Surface-scattering type turbidimeter and method for measuring turbidity

Abstract

To provide a surface-scattering type turbidimeter and turbidity measuring method that improve the accuracy of turbidity measurement by changing the positional relationship between the light irradiation position on the liquid surface and the light-receiving element.SOLUTION: A measurement tank stores the liquid to be measured. A light source irradiates the surface of the liquid stored in the measurement tank with light. A light-receiving element receives scattered light generated in the measurement tank by the light emitted from the light source. A changing mechanism changes the relative position, with respect to the horizontal component of the light traveling direction at the liquid surface, between the irradiation position of the light from the light source on the liquid surface and the light-receiving element. A turbidity value calculation unit calculates the turbidity value of the liquid to be measured on the basis of the scattered light received by the light-receiving element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface scattering type turbidimeter and a turbidity measurement method. [Background technology]

[0002] Turbidity meters are known that optically measure the turbidity of liquids such as those used in water purification plants and industrial water. Turbidity is an index that indicates the degree of cloudiness of a liquid. Measurement methods used in turbidity meters are classified into transmitted light, scattered light, transmitted scattered light, surface scattered light, and integrating sphere methods, for example.

[0003] Among these measurement methods, the surface scattered light method utilizes the fact that the intensity of scattered light is proportional to the concentration of turbidity in the liquid. In the surface scattered light method, light emitted from a light source is reflected by the turbidity of the liquid being measured stored in a measurement tank, generating scattered light. The scattered light is received by a light-receiving element and converted into an electrical signal corresponding to the light intensity, and the turbidity is calculated based on the electrical signal.

[0004] As a surface scattered light type turbidity meter, a turbidity meter that calculates turbidity by comparative calibration using scattered light of two different wavelengths has been proposed. Also proposed is a turbidity meter that measures turbidity using forward scattered light. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-144868 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-300858 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional surface scattering turbidity meters that measure turbidity using the surface scattered light method, the relative positions of the light source, measurement tank, and light receiving element are fixed, and the light from the light source is irradiated at the same position in the liquid to be measured stored in the measurement tank to determine the turbidity. Because the relative positions of the light source, measurement tank, and light receiving element are fixed, it is difficult to adjust the optical path length in the liquid, making it difficult to measure the turbidity with high accuracy according to the state of the liquid to be measured.

[0007] In this regard, even with turbidity meters that use two lights of different wavelengths or that measure turbidity using forward scattered light, the relative positions of the light source, measurement tank, and light-receiving element are fixed, making it difficult to measure turbidity with high accuracy according to the state of the liquid being measured.

[0008] One aspect of the present invention improves the accuracy of turbidity measurements. [Means for solving the problem]

[0009] A turbidity measuring device according to one aspect has the following components: a measurement tank for storing a liquid to be measured; a light source for irradiating light onto the liquid surface of the liquid to be measured stored in the measurement tank; a light receiving element for receiving scattered light generated in the measurement tank by the light from the light source; a change mechanism for changing the relative position of the light receiving element with respect to the component of the light traveling direction that is horizontal to the liquid surface and the irradiation position of the light from the light source on the liquid surface; and a turbidity value calculation unit for calculating the turbidity value of the liquid to be measured based on the scattered light received by the light receiving element. [Effects of the Invention]

[0010] According to the present invention, the accuracy of turbidity measurement can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a configuration diagram of a turbidity meter according to a first embodiment. [Figure 2] 10A and 10B are diagrams showing scattered light when the liquid surface is brought close to a light receiving element. [Figure 3] FIG. 10 is a diagram showing scattered light when the liquid surface is moved away from the light receiving element. [Figure 4] FIG. 10 is a diagram showing the relationship between the height of the measurement tank and linearity. [Figure 5] FIG. 10 is a diagram showing the correspondence between a plurality of turbidity thresholds and positions in the Z-axis direction. [Figure 6] FIG. 10 is a configuration diagram of a turbidity meter according to a second embodiment. [Figure 7] 10 is a flowchart of a turbidity value calculation process performed by a turbidimeter according to the second embodiment. [Figure 8] FIG. 2 is a hardware configuration diagram of a control terminal device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of a surface scattering type turbidity meter and a turbidity measurement method will be described with reference to the drawings. The same elements are designated by the same reference numerals, and duplicated descriptions will be omitted as appropriate. Furthermore, each embodiment can be appropriately combined within a range that does not cause inconsistencies.

[0013] (Embodiment 1) (Overall composition) 1 is a configuration diagram of a turbidity meter according to embodiment 1. The turbidity meter 1 includes a measuring tank 10, an illuminance control circuit 21, a light source 22, a light receiving circuit 30, lenses 41 and 42, and a control terminal device 50.

[0014] Light source 22 according to this embodiment emits light in a specific direction toward the liquid surface of the liquid to be measured stored in measurement tank 10. The direction of light from light source 22 according to this embodiment is fixed. The light emitted from light source 22 is condensed by lens 41 and travels toward the liquid surface of the liquid to be measured stored in measurement tank 10.

[0015] Light emitted from light source 22 and collected by lens 41 is irradiated at a fixed angle toward the liquid surface, which is kept constant in measurement tank 10, as shown by path R1 in Fig. 1. Light source 22 is, for example, a tungsten lamp.

[0016] The illuminance of the light source 22 changes due to the influence of deterioration of the light source 22, fluctuations in the power supply voltage, etc. Therefore, the illuminance control circuit 21 controls the illuminance of the light source 22 to eliminate the influence of deterioration of the light source 22, fluctuations in the power supply voltage, etc. In this way, the illuminance control circuit 21 keeps the illuminance of the light emitted from the light source 22 constant.

[0017] The light receiving circuit 30 is a circuit that converts the light scattered by the liquid to be measured into a current and outputs a current signal proportional to the scattered light to the control terminal device 50. The light receiving circuit 30 has a light receiving element 31, an amplifier 32, and a current conversion unit 33.

[0018] The light receiving element 31 is, for example, a silicon photodiode. The light receiving element 31 receives scattered light from the liquid to be measured that is focused by the lens 42. The light receiving element 31 detects the scattered light that it receives. The light receiving element 31 outputs an optical signal based on the detected light to the amplifier 32.

