel, wherein the examination gap is subsequently produced, wherein the common optical fiber is severed into a first and a separate second optical fiber. The examination gap, in particular the first and second flat sections, is preferably produced by sawing, wherein most preferably a diamond saw blade is used.The examination gap can be produced by wire EDM.

[0019] It can be provided that at least the sections of the base body where a fiber channel runs in a curved manner are manufactured using a 3D printing process. The thin and curved fiber channels can be produced economically in this way. Selective laser sintering (https: / / de.wikipedia.org / wiki / Selektives_Lasers_sintering) is preferably used as the 3D printing process. Preferably, part of the base body is manufactured conventionally, in particular by machining, with only the sections with the thin and curved fiber channels being manufactured using the 3D printing process to save costs.

[0020] Protection is further claimed for a sensor arrangement, wherein the sensor arrangement comprises a higher-level assembly and a sensor according to the invention, wherein a filter is connected in the flow path upstream of the examination gap in the direction of flow of the liquid, wherein the filter is designed to filter out particles larger than the first wall distance from the liquid. This reliably prevents particles from becoming trapped in the examination gap.

[0021] Protection is claimed for a further sensor arrangement, wherein the sensor arrangement comprises a higher-level assembly and a sensor according to the invention, wherein the inspection gap is aligned parallel to a flow direction in the higher-level assembly, so that a fluid flow in the higher-level assembly results in a flow through the inspection gap. This design is not mandatory, since diffusion effects alone can be sufficient to ensure sufficient oil exchange in the inspection gap. Ideally, however, the fluid is conveyed into the inspection gap by flow and diffusion effects.

[0022] Protection is also claimed for a method for producing a sensor according to the invention, wherein a blank of the base body is provided without the examination gap, which has a common fiber channel for each pair of a first and a second optical fiber, wherein a common optical fiber is glued into the common fiber channel, wherein the examination gap is subsequently produced, wherein the common optical fiber is severed into a first and a second optical fiber.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0024] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 shows a sensor arrangement with a sensor according to the invention; Fig. 2 a perspective partial view of the base body in the area of ​​the 3D-printed second section; Fig. 3 a rough schematic partial longitudinal section of the sensor according to Fig. 1 in the area of ​​the examination gap; and Fig. 4 a roughly schematic partial cross-section of the sensor in the area of ​​a fiber channel.

[0025] Fig. 1 shows a sensor arrangement 10 with a sensor 20 according to the invention. The sensor 20 is installed in a higher-level assembly 11 in the form of a hydraulic pipeline. The higher-level assembly 11 has a circular opening 12, which is bordered by an annular extension, which in turn is provided with an external thread 13. A union nut 35 is screwed onto the external thread 13, which clamps a fastening section 33 to the base body 30 of the sensor 20 in a fluid-tight manner. The fastening section 33 is designed here as a radially outwardly projecting fastening web 34, which is rotationally symmetrical with respect to the central axis 36 of the base body 30. The said central axis 36 coincides with a circular center of the opening 12.

[0026] The fastening section 33 delimits a first and a second side 31; 32 of the base body 30 from one another. The first side 31 is arranged within the superordinate assembly 11 in a liquid-filled cavity 15. The second side 32 is arranged outside the superordinate assembly 11. A light source 23 and a light detector 24 are attached to the second side 32. The light source 23 is, for example, a light-emitting diode that emits infrared light. The light detector 24 comprises, for example, a photodiode, wherein most preferably several photodiodes are provided that are sensitive to different spectral ranges by means of optical filters. The light detector 24 can also be designed in the manner of a spectrometer, so that a continuous decomposition of the optical spectrum is possible.The light source 23 and the light detector 24 are connected to an evaluation unit 26, which controls the light source 23 and determines at least one property of the fluid from the resulting measurement result of the light detector 24. Preferably, the aging state of hydraulic oil is determined, with a characteristic value being determined that indicates how long the hydraulic oil is expected to be usable.

