JP4087776B2 - Liquid concentration measuring device - Google Patents

Description

  The present invention relates to concentrations of solids, particles, colloidal substances, etc. contained in liquids, such as suspended substances generated in general industrial manufacturing processes including water and sewage systems, river sludge, and pulp manufacturing. The present invention relates to a liquid concentration measuring apparatus and a method thereof.

  As a measurement principle of this type of liquid concentration measurement apparatus, an optical method is known in addition to a microwave method, an ultrasonic attenuation method, and the like. Optical liquid concentration measuring devices are roughly classified into a light transmittance formula and a scattered light calculation formula. The scattered light calculation formula is classified into a forward scattered light calculation formula and a back scattered light calculation formula.

  As described in Non-Patent Document 1, as the light transmittance formula, a light source and a light receiving element are arranged opposite to each other on both sides of a liquid to be measured, and the liquid to be measured is transmitted from the light source to the light receiving element. There is known an apparatus for measuring the sludge concentration in a liquid based on the amount of attenuation of light that arrives.

  As a forward scattered light calculation formula, as described in Patent Document 1 to Patent Document 3, a light source and a light receiving element are arranged on both sides of the liquid to be measured, and the light is irradiated from the light source and reflected by sludge in the liquid. An apparatus for measuring the sludge concentration in a liquid based on the intensity of light (scattered light) that reaches the light receiving element later is known.

  As a backscattered light calculation method, as described in Patent Document 4 and Patent Document 5, a light source and a light receiving element are arranged on one side of the liquid to be measured, and the sludge concentration in the liquid is measured by the intensity of the scattered light. The device is known.

  To outline the measurement principle of the liquid concentration measurement device using the light transmittance formula and the scattered light calculation formula, first, the relationship between the transmitted light intensity or the scattered light intensity and the concentration for light of a specific wavelength is measured and stored in advance as a concentration calibration curve. Keep it. Then, the liquid to be measured is actually irradiated from the light source to the liquid to be measured, and the transmitted light intensity or the scattered light intensity is actually measured by the light receiving element. The density is determined from the actually measured value of the transmitted light intensity or scattered light intensity based on the density calibration curve.

  When the liquid color changes, the light transmittance and reflectance change. That is, when the liquid color changes from a light color to a dark color (for example, from white to brown, light brown, brown, and dark brown to black), the light transmittance and reflectance change accordingly. In particular, in a liquid close to black, changes in light transmittance and reflectance with respect to changes in liquid color are large. Therefore, when measuring liquid concentration based on the relationship between transmitted light intensity, scattered light intensity, and concentration, even if the actual liquid concentration does not change, the detection value of the liquid concentration changes due to the change in the liquid color, resulting in a measurement error. It becomes. For example, when the measurement object is the sludge concentration of sewer water, the sludge color gradually changes to black as the sludge decays. Moreover, in the sludge treatment plant treating sludge collected from a plurality of sewage treatment plants, the sludge color changes when the distribution changes. Measurement errors of liquid concentration occur due to changes in light transmittance and reflectance caused by these sludge color changes.

Patent Document 6 describes that the liquid to be measured is decolorized in order to avoid the influence of the liquid color. However, since a device for decolorization is required, the device becomes complicated and large. Patent Document 7 describes that the influence of the liquid color is corrected by the arrangement of optical fibers for light reception and signal processing. However, such correction cannot remove the influence of the liquid color and perform density measurement with high accuracy.
JP 11-108838 A JP 11-108822 A JP 7-270314 A JP 2002-243640 A Japanese Patent Laid-Open No. 7-20048 JP-A-8-166346 JP 2002-365216 A Japan Sewerage Corporation, “Design Standard (Draft) Electrical Design”, Sewerage Management Center, Chapter 6, p6.3-80, April 1987

  In view of the problems in the conventional optical liquid concentration measuring apparatus, the present invention eliminates measurement errors due to the influence of liquid color by using light of two or more wavelengths, and measures liquid concentration with high accuracy. The challenge is to do.

In the first invention, a plurality of light emitting elements that irradiate light to be measured with different wavelengths, a driving circuit that selects and drives one of the plurality of light emitting elements, and the driving circuit drives A light emitting element switching circuit for sequentially switching the light emitting elements, a light receiving element for detecting a measurement light intensity which is an intensity of scattered light or transmitted light emitted from the light emitting element to the liquid to be measured, and the light emitting element switching circuit. A light emitting element that is currently driven by the drive circuit based on an input signal is identified, a light emitting element identifying circuit that outputs a signal indicating the identification result, the measurement light intensity input from the light receiving element, and an arithmetic circuit for calculating the liquid density of the liquid to be measured from said signal input from said light-emitting element identification circuit, the operation circuit of the measurement light intensity between different illumination light of the wavelength A gain calculation unit that calculates an evaluation amount representing a degree of difference and calculates a gain value for correcting an influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount; and the gain calculation unit A multiplier that calculates a product of the calculated gain value and the measurement light intensity; a concentration calculator that calculates a liquid concentration by using the product calculated by the multiplier and a concentration calibration curve stored in advance; A liquid concentration measuring device is provided.

Each light emitting element emits light of a different wavelength, and the light emitting elements driven by the drive circuit are sequentially switched by the light emitting element switching circuit. Therefore, the wavelength of light irradiated to the measurement liquid is sequentially switched. Measurement light intensity corresponding to light having different wavelengths irradiated to the measurement liquid is detected by the light receiving element. The arithmetic circuit receives the measurement light intensity from the light receiving element and also receives a signal indicating the identification result of the currently driven light emitting element from the light emitting element identifying circuit. Therefore, the arithmetic circuit can recognize which measurement light intensity currently input from the light receiving element is the measurement light intensity corresponding to which light emitting element (light of which frequency). Therefore, the arithmetic circuit can calculate the liquid concentration using measurement light intensities corresponding to light of a plurality of types of wavelengths. In addition, by determining the liquid concentration using the scattered light intensity multiplied by the gain corresponding to the evaluation amount indicating the degree of difference in the measurement light intensity between the irradiation lights with different wavelengths, measurement due to the influence of the liquid color The liquid concentration can be measured with high accuracy by eliminating or reducing errors.

According to a second aspect of the present invention, there are provided a plurality of light emitting elements that irradiate light to be measured with different wavelengths, a plurality of drive circuits that simultaneously flash the corresponding light emitting elements at different frequencies, and the plurality of light emitting elements. A light receiving element for detecting a measurement light intensity which is an intensity of transmitted light or scattered light irradiated to the liquid to be measured from the element, and the measurement light intensity is input from the light receiving element, and the corresponding light emitting element A plurality of discriminating circuits for discriminating the measuring light intensity by the light irradiated to the liquid to be measured by using the difference in blinking frequency of each light emitting element, and the liquid to be measured from the measuring light intensity inputted from each of the discriminating circuits and an arithmetic circuit for calculating the liquid density, the arithmetic circuit calculates an evaluation value representing the degree of difference between the measurement light intensity between different illumination light of said wavelength, and calculated the estimated amount A gain calculation unit for calculating a gain value for correcting the influence of the liquid color of the liquid to be measured on the measurement light intensity, and a product of the gain value calculated by the gain calculation unit and the measurement light intensity. Provided is a liquid concentration measuring device comprising a multiplier, a concentration calculation unit for calculating a liquid concentration by using the product calculated by the multiplier and a concentration calibration curve stored in advance .

