Development Of Multifunctional Electromagnetic Receiver EMR6-A

Mineral resources of shallow earth have been drastically reduced under the large demand and utilization of industry,and the focus of exploration has gradually turned to deep earth.High precision,multi-method and intelligence are the developing trend of geophysical exploration instruments.Supported by the twelfth five-year plan “Highpower well-magnetotelluric imaging system” project,China University of Geosciences(Beijing)has developed the EMR6 electromagnetic receiver and realized data acquisition of MT,AMT,TDIP,SIP and CSAMT methods.However,there are still many deficiencies such as too many circuit board sub-modules,limited mechanical structure stability and lack of field data preprocessing software.In view of the above requirements,this paper introduces the development of hardware and program of EMR6-A multi-function electromagnetic receiver,which improves integration of the instrument,reduces volume,and realizes real-time browsing and preprocessing of data,aiming to accommodate the needs of electromagnetic exploration in complex terrain areas.Acquisition circuits of EMR6-A multi-function electromagnetic receiver consists of an analog signal acquisition board and a digital control board.Analog signal acquisition board includes a power conversion module,operational amplifiers,high speed and low speed ADC,digital isolation,etc.;Digital control board includes a power conversion module,FPGA,ARM,Ethernet port,RTC real-time clock,SD card,related peripheral storage circuits,etc..Data acquisition hardware includes two electric field channels and three magnetic field channels.Each channel is equipped with a high-speed and a low-speed analog-to-digital conversion chip to adapt to different frequencies of signal and achieve a higher signal-to-noise ratio.An oven controlled crystal oscillator on the control board outputs a high-precision clock,and time synchronization of multiple receivers and transmitters is realized with GPS.FPGA receives A/D conversion data and performs data processing,and transmits it to ARM to generate acquisition files and stores them in SD card.FPGA and ARM-Linux code completes core control of the system;PC-based Windows software of data viewing and preprocessing achieves on-site browsing and preprocessing of TDIP,SIP and CSAMT acquisition data,the program does not require attached library files,and is compatible with x86 and win32 platform.Indoor test results show that the multi-function electromagnetic receiver can accomplish data acquisition of two-channel electric field and three-channel magnetic field signals.Acquisition circuits has a DC~10kHz bandwidth.Dynamic range of electric field channel is 108.3dB,and is 112.7dB of magnetic field channel.User software program implements browsing of data time series and data preprocessing.The development of EMR6-A multi-function electromagnetic receiver has improved the intelligence of existing land instruments and is highly comprehensive,which helps to improve efficiency of geophysical field exploration.