[0019] The amplifier 32 receives an input of an optical signal from the light receiving element 31. Then, the amplifier 32 amplifies the intensity of the optical signal. After that, the amplifier 32 outputs an optical signal of the scattered light with amplified intensity to the control terminal device 50 and the current conversion unit 33.

[0020] The current converter 33 receives the optical signal of the scattered light, the intensity of which has been amplified, as input from the amplifier 32. The current converter 33 then converts the optical signal into a current signal. The current converter 33 then outputs the current signal, into which the optical signal of the scattered light has been converted, to the control terminal device 50 as a current signal indicating the intensity of the scattered light.

[0021] A dark chamber 11 and an elevating mechanism 12 are attached to the measurement tank 10. A test liquid adjusted to a constant pressure continuously flows into the measurement tank 10. The measurement tank 10 then allows the flowing test liquid to overflow, maintaining a constant liquid level. The measurement tank 10 discharges the overflowed test liquid to the outside of the measurement tank 10.

[0022] A coordinate system for the measurement tank 10 is now set. The X-axis represents the axis representing the component of the light emitted from the light source 22 that is horizontal to the liquid surface in the direction of travel. Here, the direction of the component of the light emitted from the light source 22 that is horizontal to the liquid surface in the direction of travel is defined as the positive X-axis. The normal to the liquid surface is defined as the Z-axis. Here, the direction in which light is reflected from the liquid surface, i.e., the direction from the liquid surface to the light receiving element 31, is defined as the positive Z-axis. The direction perpendicular to both the X-axis and the Z-axis is defined as the Y-axis. In other words, the Y-axis is the axis normal to the plane formed by the path R1 along which the light emitted from the light source 22 travels and the X-axis. Here, the direction pointing into the plane of the paper in FIG. 1 is defined as the positive Y-axis.

[0023] Part of the light emitted from light source 22 is reflected at position P1, the intersection point between the light and the liquid surface, as shown by path R2, and part of the light penetrates into the liquid as shown by path R3. FIG. 1 shows a case where position P1, the position where the light is reflected on the liquid surface, coincides with the center of light-receiving element 31 in the Z direction, i.e., a case where the X and Y coordinates of position P1 and the center of light-receiving element 31 coincide. Here, the Z coordinate of measuring tank 10 is set to 0 when position P1, the intersection point between the light emitted from light source 22 and the liquid surface shown in FIG. 1, coincides with the center of light-receiving element 31 in the Z direction. Hereinafter, the state of FIG. 1 where the Z coordinate of measuring tank 10 is 0 will be referred to as the "reference state."

[0024] The reflected light reflected from the liquid surface proceeds to the dark chamber 11, where it is absorbed and disappears. In addition, the transmitted light that penetrates into the liquid is also absorbed and disappears by the liquid to be measured. This reduces the influence of reflected light and transmitted light on turbidity measurement.

[0025] On the other hand, light that penetrates into the liquid from the liquid surface generates scattered light that travels from the liquid surface toward the positive direction of the Z axis due to the turbidity (turbidity components) of the liquid being measured and the liquid surface. The scattered light is collected by lens 42, which is located opposite the liquid surface, i.e., in the positive direction of the Z axis from the liquid surface, as shown by path R4, and is then irradiated onto light-receiving element 31.

[0026] The more positions where scattered light is generated in the liquid surface area that overlaps with the light-receiving element 31 in the Z-axis direction, the more light is incident on the light-receiving element 31. In other words, when considering the overall intensity of scattered light, the size of the area where the positions where scattered light is generated overlap with the light-receiving element 31 in the Z-axis direction is important. Therefore, for simplicity, the illustration shows scattered light traveling in the positive Z direction from its source position. For example, in the reference state, scattered light generated at position P on the liquid surface travels toward the center of the light-receiving element 31. Furthermore, position P2, which generates scattered light toward the end of the light-receiving element 31 in the positive X-axis direction, is the deepest position where scattered light is generated in the reference state. In the following explanation, the liquid surface area that overlaps with the light-receiving element 31 in the Z-axis direction is referred to as the "range visible from the light-receiving element 31." In reality, scattered light travels in all directions, and scattered light that is directed toward the lens 42 is collected and irradiated onto the light-receiving element 31.

[0027] The lifting mechanism 12 is a mechanism that moves the measuring tank 10 in the Z-axis direction. The lifting mechanism 12 can move the measuring tank 10 in both the positive Z-axis direction and the negative Z-axis direction. The lifting mechanism 12 according to this embodiment changes the position of the measuring tank 10 in the Z-axis direction when a user manually turns a gear. However, the lifting mechanism 12 may also be a mechanism that moves the measuring tank 10 in the Z-axis direction using a drive source such as a motor.

[0028] When the lifting mechanism 12 moves the measurement tank 10 in the positive Z-axis direction, the liquid level in the measurement tank 10 approaches the light receiving element 31. When the lifting mechanism 12 moves the measurement tank 10 in the negative Z-axis direction, the liquid level in the measurement tank 10 moves away from the light receiving element 31. The lifting mechanism 12 can move the measurement tank 10 in the Z-axis direction in 0.5 mm intervals, for example.

[0029] Fig. 2 is a diagram showing scattered light when the liquid level is brought closer to the light receiving element. Fig. 2 shows a state in which measurement tank 10 has been moved a distance L1 in the positive Z-axis direction from the reference state using lifting mechanism 12. That is, in Fig. 2, the liquid level has come closer to light receiving element 31 by a distance L1 from the reference state.

[0030] In this case, the intersection of the light emitted from light source 22 and the liquid surface, which is the position of the light on the liquid surface, is position P11, which is shifted from position P1 in the negative X-axis direction. Therefore, as shown in FIG. 2, scattered light generated at a position deeper than position P2, which is the deepest point of scattered light generation in the reference state, is incident on light-receiving element 31. Specifically, position P12 is the position that coincides with the center of light-receiving element 31 in the Z-axis direction, and position P13 is the deepest point of scattered light generation from which scattered light enters light-receiving element 31. In other words, scattered light generated by light whose optical path length in the liquid is longer than in the reference state is incident on light-receiving element 31. Furthermore, in this case, the number of positions of scattered light generation within the range visible to light-receiving element 31 increases compared to the reference state, so scattered light from more positions in the liquid is incident on light-receiving element 31, resulting in a higher measured light intensity compared to the reference state.

