| Pipeline transportation is the main way of large-scale and long-distance natural gas transportation.Due to natural erosion,geological changes and human factors,natural gas pipelines will be damaged and cause natural gas leakage,which will bring major safety hazards to people’s production and life.It is of great practical significance to cany out pipeline inspections.Compared with traditional manual inspections,drone inspections equipped with testing equipment have the advantages of strong environmental adaptability,high inspection efficiency,and low cost,and are the current development direction of natural gas pipeline inspections.Tunable Diode Laser Absorption Spectroscopy(TDLAS)has the characteristics of non-contact,fast response and high sensitivity.This paper uses TDLAS as the core to carry out the detection of natural gas concentration under the open optical path,especially for unmanned During the drone inspection,the influence of disturbances such as body vibration and gas turbulence caused by rotor rotation on the detection,and the limited space of the UAV platform,etc.,from the perspectives of de-perturbation methods,absorption optical paths,hardware structures,and concentration inversions,etc.,The detection system is designed and its deperturbation performance is verified experimentally.The main research content of the paper is as follows:(1)Based on the theory of gas absorption spectrum and Beer-Lambert law,the detection principle of TDLAS is analyzed,and the relationship between gas concentration and second harmonic is clarified,which provides a theoretical basis for the design of natural gas leakage detection system.(2)In order to remove the strong vibration and turbulence interference existing in the UAV platform detection,a de-disturbance scheme is designed:by adding a weak absorption signal of natural gas for disturbance extraction,and using it to correct the natural gas absorption signal to achieve interference removal.According to the actual operating parameters of the UAV,the interference removal effect of this scheme on different frequencies and different intensities was analyzed and compared.Simulation results show that this method has a ceitain suppression effect on low-frequency interference below 400 kHz.(3)Design and build a natural gas leakage TDLAS detection system applied to the UAV platform.In order to improve the detection sensitivity,a parallel reflection structure is designed on the support frame under the drone to increase the absorption optical path in a multi-reflection manner.In order to improve the response speed of the system,the "FPGA+DSP" architecture is used as the core of the detection system to give full play to the advantages of the two processing chips.A current drive and temperature control unit is designed to achieve fine tuning of the laser wavelength.Among them,the current drive unit is composed of a high-speed D/A,a conditioning circuit and a laser driver chip;the temperature control unit is stable after adjusting the PID parameters of the integrated temperature control chip.The resistance reaches ±0.01℃.The data acquisition unit converts the analog signal into a digital signal through a high-precision A/D for concentration inversion.In order to realize the miniaturization of the detection system,device selection,optimization and PCB layout were carried out.The size of the detection system is 10×19×3cm,and the weight is 0.39 kg.(4)According to the absorption characteristics of natural gas,1653.72 nm and 1652.78 nm are selected as the detection light wavelength and reference light wavelength,and the laser parameters are set accordingly.When carrying out experimental research,the concentration detection experiment without disturbance was carried out in the straight-through gas chamber first,and the detection performance of the system for gases with different concentrations was verified.Then,turbulent flow and vibration with different characteristics are applied in the straight-through air chamber to simulate the operation disturbance when the UAV is detected,and the de-disturbance effect of the reference optical multiplexing method is verified.The unmanned aerial vehicle detection system designed in this paper for the inspection of natural gas pipelines is expected to realize gas concentration detection.It is of great significance to apply TDLAS technology to the natural gas pipeline inspection of UAV platform. |
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