Method for determining scattered light parameter and measuring device for carrying out method

Abstract

The invention relates to a method for determining a scattered light parameter and a measuring device for carrying out the method. The invention relates to a method for determining a scattered light parameter, in particular a turbidity, in a medium by means of a measuring device (1), in particular a turbidity sensor, comprising the following steps: emitting excitation light (8) into the medium (3), wherein the excitation light (8) is scattered in the medium (3); a light path (11) receiving the light (6) scattered in the medium (3), generating excitation light (8) and scattered light (6); generating interference in the optical path (11); receiving light (6) now scattered in the medium (3); and determining a scattered light parameter, in particular a turbidity, on the basis of the scattered light (6), taking into account the influence of the interference. The invention also relates to a measuring device (1), in particular a turbidity sensor, for carrying out the method.

Description

Field of the Invention

[0001] The present invention relates to a method for determining scattering light parameters, in particular turbidity, and to a measuring device for carrying out the method. Background Art

[0002] Below, the problem to be solved is described using turbidity measurement as an example. The ISO 7027 standard related to turbidity measurement in liquids provides for the measurement of scattered light at a 90° angle for low turbidity measurements. Optical sensors for measuring the turbidity of liquids that meet this standard have the disadvantage that the signal curve is not clear in all media: as the turbidity of the liquid increases, the scattered light signal initially increases to a maximum. However, once this limit is exceeded, although the turbidity increases, the signal decreases again because, due to multiple scattering, less and less scattered light reaches the detector of the sensor.

[0003] Due to the ambiguous signal, the measurement cannot distinguish between very low and very high turbidity values and, therefore, cannot clearly determine the turbidity value and / or solid content of the liquid. For example, a black medium severely contaminated with particles is misinterpreted as a clean, transparent liquid.

[0004] Since international regulations and legal requirements usually call for turbidity measurements according to ISO 7027 and, therefore, only a single scattered light signal at a 90° angle can be used, additional measuring devices usually have to be installed in order to obtain further information about the actual turbidity value or solid content of the medium through additional measuring variables. This poses a considerable additional cost and installation effort for the operator. Summary of the Invention

[0005] The present invention is based on the object of performing an optical scattered light measurement using only one measurement channel (e.g., 90° according to ISO 7027) such that a clear distinction can be made between media with low turbidity (e.g., clear water) and liquids with very high turbidity (e.g., black wastewater with a high particle content) and / or the turbidity value / solid content of the liquid can be detected.

[0006] This object is achieved by a method comprising the following steps:

[0007] Emitting excitation light into the medium such that the excitation light is scattered in the medium; receiving the light scattered in the medium, generating an optical path of the excitation light and the scattered light; generating an interference in the optical path; receiving the light now scattered in the medium; and determining a scattered light parameter, in particular turbidity, based on the scattered light taking into account the influence of the interference.

[0008] In the claimed method, a clear distinction between a medium with low turbidity (e.g., clear water) and a liquid with very high turbidity or absorption (e.g., contaminated black wastewater with a high particle content) is achieved by generating defined interferences in the light path of the sensor and evaluating the response to these interferences.

[0009] These interferences are reflections, scatterings, or other optical interactions with fixed or moving parts, walls, other mechanical elements, or bubbles or induced anomalies such as turbulence. In one embodiment, the interference can be achieved by targeted manipulation of the turbidity value (e.g., adding ultrapure water).

[0010] Although due to the above problems, the measurement signals in very different media can be the same without interference, optical interference results in significantly different signals that change with different signs, which allows for a clear detection of the degree of contamination of the liquid: for example, while interference caused by additional wall effects in a medium with low turbidity leads to an increase in the measurement signal, the measurement signal decreases in a highly turbid medium.

[0011] Embodiments are described below.

[0012] One embodiment provides that the method further comprises the step of moving an interference element, in particular an element that reflects and / or scatters the excitation light, into the light path such that an interference is generated.

[0013] One embodiment provides that the method further comprises the step of moving the measuring device in the direction of the interference element, in particular in the direction of the element that reflects and / or scatters the excitation light, such that the excitation light is reflected and / or scattered by the element to generate an interference.

