Turbidity sensor, particularly for determining the cell density of a suspension

Description

[0001] The present invention relates to a turbidity sensor for detecting turbidity of a fluid caused by suspended matter contained in the fluid, the turbidity sensor comprising: a fluid detection area for receiving and measuring fluid, a radiation source for emitting radiation into the fluid detection area, a first radiation sensor for detecting a first part of the radiation emitted by the radiation source, and a second radiation sensor different from the first radiation sensor for detecting a second part of the radiation emitted by the radiation source, different from the first part, wherein at least a portion of the fluid sensing region is located between the first and second radiation sensors.

[0002] Such turbidity sensors, as well as the turbidity sensor of the present invention, are used, among other things, to determine the cell density of a suspension by means of a turbidity of the suspending fluid caused by the suspended cells. The cells then form the aforementioned suspended solids. The aforementioned measurement is therefore a radiation measurement, which determines the turbidity of the fluid based on the radiation emitted by the radiation source.

[0003] Turbidity sensors of the type mentioned above are used, for example, in bioreactors and the like, where cells, especially living cells, are propagated in a liquid, such as a nutrient solution. A turbidity sensor can thus be used to determine the success of cell proliferation in a bioreactor.

[0004] A turbidity sensor with the features mentioned above is known from US 2019 / 0360930 A1. In one embodiment, the known turbidity sensor comprises a plurality of radiation sensors, namely exactly three. The radiation sensors and the radiation source are arranged around the fluid detection area. A first radiation sensor is located in a straight line opposite the radiation source, so that the portion of the radiation emitted by the radiation source detected by it is a transmission component that reaches the first radiation sensor without deflection after passing through the fluid detection area.

[0005] A second radiation sensor is located on the same side of the fluid detection area as the radiation source, but circumferentially offset from the radiation source by the fluid detection area. This second radiation sensor detects a second portion of the radiation emitted by the radiation source, which is scattered by the particulate matter contained in the fluid with a radiation component opposite to the direction of incidence of the radiation emitted by the radiation source.

[0006] A third radiation sensor is located on the same side of the fluid detection area as the first radiation sensor, but offset from it in the circumferential direction by the fluid detection area. The third radiation sensor detects a portion of the radiation emitted by the radiation source, which is scattered, i.e., deflected, by the suspended particles in the fluid as it passes through the fluid detection area. A radiation component of the portion of the emitted radiation reaching the third radiation sensor, which is parallel to the direction of incidence of the emitted radiation, is aligned with the direction of incidence. The radiation reaching the third radiation sensor is less scattered, or deflected, from the direction of incidence than the radiation reaching the second radiation sensor.

[0007] The radiation components reaching the individual radiation sensors vary depending on the amount of suspended particles contained in the fluid, relative to a reference volume of the fluid. A small amount of suspended particles relative to a reference volume of the fluid decreases the proportion of radiation transmitted linearly through the fluid detection area detected by the first radiation sensor as the number of suspended particles increases, without initially increasing the proportion of scattered radiation detected by the second and third radiation sensors to the same extent.

[0008] An average amount of suspended matter relative to the reference volume of the fluid further reduces the proportion of radiation transmitted to the fluid detection area with increasing number of suspended matter, usually in a non-linear relationship with the number of suspended matter, whereby the proportion of scattered and thus deflected radiation reaching the third radiation sensor increases.

[0009] A high amount of suspended matter relative to the reference volume of the fluid further reduces the proportion of radiation transmitted to the fluid detection area, but with an increasing number of suspended matter, increases the proportion of radiation that is scattered by the suspended matter with a radiation component directed against the direction of incidence and which is consequently detected by the second radiation sensor.

[0010] The known turbidity sensor thus allows for a wide measurement range with regard to the amount of suspended matter contained in the fluid. However, the known turbidity sensor requires a relatively large installation space and a relatively complex design of the fluid detection area. The fluid detection area is largely surrounded by the radiation source and the radiation sensors and must still be accessible to the fluid to be detected.

[0011] Advantageously slim turbidity sensors with comparatively small installation space requirements are known, for example, from US 2010 / 0157304 A1, EP 1 991 859 A, EP 1 754 045 A1 and US 7060979 B2, whereby the improved use of installation space always comes at the expense of the available measuring range with regard to the amount of suspended matter contained in the fluid, over which the turbidity sensors can be used with sufficient accuracy.

[0012] The object of the present invention is to improve a turbidity sensor of the type mentioned at the outset in such a way that the turbidity of a fluid, based on a reference volume of the fluid, can be detected as accurately as possible over the largest possible range of different quantities of suspended matter contained in the fluid, while requiring as little installation space as possible.

[0013] The present invention achieves this object with a turbidity sensor according to claim 1 in that the second radiation sensor is located in the beam path of the first portion of the radiation emitted by the radiation source detected by the first radiation sensor. Thus, the first and second radiation sensors can be arranged one behind the other with respect to the radiation from the radiation source incident on the first radiation sensor. The second radiation sensor is irradiated with radiation emitted by the radiation source. An arrangement of the radiation sensor next to the radiation source or next to the fluid detection area, as known from the prior art, can thus be avoided, which enables the formation of a slim turbidity sensor.

[0014] At the same time, the second radiation sensor can detect a portion of the radiation that is scattered or reflected by the suspended matter present in the fluid detection area with a radiation component that is opposite to the direction of incidence of the radiation emitted by the radiation source into the fluid detection area. Furthermore, the first radiation sensor can detect a portion of the radiation that passes through the fluid detection area without deflection or, depending on the size of the sensor detection area of ​​the first radiation sensor, with a small deflection angle. Using the transmitted radiation portion, even small amounts of suspended matter present in the fluid detection area can be determined with good accuracy. Using the portion of the radiation scattered with a radiation component opposite to the direction of incidence, large amounts of suspended matter present in the fluid detection area can be determined with good accuracy.By appropriate calibration of the turbidity sensor, even average amounts of suspended matter between the low and high amounts can be determined with good accuracy.

[0015] Furthermore, the turbidity sensor presented here can produce a detection signal that exhibits excellent linearity depending on the amount of suspended matter in the fluid being detected. "Quantity" always refers to a quantity relative to a reference volume of fluid to ensure comparability of detection results. This advantageously high linearity ensures simple signal processing of the turbidity sensor's detection signals and thus high detection accuracy.

[0016] In principle, it is not excluded that the turbidity sensor presented here may include one or more additional radiation sensors. However, to achieve a slim turbidity sensor, it is preferred that the turbidity sensor only comprise the first and second radiation sensors. This is also sufficient to achieve high detection accuracy due to the two radiation sensors, which are preferably positioned diametrically opposite each other across the fluid detection area.

