【作者】 王静；

【导师】 林君；

【作者基本信息】 吉林大学 ， 测试计量技术及仪器， 2004， 硕士

【摘要】 本文设计实现了应用在全程瞬变电磁仪器系统发射机中的发射电流下降沿记录系统。时间域电磁方法（time domain electromagnetic methods）又称瞬变电磁法（transient electromagnetic methods），简称TEM，它是利用不接地回线（大回线，磁偶源），或接地电源（电偶源）向地下发送一次场，在一次场的间歇期间，测量由地下介质产生的感生电磁场（二次场）随时间的变化，从而探测地下不均匀体的位置，并估计其规模和导电性能。瞬变电磁法仪器系统包括接收机与发射机。随着接收仪器的数字化和智能化，发射功率的增大，数学模型计算正反演的应用，解释水平的提高，瞬变电磁法可解决的地质问题不断扩大，几乎涉及了物探工作的各个领域：矿产勘探、构造探测、水文与工程地质调、环境调查与监测以及考古等。近年来在找水、市政工程、土壤盐碱化和污染调查以及浅层石油构造填图等方面都取得了良好效果。地球物理勘探方法包括五大类，简称重力、磁力、电、地震和放射性。其中电法类的方法即多又杂，而电磁法又是电法中分类最繁杂的勘探方法。几种主要的电磁方法目前的优势探测范围是：探地雷达（GPR）：地面～地下2米；频率域（AMT）：地下1千米以下；时间域（TEM）：地下20米～1千米。由此可见，地下2～20米范围对于以上几种方法来说都是一个困难，而这一范围却与人类活动极为密切。通过多年的实践，人们已经认识到时间域电磁法跟频率域电磁法相比具有多方面的优势，特别是1千米以上范围是时间域探测的强项。所以在浅部探测中人们主要研究并采用的是时间域TEM方法。对于时间域来说，探测深度是由观测时间的早晚决定的，要探测浅层目标体，唯一的办法就是缩短延迟时间（即发射电流关断后开始记录的时间）。目前国际上最好的浅层TEM仪器EM-47的最早记录时间为6.8μs，对一个50Ω·m的模型，根据概念扩散深度公式δt=[2ρT/μ]1/2估算，最小探测深度约18米。所以，对于目前市场上的时间域TEM仪器，从地表到地下20米左右依然是一个探测盲区。解决这一盲区最可行且最有效的途径就是从时间域入手,建立全程瞬<WP=66>变电磁系统（All-time TEM, 简称ATTEM）。TEM发射机发射正负交替的矩形波时，希望电流按理想情况关断,但线圈表现出来的感性会使发射电流存在下降沿，并呈指数规律衰减。接收机虽然是从发射机开始关断处就开始采集接收二次场信号，但由于在发射电流关断过渡中的二次场信号混有直接耦合的一次场信号,无法处理，经典TEM做法是舍弃这段数据,计算和反演发射电流完全关断后的二次场数据，所以无法解决地表往下十几米的探测盲区问题。ATTEM的思想就是准确地记录发射电流关断波形，利用此波形通过算法研究，实现从二次场中扣除一次场的影响，实现无盲区探测。ATTEM仪器系统研制有三个关键技术即闪光点，其中高速、准确、不失真地记录发射电流关断波形就是其中一个，此外两个分别为接收机的双AD采样和利用发射电流关断波形的一次场扣除算法研究。算法研究的先决条件也是要依靠准确记录的关断波形数据。本论文研究内容的重点就是设计实现一套高速数据采集系统，解决发射电流关断波形准确记录问题。论文设计的高速数据采集系统硬件设计中采用了高速缓存思想，利用6ns等级的FIFO芯片做中间速度缓冲，围绕ATEML公司RISC微控制器，MAXIM公司10M、10位AD芯片MAX1426设计实现了高速采集系统的硬件部分。软件部分采用嵌入式C语言编写，模块化思想在软件编写中贯穿始终。模块编成、调试降低了软件编写和调试难度，提高了代码的可读性和重用性。软件依托硬件完成数据采集、叠加、求平均、算法滤波、计算发射电流和关断时间值到最后的一对二的串口通信，将结果数据分别送到主单片机和pc机上。论文对发射装置和前端信号取样作了相关研究，实现了发射装置一套和科学的信号取样方案。设计的数据采集系统已经成功应用在本实验室自主研发的新一代全程时间域瞬变电磁（ATTEM）仪器系统和原ATEM-II仪器系统中，并在浙江舟山连岛工程和内蒙古正镶白旗找水工程中取得了良好效果。更多还原