Each light emitting element emits light of a different wavelength and flashes simultaneously at different frequencies by a corresponding driving circuit. Accordingly, a plurality of types of light having different blinking periods are simultaneously irradiated to the measurement liquid. The measurement light intensity is input from the light receiving element to the discrimination circuit, and the discrimination circuit discriminates the measurement light intensity by the light irradiated to the liquid to be measured from the corresponding light emitting element. For this discrimination, a difference in blinking frequency of each light emitting element is used. The measurement light intensity corresponding to any one light emitting element (light of any one kind of frequency) is input from each discrimination circuit to the arithmetic circuit. Therefore, the arithmetic circuit can calculate the liquid concentration using measurement light intensities corresponding to light of a plurality of types of wavelengths. In addition, by determining the liquid concentration using the scattered light intensity multiplied by the gain corresponding to the evaluation amount indicating the degree of difference in the measurement light intensity between the irradiation lights with different wavelengths, measurement due to the influence of the liquid color The liquid concentration can be measured with high accuracy by eliminating or reducing errors.

  For example, the discriminating circuit detects a signal output from a corresponding bandpass filter circuit that passes measurement light intensity in a band including a blinking frequency of the corresponding light emitting element, and outputs the detected signal to the arithmetic circuit. And a detection circuit.

According to a third aspect of the present invention, a liquid to be measured is irradiated with light having different wavelengths, and a plurality of light emitting elements whose light emitting portions are arranged at intervals from each other, and the corresponding light emitting elements at different frequencies. A plurality of drive circuits to be blinked and a light receiving unit are arranged in proximity to the light emitting unit of the corresponding light emitting element, and a measurement light intensity which is the intensity of transmitted light or scattered light emitted from the corresponding light emitting element. A plurality of light receiving elements to be detected, and an arithmetic circuit that calculates a liquid concentration of the liquid to be measured from the measurement light intensity input from each of the light receiving elements, and the arithmetic circuit includes the irradiation light having different wavelengths. A gain calculation unit that calculates an evaluation amount that represents a degree of difference in measurement light intensity and calculates a gain value that corrects the influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount; The liquid concentration is calculated by a multiplier that calculates a product of the gain value calculated by the gain calculation unit and the measurement light intensity, the product calculated by the multiplier, and a concentration calibration curve that is stored in advance. Provided is a liquid concentration measuring device including a concentration calculating unit .

The light emitting portions of a plurality of light emitting elements that emit light having different wavelengths are arranged at intervals. The light receiving portion of each light receiving element is disposed in proximity to the light emitting portion of the corresponding light emitting element. In other words, the light emitting part and the light receiving part are arranged at intervals (physically separated) for each wavelength of light irradiated to the liquid to be measured. Therefore, each light receiving element can detect the measurement light intensity by the light from the corresponding light emitting element without interfering with the measurement light intensity from the other light emitting elements. Therefore, the arithmetic circuit can calculate the liquid concentration using measurement light intensities corresponding to light of a plurality of types of wavelengths. In addition, by determining the liquid concentration using the scattered light intensity multiplied by the gain corresponding to the evaluation amount indicating the degree of difference in the measurement light intensity between the irradiation lights with different wavelengths, measurement due to the influence of the liquid color The liquid concentration can be measured with high accuracy by eliminating or reducing errors.

According to a fourth aspect of the invention, a plurality of light emitting elements that irradiate light to be measured with different wavelengths, a driving circuit that selects and drives one of the plurality of light emitting elements, and the driving circuit drives A light emitting element switching circuit for sequentially switching the light emitting elements; a light receiving element for detecting a measurement light intensity which is an intensity of scattered light or transmitted light emitted from the light emitting element to the liquid to be measured; and A plurality of synchronous detection circuits that receive measurement light intensity, are driven by a signal input from the light emitting element switching circuit, and detect the measurement light intensity due to light emitted from the corresponding light emitting element to the liquid to be measured, A plurality of smoothing circuits that are provided for each of the synchronous detection circuits and hold the measurement light intensity output from the corresponding synchronous detection circuits, and output the measurement light intensity among the plurality of smoothing circuits. Based on a signal switching circuit that sequentially switches what to be performed and a signal input from the signal switching circuit, the plurality of smoothing circuits that currently output the measured light intensity are identified, and the identification result is shown A signal identification circuit that outputs a signal; an arithmetic circuit that calculates a liquid concentration of the liquid to be measured from the measurement light intensity input from the smoothing circuit and the signal input from the signal identification circuit; The arithmetic circuit calculates an evaluation amount indicating the degree of difference in the measurement light intensity between the irradiation lights having different wavelengths, and the calculated color from the calculated evaluation amount with respect to the measurement light intensity of the liquid color of the liquid to be measured A gain calculation unit that calculates a gain value for correcting the influence, a multiplier that calculates a product of the gain value calculated by the gain calculation unit and the measurement light intensity, and a multiplier that is calculated by the multiplier It said product, to provide a liquid concentration measuring device and a concentration calculator that calculates the liquid concentration with a previously stored density calibration curve.

Each light emitting element emits light of a different wavelength, and the light emitting elements driven by the drive circuit are sequentially switched by the switching circuit. Therefore, the wavelength of light irradiated to the liquid to be measured is sequentially switched. The measurement light intensity by the light emitted from each light emitting element is detected by the light receiving element, detected by the corresponding synchronous detection circuit, and held by each smoothing circuit. The arithmetic circuit receives the measurement light intensity from the smoothing circuit and the signal indicating the smoothing circuit that is currently outputting the measurement light intensity from the signal identification circuit. Therefore, the arithmetic circuit can recognize which smoothing circuit (which light emitting element or light of any frequency) corresponds to the currently input measurement light intensity. Therefore, the arithmetic circuit can calculate the liquid concentration using the measurement intensities corresponding to the light of a plurality of wavelengths. In addition, by determining the liquid concentration using the scattered light intensity multiplied by the gain corresponding to the evaluation amount indicating the degree of difference in the measurement light intensity between the irradiation lights with different wavelengths, measurement due to the influence of the liquid color The liquid concentration can be measured with high accuracy by eliminating or reducing errors.

  According to the first to fourth aspects of the invention, it is possible to detect the measurement light intensities corresponding to the light of a plurality of types without interfering with each other. By calculating the liquid concentration using the measurement light intensities corresponding to light of a plurality of types of wavelengths, it is possible to eliminate the measurement error caused by the influence of the liquid color and perform the liquid concentration measurement with high accuracy.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
Referring to FIGS. 1 to 3, the liquid concentration measuring apparatus according to the first embodiment includes a detector 2 that irradiates light to the liquid 1 to be measured and detects the intensity of scattered light (scattered light intensity), and a detection. And a converter 3 that calculates the liquid concentration of the liquid 1 to be measured based on the scattered light intensity detected by the device 2.