[0014] One embodiment provides that the interference is designed as an electro-optical interference and that, in addition to the scattered light, the interference light is received.

[0015] One embodiment provides that the interference is generated temporarily and periodically.

[0016] One embodiment provides that the method further comprises the step of introducing ultrapure water or a secondary medium with a defined turbidity into the medium.

[0017] It is also an object of the present invention to provide a measuring device, in particular a turbidity sensor, for carrying out the method as described above for determining the scattered light parameter, in particular turbidity, in a medium, the measuring device comprising: at least one light source which emits excitation light into the medium and emits it in the direction of the surface of the medium; at least one photodiode which receives the light scattered in the medium and converts it into an electrical signal, thereby creating an optical path from the light source through the medium to the photodiode; an interference unit which is designed to generate interference in the optical path; and a data processing unit which determines the scattered light parameter, in particular turbidity, from the electrical signal based on the scattered light taking into account the influence of the interference.

[0018] One embodiment provides that the light source emits excitation light into the medium via an optical window, wherein the photodiode receives the scattered light from the medium via the same window or a separate optical window, wherein the interference unit is designed as a reflecting and / or scattering interference element, in particular as a wiper designed to clean the optical window, and wherein the interference element generates interference when it is located in front of the optical window and thus in the optical path.

[0019] One embodiment provides that the interference unit is arranged outside the medium.

[0020] One embodiment provides that the light source emits excitation light into the medium via an optical window, wherein the photodiode receives the light scattered by the medium via the same window or a separate optical window, wherein the interference unit is designed as an air purification unit and blows air in the direction of the optical window, and wherein the air purification unit generates interference when the air is in front of the optical window and thus in front of the optical path.

[0021] One embodiment provides that the interference unit is designed as a movable element and moves the measuring device in the direction of the interference element, in particular in the direction of the element which reflects and / or scatters the excitation light, such that the excitation light is reflected and / or scattered by the element to generate interference.

[0022] One embodiment provides that the interference unit is designed as an interference light source and emits interference light in the direction of the photodiode, thereby generating interference.

[0023] One embodiment provides that the interference unit is designed as a scattering or reflecting unit, and the measuring device having the light source is positioned relative to the scattering or reflecting unit such that a long-term measurement value offset is produced at least for a slightly or not at all turbid medium.

[0024] One embodiment provides that the interference unit is designed as a secondary medium distribution unit which introduces ultrapure water or a secondary medium with a defined turbidity into the medium and generates interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] This will be explained in more detail with reference to the following drawings.

[0026] Figure 1 Shows a general view of an apparatus for measuring scattered light having an optical path.

[0027] Figure 2a / Figure 2b Shows the scattered light intensity measured according to the prior art ( Figure 2a ) and by means of the claimed measuring apparatus / method ( Figure 2b ) at different turbidities.

[0028] Figure 3 Shows the claimed measuring apparatus in one embodiment.

[0029] Figure 4a / Figure 4b Shows the claimed measuring apparatus in one embodiment and its effect in a less turbid medium ( Figure 4a ) and a more turbid medium ( Figure 4b ).

[0030] Figure 5a / Figure 5b Shows the claimed measuring apparatus ( Figure 5a ) and the effect ( Figure 5b , symbolically) in one embodiment.

[0031] Figure 6a / Figure 6b Shows the claimed measuring apparatus and its effect in a less turbid medium ( Figure 6a ) and a more turbid medium ( Figure 6b ) in one embodiment.

[0032] Figure 7a / Figure 7b Shows the claimed measuring apparatus and its effect in a less turbid medium ( Figure 7a ) and a more turbid medium ( Figure 7b ) in one embodiment.

[0033] Figure 8a / Figure 8b Shows the claimed measuring apparatus and its effect in a less turbid medium ( Figure 8a ) and a more turbid medium ( Figure 8b ) in one embodiment.

