Development Of Temperature And Pressure Control System For CO₂ Isotope Detection

Natural gas hydrate?combustible ice?is expected to be a new energy source to replace traditional energy sources such as petroleum.It has the advantages of high combustion capacity,no pollution and large reserves.Various developed countries in the world have started research on combustible ice.The biggest problem encountered in current research is the difficulty in exploration and development.China has completed preliminary exploration of combustible ice in the South China Sea and obtained a number of target areas for combustible ice resources.As the exploration of combustible ice in the main sea areas of China enters the detailed investigation stage,the existing combustible ice detection equipment has poor precision,low efficiency and cannot distinguish the geophysical and geochemical anomalies of combustible ice.It is extremely urgent to complete a high-precision in-situ combustible ice detection system..The formation process of combustible ice will cause an abnormality in the CO₂ carbon isotope ratio of seawater gas in the sea area.This abnormality can be used to effectively screen and even quantitatively analyze the source and settlement position of the isotope material,so it is necessary to accurately trace the flammable ice in the sea.Combustible ice tracing requires the detection of CO₂ carbon isotope ratios.Laser absorption spectroscopy for gas isotope detection is very beneficial for the development of a real-time online measurement system.Due to the temperature dependence of the absorption coefficient of the gas absorption line to be measured,the value will change with the change of gas temperature.The pressure of the gas to be tested will affect the absorption line type of the gas to be tested.To achieve high accuracy and good stability detection results,the temperature and pressure of the gas to be tested inside the multi-pass gas cell must be stably controlled.In this paper,a high-precision,high-stability temperature and pressure control system is designed for the CO₂ isotope sensor.In the multi-pass gas cell temperature control system,the constant current source circuit is used to drive the PT1000 temperature sensor to collect the temperature of the multi-pass gas cell,the measured temperature value is converted into a corresponding voltage value,and the signal conditioning circuit is designed to combine the A/D conversion circuit to convert analog signals to digital signals.After being converted into a digital signal,the micro controller unit?MCU?receives the voltage digital signal and calculates it,then controls the heating film driving circuit to adjust the heat of heating film.In the multi-pass gas cell pressure control system,a high-precision pressure sensor is used to collect the pressure of the gas to be tested in the multi-pass gas cell,and an A/D conversion circuit is used to convert the analog output voltage of the sensor into a digital quantity,and the MCU calculates the digital quantity.After that,the proportional valve driving circuit is controlled to drive the two proportional valves.In the experimental test part,the multi-pass gas cell temperature control system parameter setting test,temperature control lower limit experiment,temperature control upper limit experiment and internal gas temperature experiment were carried out,and the temperature fluctuation of the outer wall of the multi-pass gas cell was 0.08°C,and the internal gas temperature fluctuated at ±0.1°C.Dynamic gas experiments and long-term stability experiments of the pressure control system were carried out,and the gas pressure in the cell was controlled at 60 Torr and fluctuated within a range of 0.75 Torr.A multi-pass gas cell temperature and pressure control system was combined with other parts to build a CO₂ isotope sensor.The concentration calibration experiment and accuracy experiment were carried out.The optimal measurement accuracy of the sensor was 0.0139‰.Finally,the CO₂ isotope sensor combined with gas-liquid separator was used to test the CO₂ isotopic abundance in laboratory water for a long-term stability.The long-term measurement of isotope abundance fluctuated within 0.73‰.