Research And Design Of Portable UV₂₅₄ Detector On Testing Water Quality

As the rapid development of our society and culture,drinking water’s sanitation are commonly concerned. There is water pollution problems in all our country, but only differ in degree. Water pollution covered physics, chemistry, biology, etc. After series of traditional treatment process such as coagulation, sedimentation, filtration and disinfection,source water becomes tap water. While most of the physical and biological pollutants are removed, chemical pollution, especially toxic and harmful organic pollutants, has always existed.UV₂₅₄ value is used to characterize the absorption or transmittance of water in 254 nm ultraviolet light wave in per unit cuvette path. Common organic pollutants have benzene rings and（ or） conjugated double bonds, which will show obvious absorption peaks or characteristic peaks in the ultraviolet band. Besides, existing researches have already proved that UV₂₅₄ value is highly correlated with parameters indicating organic pollutant concentration, TOC, COD and BOD, for example. And UV₂₅₄ value can be a substitution of them. So UV₂₅₄ value is a comprehensive index which reflects the concentration of organic pollutants. The quality and toxicity of water can be predicted by UV₂₅₄ value.With ultraviolet spectrophotometer, UV₂₅₄ value could be obtained. However,ultraviolet spectrophotometer is of high cost, poor portability and is with long warm-up time. Thus the need of quick testing and portability in water quality field test will not besatisfied. At present, TDS pen, which shows TDS based on the principle of detecting the conductivity of water sample, is widely used to test water quality in water quality field test.But TDS is no certain relation with the safety of drinking water, so we can say, to a certain extent, the public is misled. In view of this, it is urgent to design and manufacture a portable UV₂₅₄ detector which can be applied to water quality field test.Based on this need, this study firstly adopts ultraviolet light emitting diode（ UVLED）and silicon photocell to act as light source and detecting probe, respectively. Then a manual portable UV₂₅₄ detector is designed and assembled. Subsequently, water samples in multiple regions are tested by this detector in order to confirm its feasibility.Secondly, in order that accuracy can be improved, a scheme on automatic portable UV₂₅₄ detector is presented, following a hardware scheme and a software develop flow.The study includes:Objective: To design and assemble a manual portable UV₂₅₄ detector on water quality test and to confirm the feasibility of this detector.Methods: After understanding the basic principle of photoelectric detection and connecting with the practice, UVLED with a peak wavelength of 265 nm, linear silicon photocell and other related materials were purchased, then a circuit was designed and a detector was assembled, an indirect UV₂₅₄ testing method was presented in the meantime.After collection of water samples in multiple regions and testing of their absorbance by ultraviolet visible spectrophotometer 752 C, conversion factor K that can be applied to indirect UV₂₅₄ testing method was obtained by statistical analysis. To verify the linear relationship between the voltage value tested by the detector and the transmittance tested by 752 C of the same sample, transmittance was used as the Y-axis and voltage value as the X-axis by drawing standard curve. Two standard curves were drawn, one for KHP,another for tap water collected from Hankou. By using the two standard curves and conversion factor K obtained, the water samples from multiple regions were tested by the detector and UV₂₅₄ value was calculated. Through comparing the two UV₂₅₄ value that wastested by 752 C and the detector, feasibility of the detector was confirmed.Results: The testing results of 752 C were regarded as true value, to calculate UV₂₅₄ by UV265, K was 1.21. The maximum theoretical error calculated by K among the water samples was 0.2%, and the minimum theoretical error was 0. The pertinency of the two standard curves is good, with R2 was 0.9999 and 0.9998, respectively. The maximum error of UV₂₅₄ among the water samples tested by the detector was 0.7%, and the minimum error was 0.1%.Conclusion: The indirect method of testing UV₂₅₄ using UVLED as light source with peak wavelength of 265 nm is feasible in the premise that the maximum allowable misalignment is 1%. The manual portable UV₂₅₄ detector using UVLED of 265 nm peak wavelength and silicon photocell as core elements is able to detecting UV₂₅₄ and meet the need for portability.Design and Prospects: Considering the cost and the development of electronic component, electronic components were selected, including UVLED, silicon photocell,operational amplifier ICL7650, MCU ATMEGA88 A, 12864 LCD with Chinese fonts,nonencoded keyboard. A hardware scheme and a software develop flow were presented.The hardware design includes the design of constant current power supply circuit and amplified circuit schematics and the confirmation of the function of keys. The software design includes the main program flow, A/D conversion flow, LCD display flow, keyboard control flow and data processing flow.The design scheme has a high degree of automation,which meet the need for portability in water quality testing, and theoretically, this automatic detector should be faster and more accurate than the manual one.