[0027] The evaluation device 26 is preferably used to continuously monitor the condition of the fluid in the higher-level assembly 11. In particular, the fluid used and its quality can be determined. The aging state of the fluid and / or its expected service life can be ascertained. Contamination, e.g., with water or other fluids, can be detected. The function of the higher-level assembly 11 can be stopped or its load reduced if it is determined that the permissible service life of the fluid has been exceeded or that the permissible quality of the fluid has fallen below the permissible limit. The evaluation device 26 is preferably connected to a cloud server via the Internet for data exchange, with computationally intensive evaluations being performed on the cloud server, and a user can retrieve the results from the cloud server, e.g., using an app.The evaluation device 26 can be connected to a local display on which the determined test results are presented in real time. Additional sensors for analyzing the fluid, such as a temperature sensor, can be arranged in the housing 66.

[0028] The light emitted by the light source 23 is guided to an examination slit 40 by means of a first optical fiber 21. The liquid to be examined is located in the examination slit 40, through which the light emerging from the first optical fiber 21 shines. Depending on the condition of the liquid, a different part of the optical spectrum is absorbed, with the light thus filtered entering at least partially into a second optical fiber 22, from which it is guided to the light detector 24. The first and second optical fibers 21; 22 are preferably each designed as glass fibers. The light source 23, the light detector 24, and the evaluation unit 26 are preferably enclosed by a housing 66, which is firmly connected to the base body 30, so that the aforementioned components are most preferably protected from environmental influences in accordance with protection class IP68.

[0029] Especially at the last mentioned light entry into the second optical fiber 22, a lot of light can be lost, whereby the loss depends largely on how large the fiber spacing (No. 51 in Fig. 2), i.e. the distance between the end faces of the first and second optical fibers 21; 22. If the fiber spacing is in the order of magnitude of the diameter of the first and second optical fibers 21; 22, the light loss is so small that it hardly interferes with the signal evaluation. The sensor according to the invention has the advantage that a first wall distance (No. 45 in Fig. 3) the examination gap 40 can be chosen to be as small as desired within the scope of manufacturability, whereby the flow within the higher-level assembly 11 is nevertheless only insignificantly disturbed.

[0030] At this point, it should be noted that the potentially very high pressure within the superordinate assembly 11 is present. Conventional optically transparent materials such as glass are normally unable to withstand such high pressure. Within the scope of the present invention, however, the high fluid pressure only acts on the very small end face of the first and second optical fibers 21; 22, which are firmly bonded to the base body 30. This arrangement can easily withstand high fluid pressures within the superordinate assembly. This is primarily the case because the Fig. 1, the sealing length marked with No. 52 can be chosen to be very large. Ideally, the first and second optical fibers 21; 22 are connected along the entire sealing length 52 over their entire circumference to the associated fiber channel (No. 50 in Fig. 4) are bonded. The bonding surface, which is large compared to the end face of the first and second optical fibers 21; 22, can easily transmit the forces resulting from the fluid pressure. It is understood that the ideal bond described above can only be realized approximately, although the bonds that can be achieved in practice are more than sufficient.

[0031] The first and second optical fibers 21; 22, taken together, have a U-shaped extension with a base and two legs. The examination slit 40 is arranged in the area of ​​the base. The two legs each pass through the fastening section 33, with the light source 23 and the light detector 24 each arranged at one end of an associated leg. Accordingly, the first and second optical fibers 21; 22, viewed individually, each extend in a J-shaped curve.

[0032] This J-shape of the fiber channels 50 makes their manufacture considerably more difficult. It should first be noted that the diameter of the fiber channels 50 in Fig. 1 is greatly exaggerated.