  The detector 2 includes a casing 4 having a casing body 4a and a rod-shaped sensor portion 4b extending from the front side of the casing body 4a. The casing body 4a includes two light emitting diodes, that is, a light emitting diode (first light emitting element) 6-1 that emits light having a wavelength λ1, and a light emitting diode (second light emitting element) 6 that emits light having a wavelength λ2. -2 are housed. Also, one photodiode (light receiving element) 7 is accommodated in the casing body 4a. Further, a light emitting circuit 8 and a light receiving circuit 9 are accommodated in the casing body 4a.

  The wavelength λ2 of the light emitted from the light emitting diode 6-2 is shorter than the wavelength λ1 of the light emitted from the light emitting diode 6-1 (λ1> λ2). The wavelengths λ1 and λ2 depend on the light absorption characteristics of the liquid to be measured, the reflection characteristics of solids (eg, mud and grass) contained in the liquid to be measured, and the light absorption characteristics of the optical system including the optical fiber. To near-infrared wavelength region. For example, the wavelengths λ1 and λ2 are set in the range of 600 nm to 1500 nm.

  The light-emitting optical fibers 11-1 and 11-2 connected to the corresponding light-emitting diodes 6-1 and 6-2 on the base end side extend to the tip of the sensor unit 4b. The light receiving optical fiber 12 whose proximal end is connected to the photodiode 7 also extends to the tip of the sensor unit 4b. As shown in FIGS. 3A and 3B, the light emitting sections 13-1 and 13-2, which are the end faces of the light emitting optical fibers 11-1 and 11-2, are connected to the light receiving optical fiber 12. The light-emitting unit 14 that surrounds the light-receiving unit 14 that is the end surface on the terminal side is disposed so that the light-emitting unit 13-1 of the light-emitting diode 6-1 and the light-emitting unit 13-2 of the light-emitting diode 6-2 are alternately adjacent to each other.

  The detector 2 of this embodiment irradiates the liquid 1 to be measured with two types of wavelengths λ1 and λ2 by sequentially emitting light from the two light emitting diodes 6-1 and 6-2, and the scattered light is emitted from the photodiode. 7 receives light. As shown in FIG. 3, the light emitting circuit 8 of the detector 2 includes an LED drive circuit (drive circuit) 16, an oscillation circuit 17, and an LED switching circuit (light emitting element switching circuit) 18. The light receiving circuit 9 includes an amplifier circuit 19 and a synchronous detection circuit 20.

  The LED drive circuit 16 selects and drives one of the two light emitting diodes 6-1 and 6-2. In order to distinguish from disturbance light, the LED drive circuit 16 blinks the light emitting diodes 6-1 and 6-2 at a frequency f determined by the oscillation circuit 17. In other words, the light emitting diodes 6-1 and 6-2 being driven by the LED drive circuit 16 repeat light emission and extinction alternately at the frequency f. The timing for switching the light emitting diodes 6-1 and 6-2 driven by the LED drive circuit 16 is determined by a signal input from the LED switching circuit 18. Which light emitting diode 6-1 and 6-2 is driven first is not particularly limited. The signal of the LED switching circuit 18 is output to the light emitting LED identification circuit 21 of the converter 3 described later via an electric wire.

  Light irradiated from the light emitting diodes 6-1 and 6-2 through the light emitting optical fibers 11-1 and 11-2 and the light emitting units 13-1 and 13-2 to the liquid 1 to be measured (two types of wavelengths λ 1 and λ 2 Is reflected by a solid matter or the like contained in the liquid 1 to be measured, and enters the photodiode 7 through the light receiving unit 14 and the light receiving optical fiber 12 as scattered light. Since the light emitting diodes 6-1 and 6-2 are driven sequentially instead of simultaneously, the photodiode 7 is scattered by the light emitted from the light emitting diode 6-1 and the light emitted from the light emitting diode 6-2. Scattered light enters sequentially. The scattered light is converted into current by the photodiode 7, and the current value is proportional to the scattered light intensity. The current converted by the photodiode 7 is amplified by the amplifier circuit 19 and converted into a voltage. The converted voltage is detected in synchronization with the oscillation frequency f of the oscillation circuit 17 by the synchronous detection circuit 20, and is output as a DC voltage signal to the A / D circuit 22 of the converter 3 to be described later via a wire.

  As shown in FIG. 3, the converter 3 includes a light emitting LED identification circuit (light emitting element identification circuit) 21, an A / D circuit 22, an arithmetic circuit 23, a D / A circuit 24, an LCD display 25, a setting switch circuit 26, And a V / I conversion circuit 27.

  The DC voltage signal from the synchronous detection circuit 20 of the detector 2 is converted into a digital signal by the A / D circuit 22 and output to the arithmetic circuit 23. As described above, the light scattered by the light emitted from the light emitting diodes 6-1 and 6-2 is sequentially incident on the photodiode 7. Therefore, in the arithmetic circuit 23, the scattered light intensity P1 corresponding to the light-emitting diode 6-1 (irradiated light having the wavelength λ1) and the scattered light intensity P2 corresponding to the light-emitting diode 6-2 (irradiated light having the wavelength λ2) are sequentially obtained. Entered. Based on the signal input from the LED switching circuit 18 of the detector 2, the light emitting LED identification circuit 21 is the one that is currently driven by the LED drive circuit 16 among the two light emitting diodes 6-1 and 6-2. A signal indicating the identification result is output to the arithmetic circuit 23. Accordingly, the arithmetic circuit 23 recognizes which light-emitting diodes 6-1 and 6-2 (which wavelengths λ1 and λ2) correspond to the scattered light intensities P1 and P2 currently input from the A / D circuit 22. be able to. The arithmetic circuit 23 calculates the liquid concentration using the input scattered light intensities P1 and P2.

  The liquid concentration calculated by the arithmetic circuit 23 is converted into an analog voltage signal by the D / A circuit 24 and further converted into a current signal by the V / I circuit 27 and then output. Various information related to the arithmetic circuit 23 including the calculated liquid concentration is displayed on the LCD display 25, and various settings of the arithmetic circuit 23 can be changed by the setting switch circuit 26.

  Next, the arithmetic circuit 23 will be described in detail. First, the measurement principle of the liquid concentration in the arithmetic circuit 23 will be described with reference to FIG. FIG. 6 schematically shows the relationship between the scattered light intensity and the liquid concentration when the liquid to be measured is irradiated with light of wavelength λ1 and light of wavelength λ2 shorter than wavelength λ1. The wavelengths λ1 and λ2 are both in the visible to near-infrared wavelength region. A dotted line indicates a case where the liquid color is relatively bright (for example, white to brown), and a solid line indicates a case where the liquid color is relatively dark (for example, dark brown to black).

  As shown in FIG. 6, the correlation between the scattered light intensity and the liquid concentration has a generally positive relationship. However, if the liquid concentration becomes too high or the liquid color approaches black, the scattered light intensity decreases and becomes saturated. In the concentration measurement, it is necessary to use a region where the correlation between the scattered light intensity and the liquid concentration shows a positive characteristic.