[0017] The fluid can be a gas or a liquid as the matrix fluid in which the suspended particles are absorbed. The suspended particles can be droplets of another liquid different from the matrix fluid; in this case, the fluid as the matrix fluid and the other liquid form an emulsion; and / or they can be solids; in this case, the fluid as the matrix fluid and the solids form a suspension. In a preferred application of the turbidity sensor discussed here, the suspended particles are biological cells, particularly living cells. However, dead cells, which usually inevitably exist alongside living cells in a bioreactor, can also be detected by the turbidity sensor.

[0018] In principle, a good measurement with meaningful results can be performed using any electromagnetic radiation emitted by the radiation source. Electromagnetic radiation with a wavelength in the visible light range or higher is preferred.

[0019] For example, radiation emitted by the radiation source with a wavelength of 590 nm or higher already provides very meaningful results. To avoid interference with turbidity measurements caused by radiation or radiation components originating from sources other than the radiation source, the radiation emitted by the radiation source preferably comprises radiation in the transition range between visible light and infrared radiation. The radiation emitted by the radiation source particularly preferably comprises so-called "near-infrared radiation" with a wavelength in the range of 775 nm to 3000 nm, with radiation with a wavelength of 780 nm to 900 nm, in particular with a wavelength of 840 nm to 865 nm, having proven particularly advantageous for turbidity measurements, especially those caused by biological cells.In the wavelength range mentioned, the turbidity sensor is insensitive to color changes of the fluid to be measured, although particularly powerful radiation sensors are available for radiation with a wavelength of 840 nm to 865 nm.

[0020] A preferred radiation source is or comprises at least one light-emitting diode due to its small size. Particularly preferably, the light-emitting diode is enclosed in a glass body as a so-called "glass LED," since the radiation emission behavior of a glass LED exhibits particularly low temperature dependence. Radiation sources other than LEDs can also be used. To achieve a turbidity sensor with a small installation space requirement, the radiation source preferably comprises exactly one LED, although multiple LEDs may also be used.

[0021] To achieve the slimmest possible turbidity sensor, the radiation source, the second radiation sensor, the fluid detection region and the first radiation sensor are preferably arranged one behind the other in the order mentioned, particularly preferably arranged one behind the other in a straight line along a radiation emission direction of the radiation source.

[0022] In principle, the second radiation sensor can be formed at least in sections from a material that is transparent to the radiation emitted by the radiation source, for example analogous to a semi-transparent mirror, with the difference that the sections of the second radiation sensor that are opaque to the emitted radiation do not necessarily comprise mirror surfaces, but rather radiation-sensitive detection surfaces.

[0023] Particularly effective transmission of the second radiation sensor through radiation emitted by the radiation source can be achieved by having the second radiation sensor with an opening through which radiation emitted by the radiation source passes essentially unhindered from the radiation source to the first radiation sensor. The use of radiation-permeable material to form the second radiation sensor is then unnecessary. The material of the second radiation sensor can then be freely selected.

[0024] The penetrating opening is preferably a single, continuous opening. However, the penetrating opening can be divided into different partial openings, which are formed at a distance from one another on the second radiation sensor. The penetrating opening is preferably an opening with a circular cross-section in order to enable the most symmetrical radiation possible through the second radiation sensor around an optical axis leading from the radiation source to the first radiation sensor. In case of doubt, the optical axis can be assumed to be the shortest radiation path from the radiation source to the first radiation sensor. However, as already indicated above, it should not be ruled out that the penetrating opening has a grid-like shape, interrupted by radiation-sensitive partial surfaces of the second radiation sensor.

[0025] In principle, it should not be ruled out that the first and / or the second radiation sensor has or have a curved radiation-sensitive sensor detection surface. However, for the most compact arrangement of the radiation sensors, it is advantageous if the first radiation sensor has a flat first radiation-sensitive sensor detection surface and if the second radiation sensor has a flat second radiation-sensitive sensor detection surface. The radiation-sensitive sensor detection surfaces of the first and second radiation sensors are arranged facing one another on the turbidity sensor, i.e. a normal vector emanating from the respective sensor detection surface has a vector component in a Cartesian component system which points to the respective other sensor detection surface.Again, a compact arrangement of the radiation sensors with the most efficient signal yield possible, even with weak incident radiation, can be achieved by arranging the first and second sensor detection surfaces parallel to each other. In the latter preferred case, the normal vectors of the two sensor detection surfaces point toward each other, i.e., they are preferably parallel and oppositely directed, within the usual tolerances during manufacturing and assembly.

[0026] To facilitate the arrangement of a defined fluid detection area in a fluid to be detected by the turbidity sensor, according to a preferred embodiment of the present invention, the radiation source, the first radiation sensor, and the second radiation sensor are accommodated in a sensor housing. As a result, these components of the turbidity sensor can be displaced together. Furthermore, the first radiation sensor and the second radiation sensor, and preferably also the radiation source, are preferably arranged immovably relative to one another in the sensor housing, so that their joint displacement by displacing the sensor housing has no influence on the measurement accuracy achievable with the turbidity sensor.

[0027] To protect against external influences, in particular against the fluid to be measured, the aforementioned components of the turbidity sensor are preferably shielded from the external environment of the sensor housing by the sensor housing. The external environment generally contains the fluid to be measured and the suspended particles expected therein. The fluid detection region is therefore preferably open to the external environment of the sensor housing, for example in the form of a fluid line passing through the sensor housing. The fluid detection region is particularly preferably a section of the external environment of the sensor housing which, with respect to the remaining external environment, only has a distinct position relative to the sensor housing, for example in the form of a groove volume of a groove formed on the sensor housing. The groove can be delimited by outer surface sections of the sensor housing and can be penetrated by radiation emitted by the radiation source.

[0028] Preferably, the sensor housing is formed at least in sections from a metal, in particular from stainless steel, so that it is particularly chemically resistant to external influences. Sections of the sensor housing may have a reflective effect and undesirably reflect radiation emitted by the radiation source into the fluid detection area toward the second radiation sensor. The second radiation sensor detects this reflected radiation. In principle, this radiation component reflected by the sensor housing can be subtracted from the total radiation component detected by the second radiation sensor through appropriate calibration in order to determine the useful radiation component scattered or reflected by the suspended matter as information about the turbidity of the fluid.However, it is more advantageous if the amount of radiation reflected by the sensor housing is as small as possible as the erroneous radiation entering the second radiation sensor. Therefore, according to a preferred development of the present invention, at least one section of the sensor housing facing the second radiation sensor is surface-treated to change, in particular to reduce, its reflection properties in the wavelength range of the radiation emitted by the radiation source. The surface treatment can consist of the formation of macroscopic facet surfaces, for example by appropriate machining. The facet surfaces can be aligned such that radiation emitted by the radiation source that strikes the facet surfaces is reflected by the facet surfaces away from the second radiation sensor and preferably also away from the fluid detection region.

