SENSOR ARRANGEMENT FOR DETERMINING TURBIDITY

Abstract

The present disclosure relates to a sensor arrangement for determining the turbidity of a liquid medium. The sensor arrangement includes a sensor section with at least one light source for sending transmission light into a measuring chamber, and at least one receiver associated with the light source for receiving reception light from the measuring chamber, wherein the transmission light is converted into the reception light in the measuring chamber by the medium by means of scattering at a measurement angle, and the reception light received by the receiver is a measure of the turbidity. The reception light is back reflected at a reflection element in contact with the medium, whereby an optical path from the light source through the measuring chamber to the reflection element and from the reflection element through the measuring chamber to the receiver results.

Claims

1. A sensor arrangement for determining the turbidity of a liquid medium, comprising: a sensor section including at least one light source for sending transmission light into a measuring chamber, and at least one receiver associated with the light source for receiving reception light from the measuring chamber, wherein the transmission light is converted into the reception light in the measuring chamber by the medium due to scattering at a measurement angle, and the reception light received by the receiver is a measure of the turbidity of the medium, wherein the reception light is back reflected at a reflection element, the reflection element in contact with the medium, and wherein an optical path is defined from the light source through the measuring chamber to the reflection element and from the reflection element through the measuring chamber to the receiver.

2. The sensor arrangement of claim 1, wherein a portion of the transmission light is additionally back reflected at the reflection element.

3. The sensor arrangement of claim 2, wherein the sensor section further includes at least one solid angle filter that directs the light scattered by the medium and back reflected by the reflection element onto the receiver, and wherein only light scattered at the measurement angle passes through the solid angle filter.

4. The sensor arrangement of claim 3, wherein the solid angle filter includes at least one optical beam-shaping component.

5. The sensor arrangement of claim 3, wherein the solid angle filter comprises a hollow cylinder having an inner diameter and a length, hollow cylinder structured to absorb at least a portion of the reception light and, due to the inner diameter and the length, to allow only the portion of the reception light that was scattered at the measurement angle to pass therethrough.

6. The sensor arrangement of claim 3, wherein the solid angle filter comprises a block including a number of openings, each opening having an opening diameter and each opening being spaced from adjacent openings by a distance, the block structured to absorb at least a portion of the reception light and, due to the number of openings, the opening diameter of the openings and the distance of the openings from one another, to allow only the portion of the reception light that was scattered at the measurement angle to pass therethrough.

7. The sensor arrangement of claim 1, wherein the sensor section includes the reflection element.

8. The sensor arrangement of claim 1, wherein transmission light is scattered at a first measurement angle and at least one second measurement angle, and the sensor arrangement further comprises a first solid angle filter for the first measurement angle and at least one second solid angle filter for the second measurement angle.

9. The sensor arrangement of claim 8, the sensor arrangement comprising a first receiver for reception light scattered at the first measurement angle and a second receiver for reception light scattered at the second measurement angle.

10. The sensor arrangement of claim 8, the sensor arrangement comprising a first light source disposed to emit transmission light into the measuring chamber at a first angle of incidence and a second light source disposed to emit transmission light into the measuring chamber at a second angle of incidence, wherein transmission light of the first light source is scattered at a first measurement angle and the transmission light of the second light source is scattered at the second measurement angle.

11. The sensor arrangement of claim 8, wherein the reflection element includes a first section and at least one second section, and wherein the first section back reflects light at a first angle of reflection, and the second section back reflects light at a second angle of reflection in the direction of the first or second solid angle filters respectively.

12. The sensor arrangement of claim 1, wherein the reflection element is disposed at an angle of other than 90 to the transmission light.

13. The sensor arrangement of claim 1, the sensor arrangement further comprising a first window and at least a second window, wherein the first window is disposed at or between the sensor section and the measuring chamber and is transparent to the transmission light, and wherein the at least second window is disposed at or between the measuring chamber and the sensor section and is transparent to the reception light.