[0031] Fig. 3 is a diagram showing scattered light when the liquid level is moved away from the light-receiving element. Fig. 3 shows a state in which measurement tank 10 has been moved a distance L2 in the negative Z-axis direction from the reference state using lifting mechanism 12. That is, in Fig. 3, the liquid level is moved a distance L2 away from light-receiving element 31 from the reference state.

[0032] In this case, the intersection of the light emitted from light source 22 and the liquid surface is position P21, which is moved from position P1 in the positive X-axis direction. In this case, position P22 coincides with the center of light-receiving element 31 in the Z direction, and the point at which scattered light originates that is deepest within the range visible to light-receiving element 31 is position P23. In other words, the longest optical path length in the liquid of scattered light incident on light-receiving element 31 is shorter than in the reference state. Furthermore, in this case, the number of positions at which scattered light originates within the range visible to light-receiving element 31 is reduced compared to the reference state, and therefore the number of positions at which scattered light is incident on light-receiving element 31 is reduced, resulting in a decrease in the amount of measured light compared to the reference state.

[0033] The lifting mechanism 12 is an example of a "changing mechanism." The lifting mechanism 12 changes the relative position between the irradiation position on the liquid surface of light from the light source 22 and the light receiving element 31, that is, the relative position with respect to the component of the light traveling direction that is horizontal to the liquid surface (i.e., with respect to the X-axis direction). From another perspective, the lifting mechanism 12 changes the position in the X-axis direction of the intersection (illumination position) of the light from the light source 22 and the liquid surface. More specifically, the lifting mechanism 12 is a mechanism that changes the above relative position by changing the distance between the measurement tank 10 and the light receiving element 31, and in particular, moves the measurement tank 10 to change the distance between the measurement tank 10 and the light receiving element 31.

[0034] The control terminal device 50 calculates and displays a turbidity value from a current signal that represents the intensity of scattered light. The control terminal device 50 has a turbidity value calculation unit 51 and a display unit 52. The control terminal device 50 is an example of a "turbidity value calculation device."

[0035] The turbidity value calculation unit 51 receives an input of a current signal indicating the intensity of scattered light from the current conversion unit 33. The turbidity value calculation unit 51 has a mathematical formula (1) in which a constant K is set according to the liquid to be measured. The turbidity value calculation unit 51 calculates the turbidity value of the liquid to be measured using the acquired current signal indicating the intensity of scattered light and mathematical formula (1). The turbidity value calculation unit 51 then outputs the calculated turbidity value of the liquid to be measured to the display unit 52. In this way, the turbidity value calculation unit 51 calculates the turbidity value of the liquid to be measured based on the scattered light received by the light receiving element 31.

[0036] The display unit 52 receives the input of the turbidity value of the liquid to be measured from the turbidity value calculation unit 51. Then, the display unit 52 displays the acquired turbidity value of the liquid to be measured on a display or the like to provide the information to the user.

[0037] (Relationship between the intersection of the light irradiated from the light source and the liquid surface and linearity) Here, the intensity of scattered light in the measurement tank 10 has the relationship shown in the following formula (1): where K is a constant, S is turbidity, Q is the amount of light from the light source, and L is the intensity of scattered light. L = K × Q × S (1)

[0038] In this way, the scattered light intensity L depends on the light source light intensity Q and the turbidity S. Therefore, if the light source light intensity Q is constant, then in theory, the turbidity S is proportional to the scattered light intensity L. The degree to which this relationship between turbidity S and scattered light intensity L approaches a linear relationship (proportional relationship) is called linearity. In other words, the closer the relationship between turbidity S and scattered light intensity L is to a linear relationship (proportional relationship), the higher the linearity, and the further it is from a linear relationship, the lower the linearity. Because the turbidity meter 1 measures the scattered light intensity L and calculates the turbidity S using equation (1), the smaller the variation in linearity, the higher the accuracy of estimating turbidity S using equation (1).

[0039] Here, in the surface scattering type turbidity meter 1, the tendency of linearity changes depending on a slight positional shift of the intersection point between the light irradiated from the light source 22 and the liquid surface. Specifically, if the position of the intersection point between the light irradiated from the light source 22 and the liquid surface is shifted in the X-axis direction, the linearity fluctuates significantly. In contrast, if the position of the intersection point between the light irradiated from the light source 22 and the liquid surface is shifted in the Y-axis direction, the amount of scattered light detected decreases, but the fluctuation in linearity is small and the effect on turbidity calculation is within an acceptable range. This is because when the position of the intersection point is shifted in the X-axis direction, the path length in the water where the scattered light is generated changes significantly, affecting the linearity.

[0040] Furthermore, when measuring the turbidity of a liquid to be measured using scattered light, the turbidity will absorb the scattered light. Therefore, if the liquid to be measured is highly turbid, the turbidity will absorb a lot of scattered light. Here, high turbidity means, for example, 250 NTU (Nephelometric Turbidity Unit) or more. On the other hand, if the liquid to be measured is low in turbidity, the turbidity will absorb less scattered light. Here, low turbidity means, for example, 0-250 NTU.

[0041] Therefore, when the liquid to be measured is highly turbid, it is preferable that the optical path length of the light that generates the scattered light in the liquid is short in order to suppress the influence of absorption of scattered light by turbid matter. Conversely, when the liquid to be measured is low in turbidity, the influence of absorption of scattered light by turbid matter is small, so the optical path length of the light that generates scattered light in the liquid can be long. Furthermore, in both cases of high and low turbidity, it is preferable that the amount of measurement light is large.

[0042] Here, when the position P1 of the intersection between the light irradiated from light source 22 and the liquid surface in the reference state is used as a reference and the position of the intersection between the light irradiated from light source 22 and the liquid surface is shifted in the negative X-axis direction as shown in Figure 2, the optical path length in the liquid within the range visible to light receiving element 31 becomes longer than in the reference state.

