Research On Key Technologies Of Transient Electromagnetic Emission Current Controllability And Acquisition

Mineral resources are an important foundation for human development.However,due to the limitation of detection technology,some mineral resources in China rely on imports,and the technical level of geological exploration still needs to be improved.The transient electromagnetic method is widely used because of its high resolution,large detection depth,and strong anti-interference ability.The transient electromagnetic response in the non-polarized region is a monotonously decaying positive curve,reflecting the resistivity information of the geological body.The detection of the polarized area will show a polarized response with a negative sign,which can reflect the information of resistivity and polarizability at the same time,and polarized geological bodies will produce different responses under different excitations.In the past,transmitters were mostly in fixed off-time mode,which could not be adjusted flexibly according to the detection conditions.In response to the above problems,this paper designs a transient electromagnetic emission system with continuous controllable off time,the main contents are as follows:1.Introduce the Cole-Cole equivalent circuit model of the polarized geological body and its response process,show that the negative response is the result of the charging and discharging process of the polarizing medium,analyze the effects of different emission parameters on the polarization detection,and explain the controllable turn-off edge pair Advantages of polarized area detection.2.Transmitter design is carried out from four aspects: main control circuit,synchronization circuit,drive circuit,and transmitting bridge,which realizes basic functions such as timing synchronization,strong and weak electrical isolation drive,and bipolar current emission,and aims at the peak of the emission current.Design the absorption circuit with oscillation to optimize the turn-off edge waveform quality.3.Design the off-time control circuit based on the constant-voltage clamping technology,realize the continuous adjustment of the turn-off edge by adjusting the clamping voltage,and realize the fixed off-time gear by matching the resistance divider.According to calculation and simulation analysis,select a reasonable current limiting resistor to maintain the clamping capacitor voltage regulation.4.Design a variable sampling rate current acquisition device based on FPGA and Gigabit Ethernet,use a high sampling rate to accurately record the details of the transmitted waveform,and use a variable sampling rate mode to achieve continuous acquisition of the transmitted waveform at different off times.Based on C #,the current acquisition host computer is compiled to realize functions such as acquisition control,waveform display,and data storage.5.Test the performance indicators such as the off-time,linearity and consistency of the emission waveform,test the variable sampling rate and noise of the current acquisition device,design a polarization equivalent circuit model based on the ColeCole anomaly loop,and verify the emission through field experiments Advantages of the system for polarization detection.