[0029] Additionally or alternatively, the surface treatment can result in an increase in the roughness of surface sections of the sensor housing, so that a correspondingly rough or roughened surface section reflects less radiation than a smooth or metallically bare surface section of the same size.

[0030] Additionally or alternatively, the surface treatment can be a surface coating with a material that absorbs the radiation in the wavelength range emitted by the radiation source. Such a surface coating can be realized, for example, by applying a varnish.

[0031] Advantageously, radiation originally emitted by the radiation source at the turbidity sensor can, after reaching the fluid detection area, travel from the fluid detection area to the radiation sensors without the radiation sensors being stressed by the fluid present in the fluid detection area. For this purpose, the sensor housing can have a first and a second disc, each of which allows radiation from the radiation source to pass through. The fluid detection area is preferably located spatially between the first and the second disc. The first disc can preferably shield the first radiation sensor and the second disc can preferably shield the second radiation sensor from the fluid detection area. For a compact design, the first and the second disc are preferably located opposite one another at a distance from one another in the beam path of the radiation source.

[0032] Particularly mechanically and chemically resistant discs can be achieved by forming the first and / or second disc from a mineral material, such as corundum. A particularly preferred material for the disc is sapphire glass, i.e., aluminum oxide. Sapphire glass is hard and extremely scratch-resistant, as well as chemically resistant.

[0033] Preferably, the first and / or second disc, particularly when formed from mineral material, is connected to the sensor housing by a fusible cement. In its molten, flowable state, the fusible cement wets both the first and / or second disc and a section of the sensor housing surrounding the first and / or second disc and then solidifies. The melting point of the cement is selected to be so high that it is significantly higher than the ambient temperatures occurring during conventional, intended measuring operation, for example of the fluid to be detected, but lower than the lower melting point of the melting point of the material of the sensor housing and the melting point of the material of the disc fixed by the cement.

[0034] In order to position the first radiation sensor clearly relative to the pane in the sensor housing using simple means, the first radiation sensor can be biased toward the first pane by a first biasing force. Additionally or alternatively, for the same reason, the second radiation sensor can be biased toward the second pane by a second biasing force.

[0035] To prevent interference from sources other than the radiation source, an optical filter can be arranged between a radiation sensor and the screen shielding it from the fluid detection area. This optical filter allows electromagnetic radiation within a predetermined wavelength range to pass through and blocks radiation outside this wavelength range. In practice, a daylight filter has proven to be a suitable optical filter. The daylight filter blocks light in the optically perceptible wavelength range and allows the passage of electromagnetic radiation of longer wavelengths.Preferably, the optical filter arranged between the radiation sensor and the pane is a filter that transmits electromagnetic radiation in the wavelength range of more than 750 nm, in particular more than 800 nm, and even more preferably more than 840 nm, and otherwise blocks electromagnetic radiation with shorter wavelengths, in particular in the wavelength range of visible light. This applies to the first and / or second radiation sensor and the pane shielding the respective radiation sensor.

[0036] According to a preferred design development of the present invention, the first radiation sensor can be accommodated in a first radiation sensor assembly. The first radiation sensor assembly can be or comprise a first mounting component. Such a mounting component can be configured such that, on the one hand, it permanently mounts the first radiation sensor, generally with the interposition of a first circuit board directly supporting the first radiation sensor, and, on the other hand, can be arranged in the sensor housing with small gap dimensions, for example with a clearance fit. The first radiation sensor assembly is preferably sealed against a first housing component of the sensor housing by a first sealing component.This seal is preferably located on the side of the first radiation sensor assembly facing away from the first disc, since the first radiation sensor assembly is shielded in the opposite direction by that first disc against fluid from the external environment, in particular from the fluid detection area. The first housing component can be a housing cover or a housing plug, which closes an opening, preferably at the end, of the sensor housing. To facilitate assembly of the turbidity sensor, the first housing component closes the opening in the sensor housing through which the first radiation sensor assembly was inserted into the sensor housing. The first radiation sensor assembly is then preferably located between the first disc and the first housing component.

[0037] In principle, a separate preloading means, such as a compression spring, an elastomer ring, or the like, can be arranged between the first housing component and the first radiation sensor assembly to exert the above-mentioned first preload force on the first radiation sensor assembly. To avoid an unnecessarily high number of components, the first sealing component preferably exerts the first preload force. The first sealing component is therefore preferably a sealing component made of an elastomeric material, such as an O-ring.

[0038] What applies to the first radiation sensor also applies alternatively or additionally, mutatis mutandis, to the second radiation sensor, with the proviso that the specification "first" is to be replaced by "second." Therefore, the second radiation sensor can preferably be accommodated in a second radiation sensor assembly, wherein the second radiation sensor assembly can be sealed against a second housing component of the sensor housing by a second sealing component. The second radiation sensor assembly can be or comprise a second mounting component. The second mounting component can be configured such that, on the one hand, it permanently mounts the second radiation sensor, generally with the interposition of a second circuit board directly supporting the second radiation sensor, and, on the other hand, can be arranged in the sensor housing with small gap dimensions, such as a clearance fit.Preferably, the second sealing component effects the second preload force, although in general a preload component, such as a compression spring, an elastomer ring or the like, may be provided to effect the preload force.

[0039] The second housing component is also preferably inserted into an opening in the sensor housing through which the second radiation sensor assembly was previously inserted into the sensor housing. The second housing component preferably comprises an electronic assembly, for example, a base circuit board with electronic components, such as at least one integrated circuit, which is designed to process signals from the first and second radiation sensors.

[0040] The part of the sensor housing accommodating the first radiation sensor assembly can be integrally connected to the first housing component, for example by gluing or welding, in particular by laser welding. Likewise, the part of the sensor housing accommodating the second radiation sensor assembly can be integrally connected to the second housing component, again for example by gluing or welding, preferably by laser welding.

[0041] Preferably, the first and second radiation sensor assemblies are accommodated in the same part of the sensor housing, which is preferably designed as a one-piece sensor housing part in which the first and / or the second disc is / are also accommodated.