  Regarding the influence of the liquid color on the scattered light intensity in the visible to near-infrared wavelength region, first, even if the liquid concentration is the same, the scattered light intensity tends to decrease as the liquid color becomes darker. For example, in FIG. 6, when the liquid concentration is C1, the scattered light intensity P1 '(wavelength λ1) when the liquid color is dark is smaller than the scattered light intensity P1 when the liquid color is bright.

  Next, when the liquid color is bright, the influence of the wavelength difference on the correlation between the scattered light intensity and the liquid concentration is small, but the influence tends to become remarkable as the liquid color becomes darker. Specifically, when the wavelength is long, the amount of decrease in the scattered light intensity due to the dark liquid color is small, and conversely, when the wavelength is short, the amount of decrease in the scattered light intensity due to the dark liquid color is large. . For example, in FIG. 6, when the liquid color is bright, the difference in correlation between the scattered light intensity due to the wavelengths λ1 and λ2 and the liquid concentration is relatively small, but when the liquid color is dark, the difference due to the wavelengths λ1 and λ2 becomes significant. ing. For the same liquid concentration C1, the difference ΔP1 ′ in scattered light intensity due to the wavelengths λ1 and λ2 when the liquid color is dark is larger than the difference ΔP1 in scattered light intensity when the liquid color is bright.

  As described above, the evaluation value indicating the ratio of two scattered light intensities obtained by irradiating the liquid to be measured with two types of light having different wavelengths, that is, the degree of difference between the two scattered light intensities, is Correlation with the liquid color of the measurement liquid. Therefore, by correcting the scattered light intensity using this correlation, the influence of the change in the liquid color can be eliminated or reduced, and the measurement accuracy of the liquid concentration can be improved. The correlation between the transmitted light intensity and the liquid concentration and the influence of the liquid color on the transmitted light intensity are opposite to those in the above scattered light intensity.

  Referring to FIG. 4, the arithmetic circuit 23 includes a gain calculation unit (correction value calculation unit) 31, a multiplier 32, and a density calculation unit 33. Scattered light intensities P1 and P2 corresponding to irradiation light of two types of wavelengths λ1 and λ2 are input to the gain calculation unit 31. Further, the scattering intensity P1 corresponding to the irradiation light having the wavelength λ1 is also input to the multiplier 32.

  The gain calculation unit 31 calculates an intensity ratio R described later. The gain calculation unit 31 stores one gain correction curve (shown in FIG. 5 and indicated by reference numeral 35 in FIG. 4), which is a relationship between the intensity ratio R and the gain G, and this gain correction curve. Thus, the gain G corresponding to the intensity ratio R is calculated. The gain G calculated by the gain calculation unit 31 is output to the multiplier 32, and the multiplier 32 multiplies the scattered light intensity P1 by the gain G. The product (P1 × G) of the scattered light intensity P1 and the gain G is output to the concentration calculation unit 33. The concentration calculation unit 33 shows one concentration calibration curve (shown in FIG. 8 and indicated by reference numeral 36 in FIG. 4) that is a relationship between the product of the scattered light intensity P1 and the gain G (P1 × G) and the liquid concentration. The liquid concentration C is calculated from the product (P1 × G) input from the multiplier 32 and the concentration calibration curve.

  The intensity ratio R is a ratio (P1 / P2) of the scattered light intensity P1 corresponding to the irradiation light with the wavelength λ1 to the scattered light intensity P2 at the wavelength λ2 (λ2 <λ1). As described with reference to FIG. 6, the evaluation amount indicating the degree of difference in scattered light intensity of irradiation light having different wavelengths has a correlation with the liquid color of the liquid to be measured. The intensity ratio R is an example of this evaluation amount.

  Next, the relationship between the intensity ratio R and the gain will be described with reference to FIG. FIG. 7 shows a correlation characteristic between the scattered light intensity P1 corresponding to the wavelength λ1 and the intensity ratio R (P1 / P2). The solid line indicates that the liquid color is light brown (when the liquid color is bright), the alternate long and short dash line indicates that the liquid color is slightly black (if the liquid color is slightly dark), and the two-dot chain line indicates that the liquid color is black (liquid color) Is dark). Moreover, a broken line shows an isodensity curve.

  When the liquid color is bright, the change in the intensity ratio R with respect to the increase in the scattered light intensity P1 is very small. Next, when the liquid color is slightly dark, the change in the intensity ratio R with respect to the increase in the scattered light intensity P1 is significantly larger than when the liquid color is bright. When comparing the same liquid concentration, the intensity ratio R when the liquid color is slightly dark is larger than that when the liquid color is bright. Further, when the liquid color is dark, the change in the intensity ratio R with respect to the increase in the scattered light intensity P1 is further increased. Further, when comparing the same liquid concentration, the intensity ratio R when the liquid color is dark is larger than when the liquid color is slightly dark. Accordingly, FIG. 7 also shows that the intensity ratio R tends to increase as the liquid color becomes darker.

  Focusing on one isoconcentration curve, the scattered light intensity P1b when the liquid color is slightly dark is smaller by α1 than the scattered light intensity P1a when the liquid color is bright. Further, the difference α2 between the scattered light intensity P1c when the liquid color is dark and the scattered light intensity P1a when the liquid color is bright is further increased. The gain G is a value (correction value) for compensating for the decrease amounts α1 and α2 of the scattered light intensity P1 that increases as the liquid color becomes darker and converted to the scattered light intensity P1 when the liquid color is bright. is there. In the present embodiment, the gain calculation unit 31 stores the relationship between the intensity ratio and the gain as the gain correction curve illustrated in FIG. 5, but may store the relationship between the two in other forms such as a table or a function. .

  The processing executed by the arithmetic circuit 23 will be described. First, the gain calculation unit 31 first calculates the intensity ratio R (P1) of the scattered light intensities P1 and P2 by the irradiation light having the wavelengths λ1 and λ2 (λ1> λ2) input from the detector 2. / P2). Next, the gain calculation unit 31 determines the gain G corresponding to the calculated intensity ratio R from the gain correction curve of FIG. The gain G is output from the gain calculation unit 31 to the multiplier 32, and the multiplier 32 multiplies the scattered light intensity P1 by the irradiation light having the wavelength λ1 by the gain G. The product (P1 × G) of the scattered light intensity P1 and the gain G is output from the multiplier 32 to the density calculation unit 33, and the density calculation unit 33 sets the density C corresponding to the input product (P1 × G) in FIG. Determine by concentration calibration curve. As described above, the intensity ratio R has a correlation with the liquid color of the liquid 1 to be measured. Therefore, by determining the liquid concentration based on the scattered light intensity P1 multiplied by the gain G in accordance with the intensity ratio R, measurement error due to the influence of the liquid color is eliminated or reduced, and the liquid concentration measurement with high accuracy is performed. It can be performed.

  9A and 9B show a modification of the detector 2 in the first embodiment. The light emitting diodes 6-1 and 6-2 are not driven simultaneously but sequentially. Therefore, the light emitting optical fiber 11 may be shared by both the light emitting diodes 6-1 and 6-2 as in this example.