[0043] When the liquid to be measured is highly concentrated, the optical path length in the liquid within the range visible to the light receiving element 31 increases, which increases the effect of absorption of scattered light by turbidity and reduces the signal level. Therefore, when the liquid to be measured is highly concentrated, linearity decreases.

[0044] Conversely, when the concentration of the liquid to be measured is low, the amount of measurement light increases when the intersection point is shifted toward the negative X-axis as shown in Figure 2. Therefore, when the concentration of the liquid to be measured is low, linearity improves.

[0045] In contrast, when the position of the intersection of the light irradiated from light source 22 and the liquid surface is shifted in the positive X-axis direction as shown in Figure 3, using position P1 of the intersection of the light irradiated from light source 22 and the liquid surface in the reference state as a reference, the optical path length in the liquid within the range visible to light receiving element 31 becomes shorter.

[0046] When the liquid to be measured is highly concentrated, the optical path length in the liquid visible from the light receiving element 31 becomes shorter, and the effect of absorption of scattered light by turbidity decreases, and surface scattering becomes dominant. Therefore, when the liquid to be measured is highly concentrated, linearity improves.

[0047] Conversely, when the concentration of the liquid to be measured is low, the amount of measurement light decreases when the intersection point is shifted in the positive X-axis direction as shown in Figure 3. Therefore, when the concentration of the liquid to be measured is low, the linearity decreases.

[0048] FIG. 4 shows the relationship between the height of the measurement tank 10 and linearity. The relationship between the height of the measurement tank 10 and linearity can be summarized as shown in Table 101 in FIG. 4. Specifically, as shown in Table 101, increasing the height of the measurement tank 10 shifts the intersection of the optical axis and the liquid level in the negative X-axis direction, decreasing linearity if the liquid being measured is highly turbid and improving linearity if the liquid being measured is low turbidity. Conversely, decreasing the height of the measurement tank 10 shifts the intersection of the optical axis and the liquid level in the positive X-axis direction, increasing linearity if the liquid being measured is highly turbid and improving linearity if the liquid being measured is low turbidity.

[0049] From the above, when the turbidity of the liquid to be measured is equal to or greater than a predetermined high turbidity threshold, it is preferable to move the Z coordinate of measurement tank 10 in the negative direction from the reference state. Conversely, when the turbidity of the liquid to be measured is less than a predetermined low turbidity threshold equal to or less than the liquid to be measured, it is preferable to move the Z coordinate of measurement tank 10 in the positive direction from the reference state.

[0050] (Turbidity measurement by adjusting the height of the measuring tank) Here, we will explain turbidity measurement by adjusting the height of the measurement tank 10. When starting turbidity measurement, the measurement tank 10 is set to the height of the reference state shown in Figure 1. Then, the user causes the turbidity meter 1 to calculate the turbidity value of the liquid to be measured in the reference state and display it on the display unit 52.

[0051] Next, the user checks the turbidity value of the test liquid under the reference condition by referring to the display unit 52. This turbidity value of the test liquid under the reference condition, which is measured first, is called the "provisional turbidity value." The user then determines whether the provisional turbidity value is equal to or greater than the high turbidity threshold, and whether the provisional turbidity value is less than the low turbidity threshold.

[0052] If the turbidity value of the provisional measurement is equal to or greater than the high turbidity threshold, the user uses the lifting mechanism 12 to move the measurement tank 10 in the negative Z-axis direction to a predetermined high turbidity measurement position. After that, with the measurement tank 10 moved to the high turbidity measurement position, the user causes the turbidity meter 1 to calculate the turbidity value of the liquid to be measured and display it on the display unit 52. The user then regards the provided turbidity value of the liquid to be measured as the actual turbidity value of the liquid to be measured.

[0053] On the other hand, if the turbidity value of the provisional measurement is less than the low turbidity threshold, the user uses the lifting mechanism 12 to move the measurement tank 10 in the positive Z-axis direction to a predetermined low turbidity measurement position. After that, with the measurement tank 10 moved to the low turbidity measurement position, the user causes the turbidity meter 1 to calculate the turbidity value of the liquid to be measured and display it on the display unit 52. The user then regards the provided turbidity value of the liquid to be measured as the actual turbidity value of the liquid to be measured.

[0054] Furthermore, if the turbidity value of the provisional measurement is equal to or greater than the low turbidity threshold and less than the high turbidity threshold, the user can set the turbidity value of the provisional measurement as the actual turbidity value of the liquid to be measured.

[0055] The low turbidity threshold and the high turbidity threshold may be the same turbidity value. In this case, the user determines the position of the measurement tank 10 by comparing one turbidity threshold with the provisionally measured turbidity value. In this case, the user does not need to use the provisionally measured turbidity value measured at the position of the measurement tank 10 in the reference state as the actual turbidity value of the liquid to be measured.

[0056] In the turbidity meter 1 according to this embodiment, the position in the X-axis direction of the intersection of the optical axis and the liquid surface is changed by changing the position in the Z-axis direction of the measurement tank 10. However, other mechanisms can also be used for the turbidity meter 1 as long as the relative position of the irradiation position on the liquid surface of light from the light source 22 and the light receiving element 31 relative to the component of the light traveling direction horizontal to the liquid surface can be changed between high and low turbidity cases.

[0057] For example, the turbidity meter 1 may change the position in the X-axis direction of the intersection between the light from the light source 22 and the liquid surface by changing the direction of the optical axis of the light source 22. In this case, the turbidity meter 1 has a change mechanism that changes the relative position by changing the direction of the optical axis of the light from the light source.

[0058] Furthermore, the turbidity meter 1 may change the position in the X-axis direction of the intersection between the optical axis and the liquid surface by moving the light source 22 in at least one of the Z-axis direction and the X-axis direction. In this case, the turbidity meter 1 has a change mechanism that changes the relative position by changing the position of the light source 22.

[0059] Alternatively, the turbidity meter 1 may move the light receiving element 31 in the X-axis direction. In this case, the turbidity meter 1 has a change mechanism that moves the light receiving element 31 to change the relative position and also changes the distance between the measurement tank 10 and the light receiving element 31.