[0042] The second sealing component is preferably an elastomeric seal, in particular an O-ring. To avoid a separate mount for the radiation source, the radiation source can also be accommodated in the second radiation sensor assembly. Preferably, the second sensor arrangement and the radiation source are mounted on a one-piece second mounting component.

[0043] To secure the radiation source in the second radiation sensor assembly, the radiation source can be in abutting engagement with the second prestressing component, in particular with the second sealing component, such that the second prestressing component, in particular the second sealing component, directly prestresses the radiation source toward the second pane. The second prestressing component, in particular the second sealing component, can thus exert a prestressing force directed toward the second pane both directly on the radiation source and indirectly on the second radiation sensor via the second mounting component. The second mounting component is then arranged between the second radiation sensor and the second prestressing component, in particular the second sealing component.

[0044] The presently discussed design of the turbidity sensor enables the use of an advantageously slim sensor housing. The sensor housing can therefore extend with its largest dimension along a longitudinal axis. The sensor housing is preferably cylindrical at least in sections, in particular where the first and second radiation sensors and particularly preferably also the radiation source are arranged. The aforementioned longitudinal axis is then preferably the cylinder axis or, in the case of a partially conical design, the cone axis. Instead of a cylindrical sensor housing, a sensor housing that is at least partially prismatic can also be used.

[0045] The first and second disks can each be mounted on the housing oriented transversely to the longitudinal axis. The fluid detection region can then be formed as a groove in the sensor housing extending transversely to the longitudinal axis. Preferably, the first and second disks are oriented orthogonally to the longitudinal axis. Likewise, a longitudinal direction of the groove forming the fluid detection region preferably runs orthogonally to the longitudinal axis of the sensor housing.

[0046] The emission characteristics of the radiation source, particularly in the preferred form of an LED, may be subject to age-related changes. Additionally or alternatively, the detection characteristics of at least one radiation sensor may be subject to age-related changes.

[0047] In order to be able to react to such changes in the emission characteristics and / or the detection characteristics and to avoid a loss of accuracy of the turbidity sensor, the present invention relates to a turbidity sensor assembly which comprises a previously described turbidity sensor and a first calibration body for correcting or calibrating the turbidity sensor.

[0048] The first calibration body preferably serves to correct or calibrate the first radiation sensor, which is reached by the fluid-transmitting radiation detection area. For quick and uncomplicated, yet secure arrangement of the first calibration body, it is preferably detachably connectable to the sensor housing. It can be slid onto the sensor housing along the longitudinal axis of the sensor as a sleeve extending along a sleeve axis, in particular a pot-shaped sleeve with a base and a side wall projecting therefrom along the sleeve axis and enclosing the sleeve axis in a closed manner. When arranged on the sensor housing, the sleeve axis is parallel or collinear to the longitudinal axis of the sensor housing.

[0049] To facilitate assembly, the first calibration body, designed as a pot-shaped sleeve, can have a channel passing through the sleeve, through which air trapped between the first calibration body and the turbidity sensor can escape when the first calibration body is arranged on the turbidity sensor. The channel is preferably formed in the bottom of the pot-shaped first calibration body because, firstly, there is no risk of disruptive light entering the fluid detection area from a channel arranged in this way, and secondly, the channel is available for air to escape until the first calibration body is completely arranged on the turbidity sensor. The same applies when removing the first calibration body from the turbidity sensor. Here, it is advantageous if air can flow into the space formed between the first calibration body and the turbidity sensor and which increases in size as a result of the removal.Then the removal does not have to be carried out against the effect of the ambient atmosphere, but only against the friction between the first calibration body and the turbidity sensor.

[0050] Alternatively, the first calibration body can be clipped onto the sensor housing as an elastic clamp that incompletely encompasses the sensor housing in the circumferential direction around its longitudinal axis, transversely to the longitudinal axis of the sensor housing, i.e. can be clamped onto the latter.

[0051] When the first calibration body is arranged on the sensor housing in such a way that light from the external environment can no longer enter the fluid detection area, a first calibration-ready operating state of the turbidity sensor assembly is reached. In this first calibration-ready operating state, the first calibration body at least contributes to shielding the fluid detection area against electromagnetic radiation of a specific wavelength range, in particular against light radiation including infrared and UV light, from the external environment. The fluid detection area can then be partially surrounded by the sensor housing and partially surrounded by the first calibration body in order to shield the fluid detection area against the above-mentioned radiation from the external environment. The first radiation sensor is therefore in the first calibration-ready operating state for ambient light orThe sensor is no longer accessible to electromagnetic radiation from the environment, but remains accessible to radiation emitted by the radiation source. Thus, the signal of the first radiation sensor can be corrected or calibrated with respect to a change in the emission characteristics of the radiation source and / or a change in the detection characteristics of the first radiation sensor.

[0052] The possible temporal change in the emission characteristics of the radiation source and / or a radiation sensor not only changes the signal provided by the first radiation sensor upon irradiation by the radiation source, but also the signal provided by the second radiation sensor. Therefore, a corresponding correction of the signal of the second radiation sensor to adapt to a changed emission characteristic and / or a change in the detection characteristic of the second radiation sensor is helpful for the accuracy achievable with the turbidity sensor.

[0053] Additionally or alternatively, the present invention therefore relates to a turbidity sensor assembly comprising a previously described turbidity sensor and a second calibration body for calibrating the turbidity sensor.

[0054] The second calibration body is used to calibrate the second radiation sensor. The second calibration body ensures that only radiation from the fluid detection area reaches the second radiation sensor, but not radiation reflected from the sensor housing or the first pane, or radiation from the outside environment.

[0055] The second calibration body is preferably detachably connectable to the sensor housing for quick, even short-term, and at the same time safe use. The second calibration body can preferably be pushed out onto the sensor housing transversely to the longitudinal axis of the sensor housing. So that the second calibration body does not have to be held permanently on the sensor housing during calibration of the second radiation sensor, the second calibration body can preferably be latched to the sensor housing, for example by the second calibration body incompletely encompassing the sensor housing in the circumferential direction around its longitudinal axis. The second calibration body can therefore be designed, at least in sections, as a clamp that can be clipped onto the sensor housing transversely to the longitudinal axis of the sensor housing.

[0056] In a second, calibration-ready operating state of the turbidity sensor assembly, the second calibration body shields the fluid detection area from light irradiation or, more generally, from electromagnetic radiation of a specific wavelength range from the external environment. In this regard, the statements regarding the first calibration body also apply to the second calibration body. In this second, calibration-ready operating state, the fluid detection area is preferably surrounded by the sensor housing and the second calibration body. These can then provide the shielding.

