Development Of Double Trapezoidal Wave Transmitting System With Controllable Turn-off Edge

Nowadays,it is an era of resources,in which mineral resources account for a large proportion of all energy resources.Although our country contains extremely rich mineral resources,it is still heavily dependent on imported minerals due to the limitation of resource exploration.Mineral resources exploration technology is an important bottleneck restricting the development of mineral resources in China.Geochemical analysis,geophysical prospecting and remote sensing are commonly used in mineral resources exploration.Among them,geophysical prospecting mainly uses the propagation mechanism of electromagnetic wave in the earth to identify electrical parameters.Time-domain electromagnetic method is a common mineral exploration method,which is widely used owing to its high lateral resolution,sensitive lowresistance response,deep detection depth and strong anti-interference ability.In the measurement of non-polarized region,the time-domain electromagnetic signal is approximated to a monotone attenuation e-exponential curve,which contains the resistivity information of the earth.However,in the polarized region,the negative signal often appears in the time-domain electromagnetic signal,which reflects the underground resistivity and polarizability information.At present,the time-domain transmitter mainly aims at the detection of induction field,without considering the influence of emission current on polarization effect.Aiming at the above problems,this paper designed and developed a double trapezoidal wave transmitting system with controllable turn-off edge.The main work contents are as follows:1.The expression of the induced polarization response of the central loop detector when the emission current is arbitrary waveform under the complex resistivity of ColeCole is introduced.Furthermore,the influence of emission current on induction polarization response is analyzed.The advantages of double trapezoidal waves with different turn-off time for measurement of induction-polarization effect are expounded.The performance index of transmitting system and the design scheme of hardware and software are proposed.2.The transmission circuit is designed and tested from four aspects: the transmission bridge circuit,the isolation drive circuit,the main control circuit and the synchronization circuit.The duty cycle adjustable trapezoidal wave transmission based on PWM technology is realized,which improves the efficiency of survey and reduces the power consumption of power supply.3.Based on the passive constant voltage clamping technology,a theoretical model of the process of transmitting current turning off is established,and on the basis of the theoretical model,the double trapezoidal wave transmission with controllable turn-off edge is realized.Aiming at the ringing phenomenon of current turn-off edge,an optimization technique of ringing effect based on timing cut-in matching impedance is proposed,which effectively improves the linearity of emission current turn-off edge.4.The acquisition of emission current drop edge with variable sampling rate is realized.The sampling rate of 256 kSPS is used to collect the fast-switching emission current,and the sampling rate of 64 kSPS is used to collect the slow-switching emission current,and the acquisition performance is tested.5.An indoor test platform was built to test the performance of double trapezoidal wave transmitting system with controllable turn-off edge.A ground loop based on the Cole-Cole model was designed,and the ground loop was used to simulate the polarized earth,and the model verification experiment was carried out in the Shaoguo town.The experimental results were in line with the theory,and the advantages of the transmitting system for the induction-polarization effect measurement was proved.