[0060] As described above, the turbidity meter 1 according to this embodiment can change the position of the intersection between the optical axis of the light emitted from the light source 20 and the liquid surface. This allows the emitted light to be scattered over an appropriate optical path length in the liquid when the liquid to be measured is highly turbid or low turbid, making it possible to improve linearity in both high and low turbidity cases. This therefore makes it possible to improve the accuracy of turbidity measurement.

[0061] (Variation) In Example 1, the position of the measurement tank 10 was determined using one high turbidity threshold and one low turbidity threshold. However, in both the case of a high turbidity measurement liquid and the case of a low turbidity measurement liquid, the position may be changed in stages depending on the turbidity.

[0062] 5 is a diagram showing the correspondence relationship between a plurality of turbidity thresholds and positions in the Z-axis direction. For example, a user has a table 200 shown in FIG. 5. In table 200, the turbidity value decreases as one moves upward on the paper. Furthermore, a turbidity threshold corresponding to a reference position does not need to be set, and is therefore omitted from table 200.

[0063] Turbidity thresholds #1 to #3 in FIG. 5 are thresholds on the low turbidity side. A turbidity value on the low turbidity side is, for example, a turbidity value of 250 NTU or less. Turbidity thresholds #3 to #1 are set as thresholds, and Z(1) to Z(3), which are positions of measurement tank 10 in the positive Z-axis direction, are associated with them. Z(1) to Z(3) are spaced apart, for example, by several millimeters, and indicate positions that increase in the Z-axis direction in this order. Turbidity threshold #3 can also be the low turbidity threshold in embodiment 1. In this case, measurement tank 10 is moved in stages according to turbidity values ​​below the low turbidity threshold.

[0064] Turbidity thresholds ##1 to ##3 are thresholds on the high turbidity side. A high turbidity value refers to, for example, a turbidity value of 250 NTU or higher. Turbidity thresholds ##1 to ##3 are each set as a threshold, and are associated with Z(-1) to Z(-3), which are positions of measurement tank 10 in the negative Z-axis direction. Z(-1) to Z(-3) are also spaced apart, for example, by several millimeters, and indicate successively lower positions in the Z-axis direction. The reference position on table 200 is the Z-axis position of measurement tank 10 in the reference state shown in FIG. 1. Turbidity threshold ##1 can also be the high turbidity threshold in embodiment 1. In this case, measurement tank 10 is moved in stages according to turbidity values ​​above the high turbidity threshold.

[0065] The user checks the turbidity value obtained by provisional measurement under standard conditions, which is displayed on the display unit 52. Then, the user compares the provisional turbidity value with the turbidity threshold values ​​#1 to #3 and ##1 to ##3.

[0066] If the turbidity value from the provisional measurement is greater than or equal to turbidity threshold #2 and less than turbidity threshold #3, the user refers to table 200 and confirms that Z(1) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates lifting mechanism 12 to move measurement tank 10 from the reference position in the positive Z-axis direction, setting the Z coordinate of measurement tank 10 to Z(1). Furthermore, if the turbidity value from the provisional measurement is greater than or equal to turbidity threshold #1 and less than turbidity threshold #2, the user refers to table 200 and confirms that Z(2) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates lifting mechanism 12 to move measurement tank 10 from the reference position in the positive Z-axis direction, setting the Z coordinate of measurement tank 10 to Z(2). Furthermore, if the turbidity value from the provisional measurement is less than turbidity threshold #1, the user refers to table 200 and confirms that Z(3) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates the lifting mechanism 12 to move the measuring tank 10 from the reference position in the positive Z-axis direction, and the Z coordinate of the measuring tank 10 becomes Z(3).

[0067] Furthermore, if the turbidity value of the provisional measurement is equal to or greater than the turbidity threshold ##1 and less than the turbidity threshold ##2, the user refers to table 200 and confirms that Z(-1) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates lifting mechanism 12 to move measurement tank 10 from the reference position in the negative Z-axis direction, setting the Z coordinate of measurement tank 10 to Z(-1). Furthermore, if the turbidity value of the provisional measurement is equal to or greater than the turbidity threshold ##2 and less than the turbidity threshold ##3, the user refers to table 200 and confirms that Z(-2) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates lifting mechanism 12 to move measurement tank 10 from the reference position in the negative Z-axis direction, setting the Z coordinate of measurement tank 10 to Z(-2). Furthermore, if the turbidity value of the provisional measurement is equal to or greater than the turbidity threshold ##3, the user refers to table 200 and confirms that Z(-3) corresponds to the Z coordinate of measurement tank 10. Therefore, the user operates the lifting mechanism 12 to move the measuring tank 10 from the reference position in the negative Z-axis direction, and set the Z coordinate of the measuring tank 10 to Z(-3).

[0068] After moving the measurement tank 10 in the Z-axis direction to match the turbidity value of the provisional measurement as described above, the user causes the turbidity meter 1 to measure the liquid to be measured and calculate the turbidity value. The user then sets the calculated turbidity value as the actual turbidity value of the liquid to be measured.

[0069] As described above, the turbidity meter 1 according to this modification can adjust the position of the measurement tank 10 in the Z-axis direction in stages according to the turbidity value. This allows the irradiated light to be scattered over an appropriate optical path length in the liquid according to the state of the liquid being measured more precisely, thereby improving linearity. This in turn improves the accuracy of turbidity measurement.

[0070] (Embodiment 2) FIG. 6 is a configuration diagram of a turbidity meter according to embodiment 2. The turbidity meter 1 according to this embodiment automatically adjusts the position of the measurement tank 10 in the Z-axis direction according to the turbidity value of the provisional measurement. The components in FIG. 6 that have the same reference numerals as those in FIG. 1 have the same functions as those in embodiment 1. The following explanation will mainly focus on the automatic adjustment of the position of the measurement tank 10 in the Z-axis direction, and the explanation of the operation of the components similar to those in embodiment 1 may be omitted.

[0071] In the turbidity meter 1 according to this embodiment, the control terminal device 50 further includes a control unit 53, as shown in FIG.