[0057] To largely prevent reflection of radiation emitted by the radiation source by the sensor housing and / or by the first pane, the second calibration body preferably has a blocking formation, which, in the second calibration-ready operating state, is arranged between the first and second radiation sensors and shields the first radiation sensor from radiation emitted by the radiation source. Preferably, the blocking formation is located between the radiation source and the first pane, in particular between the second radiation sensor and the first pane, in the second calibration-ready operating state.

[0058] The blocking formation is preferably firmly connected to a securing portion of the second calibration body, with which the second calibration body can be secured to the sensor housing, in particular in the manner described above. The blocking formation can be formed integrally with the securing portion, for example by injection molding. Alternatively, the blocking formation can comprise a holder into which a blocking body can be inserted. In this way, different blocking bodies can be arranged on the second calibration body, and thus the second calibration body can be adapted to different situations.

[0059] The present invention will be explained in more detail below with reference to the accompanying drawings. It shows: Fig. 1 shows a roughly schematic longitudinal section through the detection end of a turbidity sensor according to the invention, Fig. 2 shows a roughly schematic perspective partial sectional view of the detection end of the turbidity sensor of Fig. 1 , Fig. 3 a rough schematic longitudinal section through the detection end of the turbidity sensor of Fig. 1 with the first calibration body attached to it ready for calibration, and Fig. 4 a roughly schematic longitudinal section through the detection end of the turbidity sensor of Fig. 1 with a second calibration body attached ready for calibration.

[0060] In the Figure 1 and 2 A turbidity sensor according to the invention is generally designated 10. Specifically shown in the Figure 1 and 2the sensing end 12 of the turbidity sensor 10, on which the fluid sensing region 14 is formed. With this sensing end 12, the turbidity sensor 10 is immersed in a fluid, typically a liquid, during sensing operation to measure its turbidity. As expected, the fluid contains suspended matter, particularly biological cells.

[0061] At a connection end not shown in the figures, which is opposite the detection end 12 with respect to a longitudinal axis L, the turbidity sensor can be designed to transmit detection data, for example by means of a connection cable extending from the connection end or by means of a connection interface, such as a socket which is designed for the detachable connection of a signal transmission line.

[0062] The turbidity sensor 10 extends along the virtual longitudinal axis L and has a sensor housing 16, which is preferably made up of several parts to facilitate assembly and which, in the illustrated embodiment, has a cylindrical shape. The longitudinal axis L is then the cylinder axis of the sensor housing or at least its cylindrical sections. An exception to the cylindrical shape in the present case is a fluid detection area 14, which is designed as a groove-shaped recess 18 of a sensor housing part 16a on the detection end, but which still extends completely within a cylindrical envelope of the sensor housing or at least of the sensor housing part 16a, which lies against the cylindrical outer surfaces of the sensor housing 16. The groove-shaped recess 18 runs along a virtual groove axis N, which extends orthogonally to the virtual longitudinal axis L, which is imagined to pass centrally through the sensor housing 16, at a distance from the latter.

[0063] The fluid detection area 14 is surrounded on three sides by outer surfaces 20a, 20b, and 20c of the sensor housing 16, in particular the sensor housing part 16a. The outer surfaces 20a, 20b, and 20c of the sensor housing 16 enclosing the fluid detection area 14 are preferably flat, with pairs of adjacent outer surfaces 20a and 20b on the one hand and 20b and 20c on the other preferably enclosing a right angle between them.

[0064] The outer surface 20a is partially formed by the outer surface of a first disk 22, which is accommodated in the sensor housing 16, in particular in the sensor housing part 16a. Due to its high scratch resistance and chemical resistance, the first disk 22 is preferably made of a mineral material, with corundum being more preferred among the mineral materials and sapphire glass being the most preferred among the corundums. The opposite outer surface 20c, which is preferably parallel to the outer surface 20a, is partially formed by the outer surface of a second disk 24. The second disk 24 is preferably identical in terms of its dimensions and material to the first disk 22.

[0065] The fluid detection area 14, together with the surrounding walls of the sensor housing 16, is mirror-symmetrical with respect to a plane containing the groove axis N and parallel to the longitudinal axis L and to the plane of the drawing of Figure 1orthogonal mirror symmetry plane SE. The disks 22 and 24 are firmly and tightly connected to the remaining sensor housing 16 by a thermally meltable and solidifiable cement 26. The solidified cement 26 runs along a circumferential edge of the disks 22 and 24 in a closed manner around each of the disks 22 and 24. The remaining sensor housing 16 is preferably made of stainless steel.

[0066] Now that the structure of the fluid detection area 14 and the surrounding area of ​​the sensor housing 16 has been described, the structure of the sensor technology in the turbidity sensor 10 is explained below.

[0067] A first radiation sensor assembly 28 is arranged in the sensor housing 16 between the free longitudinal end and the fluid detection area 14. The first radiation sensor assembly 28 comprises a first mounting component 30, preferably injection-molded in one piece, on which a first radiation sensor 32 is mounted on a first circuit board 31. A first optical filter 34 is arranged between the first radiation sensor 32 and the first disk 22. This filter transmits electromagnetic radiation in the wavelength range of 840 nm or greater and blocks radiation with shorter wavelengths.

[0068] The first radiation sensor assembly 28 was inserted into the sensor housing 16 through an end opening 36 of the sensor housing 16. The opening 36 is now closed by a housing cover 38, which is firmly attached to the sensor housing 16, in particular to the sensor housing part 16a, preferably by a laser weld 40. An elastomeric O-ring 42 is arranged between the first radiation sensor assembly 28 and the housing cover 38. In the present exemplary embodiment, this O-ring 42 primarily serves to exert a prestressing force on the first radiation sensor assembly 28, acting toward the first disk 22. The O-ring 42 is in direct contact engagement with the housing cover 38 on the one hand and with the holding component 30 on the other. The prestressing force prestresses the first radiation sensor 32, together with the first optical filter 34, into contact with the inner surface of the disk 22.

[0069] A line tunnel 44 extends beneath the outer surface 20b, which bridges the outer surfaces 20a and 20c. A signal transmission line 46 runs through this tunnel from the first radiation sensor 32 to an electronic assembly 48, which is housed in the sensor housing 16, in particular in a second sensor housing part 16b. The electronic assembly 48 comprises a printed circuit board 50 with a plurality of electronic components arranged thereon.