[0034] Figure 9a - Figure 9d Shows the claimed measuring apparatus and its effect in a less turbid medium ( Figure 9a , Figure 9b ) and a more turbid medium ( Figure 9c , Figure 9d ) in one embodiment.

[0035] Figure 10 Shows the scattered light intensity measured at different turbidities for the design in FIG. 9.

[0036] In the drawings, the same features are marked with the same reference numerals. Detailed Description

[0037] Any light that impinges on particles suspended in a liquid is scattered. The intensity of this light scattering is used as a direct measure for determining turbidity in optical turbidity measurements. Different measurement angles are used for different applications - partly due to national legal regulations. For example, 90° scattered light is used for drinking water applications etc. Breweries typically use a scattered light angle in the range of 11° to 25°. In measurements in sludge, a backscattering angle of >90° (e.g., 135°) is mainly used. The "FNU" unit (Formazin Nephelometric unit) is typically used for reference measurements or for turbidity values.

[0038] Generally, a turbidity sensor based on scattered light measurement can be symbolically as Figure 1 shown. From a light source 2, excitation light 8 (see thick arrow) is radiated into the measurement chamber through a window 7 that is transparent to the excitation light 8. There, the light is scattered by particles in a medium 3, which are at a scattering point P and are measured at a measurement angle (here shown as 90° for example) and is converted into "scattered light 6" (vertical dashed line). In reality, the scattering is not a single line (ray) as shown, but a diffuse volume.

[0039] The scattered light 6 passes through a window 7 that is transparent to it (possibly using only a single window), for example via an aperture or a lens, to reach a receiver 4. The light intensity reaching the receiver 4 is a measure of the turbidity. The light path from the light source 2 through the window 7 into the medium 3, to the scattering point P, through the medium 3 and through the window 7 to the receiver 4 is generally referred to as the "light path 11" (dashed line). As mentioned above, in reality the scattering does not result in just a single line (ray), but in a diffuse volume. Thus, the "light path 11" encompasses the entire diffuse volume. As described below, interference is generated in this volume (i.e., in the light path) such that the receiver receives the scattered light caused by the interference.

[0040] The measuring device 1 according to the invention is hereinafter also referred to as a sensor or a turbidity sensor. The turbidity sensor 1 is arranged on a container, in particular on a pipeline or a barrel or an open channel. This is achieved via fastening means such as flanges. The turbidity sensor can also be arranged on immersion or quick-change fittings, etc. The medium 3 to be measured is located in the container; in particular, the medium 3 flows through the container. The medium 3 to be measured is mainly a liquid - often process and waste water. However, the device is also used for fresh water, especially drinking water. When used on a container, the turbidity sensor is arranged substantially perpendicular to the longitudinal axis of the container, such as a pipe. The turbidity sensor includes a housing 5. Stainless steel, plastic or ceramic can be used as the material of the device 1, in particular the material of the housing 5. The materials are selected such that they are suitable for the given application.

[0041] The device 1 includes at least one light source 2 and a receiver 4. The light source and the receiver are connected to a data processing unit 10 (not shown) via an electrical connection. The data processing unit 10 determines the measured value to be determined, i.e., the turbidity, based on the electrical signal of the scattered light. A calibration model is used to determine this measurement, which combines measurement information about the intensity of the received scattered light and uses this measurement information to determine the turbidity. For example, Figure 2a / Figure 2b shows the relationship between the measured scattered light intensity and the corresponding turbidity. In Figure 1 the electrical connection of the data processing unit 10 to the light source 2 and the receiver 4 is shown as a dashed line.

[0042] The receiver 4 is designed, for example, as a photodiode, which generates a receiver signal, such as a photocurrent or a photovoltage, from the received light (usually: an electrical signal).

[0043] The light source 2 (usually an LED) emits light towards the medium 3. In this regard, in the context of the present application, "light" should not be limited to the visible range of the electromagnetic spectrum, but should be understood as electromagnetic radiation of any wavelength, especially also in the ultraviolet (UV) and infrared (IR) wavelength ranges. In particular, a wavelength of 860 nm is to be used. The device can also include other optical components in the beam path after the light source, such as filters or one or more lenses. Corresponding components are also arranged on the receiver side, on the photodiode 4.