[0033] The base body 30 preferably has a conventionally manufactured, in particular by machining, first section 60 and a 3D-printed second section 61. First, the first section 60 is manufactured, followed by the second section 61 being printed onto it, so that the first and second sections 60; 61 are integrally connected to one another. The straight legs of the U-shape are arranged in the region of the first section 60. These sections of the fiber channel 50 can be easily manufactured by drilling. The drill diameter is selected to be large enough that the liquid adhesive can be easily poured there. The adhesive gap can be excessively thick there because the strength of the adhesive is not important there.

[0034] In the 3D-printed second section 61, the fiber channel 50 is first reduced to the optimal diameter for bonding by means of a funnel-like taper 55. The funnel-like taper 55 is followed by a curved section of the fiber channel 50, which, over its entire length, Fig. 4. This section of the fiber channel 50 cannot be manufactured using conventional manufacturing methods, which is why a 3D printing process, in particular selective laser sintering, was chosen. To keep the corresponding manufacturing time short, the volume of the second section 61 is minimized.

[0035] Fig. 2 shows a perspective partial view of the base body 30 in the region of the 3D-printed second section 61. The flat surface 62 on the base body 30 is preferably manufactured conventionally, serving as the starting point for the 3D printing. Two tubular sections 64 are initially printed there, which follow the desired course of the respectively associated first and second optical fibers. The tubular sections 64 each have a circular outer circumferential shape, with the associated first and second optical fibers arranged at the corresponding circle center. The outer diameter of said outer circumferential shape is preferably constant apart from the first and second side walls 41; 42. The two tubular sections 64 are preferably mirror-symmetrical to one another.

[0036] The two tubular sections 64 are stiffened by means of web 63 in such a way that in the area of ​​the flat sections (No. 43; 44 in Fig. 3) the first and second side walls 41; 42, respectively, are subjected to essentially no deformation under the influence of flow forces, which would negatively influence the evaluation result. The web 63 is designed in the form of a flat plate of constant thickness, the center plane of which coincides with the plane containing the first and second optical fibers. The thickness of the web 63 is chosen to be significantly smaller than the outer diameter of the tubular sections 64 in order to minimize volume.

[0037] Noteworthy is the recess 65 in the web 63, which is arranged as an extension of the flat sections (numbers 43; 44) of the first and second side walls 41; 42, respectively. These flat sections are preferably produced after 3D printing in a separate process step, for example, by sawing or wire EDM. The recess 65 serves as a run-out zone for the corresponding tool, i.e., a saw blade or an EDM wire. The web 65 extends from the flat surface 62 to the two tubular sections 64.

[0038] Fig. 3 shows a rough schematic partial longitudinal section of the sensor 20 according to Fig. 1 in the region of the examination gap 40. The examination gap 40 is delimited by a first and a second side wall 41; 42. The first and the second optical fiber 21; 22 each terminate at a flat first or second section 43; 44 of the associated first or second side wall 41; 42, respectively, and are flush with the latter. This can be achieved by gluing a single common optical fiber into the base body 30, wherein the common fiber is only severed into a first and a separate second optical fiber 21; 22 during the production of the first and the second flat section 43; 44. In this way, the best possible alignment of the first and the second optical fiber 21; 22 in the region of the examination gap 40 is also ensured, so that when the light passes from the first to the second optical fiber 21; 22, light loss due to misalignment is avoided.

[0039] The first and second flat sections 43; 44 run parallel to one another with a first wall distance 45. The first wall distance 45 is chosen to be small enough to allow the desired evaluation to be carried out as best as possible, while still being manufacturable. Away from the first and second flat sections 43; 44, the first and second side walls 41; 42 have a significantly larger second wall distance 46. The contour in the area of ​​the second wall distance 46 is produced using a 3D printing process. On the one hand, it is optimized for a low-turbulence flow path, which is why it has a gently curved shape. In the area of ​​the flat sections 43; 44, it is designed to create a free space that enables problem-free positioning of the tool for producing the flat sections 43; 44.The peripheral diameter of the circular flat sections 43; 44 is chosen to be just as large as necessary for the examination of the liquid. Consequently, the corresponding, separate production of the first and second flat sections 43; 44 can be carried out in the shortest possible time.

