JPH09281034A - Optical concentration measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a concentration by using one measuring cell without installing a plurality of measuring devices in which the length of every measuring cell is different when the range of a concentration to be measured is wide and when an accuracy is required in an optical concentration measuring apparatus by which a concentration is measured in such a way that light is projected on sample water and that a sample light signal which is transmitted through the sample water is compared with a reference light signal. SOLUTION: A measuring cell body 11a which comprises a short light path (x) and a long path (y) which are used to pass light projected by an identical light source 2 is installed. A semitransparent mirror 13a and a photoelectric transducing element 15a are installed on the line of the short light path (x), and a semitransparent mirror 13b and a photoelectric transducing element 15b are installed on the line of the long light path (y). When the value of a concentration to be measured is low, a sample signal (the output of the photoelectric transducing signal 15b) on the side of the long light path (y) is selected so as to be measured. When the value of the concentration to be measured is high, a sample signal (the output of the photoelectric transducing element 15a) on the side of the short light path (x) is selected so as to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device used in the fields of tap water, sewage, etc., for measuring the concentration of a target substance in water on the basis of attenuation due to absorption or scattering of light having a specific wavelength.

[0002]

2. Description of the Related Art A turbidity meter is an example of a measuring instrument that is often incorporated in a water quality monitor for water supply related to water supply and used for monitoring water quality at a water purification plant. The distribution water quality monitor is used to measure the distribution water quality (p in a distribution reservoir or distribution pipe network)
H, residual salt, turbidity, chromaticity, conductivity, water pressure, temperature) are continuously measured. The measuring instrument for measuring turbidity and chromaticity with this device is based on the principle of absorption and scattering of light related to the present invention.

This turbidity meter measures turbidity and chromaticity at the same time with a single detecting section. That is, the turbidity is set to a wavelength of 66
Measured with 0 nm light, chromaticity is 390 n wavelength with turbidity correction
It is a water quality measuring instrument that simultaneously and continuously measures light of around m, and its measurement range is a low concentration range of turbidity 0 to 4 degrees and chromaticity 0 to 10 degrees because the target is tap water.

FIG. 3 shows the structure of the turbidity meter, which is 1 _a
Is the measuring cell body. The measuring cell body 1a includes the measurement light transmitting glass window 1 _b1, 1 _b2, test water inlet 1 _c, the test water outlet 1 _d. Reference numeral 2 is a light source, 3 is a half mirror that divides light into two optical paths, 4 is a reference (reference) signal measurement photoelectric conversion element, and 5 is a sample signal measurement photoelectric conversion element. 6 is 2 measured by the photoelectric conversion elements 4 and 5
This is an amplifier circuit that performs logarithmic amplification by subtracting the types of signals.
Reference numeral 7 denotes an arithmetic processing unit that arithmetically processes a signal converted into a signal proportional to a physical quantity with reference to the reference signal in the amplifier circuit 6 and replaces it with a physical quantity such as turbidity or chromaticity.

Further, the light source 2, the half mirror 3, the measurement light transmitting glass windows 1 _b1 and 1 _b2 , and the sample signal measuring photoelectric conversion element 5 are arranged on the same axis, and the light flux from the light source 2 is also on the same line. Thus, the angles of the half mirror 3 and the measurement light transmitting glass windows 1 _b1 and 1 _b2 are adjusted.

[0006] the test water flows continuously from the test water inlet 1 _c in the measurement cell body 1 _a, and flows out from the test water outlet 1 _d. The test light in the measuring cell is irradiated with a measuring light beam from the light source 2, and calculation is performed based on two kinds of measurement signals, a sample light signal of a light beam passing through the test water and a reference light signal of a light beam not passing through the test water. Turbidity and chromaticity are obtained by the treatment.

U used for continuous measurement of the amount of organic pollutants such as sewage treated water and other discharged water.
The V meter (organic pollution monitor) is based on the following measurement principle. Ultraviolet absorption of inorganic substances is hardly observed at wavelengths of 250 nm or more, while that of organic substances is 25
It exhibits some absorption even at a wavelength of about 4 nm. Therefore 2
Absorption at wavelengths above 54 nm is mostly organic. It is possible to measure the organic pollutant concentration using this principle. This UV meter also has the same structure as in FIG.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The absorptiometric method is used as the measuring principle of an apparatus that measures the concentration of a target substance in water based on the absorption of light of a certain specific wavelength and the attenuation due to the scattering of light, such as a V meter.

The absorptiometric method is to obtain the relationship between the absorbance and the concentration of a standard solution having a series of different concentrations as a calibration curve in advance, measure the absorbance of the test water, and determine the purpose of the test water from the calibration curve. This is a method of determining the concentration of a substance.

In the measuring device, the arithmetic processing unit 7 is provided with a function of calculating the concentration using a calibration curve. This calibration curve is not widely applicable from low concentration to high concentration.
As shown in (4), when a certain concentration (a) is exceeded, a linear relationship between the measurement signal and the standard solution concentration is not established. Therefore, when the test water concentration is equal to or higher than the value a, the error becomes large, and as a result, measurement becomes impossible.