[0070] One of the electronic components of assembly 48 is an LED 52, which serves as the radiation source 54 of the turbidity sensor 10. The LED 52 emits light in the near-infrared wavelength range, preferably at a wavelength of 840 to 860 nm. The LED 52 is surrounded by a glass body 56, which ensures that the LED 52 is highly insensitive to temperature changes. The discs 22 and 24 are transparent to the radiation emitted by the LED 52.

[0071] The LED 52 is housed in a second mounting component 58, which is part of a second radiation sensor assembly 60. The second mounting component 58 is preferably injection-molded in one piece. On its side facing away from the electronic assembly 48, it supports a second radiation sensor 62 mounted on a second circuit board 61.

[0072] The second radiation sensor 62 is located directly between the LED 52 and the first radiation sensor 32. The optical axis of the LED 52 is in Figure 1 designated OA. It is the shortest distance between LED 52 and the photosensitive sensor detection surface 32a of the first radiation sensor 32 facing the first disc 22. The optical axis OA, parallel to the longitudinal axis L of the sensor housing 16, also shows a beam path of radiation emitted by the LED 52 toward the first radiation sensor 32.

[0073] The second radiation sensor 62 is arranged in this beam path. To allow radiation emitted by the LED 52 to pass through the second radiation sensor 62, the second radiation sensor 62 has an opening 64 extending through its thickness, preferably such that the optical axis OA forms a virtual center axis of the opening 64. Likewise, the second circuit board 61 has an opening 65, preferably coaxial with the opening 64. Radiation emitted by the LED 52 can initially reach the fluid detection area 14 through the openings 64 and 65. From there, the portion of the radiation that does not strike any suspended matter present in the fluid detection area 14 and is absorbed or scattered by it can transmit the fluid detection area 14 and reach the first radiation sensor 32.The radiation component which, however, is scattered or reflected by suspended matter in the fluid detection area 14 with a radiation component opposite to the direction of incidence E can reach the second radiation sensor 62.

[0074] Also located in front of the photosensitive sensor detection surface 62a of the second radiation sensor 62 is an optical filter 66, which is identical to the optical filter 34 between the first radiation sensor 32 and the first disk 22. The optical filter 66 can also have an opening extending through it in the thickness direction, which continues the opening 64 of the second radiation sensor 62 along the optical axis OA. In the present exemplary embodiment, the optical filter 66 does not have such an opening, so that radiation emitted by the LED 52 reaches the fluid detection region 14 only after passing through the optical filter 66 and thus only in the wavelength range transmitted by the optical filter 66.

[0075] Due to the simultaneous detection of straight-line transmitted radiation by means of the first radiation sensor 32 and of radiation scattered or reflected counter to the direction of incidence E by means of the second radiation sensor 62, the presently proposed arrangement, in which the second radiation sensor 62 is arranged in the beam path of radiation emitted from the LED 52 to the first radiation sensor 32, can be used to obtain a very slim turbidity sensor 10 with high measurement accuracy over a large range of quantities of suspended matter contained in a fluid to be measured.

[0076] An assignment of the signals delivered by the individual radiation sensors 32 and 62 to the turbidity of the fluid to be measured in the fluid detection area 14 and consequently, given a known type and structure of the suspended particles contained in the fluid, to the amount of suspended particles contained in a reference volume of the fluid, can be obtained by calibrating the turbidity sensor using different calibration fluids. The calibration fluids preferably differ only with respect to the amount of suspended particles contained in a reference volume of the respective calibration fluid, so that a difference in the sensor signals during calibration can be directly attributed to a difference in the amount of suspended particles relative to the fluid volume.

[0077] Experiments have shown that with the turbidity sensor 10 presented here, with preferably parallel and mutually facing flat photosensitive sensor detection surfaces 32a and 62a of the radiation sensors 32 and 62, respectively, of which the second radiation sensor 62 is located in the beam path of the LED 52 to that of the first radiation sensor 32, the detection signals supplied by the radiation sensors 32 and 62, or a cumulative detection signal determined therefrom, exhibit an extremely advantageous linear change behavior depending on a change in the amount of suspended matter in a reference volume of the fluid to be measured. This linear behavior is advantageously present over essentially the entire measuring range, related to the turbidity or the associated detectable amount of suspended matter.

[0078] For the sake of completeness, it should be mentioned that the second radiation sensor 62 is also connected to the electronic unit 48 by a signal transmission line 68.

[0079] The second sensor assembly 60 is sealed by a second elastomeric O-ring 70 relative to the sensor housing 16, in particular relative to an inner wall of the first sensor housing part 16a. The Figure 1The visible gap between the inner wall of the first sensor housing part 16a and the second O-ring 70 is merely due to the representation of the second O-ring 70 in the undeformed state. When the actual deformed state is correctly represented, the second O-ring 70 rests against the designated inner wall. At the same time, the second O-ring 70 is in abutting engagement with an end face of the second housing part 16b, so that the second O-ring 70, by abutting engagement with the second sensor assembly 60, preloads the second sensor assembly 60 toward the second disk 24.

[0080] The second O-ring 70 rests directly against the back of the LED 52 and exerts a preload force directly on the LED 52 in the direction of the second disk 24. This preloads the LED 52 into the recess in the second mounting component 58 that receives it.

[0081] On the other hand, the second O-ring 70 lies directly against the second mounting component 58 and, together with the second radiation sensor 62 held thereon, clamps it in the direction of the second disc 24 and into contact with it.

[0082] The second sensor housing part 16b can be integrally connected to the first sensor housing part 16a, preferably by a laser weld seam 72.

[0083] In Figure 3 the detection end 12 of the turbidity sensor 10 is shown again, whereby for better clarity only a part of the Figure 1 already known components and component sections in Figure 3 are again provided with reference symbols. Due to the correspondence of the representations of the detection end 12 in the Figure 1 and 3 are sufficient in Figure 3 assigned reference symbols when viewed in addition also by Figure 1 to detect the turbidity sensor 10. In Figure 3Components and component sections not designated by reference symbols are Figure 1 shown identically and provided with reference symbols.

[0084] In Figure 3 A first calibration body 74 for calibrating or correcting the first radiation sensor 32 is arranged ready for calibration at the detection end 12 of the turbidity sensor 10. The first calibration body 74 spans the fluid detection area 14, so that no ambient light from the external environment U outside the turbidity sensor 10 and outside the fluid detection area 14 reaches the fluid detection area 14 and thus the first radiation sensor 32.

[0085] The first calibration body 74, which forms a first turbidity sensor assembly 76 with the turbidity sensor 10, is pot-shaped and extends along a sleeve axis H. The sleeve axis H, which can be a rotational symmetry axis of the preferably rotationally symmetrical first calibration body 74, is in the Fig. 3 shown first calibration-ready state is collinear with the longitudinal axis L of the turbidity sensor 10.