14. The sensor arrangement of claim 13, wherein the first window and the second window are configured as a common window.

15. The sensor arrangement of claim 13, the sensor arrangement further comprising one window per measurement angle, wherein the respectively scattered reception light passes through the corresponding window.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present disclosure is explained in more detail with reference to the following figures. These show:

[0034] FIG. 1 shows a conventional turbidity sensor arrangement according to the prior art.

[0035] FIGS. 2A and 2B show the two basic principles of the present disclosure.

[0036] FIGS. 3A-3G show a step-by-step explanation of the principle of the sensor arrangement for determining turbidity according to the present disclosure.

[0037] FIG. 4 shows the sensor arrangement according to the present disclosure in an embodiment with respect to several measurement angles.

[0038] FIGS. 5A and 5B show the sensor arrangement according to the present disclosure in two additional embodiments with respect to the reflection section.

[0039] FIGS. 6A-6F show a sensor arrangement according to the present disclosure with sensor section and reflection section in different embodiments of both.

[0040] FIG. 7 shows the sensor arrangement according to the present disclosure in another embodiment with respect to the reflection element.

[0041] FIGS. 8A-8C show the sensor arrangement according to the present disclosure in another embodiment with respect to the windows.

[0042] In the figures, the same features are marked with the same reference symbols.

DETAILED DESCRIPTION

[0043] The measurement method of a turbidity sensor is known and has already been explained above. The basic features are explained only briefly, although these basic features are mostly not shown in the figures. A sensor arrangement 20 according to the present disclosure, as shown in FIG. 3A, is also referred to as turbidity sensor below. The turbidity sensor is arranged on a container, for example, on a pipe. Such an embodiment may be carried out via fastening means, such as a flange. The turbidity sensor can also be arranged on an immersion or quick-change fitting or the like. The medium 3 to be measured is located in the pipe; for example, the medium 3 flows through the pipe. The medium 3 to be measured is mostly a liquid often process and waste water. The arrangement is, however, also used in fresh water, such as drinking water. The turbidity sensor is arranged substantially orthogonally to the longitudinal axis of the pipe. The turbidity sensor comprises a housing. Stainless steel, plastic, or a ceramic can be used as materials for the arrangement 20, including for the housing. As already mentioned, the turbidity sensor is often used in drinking water or waste water. The materials are selected such that they are suitable for use in, for example, waste water. The plastic must therefore be an appropriately durable plastic, such as PTFE or the like.

[0044] The arrangement 20 comprises at least one light source 1 and a receiver 2. Via electrical connections, the light source and the receiver are connected to a control unit (not shown). The control unit is, for example, a measuring transducer, control center, etc.

[0045] The receiver 2 may be designed, for example, as a photo diode, which generates a receiver signal, such as a photocurrent or a photovoltage, in response to the light received.

[0046] The light source 1, for example an LED, sends light toward the medium 3. In this respect, light within the meaning of the present disclosure is not to be limited to the visible range of the electromagnetic spectrum, but is to be understood as electromagnetic radiation of any wavelength, for example, also in the ultraviolet (UV) and in the infrared (IR) wavelength range. A wavelength of 860 nm may be used.

[0047] In the following, only the turbidity sensor according to the present disclosure will be discussed. FIGS. 2A-7 do not show optical windows, for the sake of clarity. Various implementation options for the optical windows are illustrated in FIG. 8 and explained below. For the same reason, the optical refraction at the transition from the window to the medium is also not illustrated or discussed. Nonetheless, the optical refraction is considered to reduce the present disclosure to practice.

[0048] The boundaries are thus through the windows (not shown) transparent to arriving light. A back-reflection plane or a reflection element 11 within the meaning of the present disclosure (details below) is illustrated in the figures as a dashed surface. Light is back reflected on these dashed surfaces. Reflected light is denoted by the suffix R in the reference symbols. As used herein, back reflected light may alternately be deflected or diffracted by the back-reflection plane or a reflection element 11.