[0044] In Figure 2a the measured scattered light intensity is the same for two different turbidity values, so it is not possible to distinguish between turbid and clear water purely using the measurement (prior art).

[0045] In the claimed measuring device 1 and the claimed program, a distinct differentiation between media of low turbidity (e.g., clear water) and liquids of very high turbidity or absorption (e.g., contaminated, black wastewater with a high particle content) is achieved by generating defined interferences in the light path 11 of the sensor 1 and evaluating the response to these interferences.

[0046] Since the claimed solution eliminates the ambiguity of the signal curve, the measuring range of the sensor 1 can be significantly increased because even the decreasing part of the signal curve can be measured for high turbidity. While for prior art turbidity sensors, only the measured values on one side of the curve can be used, in this case, since the scattered light intensity measured can be clearly assigned to one of the two sides of the signal curve, both sides of the curve can be used. This leads on the one hand to a significantly larger measuring range. On the other hand, the assignment of the measured scattered light intensity to an incorrect turbidity value is avoided. Figure 2b It is shown that the left and right halves of the scattered light intensity / turbidity curve can be used.

[0047] Furthermore, the discreteness of the signal curve simplifies the user's model selection. For example, if the sensor detects a highly contaminated medium, models optimized for transparent media (e.g., drinking water) can be excluded in advance or actively blocked by the software of the sensor 1.

[0048] The interference in the above-mentioned light path 11 can be generated by the interference unit 15. For example, this can be done temporarily.

[0049] One embodiment includes an interference element 12, which reflects and / or scatters and is designed as a movable external element in the light path 11 of the sensor 1, which is, for example, fixedly positioned. As described above, the light path 11 includes the entire diffusive volume of the scattered light, especially in the case of generating an interference, such that the receiver receives the scattered light caused by the interference.

[0050] Figure 3 An embodiment is shown. For example, a wiper cleaning unit mounted on the sensor 1 or its wiper arm and wiper lip can be guided in a defined manner over the optical window 7, and the measurement signal and / or the response to this optical interference can be evaluated. The wiper serves as the interference unit 15 and / or as the interference element 12 that reflects and / or scatters. In this way, the cleaning of the optical window 7 can be advantageously combined with the detection of the degree of contamination of the medium 3.

[0051] Furthermore, any other movable element (plate, wing, etc.) can be temporarily pivoted into the light path of the sensor. The movement of the interference element 12 into the light path 11 is symbolically shown by the Figure 4a / Figure 4b vertical arrow in. Figure 4a The effect in a less turbid medium is shown,Figure 4b Shows the effects in a more turbid medium. These effects are represented by arrows of different thicknesses for the excitation light 8 and the reflected light 6. In a very turbid medium ( Figure 4b ), the light is more strongly absorbed and less / no light reaches the receiver 4.

[0052] In all figures, thick arrows mean "more" light and thin arrows mean "less" light. In some figures, the arrows representing light are broken. Of course, this is only to be understood symbolically. Physically, the light attenuates along the arrow (or spherically).

[0053] When using a fitting made of a transparent or partially transparent material, the above-mentioned movable element 12 can also be mounted outside the medium 3 to generate interference. In this embodiment, the sensor 1 must be positioned such that it detects the interference element 12 through the wall in the medium 3 with low turbidity (e.g., clear water) and / or responds to the interference in its light path 11 by measuring an increase in the signal.

[0054] Figure 5a / Figure 5b An embodiment with an air purification unit 16 attached to the sensor head is shown, which serves as the interference unit 15. Figure 5a The design is shown; Figure 5b The design is symbolically shown with bubbles. The air purification unit 16 temporarily blows bubbles into the light path 11 of the sensor 11. The subsequent measurement signals with and without interference are evaluated.

