CN216051366U - Water quality on-line detection system based on liquid core waveguide - Google Patents
Water quality on-line detection system based on liquid core waveguide Download PDFInfo
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Abstract
The utility model relates to a water quality online detection system based on liquid core waveguide, which comprises a broadband light source, an input multimode optical fiber, a liquid core waveguide tube, a water sample inflow hole, a water sample outflow hole, an output multimode optical fiber, a spectrometer and a computer, wherein the broadband light source is connected with the input multimode optical fiber; the light beam emitted from the light source is transmitted to the liquid core waveguide tube through the input multimode fiber, simultaneously, a water sample to be detected flows through the liquid core waveguide tube to absorb the light beam, the absorbed light beam enters the spectrometer through the output multimode fiber, the spectrometer is used for converting an electric signal into a digital signal and outputting the digital signal to the computer, and three important indexes for indicating the water quality can be obtained through signal analysis: water body chromaticity, chemical oxygen demand and organic matter content; in the utility model, the liquid core waveguide tube wall has a refractive index lower than that of water, a waveguide structure with a total internal reflection effect is formed, detection light is bound in the waveguide tube, the path length of interaction between the light and a substance is increased, the transmission loss of an optical signal is reduced, and the sensitivity of the detector is improved.
Description
Technical Field
The utility model relates to the technical field of spectral analysis and photoelectric detection, in particular to a water quality online detection system and a water quality online detection method based on liquid core waveguide.
Background
China is a country with serious water shortage, and has serious water pollution problem and shortage of fresh water resources. Water environment monitoring and evaluation are basic means for controlling water pollution and preventing water environment degradation.
Compared with the traditional methods of chemical analysis, electrochemical analysis, chromatographic analysis and the like, the water quality detection based on the spectral analysis technology has the advantages of simple and convenient operation, no chemical reagent consumption, good repeatability, high measurement precision and quick detection, and can be quickly and conveniently applied to the online monitoring of water samples.
The water quality detection method based on the optical fiber sensor is widely applied. The optical fiber sensor has compact structure and higher detection precision and sensitivity, but has the defects that the detection signal is greatly influenced by the fluctuation of the light source intensity, the loss change of the connector and the like, the manufacturing steps are more complicated, and the cost is higher.
Disclosure of Invention
The utility model aims to provide an on-line water quality detection system based on a liquid core waveguide, aiming at the defects of the prior art. Because the refractive index of the Teflon AF is lower than that of water, when a pipeline made of the Teflon AF is filled with water or aqueous solution, incident light can be totally reflected at the interface of the Teflon AF and the water, the incident light is bound in the waveguide to be transmitted to form the liquid core waveguide, the path length of interaction between the light and a substance is increased, the transmission loss of an optical signal is reduced, and the sensitivity of the detector is improved.
The utility model relates to a water quality online detection system based on liquid core waveguide, which is shown in the attached figure 1 and comprises a broadband light source, an input multimode optical fiber, a liquid core waveguide tube, a water sample inflow hole, a water sample outflow hole, an output multimode optical fiber, a spectrometer and a computer; the light beam emitted from the light source is transmitted to the liquid core waveguide tube through the input multimode fiber, simultaneously, a water sample to be detected flows through the liquid core waveguide tube to absorb the light beam, the absorbed light beam enters the spectrometer through the output multimode fiber, the spectrometer is used for converting an electric signal into a digital signal and outputting the digital signal to the computer for processing, and three abstract indexes which indicate water quality can be obtained through signal analysis: the water chromaticity, the chemical oxygen demand and the organic matter content are detected by utilizing the liquid core waveguide total emission absorption light path, the light path and the utilization rate of the exciting light are increased, the sensitivity of the detector is improved, and the actual water sample can be detected quickly and conveniently.
The broadband light source adopts a deuterium lamp-halogen tungsten lamp as a test light source, and the wavelength range is 200-1100 nm.
The liquid core waveguide tube adopts a Teflon capillary tube with the refractive index of 1.29, the inner diameter is 401 mu m, and the outer diameter is 889 mu m. The transmission fiber is a multimode fiber with an inner diameter of 400 μm and an outer diameter of 730 μm. According to the Lambert-beer law, the water quality parameters are calculated by analyzing the spectral change of a water sample while the water sample circulates.
The water inlet and outlet holes on the liquid core waveguide tube are manufactured by femtosecond laser, and the diameter of the water inlet and outlet holes is 100-150 mu m.
The liquid core waveguide tube and the transmission optical fiber are connected through AB glue.
The utility model discloses three important indexes for indicating water quality: obtaining the water chromaticity by using a water chromaticity determination method based on three-wavelength transmittance; the chemical oxygen demand is obtained by comparing the spectral area integral of the actual water sample with the spectral area integral of the potassium hydrogen phthalate standard solution; and (3) calculating the 'light absorption coefficient' of each organic matter in the actual water sample by using a least square method and a Lambert-beer law superposition principle to obtain the concentration of each component of the organic matter.