[0072] At the start of turbidity measurement, measurement tank 10 is set to the height of the reference state shown in Figure 1. Therefore, turbidity value calculation unit 51 calculates a provisionally measured turbidity value using scattered light in measurement tank 10 in the reference state. Next, after control unit 53 moves measurement tank 10 in the Z-axis direction to match the provisionally measured turbidity value, turbidity value calculation unit 51 receives an input of a current signal indicating the intensity of scattered light and recalculates the turbidity value. Then, turbidity value calculation unit 51 outputs the recalculated turbidity value of the measurement target liquid to display unit 52, causing the remeasured turbidity value of the measurement target liquid to be displayed on a display or the like.

[0073] Furthermore, when the turbidity value calculation unit 51 receives a notification of the turbidity value determination from the control unit 53, it outputs the provisionally measured turbidity value to the display unit 52, causing it to be displayed on a display or the like as the turbidity value of the liquid to be measured.

[0074] Here, the provisionally measured turbidity value is an example of a "first turbidity value." Furthermore, the turbidity value measured by the turbidity value calculation unit 51 after the measurement tank 10 has been moved according to the provisionally measured turbidity value is an example of a "second turbidity value." The turbidity value calculation unit 51 then calculates the first turbidity value of the liquid to be measured at a predetermined position in the measurement tank 10, and calculates the second turbidity value of the liquid to be measured after the measurement tank 10 has been moved from the predetermined position.

[0075] Control unit 53 has a communication path between it and lifting mechanism 12, and sends a command signal via the communication path to drive lifting mechanism 12 to change the position of measurement tank 10 in the Z-axis direction. Control unit 53 also has table 200, which associates the turbidity threshold value shown in FIG. 5 with the position of measurement tank 10 in the Z-axis direction, for example.

[0076] The control unit 53 acquires the provisionally measured turbidity value from the turbidity value calculation unit 51. Next, the control unit 53 compares the provisionally measured turbidity value with the turbidity threshold values ​​#1 to #3 and ##1 to ##3, which are threshold values ​​registered in the table 200.

[0077] If the turbidity value of the provisional measurement is equal to or greater than turbidity threshold #2 and less than turbidity threshold #3, control unit 53 drives lifting mechanism 12 to move measurement tank 10 in the positive Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(1). If the turbidity value of the provisional measurement is equal to or greater than turbidity threshold #1 and less than turbidity threshold #2, control unit 53 drives lifting mechanism 12 to move measurement tank 10 in the positive Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(2). If the turbidity value of the provisional measurement is less than turbidity threshold #1, control unit 53 drives lifting mechanism 12 to move measurement tank 10 in the positive Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(3).

[0078] Furthermore, if the turbidity value of the provisional measurement is equal to or greater than turbidity threshold ##1 and less than turbidity threshold ##2, control unit 53 drives lifting mechanism 12 to move measurement tank 10 in the negative Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(-1). If the turbidity value of the provisional measurement is equal to or greater than turbidity threshold ##2 and less than turbidity threshold ##3, control unit 53 drives lifting mechanism 12 to move measurement tank 10 in the negative Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(-2). If the turbidity value of the provisional measurement is equal to or greater than turbidity threshold ##3, control unit 53 drives lifting mechanism 12 and operates lifting mechanism 12 to move measurement tank 10 in the negative Z-axis direction from the reference position, setting the Z coordinate of measurement tank 10 to Z(-3).

[0079] Furthermore, if the provisionally measured turbidity value is equal to or greater than the turbidity threshold #3 and less than the turbidity threshold ##1, the control unit 53 notifies the turbidity value calculation unit 51 of the turbidity value determination that the provisionally measured turbidity value is the actual turbidity value.

[0080] In this way, the control unit 53 causes the lifting mechanism 12, which is a change mechanism, to move the measurement tank 10 from a predetermined position based on the first turbidity value. Furthermore, the turbidity threshold #1 can be a low turbidity threshold, and the turbidity threshold ##1 can be a high turbidity threshold. That is, when the first turbidity value is equal to or greater than a predetermined high turbidity threshold, the control unit 53 moves the measurement tank 10 in a direction away from the light receiving element 31 in stages according to the first turbidity value. Furthermore, when the first turbidity value is less than the low turbidity threshold, the control unit 53 moves the measurement tank 10 in a direction toward the light receiving element 31 in stages according to the first turbidity value.

[0081] Although the above description has been given for the case where three or more turbidity thresholds are used, control unit 53 may adjust the position of measurement tank 10 in the Z-axis direction using a high turbidity threshold and a low turbidity threshold, as in embodiment 1. That is, control unit 53 can move measurement tank 10 away from light-receiving element 31 when the first turbidity value is equal to or greater than a predetermined high turbidity threshold, and can move measurement tank 10 closer to light-receiving element 31 when the first turbidity value is less than a low turbidity threshold that is equal to or less than the high turbidity threshold.

[0082] Here, control unit 53 may use the same value as the high turbidity threshold and the low turbidity threshold. In this case, control unit 53 determines the position of measurement tank 10 in the Z-axis direction depending on whether the turbidity is equal to or greater than that one turbidity threshold.

[0083] (Turbidity value calculation process flow) Fig. 7 is a flowchart of the turbidity value calculation process performed by the turbidity meter according to embodiment 2. Fig. 7 illustrates an example of the process for adjusting the position of the measurement tank 10 in the Z-axis direction using a high turbidity threshold value and a low turbidity threshold value. Next, the flow of the turbidity value calculation process performed by the turbidity meter 1 according to embodiment 2 will be described with reference to Fig. 7.

[0084] The measuring tank 10 is placed at a position in a reference state (step S1).

[0085] The light source 22 irradiates the liquid surface of the liquid to be measured stored in the measurement tank 10 with light via the lens 41 (step S2).

[0086] The light receiving element 31 receives the light emitted from the light source 22 on the liquid surface and scattered light in the liquid via the lens 42 (step S3).

[0087] The light receiving element 31 detects the received scattered light. The amplifier 32 amplifies the intensity of the scattered light. The current conversion unit 33 converts the optical signal of the scattered light into a current signal indicating the intensity of the scattered light and outputs it to the control terminal device 50. The turbidity value calculation unit 51 calculates the turbidity value of the liquid to be measured using the current signal indicating the intensity of the scattered light (step S4).