(Second Embodiment)
The second embodiment of the present invention shown in FIG. 10 is different from the first embodiment in that the structure of the detector 2 and the converter 3 are not provided with the light emitting LED identification circuit 21 (see FIG. 2). The process executed by is the same as in the first embodiment. In the second embodiment, two types of scattered light intensities P1 and P2 are discriminated by causing the two light emitting diodes 6-1 and 6-2 to emit light intermittently at different frequencies.

  The light emitting circuit 8 of the detector 2 includes two LED drive circuits 16-1 and 16-2 for driving the light emitting diodes 6-1 and 6-2, respectively. One LED driver circuit 16-1 drives the light emitting diode 6-1 having the wavelength λ1 at the frequency f1 determined by the oscillation circuit 17-1. The other LED driver circuit 16-2 drives the light emitting diode 6-2 having the wavelength λ2 at the frequency f2 determined by the oscillation circuit 17-1. The frequency f1 and the frequency f2 are different from each other.

  The light receiving circuit 9 of the detector 2 includes two band pass filter (BPF) circuits 37-1 and 37-2 connected to the amplifier circuit 19. The BPF circuit 37-1 passes a signal in a band including the frequency f1 but not including the frequency f2. The BPF circuit 37-2 passes a signal in a band that includes the frequency f2 but does not include the frequency f1. Detection circuits 38-1 and 38-2 are connected to these BPF circuits 37-1 and 37-2, respectively. The detection circuits 38-1 and 38-2 are connected to the A / D circuits 22-1 and 22-2 of the arithmetic circuit 23, respectively. The BPF circuits 37-1 and 37-2 and the detection circuits 38-1 and 38-2 constitute a discrimination circuit.

  The light emitting diode 6-1 driven by the LED drive circuit 16-1 blinks at the frequency f1, and this blinking light (wavelength λ1) passes through the light emitting optical fiber 11-1 and the light emitting unit 13-1 to the liquid 1 to be measured. Irradiated. At the same time, the light-emitting diode 6-2 driven by the LED drive circuit 16-2 blinks at the frequency f2, and this blinking light (wavelength λ2) passes through the light-emitting optical fiber 11-2 and the light-emitting portion 13-2 to be measured liquid. 1 is irradiated. Scattered light of two types of light (light having a light emission wavelength λ1 blinking at a frequency f1 and light having a light emission wavelength λ2 blinking at a frequency f2) simultaneously irradiated onto the liquid 1 to be measured is a light receiving unit 14 and a light receiving optical fiber 12. Then, the light enters the photodiode 7. The current converted from the incident light by the photodiode 7 is amplified by the amplifier circuit 19, converted into a voltage, and output to the two BPF circuits 37-1 and 37-2.

  By discriminating the signal of the frequency component f1 by the BPF circuit 37-1, only the signal component of the scattered light due to the irradiation light (wavelength λ1) from the light emitting diode 6-1 is detected by the detection circuit 38-1, and the converter 3 To the A / D circuit 22-1. Similarly, by discriminating the signal of the frequency component f2 by the BPF circuit 37-2, only the signal component of the scattered light due to the irradiation light (wavelength λ2) from the light emitting diode 6-2 is detected by the detection circuit 38-2. It is output to the A / D circuit 22-2 of the converter 3. A DC signal indicating scattered light intensity P1 corresponding to the light emitting diode 6-1 (irradiation light having the wavelength λ1) is input from the A / D circuit 22-1 to the arithmetic circuit 23 of the converter 3, and the A / D circuit 22 is supplied. -2 is input with a DC signal indicating the scattered light intensity P2 corresponding to the light emitting diode 6-2 (irradiated light having the wavelength λ2). In other words, two types of scattered light intensities P1 and P2 are separately input to the arithmetic circuit 23. Therefore, the arithmetic circuit 23 can calculate the liquid concentration using these two types of scattered light intensities P1 and P2.

  Other configurations and operations of the second embodiment are the same as those of the first embodiment.

(Third embodiment)
In the third embodiment of the present invention shown in FIGS. 11 and 12, the light emitting part and the light receiving part are arranged with a sufficient interval in order to receive the scattered light of the two types of irradiation light without interfering with each other. Yes.

  The detector 2 includes two photodiodes 7-1 and 7-2. As shown in FIG. 11A, the light receiving sections 14-1 and 14-, which are end faces on the terminal side of the light receiving optical fibers 12-1 and 12-2 connected to the photodiodes 7-1 and 7-2, respectively. 2 are arranged at a sufficient distance from each other. Further, the light emitting unit 13-1 of the light emitting diode 6-1 is disposed surrounding the light receiving unit 14-1, and the light emitting unit 13-2 of the light emitting diode 6-2 is disposed surrounding the light receiving unit 14-2. Has been.

  The light emitting circuit 8 is the same as that of the second embodiment (FIG. 10), and the LED drive circuits 16-1 and 16-2 correspond to the light emitting diodes 6 corresponding to different frequencies f1 and f2 determined by the oscillation circuits 17-1 and 17-2. −1, 6-2 are driven.

  The light receiving circuit 9 processes the signal output from the photodiode 7-1, the amplifier circuit 19-1 that processes the signal output from the photodiode 7-1, the BPF circuit 37-1, the detection circuit 38-1. The amplifier circuit 19-2, the BPF circuit 37-2, and the detection circuit 38-2 are provided separately.

  The light emitting diodes 6-1 and 6-2 are driven by the corresponding LED drive circuits 16-1 and 16-2 so as to blink simultaneously at mutually different frequencies f 1 and f 2. The liquid 1 to be measured is irradiated from 1 and 13-2. The scattered light of the light (wavelength λ1) emitted from the light emitting unit 13-1 of the light emitting diode 6-1 passes through the light receiving unit 14-1 disposed in the vicinity of the light emitting unit 13-1, and then enters the photodiode 7-1. Incident. Further, the scattered light of the light (wavelength λ2) emitted from the light emitting unit 13-2 of the light emitting diode 6-2 passes through the light receiving unit 14-2 disposed in the vicinity of the light emitting unit 13-2, and then the photodiode 7−. 2 is incident.

  The current converted from the incident light by the photodiode 7-1 is amplified by the amplifier circuit 19-1, converted into a voltage, and output to the BPF circuit 37-1. By discriminating the signal of the frequency component f1 by the BPF circuit 37-1, only the signal component of the scattered light (corresponding to the scattered light intensity P1) due to the irradiation light (wavelength λ1) from the light emitting diode 6-1 is detected. 38-1 is detected and output to the A / D circuit 22-1. Similarly, by discriminating the signal of the frequency component f2 by the BPF circuit 37-2, only the signal component of the scattered light (corresponding to the scattered light intensity P2) due to the irradiation light (wavelength λ1) from the light emitting diode 6-2 is obtained. The signal is detected by the detection circuit 38-2 and output to the A / D circuit 22-2 of the converter 3. Accordingly, two types of scattered light intensities P1 and P2 are separately input from the A / D circuits 22-1 and 22-2 to the arithmetic circuit 23, and the liquid concentration is determined using these two types of scattered light intensities P1 and P2. Can be calculated.

  Other configurations and operations of the third embodiment are the same as those of the first embodiment.