[0086] The first calibration body 74 comprises a jacket wall 74a surrounding the sensor housing 16, more precisely the first sensor housing part 16a in the illustrated example in the circumferential direction around the longitudinal axis L, and comprises a bottom wall 74b extending orthogonally to the longitudinal axis L and closing the jacket wall 74a at one longitudinal end. The bottom wall 74b, which is located at the longitudinal end of the first calibration body 74 opposite the insertion opening 74a1 of the first calibration body 74, is not functionally absolutely necessary, but serves as an advantageous end stop, so that the user, who slides the first calibration body 74 onto the turbidity sensor 10, preferably along the longitudinal axis L from the detection end 12, can also haptically recognize the correct relative position of the first calibration body 74 relative to the turbidity sensor 10. It is sufficient for the production of the Figure 3shown first calibration-ready state of the first turbidity sensor assembly 76, the first calibration body 74 is pushed axially over the detection end 12 along the longitudinal axis L until the bottom wall 74b physically rests against the free end face of the detection end 12 of the turbidity sensor 10.

[0087] To facilitate the sliding of the first calibration body 74 onto and off the sensor housing 16, in particular onto and off the first sensor housing part 16a, the first calibration body 74 in the illustrated embodiment has a thickened portion 74c on its casing wall 74a, the flanks 74c1 and 74c2 of which also point along the longitudinal axis L, facilitating manual force application by a user. The thickened portion 74c preferably extends circumferentially in a closed manner.

[0088] To further facilitate the sliding of the first calibration body 74 onto and off the sensor housing 16, a channel 75 passing through the bottom wall 74b is formed in the bottom wall 74b, through which channel air can flow from one side of the bottom wall 74b to the other side for pressure equalization.

[0089] An elastomer ring 78, for example in the form of an O-ring, which is received on the inside of the casing wall 74a in a groove 74d, is deformed in the illustrated first calibration-ready state between the inside of the casing wall 74a and the outside of the sensor housing 16, in particular of the first sensor housing part 16a, and thus holds the first calibration body 74 in a frictionally engaged manner in the Figure 3shown first calibration-ready state on the turbidity sensor 10. The clear width of the calibration body 74 to be measured orthogonally to the longitudinal axis L is slightly larger than the diameter of the section of the sensor housing 16 inserted into the first calibration body 74. The recess of the calibration body 74 can be formed with a clearance fit with respect to the outer diameter of the section of the sensor housing 16 to be inserted into the first calibration body 74.

[0090] Of the clear depth of the first calibration body 74 to be measured along the longitudinal axis L, along which the detection end 12 of the turbidity sensor 10 projects into the calibration body 74, the elastomer ring 78 is preferably arranged in the last quarter, particularly preferably in the last fifth, in order to ensure that the first calibration body 74 is only held frictionally by the elastomer ring 78 at the detection end 12 of the turbidity sensor 10 when the first calibration body 74 reliably shields the fluid detection area 14 from the outside environment against light incidence.

[0091] In the first calibration-ready state of the first turbidity sensor assembly 76, only radiation emitted by the radiation source 54, i.e., the LED 52, reaches the first radiation sensor 32. Thus, a detection state of the radiation sensor 32 can be qualitatively and / or quantitatively assigned to a current supply state of the LED 52. As a result, any age-related change in the emission characteristic of the LED 52 and / or any age-related change in the detection characteristic of the first radiation sensor 32 compared to a respective new state can be taken into account and corrected by assigning detection states of the first radiation sensor 32, so that the age-related change in the emission characteristic and / or the detection characteristic does not lead to erroneous detections by the first radiation sensor 32.

[0092] In Figure 4a second turbidity sensor assembly 79 is shown, which replaces the turbidity sensor 10 of Figure 1 and a second calibration body 80. As in the case of Figure 3 is also in Figure 4 For the sake of clarity, only some of the components and component sections of the turbidity sensor 10 are provided with reference numerals. By comparison with Figure 1 The components and component sections of the turbidity sensor 10 that are not provided with reference symbols can be Figure 4 easily identify.

[0093] The second calibration body 80 is designed as a clamp, which is in the Figure 4illustrated second calibration-ready state of the second turbidity sensor assembly 78 incompletely encompasses the section of the turbidity sensor 10 having the fluid detection area 14 in the circumferential direction about the longitudinal axis L. The second calibration body 80 encompasses the turbidity sensor 10, in particular the section of the first sensor housing part 16a having the fluid detection area 14, but by more than half the circumference of the first sensor housing part 16a, so that the second calibration body 80 can be locked to the turbidity sensor 10 due to its component elasticity.

[0094] In contrast to the first calibration body 74, which is pushed along the longitudinal axis L onto the detection end 12 of the turbidity sensor 10, the second calibration body 80 in the example shown is clipped onto the turbidity sensor 10 orthogonally to the longitudinal axis L.

[0095] In further contrast to the first calibration body 74, the second calibration body 80 has a blocking formation 82 protruding from the inside on its inner side facing the turbidity sensor 10. In the illustrated embodiment, the blocking formation 82 is formed by a radiation-tight block 84 for radiation from the LED 52, which, in the second calibration-ready state, protrudes into the fluid detection area 14 and fills the fluid detection area 14 to such an extent that the disk 22 and its housing surroundings are not reached by radiation from the LED 52 and thus no radiation reflected by the disk 22 and its housing surroundings can enter the second radiation sensor 62.

[0096] The block 84 is detachably connected to a clamp component 80a designed for locking attachment to the turbidity sensor 10 via a screw 86, shown only in partial section. If necessary, the block 84 can be exchanged for another block of a different color and / or surface finish.

[0097] Otherwise, the clamp component 80a or the second calibration body 80 shields the fluid detection area 14 against electromagnetic radiation from the external environment U. Thus, only radiation emitted by the LED 52, i.e., by the radiation source 54, reaches the second radiation sensor 62.

[0098] Thus, the detection characteristic of the second radiation sensor 62 can be adapted, if necessary, to an age-related change in the emission characteristic of the LED 52 and / or to an age-related change in the detection characteristic of the second radiation sensor 62, and thus an incorrect detection of the second radiation sensor 62 due to a change in the emission characteristic of the LED 52 and / or due to a change in the detection characteristic of the second radiation sensor 62 can be avoided or corrected.