[0088] The turbidity value calculation unit 51 determines whether the measurement that has been carried out is a provisional measurement (step S5).

[0089] If the executed measurement is a provisional measurement (step S5: Yes), the turbidity value calculation unit 51 outputs the provisionally measured turbidity value to the control unit 53. The control unit 53 determines whether the provisionally measured turbidity value is equal to or greater than the high turbidity threshold value (step S6).

[0090] If the provisionally measured turbidity value is equal to or greater than the high turbidity threshold value (step S6: Yes), the control unit 53 moves the measurement tank 10 in the negative Z-axis direction using the lifting mechanism 12 to the high turbidity measurement position (step S7). After that, the turbidity value calculation process returns to step S2.

[0091] On the other hand, if the provisionally measured turbidity value is less than the high turbidity threshold (step S6: No), the control unit 53 determines whether the provisionally measured turbidity value is less than the low turbidity threshold (step S8).

[0092] If the provisionally measured turbidity value is less than the low turbidity threshold value (step S6: Yes), the control unit 53 moves the measurement tank 10 in the positive Z-axis direction using the lifting mechanism 12 to the low turbidity measurement position (step S9). After that, the turbidity value calculation process returns to step S2.

[0093] On the other hand, if the turbidity value of the provisional measurement is equal to or greater than the low turbidity threshold (step S6: Yes), the control unit 53 notifies the turbidity value calculation unit 51 of the determination of the turbidity value. If the turbidity value calculation unit 51 is notified of the determination of the turbidity value by the control unit 53 or if the measurement that has been performed is not a provisional measurement (step S5: No), the turbidity value calculation unit 51 displays the calculated turbidity value on the display unit 52 as the turbidity value of the actual liquid to be measured (step S10).

[0094] As described above, the turbidity meter 1 according to this embodiment performs a provisional measurement of the turbidity value using the measurement tank 10 in the reference state, and automatically adjusts the position of the measurement tank 10 in the Z-axis direction based on the calculation result of the provisionally measured turbidity value. The turbidity meter 1 then recalculates the turbidity value using the measurement tank 10 in the adjusted position, and provides the recalculated value to the user as the turbidity value of the actual ratio measurement liquid.

[0095] This allows the Z-axis position of the measurement tank 10 to be automatically and accurately adjusted in stages to match the turbidity value without requiring any user intervention. This allows the scattered light to be obtained with an appropriate optical path length in the liquid, based on the irradiated light that is more precisely tailored to the state of the liquid being measured, thereby improving linearity. This reduces the burden on the user and reduces human error, while improving the accuracy of turbidity measurements.

[0096] As described above, in the second embodiment, the control unit 53 automatically adjusts the position of the measurement tank 10 in the Z-axis direction in accordance with the turbidity value of the provisional measurement. However, if the turbidimeter 1 has a mechanism for changing the orientation of the optical axis of the light source 22, the control unit 53 may control such a mechanism to automatically change the orientation of the optical axis of the light source 22 in accordance with the turbidity value of the provisional measurement. Alternatively, if the turbidimeter 1 has a mechanism for changing the position of the light source 22, the control unit 53 may control such a mechanism to automatically change the position of the light source 22 in accordance with the turbidity value of the provisional measurement. Alternatively, if the turbidimeter 1 has a mechanism for changing the position of the light-receiving element 31, the control unit 53 may control such a mechanism to automatically change the position of the light-receiving element 31 in accordance with the turbidity value of the provisional measurement.

[0097] (system) The information including the processing procedures, control procedures, specific names, various data and parameters shown in the above documents and drawings can be changed arbitrarily unless otherwise specified.

[0098] Furthermore, the components of each device shown in the figure are functional concepts and do not necessarily have to be physically configured as shown. In other words, the specific form of distribution and integration of each device is not limited to that shown. In other words, all or part of them can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

[0099] Furthermore, each processing function performed by each device can be realized, in whole or in part, by a CPU (Central Processing Unit) and a program analyzed and executed by the CPU, or can be realized as hardware using wired logic.

[0100] (Hardware) Next, an example of the hardware configuration of the control terminal device 50 will be described. Fig. 8 is a hardware configuration diagram of the control terminal device. As shown in Fig. 8, the control terminal device 50 has a processor 91, a memory 92, a hard disk 93, a network interface 94, and a display device 95. The processor 91 is also connected to the memory 92, the hard disk 93, the network interface 94, and the display device 95 via a bus.

[0101] The network interface 94 is a network interface card or the like, and is used for communication with other information processing devices. The display device 95 is a monitor, display, or the like, and realizes the function of the display unit 52.

[0102] The hard disk 93 is an auxiliary storage device. The hard disk 93 may store, for example, the table 200 shown in Fig. 5. The hard disk 93 also stores various programs including programs for realizing the functions of the turbidity value calculation unit 51 and the control unit 53.

[0103] The processor 91 reads out various programs stored in the hard disk 93, loads them into the memory 92, and executes them. In this way, the processor 91 realizes the functions of the turbidity value calculation unit 51 and the control unit 53.

[0104] In this way, the control terminal device 50 operates as an information processing device that executes various processing methods by reading and executing a program. The control terminal device 50 can also realize functions similar to those of the above-described embodiment by reading the program from a recording medium using a media reader and executing the read program. Note that the program referred to here is not limited to being executed by the control terminal device 50. For example, the present invention can also be applied in the same way to cases where another computer or server executes a program, or where these execute a program in cooperation with each other.

[0105] This program can be distributed via a network such as the Internet. In addition, this program can be recorded on a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, a magneto-optical disk (MO), or a digital versatile disk (DVD), and can be executed by being read from the recording medium by a computer.

[0106] Some examples of combinations of the disclosed technical features are set out below.