[0049] Light already scattered is illustrated in the figures as a dashed line.

[0050] The present disclosure is based upon two principles, which are explained in FIGS. 2A and 2b: reflection and solid angle filtering. In this respect, the solid angle filtering can be considered facultative, but advantageous. The law of reflection (angle of incidence=angle of reflection) applies to at least one certain angle here, the scattered light angle , also called measurement angle . In a first embodiment, the reflection element is thus a mirror. A solid angle filter 12 is a passive component, in which only light with a certain angle of incidence range is allowed to pass through. Such light rays are indicated with the reference symbol 12a. Light with an angle of incidence outside the pass range is blocked by the solid angle filter, by either absorption, deflection, etc. Such light beams are marked with the reference symbol 12b. A simple solid angle filter is, for example, a black pipe that defines by its measurements with respect to inner diameter and length a certain angle range that is allowed to pass through, whereas other angles are absorbed by the material. Generally, the solid angle filter is a hollow cylinder that absorbs at least a portion of the reception light. In this case, the hollow cylinder can, as mentioned, have a circle as base, whereby the hollow cylinder is designed as a pipe. However, the base may just as well be angular, such as square, generally rectangular, or comprising any number of corners. Due to its inner diameter and its length, the hollow cylinder allows only reception light to pass through that was scattered at the measurement angle. Even though the term inside diameter connotes a circular base be used, in the context of the present disclosure, it is to mean the minimum distance between two opposite surfaces when the base is not circular. In an embodiment with regard to the hollow cylinder, pinholes with a distance defining the measurement angle can also be seen. Another advantageous embodiment of a solid angle filter for the present disclosure is a black, absorbing base block, in which long, thin holes are introduced at narrow distances. The block is defined by the number of openings, the inner diameter of the openings, and the distance of the openings from one another. In the same way, one or more glass fibers or glass fiber bundles can be arranged accordingly. Another alternative is to be seen in a film stack. A solid angle filter can also comprise one or more beam-shaping components, such as lenses. Naturally, a combination of the embodiments presented is also possible.

[0051] The sensor arrangement for determining turbidity according to the present disclosure, in its entirety, has the reference symbol 20. Its functionality will now be explained. The arrangement 20 comprises at least one sensor section S with the light source 1 and the light receiver 2.

[0052] First, transmission light 7 is generated using a light source 1, which transmission light may be focused and aligned by one or more optical components (apertures, lenses, etc.; not shown). This light 7 then passes through an optical window (not shown) to first arrive in a measuring chamber 5 with the medium 3 and then on a reflection element 11, here shown as a simple mirroring surface. In this regard, see FIG. 3A. The reflection element 11 is thus in contact with the medium 3. A reflection section R comprises the reflection element 11. In a first embodiment, the reflection section R is not mechanically connected to the sensor section S. This first embodiment comprises at least two variants. In the first variant, the reflection section R with the reflection element 11 is formed by a second housing section of the sensor arrangement 20, said housing section being associated with the sensor section S and arranged, for example, on the opposite side of the container. In a second variant, the reflection section R with the reflection element 11 is formed by the container itself by its wall, for example.

[0053] In the next step, the transmission light 7 is reflected at the same angle as it arrives; see FIG. 3B (or FIG. 2B) with the reflected transmission light 7.R.

[0054] In the medium 3, the transmission light 7 coming from the light source 1 is scattered by particles at different scattering points P at all solid angles. The distribution of the scattering intensity to the different solid angles is, in the process, dependent upon the particles. In FIG. 3C, only the scattered light that is scattered at the measurement angle, i.e., for example, =25, is indicated. This scattered light is again deflected by the reflection element 11 toward the light source 1 or toward the receiver 2. In the process, the angle is preserved (law of reflection), i.e., the angle of incidence equals the angle of reflection. By the scattering, the transmission light 7 is converted into reception light 8. The converted light is referred to as reception light 8 in the present disclosure. The reception light reflected by the reflection element 11 is marked with the reference symbol 8.R. Light already scattered is shown with dashed lines.