[0055] In one embodiment, the sensor 1, as a movable element, is temporarily moved to a fixedly positioned interference unit 15, which is reflective (reference numeral 12). For example, the sensor 1 can be moved or rotated via a movable holding device 20 such that the wall of a container or barrel temporarily interferes with the signal in the light path 11 in order to evaluate the response to this interference. Figure 6a Shows the effects in a less turbid medium, Figure 6b Shows the effects in a more turbid medium. The movement of the sensor 1 into the light path 11 by means of the movable element 20 is symbolized by the Figure 6a / Figure 6b horizontal arrow in.

[0056] Figure 7a / Figure 7b An embodiment is shown. This temporarily generates an electro-optical interference, which causes different responses in the fixedly positioned sensor 1 depending on the medium 3. Figure 7a Shows the effects in a less turbid medium 3, Figure 7bShows the effect in a more turbid medium 3. For example, the light source 17 (such as an LED) can be temporarily turned on as the interference element 15, which results in a significant increase in the measured value in the transparent medium, while the measured value hardly changes or only slightly changes in the severely contaminated medium.

[0057] As an example of the interference temporarily introduced into the optical path 11 with different states (with or without interference) as described above, the interference can be introduced permanently. This has the advantage of not requiring additional moving elements, controls, etc.

[0058] For example, the sensor can be positioned close enough to the container, barrel or fitting wall 18. In clean water, a defined offset of, for example, +1 FNU is generated by scattering or reflection on the pool wall. The wall 18 then serves as the interference element 15 ("scattering or reflection unit"). This is shown in Figure 8a and Figure 8b shown. Figure 8a Shows the effect in a less turbid medium 3, Figure 8b the effect in a more turbid medium 3.

[0059] Then, since the reflection on the tank wall does not penetrate to the detector of the sensor, a severely contaminated medium can be clearly detected by a measured value below this minimum. Of course, the "setup" offset can be corrected in the signal processing chain so that the correct turbidity value is output in the final measured value display.

[0060] In one embodiment, the interference is generated in the form of a short-term active manipulation of the turbidity value (of a liquid with a defined turbidity; reference numeral 14). As the secondary medium distribution unit 19 of the interference unit 15, the medium 14 is added. This is shown in Figure 9a - Figure 9d shown. Figure 9a / Figure 9b Shows the effect in a less turbid medium 3, Figure 9c / Figure 9d shows the effect in a more turbid medium 3. Figure 9a / Figure 9c Shows the case without interference; Figure 9b / Figure 9d shows the case with interference by adding a second medium with a defined turbidity.

[0061] Figure 10 Shows the scattered light intensity measured compared to the turbidities T1 and T2 and the effect of introducing ultrapure water 14 according to the embodiment in Figure 9a - Figure 9d For example, adding ultrapure water in a medium with low turbidity ( Figure 9a / Figure 9b ) results in a decrease in the measured value (reference numeral 21), while in a severely contaminated medium ( Figure 9c / Figure 9dThe measured value increases when ultrapure water is added (reference numeral 22).

[0062] List of reference numerals

[0063] 1 Measuring device

[0064] 2 Light source

[0065] 3 Medium

[0066] 4 Photodiode

[0067] 5 Housing

[0068] 6 Scattered light

[0069] 7 Optical window

[0070] 8 Excitation light

[0071] 9 Reflected light

[0072] 10 Data processing unit

[0073] 11 Light path

[0074] 12 Interference element

[0075] 13 Interference light

[0076] 14 Ultrapure water / secondary medium

[0077] 15 Interference unit

[0078] 16 Air purification unit

[0079] 17 Light source

[0080] 18 Scattering or reflection unit

[0081] 19 Secondary medium distribution unit

[0082] 20 Moving element

[0083] 21 Decrease in measured value

[0084] 22 Increase in measured value

[0085] P Scattering point

[0086] T1 Turbidity

[0087] T2 Turbidity

[0088] α Measuring angle

Claims

1. A method for determining a scattered light parameter in a medium by means of a measuring device (1), the measuring device (1) being in particular a turbidity sensor, the scattered light parameter being in particular turbidity, the method comprising the following steps: - emitting excitation light (8) into the medium (3), wherein the excitation light (8) is scattered in the medium (3); - receiving light (6) scattered in the medium (3) and generating a light path (11) of the excitation light (8) and the scattered light (6); - generating interference in the optical path (11); - receiving light (6) now scattered in said medium (3); and - taking into account the influence of the interference, determining the scattered light parameter, in particular the turbidity, based on the scattered light (6).

