Development Of Data Acquisition And Communication System For Detecting Carbon Dioxide Near Seabed

As a new type of clean energy,natural gas hydrates have received widespread attention at both home and abroad.In order to speed up the layout of energy strategies,China officially launched natural gas hydrate resource exploration at the end of the last century.With the successful trial exploitation of natural gas hydrates in the South China Sea,the current exploration of natural gas hydrates has reached a new stage.In view of the shortcomings of low efficiency and poor accuracy of existing instruments,focusing on the urgent demand for fine exploration of natural gas hydrate in China,based on the principle of infrared absorption spectrum,the in-situ sensor of dissolved gas in seawater is developed by using Tunable Diode Laser Absorption Spectroscopy?TDLAS?combined with Wavelength Modulation Spectroscopy?WMS?.In this paper,a data acquisition and communication system for carbon dioxide?CO₂?near seabed is developed for the seawater dissolved gas in-situ sensor.Comparing the research status of seawater in-situ detection technique at home and abroad,it is pointed out that it is urgent to develop core technique and systems with independent intellectual property and rights.Firstly,the overall structure of the sensor was designed,and then the hardware circuits of the data acquisition and communication system were designed,including the core circuit of the system,the data acquisition circuit,and communication circuit.The printed circuit board?PCB?was drawn,and the circuit was soldered and debugged.After the hardware circuit design of the system was completed,the software design of the system was started.Firstly,the software development platform was built,the structure and flow of the software was designed,and then the program of each module was carried out,including the initialization program,A/D acquisition program,interrupt program and communication program.Finally,the communication protocol and upper computer monitoring platform based on LabVIEW were designed.After the hardware circuit and software design of the system was completed,experiments were carried out to test the performance of the system.Two series of experiments of second harmonic signal acquisition,dynamic and static gas pressure detection prove that the system has good data acquisition and communication performance.Using dynamic gas distribution method,the concentration of ¹²CO₂ and¹³CO₂ was calibrated,and the calibration curves were obtained.Finally,the sensor was integrated and tested in the Shenhu sea area in the north of the South China Sea in November 2019.From the analysis of the collected data,it can be seen that the laser temperature and chamber pressure fluctuate around 0?and 40 Torr respectively,which is consistent with the set target value.The concentration of CO₂gas fluctuates around 400 ppm,and its isotope abundance value is stable at-25‰.Moreover,the concentration,isotope abundance and chamber pressure of CO₂ gas show good repeatability.The concentration of dissolved CO₂ at different depths of sea water was observed.The practicability of the data acquisition and communication system developed in this paper was verified.The experimental results were summarized and the sensor will be improved in the next to prepare for the following field deployment in the South China sea.The main innovation of this paper:In order to meet the needs of deep-sea gas hydrate exploration,a data acquisition and communication system for underwater in-situ mid-infrared CO₂ and carbon isotope sensors was developed.The function test and deployment in South China Sea were carried out to verify the function and practicability of the system.