Design And Development Of Portable Optical Dissolved Oxygen Detector In Seawater

Dissolved oxygen is one of the parameters used in conventional seawater quality monitoring,and plays a key role in the assessment of the ocean carbon cycle.Accurate,high-quality observations of dissolved oxygen had contributed to a deeper understanding of the ever-changing ocean.And these needs had driven the development of instruments for measuring dissolved oxygen in seawater.In this paper,the research status of the detection methods and instruments for the concentration of dissolved oxygen in seawater at home and abroad was summarized.A portable optical dissolved oxygen detector suitable for field measurement of dissolved oxygen concentration in seawater was designed and developed.Firstly,the detection method of dissolved oxygen concentration based on fluorescence quenching principle was introduced in this paper.Based on the principle of fluorescence lifetime detection and the weak fluorescence signal detection method of phase-locked amplification,the system design scheme of the portable seawater optical dissolved oxygen detector was determined,and the design indexes were defined.Then,the portable optical dissolved oxygen detector for seawater is designed and developed by modular design method.Detector is mainly composed of two parts:underwater detection unit and handheld terminal.Among them,the underwater detection unit obtained fluorescence lifetime by detecting phase difference,and finally detected the concentration of dissolved oxygen in seawater.An independent optical path detection structure was designed and developed.The optoelectronic devices were selected according to the fluorescence detection characteristics.Focusing on the detection of weak fluorescence signal under strong background light interference,a double-channel phaselocked amplification detection method suitable for optical dissolved oxygen detector was studied and a detection circuit was designed and developed.The mechanical design mainly considered the deployment environment of the instrument,selected the corrosionresistant enclosure material,and carried out the sealing test in the seawater field.In order to realize the portable on-site measurement of dissolved oxygen concentration in seawater,a handheld terminal device was designed and developed based on STM32 microcontroller,which realized the functions of data acquisition,real-time storage and data self-correction.Focusing on the traditional laboratory calibration method of optical dissolved oxygen detectors had the disadvantages of complicated operation,strict conditions and time-consuming process.In this paper,a calibration method of seawater optical dissolved oxygen detector based on intelligent learning algorithm is established.The calibration experiment method of random sampling is proposed and the calibration device is designed and developed.The calibration experiment is easy to operate,the high accuracy calibration of the dissolved oxygen detector can be achieved with a short calibration period.Finally,the performance of the portable seawater optical dissolved oxygen detector designed and developed was tested by laboratory and seawater field experiments.The test results showed that the instrument had achieved the design goal,and had the function of measuring the concentration of dissolved oxygen in seawater field for a long time,stably and accurately.