[0055] As explained above, this preservation of the angle is decisive, since the reflected transmission light 7.R also strikes particles and is there scattered at additional scattering points P.R, as shown in FIG. 3D. As a result of the preservation of the angle, all scattered light rays that were scattered at the same angle run parallel. As above, light already scattered is here also shown dashed. In FIG. 3D, the upper three beams, marked with reference symbol 8.R1, are formed by reflected transmission light 7.R. On the other hand, the lower three beams, marked with reference symbol 8.R2, are first scattered, and then reflected. In both cases, parallel reception light 8.R is formed.

[0056] Naturally, both on the path to the reflection element 11 and on the path from the reflection element 11, light is scattered at other angles, i.e., not at the measurement angle . These light rays are marked with reference symbol 13, in this regard, as shown in FIG. 3E.

[0057] As shown in FIG. 3F, the rays that were scattered at an angle other than the measurement angle are now extinguished by the solid angle filter 12, whereas all rays that were scattered at the measurement angle pass through the solid angle filter 12. Then, these rays arrive, possibly by means of a fiber-optic cable 10, at the receiver 2, where they are converted into a corresponding measurement signal, from which the turbidity value is calculated.

[0058] As mentioned, two possible paths starting from the light source 1 can be distinguished. In one, light is first scattered, then back reflected (reference symbol 8.R2). In the other, light is first back reflected and then scattered (reference symbol 8.R1). In the case mentioned last, a distinction cannot be made between back reflection and light scattering at the measurement angle and light scattering of the incident transmission light 7 at the associated supplementary angle . The supplementary angle is defined as 180 less the measurement angle .

[0059] FIG. 3F shows an arrangement in which the transmission light scattered after the back reflection (i.e. 8.R1) is not directed onto the detector. On the other hand, FIG. 3G shows an arrangement that directs both types 8.R1 and 8.R2 onto the receiver.

[0060] The frequent case of the 90 scattered light measurement, i.e. =90, is to be mentioned again with reference to FIG. 5B. The limitation mentioned above does not occur in this case, since ==90. The light yield at the receiver is improved, since the light that is scattered at the scattering point arrives twice at the receiver (once from the incident light and once from the back-reflected light). The same applies if a general scattering angle and the associated supplementary angle do not have to be distinguished, e.g., in scattering media that have the same emission characteristics for these two angles, or in cases where this distinction is not required. For 90 scattered light measurements and for cases where a distinction between a scattered light angle and its supplementary angle does not need to be made, a higher measurement signal results, and thus a more sensitive measurement.

[0061] In the process, the solid angle filter 12 used filters, not precisely the measurement angle , but light that arrives within a tolerance range, i.e., for example, within 10, including 5, or including 2.5.

[0062] In another embodiment, as shown in FIG. 4, the sensor arrangement 20 can determine turbidity not just at a single measurement angle, but also at several measurement angles .sub.1, .sub.2. In the following, this is explained using two different measurement angles, but additional measurement angles can, naturally, also be used. For this purpose, the sensor arrangement 20 respectively comprises, for each measurement angle .sub.1, .sub.2, a solid angle filter 12.sub.1, 12.sub.2. Each measurement angle .sub.1, .sub.2 is then associated with its own receiver 2.sub.1, 2.sub.2.

[0063] The distribution of the measurement of different angles to a light source 1 and several receivers 2.sub.1, 2.sub.2 can also be reversed, so that light from several light sources 1.sub.1, 1.sub.2 is sent exclusively at different angles .sub.1, .sub.2 and received by a single receiver 2 (not shown). A combination of the two possibilities is also conceivable, wherein several light sources 1.sub.1, 1.sub.2 and several receivers 2.sub.1, 2.sub.2 are used.

