Development Of Dissolved Oxygen Sensor Based On Fluorescence Method

The measurement of dissolved oxygen is of great significance to aquaculture.However,the current dissolved oxygen sensors on the market in China are difficult to promote and play a role in the Internet of things in aquaculture due to their high price,inability to continuously measure online and difficulty in maintaining updated components.Based on the principle of fluorescence quenching,this study uses the relationship between the dissolved oxygen concentration in water and the phase difference of the fluorescence signal to develop a low-cost and easy-to-maintain dissolved oxygen sensor.The main work of this paper is as follows:(1)Design and research of optical structure and hardware circuit of dissolved oxygen sensor based on fluorescence quenching principle.The optical structure design adopts the blue LED with the central wavelength of 460 nm as the excitation light source,and the red LED with the central wavelength of 660 nm as the reference light source.The optical fiber conducts the light guiding,and the photodiode receives the light signal.The hardware circuit takes STM32H743VIT6 as the main control core,and completes the design of six key circuit modules,including power management circuit,LED driver circuit,photoelectric conversion circuit,amplification and filtering circuit,temperature measurement circuit and wireless communication circuit.Finally,the optical structure and circuit were tested.The excitation light signal and fluorescence signal received were strong with low noise,and the signal waveform was the same frequency as the sinusoidal wave driving LED.Tap water was tested at room temperature,and the phase difference between fluorescence signal and excitation light signal was about 30°,indicating obvious phase difference.(2)Design and development of software system for dissolved oxygen sensor based on fluorescence quenching principle.The lower computer program of six main modules of dissolved oxygen sensor,such as DAC drive,ADC acquisition,temperature acquisition,fast Fourier transform calculation,dissolved oxygen concentration calculation and wireless communication,is designed to complete the control of dissolved oxygen sensor and the acquisition of dissolved oxygen concentration and temperature.Finally,the upper computer program is designed to complete the visualization and persistence of the measurement data and realize the remote monitoring function of dissolved oxygen concentration.(3)Calibration of dissolved oxygen sensor based on fluorescence quenching principle.By designing two-point calibration experiments,the relationship between phase difference and temperature in anaerobic water and between phase difference and temperature in saturated dissolved oxygen water are obtained.Combined with the relationship between dissolved oxygen concentration and temperature under standard atmospheric pressure,the calculation model of dissolved oxygen concentration,phase difference and temperature is established.Finally,the measurement results of self-made dissolved oxygen sensor are compared with those of chemical iodometry.The error of self-made dissolved oxygen sensor is less than 0.3mg/L.After 12 days of continuous measurement,the maximum difference between the measured values of dissolved oxygen sensor is 0.15mg/L,which has good stability and good repeatability.After testing,the measurement range of the dissolved oxygen sensor is 0-20mg/L,the measurement error is within 0.3mg/L,and the response delay is less than 2s.The service life of the dissolved oxygen sensitive film is about 1 year,and the concentration of dissolved oxygen can be measured in real time without interruption,and the measurement results are stable.At the same time,the sensor has the characteristics of convenient measurement,low production cost,small volume and so on,which has laid a good foundation for the research and development and market of low-cost dissolved oxygen sensor for aquaculture in China.