(Fourth embodiment)
In 4th Embodiment of this invention shown in FIG.13 and FIG.14, the light emitting diode is further added to the detector 2 (refer FIG. 3) of 1st Embodiment. That is, the detector 2 includes light emitting diodes 6-3 to 6-N (N ≧ 3) in addition to the light emitting diodes 6-1 and 6-2. The light emitting wavelengths λ1 to λN of the light emitting diodes 6-1 to 6-N are different from each other, and the light emitting wavelengths of the i th and i + 1 th light emitting diodes have a relationship of λi> λi + 1. The LED drive circuit 16 drives any one of the light emitting diodes 6-1 to 6 -N at a frequency f determined by the oscillation circuit 17. The LED switching circuit 18 sequentially switches the light emitting diodes 6-1 to 6 -N driven by the LED drive circuit 16. Accordingly, the scattered light intensities P1 to PN corresponding to the light emitting diodes 6-1 to 6-N (irradiated light of wavelengths λ1 to λN) are sequentially input to the arithmetic circuit 23 of the converter 3 via the A / D circuit 22. The Since a signal indicating the currently driven one of the light emitting diodes 6-1 to 6 -N is input from the light emitting LED identification circuit 21, the arithmetic circuit 23 has the scattered light intensity currently input from the A / D circuit 22. It can be recognized which light-emitting diodes 6-1 to 6-N (which frequencies λ1 to λN) correspond to P1 to PN.

  Referring to FIG. 14, the gain calculation unit 31 of the arithmetic circuit 23 stores a plurality of gain correction curves 35. Each gain correction curve 35 corresponds to a combination of scattered light intensities P1 to PN used for calculating the intensity ratio R. That is, in addition to the gain correction curve 35 indicating the relationship between the intensity ratio R calculated from the scattering intensities P1 and P2 and the gain G, for example, the gain correction curve indicating the relationship between the intensity ratio R calculated from the scattering intensities P3 and P4 and the gain G, for example. 35 is stored in the gain calculation unit 31. Further, the concentration calculation unit 33 stores a plurality of concentration calibration curves 36 corresponding to the combinations of scattered light intensities P1 to PN used for calculating the intensity ratio R.

  The arithmetic circuit 23 includes a storage unit 41 that stores a plurality of scattered light intensities P <b> 1 to PN input from the detector 2. The arithmetic circuit 23 includes a selection unit 42 that selects a combination of scattered light intensities P1 to PN used for liquid concentration calculation, as will be described later.

  All scattered light intensities P <b> 1 to PN inputted from the detector 2 to the arithmetic circuit 23 are stored in the storage unit 41. Further, the scattered light intensities P <b> 1 and P <b> 2 are input to the gain calculation unit 31. The gain calculation unit 31 calculates the intensity ratio R from the scattered light intensities P1 and P2, and calculates the gain G from the calculated intensity ratio R and the gain correction curve 35 corresponding to the scattered light intensities P1 and P2. calculate. The calculated gain G is multiplied by the scattered light intensity P 1 by the multiplier 32, and the product (P 1 × G) is output to the concentration calculation unit 33. The concentration calculation unit 33 calculates the liquid concentration C from the product (P1 × G) and the one corresponding to the scattered light intensities P1 and P2 among the plurality of concentration calibration curves 36. The concentration C is output to the selection unit 42.

  The selection unit 42 selects two types of scattered light intensities most suitable for liquid concentration calculation in the concentration region including the liquid concentration C that is input from among the scattered light intensities P1 to PN. Further, the selection unit 42 causes the gain calculation unit 31, the multiplier 32, and the concentration calculation unit 33 to recalculate the liquid concentration using the selected scattered light intensity. For example, when the selection unit 42 selects the scattered light intensities P2 and P3, the scattered light intensities P2 and P3 are input from the storage unit 41 to the gain calculation unit 31, and the scattered light intensity P2 is input to the multiplier 32. The gain calculation unit 31 calculates the intensity ratio R of the scattered light intensities P2 and P3, and calculates the gain G from the calculated intensity ratio R and the gain correction curve 35 corresponding to the scattered light intensities P2 and P3. The calculated gain G is multiplied by the scattered light intensity P 2 by the multiplier 32, and the product (P 2 × G) is output to the concentration calculation unit 33. The concentration calculation unit 33 calculates the liquid concentration C from the input product (P2 × G) and the concentration calibration curve 36 corresponding to the scattered light intensities P2 and P3. The recalculated liquid concentration C is output from the arithmetic circuit 23.

  As described above, in the fourth embodiment, the liquid concentration C using the scattered light intensities P1 and P2 is calculated, and the two types of scattered light intensities most suitable for calculating the liquid concentration in the concentration region including the liquid concentration C are obtained. Use to recalculate liquid concentration. Therefore, the liquid concentration can be measured with higher accuracy.

  Other configurations and operations of the fourth embodiment are the same as those of the first embodiment.

(Fifth embodiment)
In the fifth embodiment of the present invention shown in FIG. 15, light emitting diodes 6-3 to 6-N (light emission wavelengths λ3 to λN) are added to the detector 2 (see FIG. 10) of the second embodiment, and each light emitting diode. LED drive circuits 16-3 to 16-N and oscillation circuits 17-3 to 17-N (oscillation frequencies f3 to fN) are provided for each of 6-3 to 6-N. Further, BPF circuits 37-3 to 37 -N and detection circuits 38-3 to 38 -N corresponding to the light emitting diodes 6-3 to 6 -N are added to the light receiving circuit 9. Further, A / D circuits 23-3 to 22-N corresponding to the detection circuits 38-3 to 38-N are added to the converter 3, respectively.

  Each of the light emitting diodes 6-1 to 6-N is driven by the corresponding LED drive circuit 16-1 to 16-N and blinks at different frequencies f1 to fN. Light scattered from the light emitting diodes 6-1 to 6 -N to the liquid 1 to be measured is incident on the photodiode 7, and an electric signal obtained by photoelectric change passes through the amplifier circuit 19 and the BPF circuits 37-1 to 37-37. -N is output. By discriminating the signals of the frequency components f1 to fN by the BPF circuits 37-1 to 37-N, respectively, the signal components of the scattered light by the corresponding light emitting diodes 6-1 to 6-N (corresponding wavelengths λ1 to λN). Only the detection circuits 38-1 to 38-N detect the signal, and output to the arithmetic circuit 23 through the A / D circuits 22-1 to 22-2. Therefore, the scattered light intensities P1 to PN are separately input to the arithmetic circuit 23. The configuration of the arithmetic circuit 23 (see FIG. 14) and the processing executed by the arithmetic circuit 23 are the same as in the fourth embodiment.

(Sixth embodiment)
In the sixth embodiment of the present invention shown in FIG. 16, light-emitting diodes 6-3 to 6-N (light emission wavelengths λ3 to λN) are added to the detector 2 (see FIG. 12) of the third embodiment, and corresponding thereto. Then, photodiodes 7-3 to 7-N are added. LED drive circuits 16-3 to 16-N and oscillation circuits 17-3 to 17-N (oscillation frequencies f3 to fN) are provided for the respective light emitting diodes 6-3 to 6-N. Further, BPF circuits 37-3 to 37 -N and detection circuits 38-3 to 38 -N corresponding to the light emitting diodes 6-3 to 6 -N are added to the light receiving circuit 9. Further, A / D circuits 23-3 to 22-N corresponding to the detection circuits 38-3 to 38-N are added to the converter 3, respectively.