[0107] (1) a measurement tank for storing the liquid to be measured; a light source that irradiates light onto the liquid surface of the liquid to be measured stored in the measurement tank; a light-receiving element that receives scattered light generated in the measurement tank by light from the light source; a change mechanism for changing a relative position of the light receiving element with respect to a horizontal component of the light travelling direction with respect to the liquid surface; and a turbidity value calculation unit that calculates the turbidity value of the liquid to be measured based on the scattered light received by the light receiving element; A surface scattering type turbidity meter comprising: (2) The surface scattering type turbidity meter according to (1), wherein the change mechanism changes the relative position by changing the distance between the measurement tank and the light receiving element. (3) The surface scattering type turbidity meter according to (2), wherein the change mechanism is a mechanism that moves the measurement tank to change the distance between the measurement tank and the light receiving element. (4) the turbidity value calculation unit calculates a first turbidity value of the liquid to be measured when the relative position is in a first state, and calculates a second turbidity value of the liquid to be measured when the relative position is in a second state; a control unit that controls the change mechanism so as to change the relative position from the first state to the second state based on the first turbidity value. The surface scattering type turbidimeter according to (3) above. (5) The surface scattering type turbidity meter described in (4) is characterized in that, when the first turbidity value is equal to or greater than a high turbidity threshold, the control unit controls the change mechanism to change the relative position so as to shorten the optical path length of the light in the measured liquid, and when the first turbidity value is less than a low turbidity threshold that is equal to or less than the high turbidity threshold, the control unit controls the change mechanism to change the relative position so as to lengthen the optical path length. (6) The surface scattering type turbidity meter described in (5) is characterized in that, when the first turbidity value is equal to or greater than the high turbidity threshold, the control unit controls the change mechanism to change the relative position so that the optical path length is gradually shortened according to the first turbidity value, and when the first turbidity value is less than the low turbidity threshold, the control unit controls the change mechanism to change the relative position so that the optical path length is gradually lengthened according to the first turbidity value. (7) The surface scattering type turbidity meter according to (2), wherein the change mechanism is a mechanism that moves the light receiving element to change the distance between the measurement tank and the light receiving element. (8) The surface scattering type turbidity meter described in any one of (1) to (7) is characterized in that the change mechanism changes the relative position by changing the direction of the optical axis of the light from the light source. (9) The surface scattering type turbidimeter according to any one of (1) to (8), wherein the change mechanism changes the relative position by changing the position of the light source. (10) A turbidity measurement method using a surface scattering type turbidimeter having a measurement tank for storing a liquid to be measured, a light source for irradiating light onto the liquid surface of the liquid to be measured stored in the measurement tank, and a light receiving element for receiving scattered light generated in the measurement tank by the light from the light source, a change mechanism for changing a relative position between the irradiation position of the light from the light source on the liquid surface and the light receiving element with respect to a component of the traveling direction of the light that is horizontal to the liquid surface; The turbidity value of the liquid to be measured is calculated by a turbidity value calculation device based on the scattered light received by the light receiving element. A turbidity measurement method characterized by: [Explanation of symbols]

[0108] 1 Turbidity meter 10 Measuring tank 11 Darkroom 12 Lifting mechanism 21 Illuminance control circuit 22 Light source 30 Photodetector circuit 31 Photodetector 32 Amplifier 33 Current conversion section 41,42 Lens 50 Control terminal device 51 Turbidity value calculation unit 52 Display section 53 Control Unit

Claims

1. a measurement tank for storing the liquid to be measured; a light source that irradiates light onto the liquid surface of the liquid to be measured stored in the measurement tank; a light-receiving element that receives scattered light generated in the measurement tank by light from the light source; a change mechanism for changing a relative position of the light receiving element with respect to a horizontal component of the light travelling direction with respect to the liquid surface; and a turbidity value calculation unit that calculates the turbidity value of the liquid to be measured based on the scattered light received by the light receiving element; A surface scattering type turbidity meter comprising:

2. 2. The surface scattering type turbidity meter according to claim 1, wherein the change mechanism changes the relative position by changing the distance between the measurement tank and the light receiving element.

3. 3. The surface scattering type turbidimeter according to claim 2, wherein the change mechanism is a mechanism that moves the measuring tank to change the distance between the measuring tank and the light receiving element.

4. the turbidity value calculation unit calculates a first turbidity value of the liquid to be measured when the relative position is in a first state, and calculates a second turbidity value of the liquid to be measured when the relative position is in a second state; a control unit that controls the change mechanism so as to change the relative position from the first state to the second state based on the first turbidity value.

4. The surface scattering type turbidimeter according to claim 3.

5. The surface scattering type turbidity meter described in claim 4, characterized in that when the first turbidity value is equal to or greater than a high turbidity threshold, the control unit controls the change mechanism to change the relative position so that the optical path length of the light in the measured liquid becomes shorter, and when the first turbidity value is less than a low turbidity threshold that is equal to or less than the high turbidity threshold, the control unit controls the change mechanism to change the relative position so that the optical path length becomes longer.

6. The surface scattering type turbidity meter according to claim 5, wherein the control unit controls the change mechanism to change the relative position so that the optical path length is gradually shortened according to the first turbidity value when the first turbidity value is equal to or greater than the high turbidity threshold, and controls the change mechanism to change the relative position so that the optical path length is gradually lengthened according to the first turbidity value when the first turbidity value is less than the low turbidity threshold.

7. 3. The surface scattering type turbidity meter according to claim 2, wherein the change mechanism is a mechanism that moves the light receiving element to change the distance between the measurement tank and the light receiving element.

8. 2. The surface scattering type turbidimeter according to claim 1, wherein the change mechanism changes the relative position by changing the direction of the optical axis of the light from the light source.

9. 2. The surface scattering type turbidimeter according to claim 1, wherein the change mechanism changes the relative position by changing the position of the light source.

10. A turbidity measurement method using a surface scattering type turbidimeter having a measurement tank for storing a liquid to be measured, a light source for irradiating light onto the liquid surface of the liquid to be measured stored in the measurement tank, and a light receiving element for receiving scattered light generated in the measurement tank by the light from the light source, a change mechanism for changing a relative position between the irradiation position of the light from the light source on the liquid surface and the light receiving element with respect to a component of the traveling direction of the light that is horizontal to the liquid surface; The turbidity value of the liquid to be measured is calculated by a turbidity value calculation device based on the scattered light received by the light receiving element. A turbidity measurement method characterized by:

Images