Research On Dissolved Oxygen Technology Based On Fluorescence

Dissolved oxygen is essential for the survival of aquatic organisms.Dissolved oxygen concentration is an important indicator of water quality,which is affected by organic pollutants and reducing pollutants.Therefore,it is of great significance to study dissolved oxygen detection technology.This article has conducted in-depth research on dissolved oxygen sensor technology based on fluorescence.The main research contents are as follows.(1)The theory of dissolved oxygen concentration measurement based on the principle of fluorescence quenching is studied and a dissolved oxygen concentration measurement model based on the combination of fluorescence intensity and fluorescence lifetime was constructed.The quenching effect of dissolved oxygen on fluorescence reduces the intensity of fluorescence and shortens the lifetime of fluorescence.When a forward-biased sinusoidal signal is used as the excitation signal,the output signal is also a forward-biased sinusoidal signal.The DC component of the signal reflects the fluorescence intensity,which can be directly measured;the phase response of the sinusoidal component,the fluorescence lifetime,can be converted into a phase shift measurement.Combining fluorescence intensity and fluorescence lifetime can improve the reliability and accuracy of measurement.(2)A phase difference detection technique for sinusoidal signals with the same frequency is designed.The double-T negative feedback narrow-band filtering technique is used to preprocess the signal to filter out the interference signal,and the adaptive amplification technique is used to adjust the amplitude of the input signal to be consistent,and finally the phase difference is determined according to the amplitude of the difference signal.For the sinusoidal signal near 4k Hz,the measurement accuracy of the phase difference can reach 0.11 °.Using an analog circuit for measurement,there is no obvious delay,and the measurement speed is improved on the basis of ensuring the measurement accuracy.(3)The effect of ambient temperature on the fluorescence intensity,fluorescence lifetime and stern-volmer constant was studied,and a temperature compensation model was proposed based on the curve of the fluorescence intensity,fluorescence lifetime and stern-volmer constant with temperature.Experimental results show that this model can effectively solve the influence of temperature on the measurement results.(4)The optical structure of the dissolved oxygen sensor by fluorescence method is designed,and the software and hardware for measuring fluorescence intensity and fluorescence lifetime are developed,and the sensor for measuring dissolved oxygen in water by fluorescence method is realized.In the optical path design,the incident angle of the excitation light is adjusted to spatially separate the excitation light and the fluorescence,and then the fluorescence is band-pass filtered and focused to reduce interference.In the data processing,the error theory is used to combine the fluorescence intensity and the fluorescence lifetime to improve the reliability of the measurement,and the measurement accuracy is increased from 0.21mg/L and0.18mg/L to 0.12mg/L.