2. The method according to claim 1, in, The interference is reflection, scattering or another optical interaction.

3. The method according to claim 1 or 2, further comprising the following steps: - moving an interference element (12), in particular an element which reflects and / or scatters the excitation light (8), into the light path (11) such that the interference is generated.

4. The method according to claim 1 or 2, further comprising the following steps: - moving the measuring device (1) in the direction of the interference element (12), in particular in the direction of the element reflecting and / or scattering the excitation light (8), so that the excitation light (8) is reflected and / or scattered thereon, thereby generating the interference.

5. The method according to claim 1 or 2, further comprising the following steps: in, The interference is designed as electro-optical interference and, in addition to the scattered light (6), interference light (13) is received.

6. The method according to any one of the preceding claims, in, The interference is generated temporarily and regularly.

7. The method according to claim 1 or 2, further comprising the following steps: - Ultrapure water or a secondary medium (14) with defined turbidity is introduced into the medium (3).

8. A measuring device (1), in particular a turbidity sensor, for carrying out the method according to any of the preceding claims, for determining a scattered light parameter, in particular turbidity, in a medium (3), the measuring device (1) comprising: - at least one light source (2) which emits excitation light (8) into the medium (3) and in the direction of the surface of the medium; - at least one photodiode (4) which receives light (6) scattered in the medium (3) and converts it into an electrical signal, thereby creating a light path (11) from the light source (2) through the medium (3) and to the photodiode (4); - an interference unit (15) designed to generate interference in the light path (11); as well as A data processing unit (10) for determining the scattered light parameter, in particular the turbidity, from the electrical signal based on the scattered light, taking into account the influence of the interference.

9. The measuring device (1) according to the preceding claim, in, The light source (2) emits the excitation light (8) into the medium (3) via an optical window. wherein the photodiode (4) receives light (6) scattered by the medium (3) via the same window (7) or a separate optical window (7), The interference unit (15) is designed as a reflective and / or scattering interference element (12), in particular as a wiper for cleaning the optical window (7). Therein, the interference element (12) generates the interference when the interference element (12) is positioned in front of the optical window (7) and thus in the light path (11).

10. The measuring device (1) according to claim 9, in, The interference unit (15) can be arranged outside the medium (3).

11. The measuring device (1) according to claim 8, in, The light source (2) emits excitation light (8) into the medium (3) via the optical window (7). wherein the photodiode (4) receives light scattered from the medium (3) via the same window (7) or a separate optical window (7), The interference unit (15) is designed as an air purification unit (16) and blows air in the direction of the optical window (7). Therein, the air purification unit (16) generates the interference when air is located in front of the optical window (7) and therefore in front of the light path (11).

12. The measuring device (1) according to claim 8, in, The interference unit (15) is designed as a moving element (20) and moves the measuring device (1) in the direction of the interference element (12), in particular in the direction of the element reflecting and / or scattering the excitation light (8), so that the excitation light (8) is reflected and / or scattered thereby to generate the interference.

13. The measuring device (1) according to claim 8, in, The interference unit (15) is designed as an interference light source (17) and emits interference light in the direction of the photodiode (4), thereby generating the interference.

14. The measuring device (1) according to claim 8, in, The interference unit (15) is designed as a scattering or reflecting unit (18), and the measuring device (1) with the light source (2) is positioned relative to the scattering or reflecting unit (18) in such a way that a permanent measured value shift occurs at least for slightly or not at all turbid media (3).

15. The measuring device (1) according to claim 8, in, The interference unit (15) is designed as a secondary medium distribution unit (19) which introduces ultrapure water or a secondary medium (14) with a defined turbidity into the medium (3) and generates the interference.

Images