Research On In-situ Calibration Method Of Oxygen Optodes In Seawater

Dissolved oxygen is an important parameter to measure the water quality of seawater and evaluate the Marine ecological environment,which has very important research significance and observation value.The seawater optical dissolved oxygen sensor based on the fluorescence quenching principle has been widely used in the field of Marine environmental monitoring because of its advantages such as high measurement accuracy,no oxygen consumption and no pollution,and it can be flexibly mounted on various Marine monitoring platforms and obtain long-term continuous observation data.However,the data drift of the optical dissolved oxygen sensor affects the long period,continuous and accurate measurement on the offshore automatic monitoring platform,and the traditional method of regularly bringing the sensor back to the laboratory for calibration affects the continuity of monitoring data,and also increases the maintenance cost.Therefore,it is necessary to solve the problem of in situ calibration of seawater optical dissolved oxygen sensor carrying platform for automatic monitoring.In this,the research status of the calibration methods of seawater optical dissolved oxygen sensor at home and abroad was summarized.The in-situ calibration study of seawater optical dissolved oxygen sensor was carried out,the in-situ calibration model was established,and an insitu calibration system device adapted to the in-situ calibration method was designed and developed,and experimental verification was carried out.Firstly,the in situ calibration method is established by studying the difference of response characteristics of seawater optical dissolved oxygen sensor in two different environmental media,water and air.Optical design structures,experimental apparatus,the research in a laboratory seawater dissolved oxygen sensor in two different media in water and air show different response characteristics,the curve of the optical dissolved oxygen sensor to judge data drift model is set up and in situ calibration method,fixed a two-point calibration model of saturated air calibration value,the accuracy of the calibration method is verified by experiment.Then,a suitable system is designed and developed for the in-situ calibration method of optical dissolved oxygen sensor in seawater.According to the requirements of sealing and corrosion resistance,the design of sealed pressure reaction tank and the selection of some key components are completed.Based on STM32 microcontroller,the MCU master module,RS485 communication module and TFT-LCD display module of the in-situ calibration system were designed and developed,and the data acquisition,control and processing programs were written.The routine monitoring of the seawater optical dissolved oxygen sensor,the judgment of data drift and the in-situ automatic calibration under the drifting condition were realized.Finally,the in-situ calibration of the optical dissolved oxygen sensor in seawater was carried out in laboratory and seawater field experiments.The experimental results show that the in-situ calibration method established in thes and the corresponding device can meet the requirements of offshore applications,and have the functions of long-term,automatic and continuous monitoring of the concentration of dissolved oxygen in seawater and automatic in-situ calibration when the sensor data drift occurs.