Further, when the measurement of the concentration a or more is required, it can be dealt with by reducing the length of the optical path that passes through the test water defined by the length of the measuring cell. According to Lambert-Beer's law, if the concentration of the sample water is the same, if the length of the optical path is halved, the measurement signal will also be halved. That is, when the length of the optical path is halved, the measured density range is doubled, and the density 2 · a value can be measured.

Conventionally, even if the range of test water concentration to be measured is wide and its measurement accuracy is required for water quality management and control even at a low concentration level, measuring instruments with different measuring cell lengths are used. There was a problem that it was necessary to install multiple units and measure from low level to high level.

The present invention has been made in view of the above points, and an object thereof is to provide a measuring cell having a wide measuring concentration range and high accuracy without installing a plurality of measuring instruments having different measuring cell lengths. An object of the present invention is to provide an optical density measuring device capable of measuring in one measuring cell.

[0014]

In order to achieve the above-mentioned object, the present invention (1) projects light onto a test water and compares the sample optical signal transmitted through the test water with a reference optical signal. In an optical concentration measuring device that performs concentration measurement, an optical path for passing light projected from the same light source, having a plurality of optical paths of different lengths, and providing a measuring cell through which the test water flows, The density is measured by switching the plurality of optical paths in accordance with the density measurement value. (2) The means for switching the plurality of optical paths is configured to convert a sample optical signal obtained by a photoelectric conversion element provided for each optical path. (3) The means for switching the plurality of optical paths is configured to move the measurement cell to select a desired optical path among the plurality of optical paths from among photoelectric conversion elements provided for each optical path. Connect one photoelectric conversion element and light source (4) Switching of the plurality of optical paths is performed by switching to a long optical path when the concentration measurement value is equal to or less than a predetermined value and switching to a short optical path when the concentration measurement value is equal to or more than a predetermined value. I am trying.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1, the same parts as those in FIG. 3 are indicated by the same reference numerals. 1 is different from FIG. 3 in that the measurement cell main body 11a is formed so that the short optical path x and the long optical path y are formed in parallel with each other.
1 _b1 , 11 _b2 , 11 _b3 , a test water inlet 11 _c , and a test water outlet 11 _d , and a half mirror 13a on the line of the short optical path x.
The photoelectric conversion element 15a and the half mirror 13b and the photoelectric conversion element 15b are arranged on the line of the long optical path y.

Reference numeral 8 is a lens for collimating the light flux of the light source, and 13
Reference numerals a and 13b denote half mirrors for splitting the parallelized light on the short optical path x side and the long optical path y side into two optical paths. 14
Reference numerals a and 14b are photoelectric conversion elements that measure a reference signal (reference signal) for measurement calculation, and reference numerals 15a and 15b are photoelectric conversion elements that measure a measurement signal (sample signal) of water detection. Reference numeral 16 is a photoelectric conversion element 14 for measuring a reference signal.
a, 14b and the photoelectric conversion element 15a for measuring the sample signal,
It is an amplifier circuit that performs logarithmic amplification by subtracting each of the two types of signals measured at 15b. Reference numeral 17 denotes an arithmetic processing unit that arithmetically processes the signal converted into a signal proportional to the physical quantity in the amplifier circuit 16 with the reference signal as a reference and replaces it with a physical quantity such as turbidity or chromaticity.

The half mirror 13a, the measurement light transmitting glass windows _11b1 and _11b3 , and the sample signal measuring photoelectric conversion element 15a are arranged on the same axis of the short optical path x, and the light source 2
The angles of the half mirror 13a and the measurement light transmitting windows _11b1 and _11b3 are adjusted so that the light beams from the lens 8 onward are on the same line.

Further half mirror 13b, the measuring light transmitting glass window 11 _b1, 11 _b2, the sample signal measuring photoelectric conversion element 15b is disposed on the same axis of Nagamitsuro y, the light source 2
The angles of the half mirror 13b and the measurement light transmission windows _11b1 and _11b2 are adjusted so that the light beams from the lens 8 onward are on the same line.

In the apparatus of FIG. 1, in the normal measurement in the range of the proportional limit value a value or less shown by the calibration curve of FIG. 4, the long optical path y
The arithmetic processing unit 17 determines that the result measured on the side is output. In the unlikely event that the measured value output exceeds the a value,
According to the Lambert-Beer law, the maximum measurable value (y / x) calculated by comparing the optical path lengths (y / x) × a is measured and output in the measuring range on the short optical path x. If the measurement value on the short optical path x side becomes (x / y) × a or less, the measurement on the long optical path y becomes possible again, and the operation is switched to the measurement on the long optical path y side.