Compared with the prior art, the utility model has the following advantages:
(1) the utility model adopts the liquid core waveguide structure to detect the water sample, and has simpler structure, easy realization and high feasibility compared with an optical fiber sensor.
(2) According to the utility model, the Teflon capillary tube is adopted to manufacture the liquid core waveguide tube, the liquid core waveguide tube is adopted to be designed by adopting the liquid core waveguide full-emission absorption light path, and when a water sample to be detected flows through the capillary tube, a liquid waveguide structure with a high refractive index outside and a low refractive index inside is formed, so that the detection light signal is limited in the waveguide, the light loss is greatly reduced, and the detection precision is improved.
Drawings
FIG. 1 is a schematic diagram of a water quality on-line detection system device based on a liquid core waveguide.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. These specific embodiments and examples are intended to illustrate the utility model, but not to limit the utility model.
Referring to the experimental device diagram in the attached drawing 1, during measurement, light beams emitted from a light source (1) are transmitted to a liquid core waveguide tube (3) through an input multimode fiber (2), a water sample to be measured enters the liquid core waveguide tube (3) from a water sample inflow hole (4), the light beams are absorbed and then flow out from a water sample outflow hole (5), the absorbed light beams enter a spectrometer (7) through an output multimode fiber (6), the spectrometer is used for converting electric signals into digital signals and outputting the digital signals to a computer (8) for processing, and three important indexes indicating water quality can be obtained through signal analysis: the water chromaticity, the chemical oxygen demand and the organic matter content can be detected quickly and conveniently.
Water body chromaticity determination method based on three-wavelength transmittance
(1) Preparing a colorimetric standard solution, selecting 595nm, 555nm and 445nm as characteristic wavelengths for measuring the water body chromaticity, and recording lambda1M＝595nm、λ2M＝555nm、λ3M＝445nm。
(2) According to the calculation formula of the tristimulus value X, Y, Z of the CIE1931 standard colorimetry system given by the national standard GB/T3977-:
in the formula, k represents a normalization coefficient;
a spectral distribution representing a color stimulus function;
expressing a CIE1931 standard colorimetric system color matching function; Δ λ represents a wavelength interval;
color stimulus function:
wherein τ (λ) represents the spectral transmittance of the object; s (λ) represents the relative spectral power distribution of the standard illuminant employed.
Setting three characteristic wavelengths lambda1M、λ2M、λ3MThree parameters tau are introduced corresponding to three peaks of the product of the relative spectral power distribution S (lambda) and the color matching function respectively1、τ2、τ3:
In the formula, τ1、τ2、τ3Respectively taking lambda as the integral domain1M、λ2M、λ3MIn the vicinity of the peak.
The transmission is given as a percentage, i.e.:
Ti＝τi×100％
the above formulas are combined to obtain an approximate calculation formula of the tristimulus values:
X＝(0.733×T1)+(0.1974×T3)
Y＝T2
Z＝1.1822×T3
in the formula, T1、T2、T3Respectively represent lambda1M、λ2M、λ3MThe percent transmission of (d);
(3) and calculating the intermediate color difference of the water sample chromaticity by using the tristimulus values, and then establishing correlation with the chromaticity standard solution to calculate the final chromaticity value.
Directly substituting tristimulus values into CIE LAB color difference formulas in different uniform color spaces recommended by national standards to calculate the color difference value of a chromaticity standard solution relative to reagent water;
secondly, a correction factor F is calculated by using a formula,
in the formula CnExpressing the colorimetric value of the colorimetric standard solution; l represents the absorption optical path of the water sample, namely the length of the cuvette, and the measurement range unit is cm; (DE)nDE value of the colorimetric standard solution.
And thirdly, performing curve fitting on the data result obtained in the step two to obtain a linear fitting curve. In order to calculate the colorimetric value of the water sample conveniently, a working curve based on a national standard color difference formula is expressed as
Form, the following results were obtained:
the water chromaticity C can be obtained by the above formula.
Chemical oxygen demand measuring method
(1) Preparing a potassium hydrogen phthalate solution: and (3) putting a proper amount of potassium hydrogen phthalate in a drying box, and drying for 2 hours at the temperature of 105 ℃. 0.4251g of dried hydrogen phthalate is dissolved in pure water, diluted to a scale mark in a 1000mL volumetric flask and shaken up. The theoretical chemical oxygen demand value of the prepared stock solution is 500 mg/L.
(2) The water quality detection system based on the liquid core waveguide, which is constructed by the utility model, is used for measuring the absorption spectrum of the potassium hydrogen phthalate standard solution in the 200-400nm ultraviolet band.
