| The development of the transient electromagnetic method to today,its application has been very extensive,including the survey of abnormal geological bodies on the ground with large loop and the detection of the water source of the underground engineering tunnel with the small loop.At present,there are many researches on the interference factors of TEM,among which there are abundant researches on random noise,ferromagnetic material and tunnel space interference of TEM,and few researches on the influence of device factors.Aiming at the problem of the influence of current transient electromagnetic device factors on the detection results,this paper through the analysis of transient electromagnetic transient process,uses Simulink circuit simulation software as the basis to simulates the transient electromagnetic equivalent circuit,systematically studies the influence of the change of device factors on the transient electromagnetic field,explores the causes and solutions of the low apparent resistivity of the commonly used multi-turn small loop device,and provides some ideas and references for the development of transient electromagnetic theory and the manufacture of instruments and devices in the future.In the transient electromagnetic method,in addition to the field changes caused by the LCR characteristics of the transmitter and receiver device itself,the observation errors of the turn-off current and the receiving loop are also relatively important factors.The former affects the whole transient electromagnetic process,including the primary field and the geological vortex current,while the latter affects the quality of the observation signal.This paper firstly studies the influence of R,L and C changes of transmitting loop and receiving loop on the transient electromagnetic field and the turnoff current,analyzes the influence characteristics of transmitting voltage and transmitting waveform on the turn-off current.Then the effects of different time constants and different parameters of the same time constant on the transient electromagnetic field and the turn-off current of the loop are studied.The effects of different damping coefficients on the observed results and the turn-off current are analyzed.Discuss the problem and influence of multiple mutual inductances between sending and receiving devices.At last,the observation errors caused by the transition process of receiving loop are studied.By comparing the errors of the induction signal and observation signal of receiving loop,and combining with the actual side length and number of turns,it is found that the smaller the side length and the larger the number of turns,the greater the device error,and the influence of the side length is greater.Based on all the researches,this paper believes that there are two reasons that affect the apparent resistivity of multiturn small loop.One is the influence of the primary field signal on the early signal.Due to the characteristics of multi-turn small loop's LCR,the duration of the impact may increase,it can be corrected by means of current element integration of the turn-off current.The second is the influence of the observation error of the receiving loop,which leads to the increase of the time delay of the multi-turn small loop's transient electromagnetic field and the rise of the curve amplitude,thus causing the signal distortion.Since the equivalent circuit of the receiving loop can be regarded as a linear time-invariant system,the error can be corrected by deconvolution method. |
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