How to Detect Water Chroma by Fiber Optics Sensor
author: Susan
2022-01-04
Challenge
The methods used by my country's environmental protection agencies to measure water chroma still use the national standard, namely, visual colorimetry and dilution multiples. These two methods are highly subjective and can easily lead to huge deviations in test results. As a common method for measuring water quality parameters, the transmission method can be used for the detection of water chroma. By analyzing spectral data, the stability of water chroma detection and the average value of relative errors have been greatly improved. The plastic optical fiber evanescent wave sensor has the characteristics of high sensitivity and low detection limit. In this section, the sensor is used for water chroma detection and its spectral data is analyzed.
Water chroma solution
The main components of the system structure include light sources, conductive fiber, plastic fiber evanescent wave sensor, reaction cell, miniature spectrometer and PC. Figure 1, the performance parameters of each part are as follows:
The methods used by my country's environmental protection agencies to measure water chroma still use the national standard, namely, visual colorimetry and dilution multiples. These two methods are highly subjective and can easily lead to huge deviations in test results. As a common method for measuring water quality parameters, the transmission method can be used for the detection of water chroma. By analyzing spectral data, the stability of water chroma detection and the average value of relative errors have been greatly improved. The plastic optical fiber evanescent wave sensor has the characteristics of high sensitivity and low detection limit. In this section, the sensor is used for water chroma detection and its spectral data is analyzed.
Water chroma solution
The main components of the system structure include light sources, conductive fiber, plastic fiber evanescent wave sensor, reaction cell, miniature spectrometer and PC. Figure 1, the performance parameters of each part are as follows:
Fig. 1 Water chroma detection system
Optosky Halogen Tungsten Light source ATG1100, output spectrum 360~2500nm with SMA905 interface;
Conductive fiber: UV-Visible fiber, 600μm diameter UV/Visible fiber, optical fiber connector is a SMA905 standard interface;
Miniature spectrometer: ATP2000P optical fiber spectrometer, spectrum receiving range: 200~1100nm, signal-to-noise ratio> 600:1, resolution of 0.05~3nm, USB interface, can reflect the change of the test volume in real time.
The main working principle of the system
The light source is turned on for 30 minutes and the output spectrum is stable, and then the test is started.
The light source outputs light covering the entire visible range and is coupled into the conductive fiber. In the reaction cell, the light beam passes through the optical fiber evanescent wave sensor to generate information interaction with the external environment, and the light beam is transmitted to the miniature spectrometer for demodulation, and the spectrum data changes are read in real time on the PC. , And use the 1976 (LUV) color difference formula to analyze and interpret the spectral data to obtain the chroma parameters, and at the same time, the degree of pollution of the water body can be judged.
Test Result
Set up the water quality color measurement system with the optical fiber sensor according to Figure 1, and configure the platinum-cobalt standard experimental solution. The image of the change in absorbance of the platinum-cobalt standard solution with wavelength when the optical fiber sensor is used is shown in Figure 2.
Conductive fiber: UV-Visible fiber, 600μm diameter UV/Visible fiber, optical fiber connector is a SMA905 standard interface;
Miniature spectrometer: ATP2000P optical fiber spectrometer, spectrum receiving range: 200~1100nm, signal-to-noise ratio> 600:1, resolution of 0.05~3nm, USB interface, can reflect the change of the test volume in real time.
The main working principle of the system
The light source is turned on for 30 minutes and the output spectrum is stable, and then the test is started.
The light source outputs light covering the entire visible range and is coupled into the conductive fiber. In the reaction cell, the light beam passes through the optical fiber evanescent wave sensor to generate information interaction with the external environment, and the light beam is transmitted to the miniature spectrometer for demodulation, and the spectrum data changes are read in real time on the PC. , And use the 1976 (LUV) color difference formula to analyze and interpret the spectral data to obtain the chroma parameters, and at the same time, the degree of pollution of the water body can be judged.
Test Result
Set up the water quality color measurement system with the optical fiber sensor according to Figure 1, and configure the platinum-cobalt standard experimental solution. The image of the change in absorbance of the platinum-cobalt standard solution with wavelength when the optical fiber sensor is used is shown in Figure 2.
Figure 2 The absorbance of the platinum-cobalt solution measured by the fiber optics sensor Figure 3 The tristimulus value of the platinum-cobalt solution measured by the fiber optics sensor
It can be seen that the change trend of the absorbance image curve measured by the optical fiber evanescent wave sensor is similar to that of the transmission method. The curve in Figure 2 is more noisy. At the same time, the absorbance value measured by the sensor is much larger than the transmission method (1cm cuvette). The larger the ordinate value of the absorbance curve, the more accurate the measured tristimulus value of the solution spectrum. Perform average filtering (∆λ=5) on the data in Figure 2 to remove noise, and calculate the tristimulus values of different chroma as shown in Figure 3.
It can be seen that the change trend of the absorbance image curve measured by the optical fiber evanescent wave sensor is similar to that of the transmission method. The curve in Figure 2 is more noisy. At the same time, the absorbance value measured by the sensor is much larger than the transmission method (1cm cuvette). The larger the ordinate value of the absorbance curve, the more accurate the measured tristimulus value of the solution spectrum. Perform average filtering (∆λ=5) on the data in Figure 2 to remove noise, and calculate the tristimulus values of different chroma as shown in Figure 3.
Figure 4 The chromatic aberration measured by the transmission method and the optical fiber sensor changes with the chroma
Figure 5 The second-order fitting curve of the transmission method and the optical fiber sensor
Figure 5 The second-order fitting curve of the transmission method and the optical fiber sensor
It can be seen from Figure 5 that the goodness of fit of the second-order fitting curve of the plastic optical fiber evanescent wave sensor is greater than that of the transmission method. Through analysis and calculation, the sensitivity of the plastic optical fiber sensor is 2.65 times that of the transmission method, the lowest detection limit is 0.065372/C, and the average relative error is 1.6%. By studying the application of plastic optical fiber evanescent wave sensor in water chroma, analyzing and comparing the spectral data, the secondary fitting formula of color difference and chroma under the condition of using the sensor is obtained: ∆E=0.36+0.04C+0.00002C2 (R2=0.99351), through calculation, the conclusion is drawn that the plastic optical fiber sensor is The detection sensitivity is 2.65 times that of the transmission method, and the lowest detection limit is 0.065372/C. At this time, the average relative error is 1.6%.
Conclusion
In this experiment, a plastic optical fiber sensor based on the principle of evanescent wave was developed. The sensor can effectively overcome the influence of subjective factors. Combined with the optical fiber spectrometer, it can realize online in-situ measurement and improve water chroma.
Compared with the transmission method, the sensitivity is increased by 2.65 times, the lowest detection limit is 0.065372/C, and the average relative error is 1.6%.
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ATP2000P 100W Halogen Tungsten Light Source UV-Visible Fibers
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Conclusion
In this experiment, a plastic optical fiber sensor based on the principle of evanescent wave was developed. The sensor can effectively overcome the influence of subjective factors. Combined with the optical fiber spectrometer, it can realize online in-situ measurement and improve water chroma.
Compared with the transmission method, the sensitivity is increased by 2.65 times, the lowest detection limit is 0.065372/C, and the average relative error is 1.6%.
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ATP2000P 100W Halogen Tungsten Light Source UV-Visible Fibers
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