[0040] In Fig. 3 also shows the adhesive gap 56 filled with adhesive 57 between the first and second optical fibers 21; 22 and the respective associated fiber channel 50. In the Fig. In the area shown in Figure 3, the stress on the adhesive layer is particularly high due to the pressure of the liquid. The adhesive layer thickness is optimized there, particularly with regard to optimal bond strength. It is understood that the adhesive layer thickness and the diameter of the first and second optical fibers 21; 22 in Fig. 3 are highly exaggerated.

[0041] Fig. Figure 4 shows a rough schematic partial cross-section of the sensor 20 in the area of ​​a fiber channel 50. The cutting plane runs in the area of ​​the sealing length (No. 52 in Fig. 1) perpendicular to the first and second optical fibers 21; 22, respectively. The first and second optical fibers 21; 22 have a circular first cross-sectional shape 53 along their entire length on their outer circumference. The second cross-sectional shape 54 of the fiber channel 50 is equidistantly adapted to the first cross-sectional shape 53, so that in this case it is also circular. Half the diameter difference between the first and second cross-sectional shapes 53; 54 corresponds to the nominal thickness of the adhesive gap 56. It is understood that precisely centering the first and second optical fibers 21; 22 in the associated fiber channel 50 is difficult to achieve. This is irrelevant within the scope of the present invention as long as sufficient tightness and strength of the adhesive bond is achieved. Reference symbol 10 Sensor arrangement 11 higher-level assembly 12 Opening 13 external threads 14 Flow direction 15 fluid-filled cavity 20 sensors 21 first optical fiber 22 second optical fiber 23 Light source 24 light detector 25 Examination room 26 Evaluation unit 30 basic bodies 31 first page 32 second page 33 Fastening section 34 Mounting bar 35 union nut 40 Examination gap 41 first side wall 42 second side wall 43 first level section 44 second level section 45 first wall distance 46 second wall distance 47 largest transverse dimension 50 fiber channel 51 fiber pitch 52 sealing length 53 first cross-sectional shape 54 second cross-sectional shape 55 funnel-shaped taper 56 adhesive gap 57 Adhesive 60 first section of the main body 61 second section of the main body 62 flat surface 63 jetty 64 tubular section 65 recess 66 housings QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 10 2021 201 017 A1

[0002] WO 2014 / 090309 A1

[0003]