[0020]

EXAMPLE The switching between the short optical path x and the long optical path y may be accomplished by moving the measuring cell body 11a by the external drive motor 19 as shown in FIG. That is, half mirror 1
3, one photoelectric conversion element 15 is provided, and the arithmetic processing unit 27
Is used to drive and control the external drive motor 19 to move the measurement cell body 11a.

In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 13 is a half mirror that divides the light source into two optical paths, and 14 is a photoelectric conversion element that measures a reference signal (reference signal) for measurement calculation. Reference numeral 15 denotes a photoelectric conversion element that measures a measurement signal (sample signal) of water detection, and is arranged on an extension of a line connecting the light source 2 and the half mirror 13. Reference numeral 26 denotes a photoelectric conversion element 14 for measuring a reference signal and a photoelectric conversion element 15 for measuring a sample signal.
This is an amplifier circuit that performs logarithmic amplification by subtracting the two types of signals measured in. An arithmetic processing unit 27 performs arithmetic processing on the signal converted into a signal proportional to the physical quantity in the amplifier circuit 26 with reference to the reference signal and replaces it with a physical quantity such as turbidity or chromaticity.

The light source 2, the half mirror 13, the measurement light transmitting glass windows 11 _b1 and 11 _b2 or 11 _b3 , and the sample signal measuring photoelectric conversion element 15 are arranged on the same axis line in each optical path, and the light source 2 From the half mirror 13 and the measurement light transmitting glass window 11 _b1 so that the light flux from
And 11 _b2 or 11 _b3 are adjusted respectively.

The measuring cell body 11a having two long and short optical paths has a function of switching the measuring optical path to the x or y side according to the output result of the arithmetic processing unit 27 by the external drive motor 19 to perform measurement.

Even in the case of such a configuration, in the normal measurement within the range of the proportional limit value a value or less, the arithmetic processing unit 27 controls the position by the external drive motor 19 so as to measure on the long optical path y side. . Should the measured value output exceed the a value, the maximum measurable value (y / x) calculated by comparing the optical path lengths according to Lambert-Beer's law (y / x) x measured in the measurement range of the short optical path x As possible, the external drive motor 19 is swiftly moved by the control signal from the arithmetic processing unit 27 to form the short optical path x measurement path.

The measured value on the short optical path x side is (x / y) ×
If it becomes a or less, measurement on the long optical path y side becomes possible again, so the measurement cell body 11a is moved by the external drive motor 19 to switch to measurement on the long optical path y side.

[0026]

As described above, according to the present invention,
The following excellent effects can be obtained.

(1) By having a plurality of optical path lengths in the measuring cell, it is possible to measure a wide range beyond the normal measuring range from low level to high level without degrading the accuracy. For example, when the normal measurement range of turbidity is 0 to 4 degrees, the maximum turbidity of 40 degrees can be measured by providing an optical path with an optical path length of 1/10.

(2) With the measuring device of the present invention, a turbidity meter, a chromaticity meter, a UV meter, etc., which have conventionally been used separately for water supply and sewerage due to the limitation of the measurement concentration range, can be used as common equipment specifications.

(3) For confirming the cleaning effect at the time of backwashing the water purification plant filtration tank, controlling the cleaning water passage time, calculating the pollution load, etc.
The measuring device of the present invention can be used.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional turbidity meter.

FIG. 4 is a characteristic diagram showing a calibration curve of a measuring device.

[Explanation of symbols]

2 ... Light source 8 ... Lens 11a ... Measuring cell main body 13, 13a, 13b ... Half mirror 14, 14a, 14b, 15, 15a, 15b ... Photoelectric conversion element 16, 26 ... Amplification circuit 17, 27 ... Arithmetic processing section

Claims (6)

[Claims] 1. An optical concentration measuring device for projecting light onto a sample water and comparing the sample optical signal transmitted through the sample water with a reference optical signal to measure the concentration. It is an optical path for passing, has a plurality of optical paths of different lengths, provides a measurement cell through which the test water flows, and switches the plurality of optical paths according to the concentration measurement value to perform concentration measurement. Characteristic optical density measuring device. 2. The optical density measuring device according to claim 1, wherein the means for switching the plurality of optical paths is performed by switching a sample optical signal obtained by a photoelectric conversion element provided for each optical path. 3. The means for switching the plurality of optical paths is configured to move the measurement cell so that one of the photoelectric conversion elements provided with a desired optical path among the plurality of optical paths. The optical density measuring device according to claim 1, wherein the optical density measuring device is performed by matching with a path connecting the light source and the light source. 4. The switching of the plurality of optical paths is performed by switching to a long optical path when the density measurement value is a predetermined value or less and switching to a short optical path when the density measurement value is a predetermined value or more. The optical density measuring device described. 5. The optical concentration measuring device according to claim 1, wherein the plurality of optical paths of the measuring cell are two optical paths, a long optical path and a short optical path. 6. The optical density measuring apparatus according to claim 3, wherein an external driving motor is used as the moving unit of the measuring cell.