| The semi-aviation electromagnetic detection takes into account the efficiency of the aeronautical electromagnetic method and the accuracy of the ground electromagnetic method,and is widely used in petroleum,metal ore,geological structure exploration and other fields with the maturity of the UAV technology.The existing acquisition system with industrial computer plus capture card combination often weighs more than 3kg,which is not suitable for UAV platform,and the performance of the micro-controller-based acquisition system is low,only a single channel 50 kSPS sampling rate.In order to realize the multichannel frequency domain signal acquisition based on the UAV platform,this paper studies the semi-airborne frequency domain electromagnetic embedded acquisition system.As a key part of the electromagnetic detection system,the acquisition system is mainly used to receive and store the total field information including the secondary field information induced by the underground geological structure.According to the miniaturization and low power consumption requirements of the UAV platform,the feasibility of the acquisition system scheme is analyzed according to the continuous characteristics of the frequency domain signal,and the design scheme of FPGA and STM32 as the control core is adopted.The total field signal is converted into a voltage signal by a coil structure sensor,and the weak signal is amplified by a differential amplifying circuit,and a 4-channel synchronous acquisition circuit is designed according to the signal characteristics using a high-precision 24-bit ADC,and the data reception timing,buffering timing,transmission timing and storage timing are analyzed and studied.Using FPGA internal FIFO cache and integration data,and designed a parallel transmission method with less port resources to transfer the cached data to STM32,STM32 stores data to Micro SD by transplanting FAT32 file system to achieve continuous data collection and storage.In terms of system synchronization,the GPS module is affected by the weather and other factors,the time synchronization information is lost in a short time,and the synchronization method of the existing acquisition system is analyzed.A time synchronization system based on FPGA hardware time flow and GPS is designed.The system can supplement lost synchronization information with linear interpolation methods during data processing.Finally,using the virtual instrument technology,the data extraction and integration procedures were written on the LabVIEW platform,and time domain signals were converted to frequency domain signals by the FFT power spectrum module,and then the frequency information is extracted to realize the data preprocessing.Firstly,the test is carried out by the acquisition signal generator.The results showed that the acquisition system can realize 24-bit 4-channel continuous acquisition and storage,and the sampling rate can reach 97.66 kSPS,and the synchronization accuracy is about 62.2ns.Increased data volume compared to past microcontroller-based acquisition systems.Secondly,the system noise was tested in the electromagnetic shielding room.The test results showed that the system noise was about-110.71 dB,which met the requirements of the index.Finally,field experiments were carried out in the mining area near Kaili,Guizhou.The collected signal can effectively reflect the position of the 50 Hz power line and has practical application value. |
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