Claims

[1] A sensor (20) for the optical examination of a liquid flowing in a higher-level assembly (11), wherein the sensor (20) comprises a light source (23) and a light detector (24), wherein an examination chamber (25) of the sensor (20) is arranged within the higher-level assembly (11), wherein at least one first optical fiber (21) runs from the light source (23) to the examination chamber (25), wherein a second optical fiber (22) is assigned to each of the at least one first optical fiber (21), which second optical fiber runs from the examination chamber (25) to the light detector (24), wherein a first and an assigned second optical fiber (21; 22) are opposite one another in the region of the examination chamber (25) in such a way that light emitted by the light source (23) can reach the light detector (24) via said first optical fiber (21), further via the liquid in the examination chamber (25), and further via said second optical fiber (22), characterized byin that the sensor (20) comprises a base body (30) with a fastening section (33), wherein the base body (30) can be inserted into an associated opening (12) of the higher-level assembly (11), wherein it can be fastened to the fastening section (33) on the higher-level assembly (11), wherein the fastening section (33) delimits a first and a second side (31; 32) of the base body (30) from one another, wherein the base body (30) forms the examination space (25) on the first side (31), wherein the light source (23) and the light detector (24) are arranged on the second side (32), wherein the at least one first optical fiber (21) and the at least one second optical fiber (22) are arranged within the base body (30), wherein they each pass through the fastening section (33). [2] Sensor (20) according to claim 1, wherein the at least one first optical fiber (21) and the at least one second optical fiber (22) each extend in a J-shape such that a first optical fiber (21) and an associated second optical fiber (22) together extend in a U-shape, wherein the corresponding U-shape comprises a base and two legs, wherein the examination space (25) is arranged in the region of the base, wherein the light source (23) and the light detector (24) are each arranged at a free end of an associated leg. [3] Sensor (20) according to one of the preceding claims, wherein the examination space (25) is formed by an examination gap (40) which has a constant first wall distance (45) in sections, wherein the at least one first optical fiber (21) and the at least one second optical fiber (22) open out in the region of the constant first wall distance (45). [4] Sensor (20) according to claim 3, wherein the examination gap (40) has a first side wall (41) with a first planar section (43) and a second side wall (42) with a second planar section (44), wherein the first and the second section (43; 44) run parallel to each other with the first wall distance (45), wherein all first optical fibers (21) open out at the first planar section (43), wherein all second optical fibers (22) open out at the second planar section (44). [5] Sensor (20) according to claim 4, wherein a second wall distance (46) between the first and second side walls (41; 42), which is measured away from the first and second planar portions (43; 44), is greater than the first wall distance (45). [6] Sensor (20) according to one of claims 3 to 5, wherein the examination gap (40) is open on the side of the base body (30) facing away from the fastening section (33). [7] Sensor (20) according to one of the preceding claims, wherein the first wall distance (45) is selected such that a first and an associated second optical fiber (21; 22) are opposite each other at a fiber distance (51) which is between 30 µm and 300 µm, preferably between 50 µm and 200 µm. [8] Sensor (20) according to one of the preceding claims, wherein at least one first optical fiber (21) and / or at least one second optical fiber (22) is individually accommodated in a respective associated fiber channel (50) in the base body (30), wherein it is in each case glued to at least a portion of the fiber channel (50). [9] Sensor (20) according to claim 8, wherein the at least one first optical fiber (21) and / or the at least one second optical fiber (22) each have a constant first cross-sectional shape (53) over their entire length, wherein the associated fiber channel (50) runs along a sealing length (52) with a constant second cross-sectional shape (54) which is equidistantly adapted to the first cross-sectional shape (53), so that an adhesive gap (56) is formed between the first and the second cross-sectional shape, wherein the adhesive gap (56) is filled with adhesive (57) in such a way that, on the one hand, the respective first or the respective second optical fiber (21; 22) is firmly connected to the base body (30), and, on the other hand, the passage of liquid from within the higher-order assembly (11) through the adhesive gap (56) to outside the higher-order assembly (11) is prevented. [10] Sensor (20) according to claim 9, wherein the fiber channel (50) with the second cross-sectional shape (54) opens out at the first or second side wall (41; 42). [11] Sensor (20) according to one of claims 8 to 10, wherein at least the sections of the base body (30) on which a fiber channel (50) runs in a curved manner are produced in a 3D printing process. [12] Sensor arrangement (10) with a higher-level assembly (11) and a sensor (20) according to one of the preceding claims, wherein a filter is connected in the flow path in front of the examination gap (40) in the flow direction (14) of the liquid, wherein the filter is designed such that it filters out particles which are larger than the first wall distance (45) from the liquid. [13] Sensor arrangement (10) with a higher-level assembly (11) and a sensor (20) according to one of claims 3 to 11, which is optionally designed according to claim 12, wherein the examination gap (40) is aligned parallel to a flow direction (14) in the higher-level assembly (11), so that a liquid flow in the higher-level assembly (11) results in a flow through the examination gap (40). [14] Method for producing a sensor (20) according to one of claims 8 to 11, insofar as these are dependent on claim 3, wherein a blank of the base body (30) is provided without the examination gap (40), which has a common fiber channel for each pair of a first and a second optical fiber (21; 22), wherein a common optical fiber is glued into the common fiber channel, wherein the examination gap is subsequently produced, wherein the common optical fiber is severed into a first and a second optical fiber (21; 22).

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