  Each of the light emitting diodes 6-1 to 6-N is driven by the corresponding LED drive circuit 16-1 to 16-N and blinks at different frequencies f1 to fN. The scattered light of the light irradiated from the light emitting diodes 6-1 to 6-N to the liquid 1 to be measured is incident on the corresponding photodiodes 7-1 to 7-N, and the electric signals obtained by photoelectric conversion correspond to the scattered light. The data is output to the arithmetic circuit 23 via the amplifier circuits 19-1 to 19-N, the BPF circuits 37-1 to 37-N, and the A / D circuits 22-1 to 22-N. Therefore, the scattered light intensities P1 to PN are separately input to the arithmetic circuit 23. The configuration of the arithmetic circuit 23 (see FIG. 14) and the processing executed by the arithmetic circuit 23 are the same as in the fourth embodiment.

(Seventh embodiment)
In the seventh embodiment of the present invention shown in FIG. 17, the light receiving circuit 8 of the detector 2 is similar to the first embodiment (see FIG. 3) in the LED drive circuit 16, the oscillation circuit 17, and the LED switching circuit. 18, the light emitting diode 6-1 (wavelength λ1) and the light emitting diode 6-2 (wavelength λ2) are sequentially blinked. The light receiving circuit 9 of the detector 2 includes two synchronous detection circuits 20-1 and 20-2 each connected to an amplifier circuit 19. Each of the synchronous detection circuits 20-1 and 20-2 detects the output from the amplifier circuit 19 at a frequency determined by the oscillation circuit 17. In addition, a signal from the LED switching circuit 18 is input to each of the synchronous detection circuits 20-1 and 20-2. Further, smoothing circuits 50-1 and 50-2 are connected to the respective synchronous detection circuits 20-1 and 20-2. The signal switching circuit 51 sequentially connects the two smoothing circuits 50-1 and 50-2 to the A / D circuit 22 of the converter 3 at a predetermined timing. The signal of the signal switching circuit 51 is also output to the signal identification circuit 52 of the converter 3.

  The scattered light intensities P1 and P2 of the light emitted from the light emitting diodes 6-1 and 6-2 are photoelectrically converted by the photodiode 19 and output to the synchronous detection circuits 20-1 and 20-2. Based on the signal input from the LED switching circuit 18, one of the two synchronous detection circuits 20-1 and 20-2 is driven. For example, when one of the light emitting diodes 6-1 is driven, the periodic detection circuit 20-1 detects the output (scattered light intensity P1) from the amplifier circuit 19, and a voltage signal corresponding to the scattered light intensity P1 is generated. It is held in the smoothing circuit 50-1. Conversely, when the other light emitting diode 6-2 is being driven, the synchronous detection circuit 20-2 detects the output (scattered light intensity P2) from the amplifier circuit 19, and a voltage signal corresponding to the scattered light intensity P2. Is held in the smoothing circuit 50-2. The signal switching circuit 51 sequentially connects the two smoothing circuits 50-1 and 50-2 to the A / D circuit 22 and outputs the scattered light intensities P 1 and P 2 to the arithmetic circuit 23.

  Based on the signal input from the signal switching circuit 51, the signal identification circuit 52 identifies one of the two smoothing circuits 50-1 and 50-2 that is currently connected to the A / D circuit 22, A signal indicating the identification result is output to the arithmetic circuit 23. Therefore, the arithmetic circuit 23 recognizes which light-emitting diodes 6-1 and 6-2 (which wavelengths λ1 and λ2) correspond to the scattered light intensities P1 and P2 currently output from the A / D circuit 22. be able to. Therefore, the arithmetic circuit 23 can calculate the liquid concentration using these scattered light intensities P1 and P2.

  Other configurations and operations of the seventh embodiment are the same as those of the first embodiment.

(Eighth embodiment)
In the eighth embodiment of the present invention shown in FIG. 18, in addition to the light emitting diodes 6-1 and 6-2, the light emitting diodes 6-3 to 6-N (N ≧ 3) is added, and synchronous detection circuits 20-3 to 20-N and smoothing circuits 50-3 to 50-N are added accordingly. When the light emitting diodes 6-1 to 6-N are sequentially driven by the LED drive circuit 16, the oscillation circuit 17, and the LED switching circuit 18, the scattered light intensities P1 to PN are generated by the corresponding synchronous detection circuits 20-1 to 20-N. Are synchronously detected and held in the smoothing circuits 50-1 to 50-N. The smoothing circuits 50-1 to 50 -N are sequentially connected to the A / D circuit 22 by the signal switching circuit 51, and the scattered light intensities P 1 to PN are sequentially output to the arithmetic circuit 23. Based on the signal input from the signal identification circuit 52, the arithmetic circuit 23 recognizes to which light emitting diodes 6-1 to 6-N the scattered light intensities P1 to PN currently input from the A / D circuit 22 correspond. be able to. The processing executed by the arithmetic circuit 23 is the same as that in the fourth embodiment.

(Ninth embodiment)
The liquid concentration measuring apparatus according to the first to eighth embodiments can be changed to the light transmittance type. For example, when the apparatus of the first embodiment is changed to the light transmittance type, the light emitting diodes 6-1 and 6-2 and the photodiode 7 are formed at the tip of the sensor unit 4b of the detector 2 as shown in FIG. Should be opposed to each other. As shown in FIG. 20, the relationship between the transmitted light intensity (product of gain G and transmitted light intensity) and the liquid concentration is a negative characteristic.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, another type of light source can be used as the light emitting element instead of the light emitting diode. Moreover, it can replace with a photodiode and can use other light receiving elements, such as a phototransistor and a photoelectric element.

  Instead of the intensity ratio R (P1 / P2), an evaluation value indicating the degree of difference between the two types of scattered light intensities such as the difference in scattered light intensity (P1-P2) can be used. Further, instead of multiplying the scattered light intensity P1 by the gain G, the influence of the liquid color on the scattered light intensity P1 may be corrected using another correction value calculated from an evaluation value such as an intensity ratio.