[0099] The second calibration body 80, with its blocking formation 82, interacts with the sensor housing 16 and the fluid detection area 14 formed thereon according to the key-lock principle. To facilitate handling of the second calibration body 80, this body, in particular the clamp component 80a, also has a thickened portion 80c. Reference numeral 80b indicates the edge of the clamp jaws of the clamp component 80a, which are located in front of and behind the plane of the drawing and which incompletely encompass the sensor housing 16 in the circumferential direction.

[0100] In the illustrated embodiment, the block 84 is located between two cheeks 88, which are preferably formed integrally with the clamp component 80a and each have an opening 88a through which the block 84 is accessible for radiation from the LED 52. The block 84 has defined reflection properties which, when a brand-new LED 52 is energized at a predetermined current, allow a predetermined radiation component to be expected to be incident on the second radiation sensor 62. If the radiation component actually incident on the second radiation sensor 62 deviates from the predetermined expected radiation component, the detection behavior of the second radiation sensor 62 can be corrected based on the deviation.

[0101] When correcting aging-related changes to the LED 52 and the first or second radiation sensor 32 or 62, respectively, the LED 52 and the respective radiation sensor 32 or 62 can be viewed as a functional unit consisting of radiation source and sensor and corrected as a unit. It then advantageously does not matter which component is subject to what degree of functional changes.

Claims

1. A turbidity sensor (10) for detecting a clouding of a fluid due to suspended matter contained in the fluid, the turbidity sensor (10) comprising: - a fluid detection area (14) for accommodating and for metrologically detecting fluid - a radiation source (54) for emitting radiation into the fluid detecting region (14), - a first radiation sensor (32) for detecting a first part of the radiation emitted by the radiation source (54), and - a second radiation sensor (62), which is different from the first radiation sensor (32), for detecting a second part, which is different from the first part, of the radiation emitted by the radiation source (54), at least a section of the fluid detection region (14) being located between the first (32) and the second radiation sensor (62), characterized in that the second radiation sensor (62) is located in the beam path (OA) of the first part of the radiation emitted by the radiation source (54), which first part is detected by the first radiation sensor (32).

2. The Turbidity sensor (10) according to claim 1, characterized in that the second radiation sensor (62) has an aperture (64) penetrating it, through which radiation emitted by the radiation source (54) passes from the radiation source (54) to the first radiation sensor (32).

3. The Turbidity sensor (10) according to claim 1 or 2, characterized in that the first radiation sensor (32) has a planar first radiation-sensitive sensor detection surface (32a) which faces the second radiation sensor (62), and in that the second radiation sensor (62) has a planar second radiation-sensitive sensor detection surface (62a) which which faces the first radiation sensor (32).

4. The Turbidity sensor (10) according to claim 3, characterized in that the first (32a) and the second sensor detection surface (62a) are arranged parallel to one another.

5. The Turbidity sensor (10) according to one of the preceding claims, characterized in that the radiation source (54), the first radiation sensor (32) and the second radiation sensor (62) are accommodated in a sensor housing (16) and are screened by the sensor housing (16) against the external environment (U) of the sensor housing (16), wherein the fluid detection region (14) is open to the external environment of the sensor housing (16).

6. The Turbidity sensor (10) according to claim 5, characterized in that at least one section (20a) of the sensor housing (16) facing the second radiation sensor (62) is surface-treated to change its reflective properties in the wavelength range of the radiation emitted by the radiation source (54).

7. The Turbidity sensor (10) according to claim 5 or 6, characterized in that the sensor housing (16) has a first (22) and a second panel (24), preferably made of mineral material, which each transmit radiation from the radiation source (54), wherein the first (22) and the second panel (24) are situated opposite one another at a distance from one another in the beam path (OA) of the radiation source (54) and wherein the first panel (22) screens the first radiation sensor (32) and the second panel (24) screens the second radiation sensor (62) from the fluid detection region (14) situated between the first (22) and the second panel (24)8. The Turbidity sensor (10) according to claim 7, characterized in that the first radiation sensor (32) is biased in the direction of the first panel (22) by a first biasing force and / or in that the second radiation sensor (62) is biased in the direction of the second panel (24) by a second biasing force.

9. The Turbidity sensor (10) according to claim 8, characterized in that the first radiation sensor (32) is accommodated in a first radiation sensor assembly (28), the first radiation sensor assembly (28) being sealed against a first housing component (38) of the sensor housing (16) by a first seal component (42), wherein the first seal component (42) effects the first biasing force.

10. The Turbidity sensor (10) according to one of claims 8 or 9, characterized in that the second radiation sensor is accommodated in a second radiation sensor assembly (60), the second radiation sensor assembly (60) being sealed against a second housing component (16b) of the sensor housing (16) by a second seal component (70), the second seal component (70) effecting the second biasing force.

11. The Turbidity sensor (10) according to claim 10, characterized in that the second radiation sensor assembly (60) also houses the radiation source (54).

12. The turbidity sensor (10) of claim 11, characterized in that the radiation source (54) is in abutting engagement with the second seal component (70), so that the seal component (70) directly biases the radiation source (54) toward the second panel (24).

13. Turbidity sensor (10) according to one of the preceding claims, incorporating claim 7, characterized in that the sensor housing (16) extends with its largest dimension along a longitudinal axis (L), wherein the first (22) and the second (24) panels are each received on the sensor housing (16) oriented transverse to the longitudinal axis (L).

14. A turbidity sensor assembly (76, 79) comprising a turbidity sensor (10) according to claim 13, and a first calibration body (74) for calibrating the turbidity sensor (10), characterized in that the first calibration body (74) is detachably connectable to the sensor housing (16) in such a way that in a first operating state of the turbidity sensor assembly (76, 79) in which it is ready for calibration, the first calibration body (74) at least contributes to screening the fluid detection region (14) from irradiation of light from the external environment (U) of the turbidity sensor assembly (76, 79), wherein the first radiation sensor (32) is accessible in the first calibration-ready operating state for radiation emitted by the radiation source (54).

15. The turbidity sensor assembly (76, 79), in particular according to claim 14, comprising a turbidity sensor (10) according to claim 13, and a second calibration body (80) for calibrating the turbidity sensor (70), characterized in that the second calibration body (80) can be detachably connected to the sensor housing (16) in such a way that in a second operating state in which the turbidity sensor assembly (76, 79) is ready for calibration, the second calibration body (80) at least contributes to screening the fluid detection region (14) from irradiation of light from the external environment (U) of the turbidity sensor assembly (76, 79), wherein the second calibration body (80) has a blocking deformation (82) which, in the second calibration-ready operating state, is arranged between the first (32) and the second radiation sensor (62) and shields the first radiation sensor (32) from radiation emitted by the radiation source (52).