[0064] FIGS. 5A and 5B show that the reflection element 11 does not necessarily need to be aligned in parallel to the optical window. It can be advantageous for some applications to deviate from the parallelism. In other words, the reflection element 11 is arranged at an angle other than 90 relative to the transmission light 7.

[0065] FIG. 5A shows an angle <90. In this case, in contrast to the previous figures, the transmission light 7 is not directly back reflected again, but, as reflected light 7.R, is scattered at an angle or arrives then at the solid angle filter 12 at an angle.

[0066] In FIG. 5B, the reflection element 11 is divided into different sections D.sub.1 and D.sub.2. The arriving light is back reflected on these sections D.sub.1, D.sub.2 at an angle of reflection . An angle of reflection of about =90 is shown. Only by the division into different sections is it possible with certain measurement angles to use the effect of the back reflection. In the example, light at a measurement angle of =90 can first be back reflected by section D.sub.2, which is arranged at an angle =45.

[0067] As explained in the previous examples and above, the reflection element 11 in the reflection section R can be arranged to be offset from the sensor section S. The reflection section R and the sensor section S can, however, also be designed as one piece. In other words, the sensor arrangement 20 then comprises the sensor section S and the reflection section R. These embodiments are shown in FIGS. 6C-6F.

[0068] Furthermore, different, advantageous embodiments are possible, as long as the law of reflection (angle of incidence=angle of reflection) is complied with for at least one definite angle . FIGS. 6A-6F show certain possible embodiments with different angles of the reflection element 11 relative to the transmission light 7 or different sections D.

[0069] FIG. 6F, which shows four sections D.sub.1, D.sub.2, D.sub.3, D.sub.4 of the reflection element 11, will be explained briefly. By using several sections with respectively different arrangements with respect to the transmission light 7, and thus with different angles .sub.1, .sub.2, .sub.3, different measurement angles .sub.1, .sub.2, .sub.3 can be realized in a relatively space-saving manner. Despite the different measurement angles .sub.1, .sub.1, .sub.3, the reception light 8.sub.1.R, 8.sub.2.R, 8.sub.3.R is back reflected parallel to the transmission light 7, due to the different sections D.sub.1, D.sub.2, D.sub.3 with the arrangement with the angles .sub.1, .sub.2, .sub.3. The respectively associated solid angle filters 12.sub.1, 12.sub.2, 12.sub.3 and receivers 2.sub.1, 2.sub.2, 2.sub.3 are arranged along the longitudinal direction, and, for example, offset. In this way, the sensor arrangement 20 is indeed longer but not wider. This further results in a more flexible and simpler construction.

[0070] In another embodiment, the reflection element 11 is implemented as a prism, for example, a reflection prism or the like. In this regard, see FIG. 7.

[0071] As mentioned, the sensor arrangement 20 respectively comprises an optical window 6 in the boundary area between the sensor section S and the measuring chamber 5, as well as between the measuring chamber 5 and the reflection section R. For example, the optical window 6 toward the medium 3 can be designed according to different, advantageous possibilities: a window 6 for incoming transmission light 7 and all reflected reception light 8 (see FIG. 8A). Or, a common window 6a for incoming and directly-reflected transmission light 7, 7.R and another window 6b for reflected reception light 8 (see FIG. 8B). Or, for each reception light 8.sub.1.R, 8.sub.2.R that was scattered at different measurement angles .sub.1, .sub.2, its own window 6.sub.1, 6.sub.2 (see FIG. 8C).

[0072] Generally, the window 6 is made of, for example, sapphire glass, quartz glass, or the like. The window 6 and the housing of the sensor arrangement 20 are rigidly connected to one another. For example, the window 6 and the housing are connected to one another in a medium-tight manner. The window 6 and the housing are, for example, connected to one another by gluing, soldering, etc.