(3) The chemical oxygen demand of the potassium hydrogen phthalate standard solution is measured by using an area integration method. Taking the area integral of the ultraviolet absorption spectrum of the potassium hydrogen phthalate standard solution as an independent variable and marking the area integral as x, taking the chemical oxygen demand value of the standard solution as a dependent variable and marking the area integral as y, and performing linear fitting on x and y by using a least square method to establish a standard calibration curve.
(4) And comparing the spectral area integral of the actual water sample with the spectral area integral of the potassium hydrogen phthalate standard solution to obtain the chemical oxygen demand of the actual water sample.
Analysis of organic content
(1) The water quality detection system based on the liquid core waveguide, which is built by the utility model, is used for measuring the absorption spectrum of an actual water sample in an ultraviolet band, and performing multi-component analysis on mixed organic matters, namely benzene, dimethylbenzene, chlorobenzene and nitrobenzene.
(2) And (3) carrying out multi-component analysis on the actual water sample by using a least square method.
The absorbance of an actual water sample at the jth characteristic wavelength can be expressed as follows according to the Lambert-beer law superposition principle:
Aj＝αj1V1+αj2V2+αj3V3+αj4V4
in the formula, V1、V2、V3、V4Respectively representing the volume concentrations of benzene, dimethylbenzene, chlorobenzene and nitrobenzene in an actual water sample; alpha is alphaj1、αj2、αj3、αj4Respectively represents the corresponding 'absorptivity' of benzene, dimethylbenzene, chlorobenzene and nitrobenzene at the jth characteristic wavelength.
② multi-component analysis is carried out on the actual water sample by selecting the characteristic wavelengths of 250nm, 225nm, 260nm, 265nm and 270nm, namely j is 5. A set of linear equations is obtained
{Ai＝αj1V1+αj2V2+αj3V3+αj4V4；j＝1，2，…，5}
Thirdly, the absorption coefficient is obtained by a standard curve method.
Taking the solution of the "absorption coefficient" of one of the organic substances as an example, the absorption spectra of the organic substances at different concentrations are measured, the volume concentration is taken as an independent variable, the absorbance values at the respective characteristic wavelengths are taken as dependent variables, curve fitting is carried out, and the slope of the obtained fitted straight line is the "absorption coefficient" of the organic substance at the corresponding characteristic wavelength. The solution method of the absorption coefficient of other organic matters also adopts a standard curve method.
Substituting the alpha obtained by calculation into a formula
V＝(αTα)-1αTA
And (4) calculating the concentration of each component in the mixed solution.
Claims (6)
1. The utility model provides an online detecting system of quality of water based on liquid core waveguide which characterized in that: the detection system comprises a broadband light source (1), an input multimode optical fiber (2), a liquid core waveguide tube (3), a water sample inflow hole (4), a water sample outflow hole (5), an output multimode optical fiber (6), a spectrometer (7) and a computer (8); light beam from broadband light source (1) sends transmits liquid core waveguide pipe (3) through input multimode fiber (2), the water sample that awaits measuring simultaneously gets into liquid core waveguide pipe (3) from water sample inflow hole (4), the water sample that awaits measuring takes place the absorption effect to the light beam of transmission in the waveguide pipe, then flow out from water sample outflow hole (5), the light beam after being awaited measuring water sample part absorption gets into spectrum appearance (7) through output multimode fiber (6) in, utilize the spectrum appearance to convert the electrical signal to digital signal output to computer (8), can obtain the three important index that indicates quality of water through signal analysis: water chromaticity, chemical oxygen demand, and organic matter content.
2. The on-line water quality detection system based on the liquid core waveguide as claimed in claim 1, wherein: the broadband light source (1) is a deuterium lamp-halogen tungsten lamp, and the wavelength range is 200-1100 nm.
3. The on-line water quality detection system based on the liquid core waveguide as claimed in claim 1, wherein: the inner diameter of the multimode optical fiber is 600 μm, and the outer diameter of the multimode optical fiber is 960 μm.
4. The on-line water quality detection system based on the liquid core waveguide as claimed in claim 1, wherein: the liquid core waveguide tube (3) adopts a Teflon capillary tube with the refractive index of 1.29, the inner diameter is 1000 mu m, and the outer diameter is 1600 mu m.
5. The on-line water quality detection system based on the liquid core waveguide as claimed in claim 1, wherein: the water sample inflow hole (4) and the water sample outflow hole (5) on the liquid core waveguide tube (3) are processed by laser, and the diameter of the water sample inflow hole and the water sample outflow hole is 100-150 micrometers.
6. The on-line water quality detection system based on the liquid core waveguide as claimed in claim 1, wherein: the liquid core waveguide tube (3) is connected with the transmission optical fiber in a sealing mode through AB glue.
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| CN202121105158.7U CN216051366U (en) | 2021-05-20 | 2021-05-20 | Water quality on-line detection system based on liquid core waveguide |
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| CN202121105158.7U CN216051366U (en) | 2021-05-20 | 2021-05-20 | Water quality on-line detection system based on liquid core waveguide |
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