1 is a schematic cross-sectional view showing a liquid concentration measuring apparatus according to a first embodiment of the present invention. (A) is a front view which shows the front-end | tip part of the detector in 1st Embodiment, (B) is sectional drawing in the II-II line of (A). The block diagram which shows the detector and converter in 1st Embodiment. The block diagram which shows the calculating part in 1st Embodiment. The diagram (gain correction curve) which shows the relationship between an intensity ratio and a gain. The diagram which shows the relationship between a liquid concentration and scattered light intensity | strength. The diagram which shows the relationship between intensity ratio and scattered light intensity. A diagram (concentration calibration curve) showing the relationship of liquid concentration to the product of gain and scattered light intensity. The modification of a detector is shown, (A) is a front view which shows the front-end | tip part of a detector, (B) is sectional drawing in the IX-IX line of (A). The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 2nd Embodiment of this invention is provided. The detector with which the liquid concentration measuring apparatus of 3rd Embodiment of this invention is provided is shown, (A) is a front view which shows the front-end | tip part of a detector, (B) is sectional drawing in the XI-XI line of (A). The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 3rd Embodiment of this invention is provided. The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 4th Embodiment of this invention is provided. The block diagram which shows the converter in 4th Embodiment. The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 5th Embodiment of this invention is provided. The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 6th Embodiment of this invention is provided. The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 7th Embodiment of this invention is provided. The block diagram which shows the detector and converter with which the liquid concentration measuring apparatus of 8th Embodiment of this invention is provided. The schematic sectional drawing which shows the liquid concentration measuring apparatus of 9th Embodiment of this invention. A diagram (concentration calibration curve) showing the relationship of liquid concentration to the product of gain and transmitted light intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid to be measured 2 Detector 3 Converter 4 Casing 4a Casing body 4b Sensor part 6 Light emitting diode 7 Photodiode 8 Light emitting circuit 9 Light receiving circuit 11 Light emitting optical fiber 12 Light receiving optical fiber 13 Light emitting part 14 Light receiving part 16 LED drive circuit DESCRIPTION OF SYMBOLS 17 Oscillation circuit 18 LED switching circuit 19 Amplifier circuit 20 Synchronous detection circuit 21 Light emission LED identification circuit 22 A / D circuit 23 Arithmetic circuit 24 D / A circuit 25 LCD display 26 Setting switch circuit 27 V / I conversion circuit 31 Gain calculation part 32 Multiplier 33 Density Calculation Unit 37 Band Pass Filter Circuit 38 Detection Circuit 41 Storage Unit 42 Selection Unit

Claims (5)

A plurality of light emitting elements that irradiate the liquid under measurement with irradiation light having different wavelengths,
A drive circuit for selecting and driving one of the plurality of light emitting elements;
A light emitting element switching circuit for sequentially switching light emitting elements driven by the drive circuit;
And a single light receiving element for detecting the measurement light intensity is an intensity of scattered light or transmitted light of the illumination light from the light emitting element is irradiated the the liquid to be measured,
A light emitting element identifying circuit for identifying a light emitting element currently driven by the drive circuit based on a signal input from the light emitting element switching circuit and outputting a signal indicating the identification result;
An arithmetic circuit that calculates the liquid concentration of the liquid to be measured from the measurement light intensity input from the light receiving element and the signal input from the light emitting element identification circuit ;
The arithmetic circuit is:
A gain value for calculating an evaluation amount indicating the degree of difference in the measurement light intensity between irradiation lights having different wavelengths, and correcting an influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount A gain calculation unit for calculating
A multiplier for calculating a product of the gain value calculated by the gain calculation unit and the measurement light intensity;
A concentration calculator that calculates a liquid concentration from the product calculated by the multiplier and a concentration calibration curve stored in advance;
A liquid concentration measuring device comprising: A plurality of light emitting elements that irradiate the liquid under measurement with irradiation light having different wavelengths, and
A plurality of drive circuits for simultaneously flashing the corresponding light emitting elements at different frequencies, and
A single light receiving element for detecting a measurement light intensity which is an intensity of transmitted light or scattered light of light irradiated on the liquid to be measured from the plurality of light emitting elements;
A plurality of discriminations for discriminating the measurement light intensity by the light irradiated to the liquid to be measured from the corresponding light emitting element by using the difference in the blinking frequency of each light emitting element, each of which receives the measurement light intensity from the light receiving element. Circuit,
An arithmetic circuit for calculating the liquid concentration of the liquid to be measured from the measurement light intensity input from each discrimination circuit , and
The arithmetic circuit is:
A gain value for calculating an evaluation amount indicating the degree of difference in the measurement light intensity between irradiation lights having different wavelengths, and correcting an influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount A gain calculation unit for calculating
A multiplier for calculating a product of the gain value calculated by the gain calculation unit and the measurement light intensity;
A concentration calculator that calculates a liquid concentration from the product calculated by the multiplier and a concentration calibration curve stored in advance;
A liquid concentration measuring device comprising: The discrimination circuit is:
A band-pass filter circuit that allows measurement light intensity in a band including a blinking frequency of a corresponding light-emitting element to pass;
The liquid concentration measuring device according to claim 2, further comprising: a detection circuit that detects a signal output from a corresponding bandpass filter circuit and outputs the signal to the arithmetic circuit. A plurality of light emitting elements, each of which emits light having a different wavelength to the liquid to be measured, and whose light emitting portions are spaced from each other;
A plurality of drive circuits for causing the corresponding light emitting elements to blink at different frequencies;
A plurality of light receiving elements, each of which is disposed in proximity to a light emitting part of the corresponding light emitting element, and detects a measurement light intensity that is transmitted light or scattered light intensity emitted from the corresponding light emitting element;
An arithmetic circuit that calculates the liquid concentration of the liquid to be measured from the measurement light intensity input from each of the light receiving elements , and
The arithmetic circuit is:
A gain value for calculating an evaluation amount indicating the degree of difference in the measurement light intensity between irradiation lights having different wavelengths, and correcting an influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount A gain calculation unit for calculating
A multiplier for calculating a product of the gain value calculated by the gain calculation unit and the measurement light intensity;
A concentration calculator that calculates a liquid concentration from the product calculated by the multiplier and a concentration calibration curve stored in advance;
A liquid concentration measuring device comprising: A plurality of light emitting elements that irradiate light of different wavelengths to the liquid to be measured;
A drive circuit for selecting and driving one of the plurality of light emitting elements;
A light emitting element switching circuit for sequentially switching light emitting elements driven by the drive circuit;
A light receiving element for detecting a measurement light intensity which is an intensity of scattered light or transmitted light of the light emitted from the light emitting element to the liquid to be measured;
Each of the measurement light intensities is input from the light receiving element, and is driven by a signal input from the light emitting element switching circuit, and detects a plurality of measurement light intensities by light irradiated on the liquid to be measured from the corresponding light emitting elements. A synchronous detection circuit;
A plurality of smoothing circuits provided for each of the synchronous detection circuits, respectively, for holding the measurement light intensity output from the corresponding synchronous detection circuit;
A signal switching circuit for sequentially switching one of the plurality of smoothing circuits that outputs the measurement light intensity;
Based on a signal input from the signal switching circuit, a signal identifying circuit that identifies a current output of the measured light intensity among the plurality of smoothing circuits, and outputs a signal indicating the identification result;
An arithmetic circuit that calculates the liquid concentration of the liquid to be measured from the measurement light intensity input from the smoothing circuit and the signal input from the signal identification circuit ;
The arithmetic circuit is:
A gain value for calculating an evaluation amount indicating the degree of difference in the measurement light intensity between irradiation lights having different wavelengths, and correcting an influence of the liquid color of the liquid to be measured on the measurement light intensity from the calculated evaluation amount A gain calculation unit for calculating
A multiplier for calculating a product of the gain value calculated by the gain calculation unit and the measurement light intensity;
A concentration calculator that calculates a liquid concentration from the product calculated by the multiplier and a concentration calibration curve stored in advance;
A liquid concentration measuring device comprising:

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