【Abstract】 A record system of transmitted current used in All-time Transient Electromagnetic System transmitter is implemented in this thesis. Time Domain electromagnetic Methods, or which calls Transient Electromagnetic (TEM) methods, which utilizes re-line untouched to ground (big re-line or magnetism even source) or electricity power touched to ground (electricity-even-source), it sends the first field and measures the induced electromagnetic field (the second field) changed with time which is created by underground substance. So it can measure the position of underground inhomogeneous substance and estimate its scale and electricity capability. The TEM instrument system includes receiver and transmitter. With the development of digital and intellectual receiver, the accretion of emit power, the use of forward computation and inversion of digital model computer, the improvement of explanation level, TEM can resolve a larger range of geology problems which almost includes every field of geophysical exploration: ore exploration, constitution exploration, hydrogeology and engineering geology investigation, environment survey supervising and archaeology and so on. In recent years, TEM has make it easier in searching water, city government engineer, salt and alkali soil, pollution survey and shallow layer petroleum constitution graph and so on.Physical geography’s reconnoiter methods is divided to five kinds called gravity、magnetic force、electricity、quake and radioactivity. For these five kinds of methods the electricity has not only many but also motley classify ways. The electromagnetic methods is the reconnoiter methods that has the most multifarious classify ways in electricity methods. The detect dominance of several mainly electromagnetic <WP=68>methods is given out as follow, for GPR is from ground to 2 meters, for AMT is below 1000 meters, for TEM is for 20 meters to 1000 meters. We can find out that from 2 meters to 20 meters is a difficulty for the several mainly electromagnetic methods, but this domain is closed related with human’s activity. After years of practice, people have found that Time Domain electromagnetic Methods have advantages in many aspects compare with Frequency Electromagnetic Methods. Especially above one thousand meter is a detect dominance of Time Domain electromagnetic Methods. So Time Domain electromagnetic Methods is mainly researched and used in low target detecting. For Time Domain Electromagnetic Methods detect depth is decided by sooner or later of observation time. So, in order to detect low target the only way is to decrease delay time (the start record time after transmitted current’s shut off). The delay time of the best low floor target detecting TEM instruments EM-47 is 6.8us. Suppose a 50Ω·m model the most shallow target can be detected is about 18 meter calculated by formula of δt=[2ρT/μ]1/2. So from the earth’s surface to about 20 meters is a detecting blind region for all of the marketable Time Domain electromagnetic Methods instruments. The most possible and effective way to solve the detecting blind domain is to establish All-time Transient Electromagnetic (All-time TEM, simply called ATTEM) System use Time Domain electromagnetic Methods.When TEM transmitter launches the plus and minus alternative rectangle wave, ideally we hope the transmitted current will be cut out instant. However, the winding’s inductance will make transmitted current has exponential attenuation falling-down wave. Although receiver acquires second field data as noon as transmitter starts cut out, however, during the time of transmitted current’s cutting the second field data mixes the first field data what we can not deal with. The classic way of TEM <WP=69>instruments is to give up this part of data, only calculate and anti-demonstrate the data after the transmitted current have cut out completely; therefore, these TEM instruments can not deal with the detecting blind domain. ATTEM is designed to record the falling-down wave of the launching electric correctly, and use it to更多还原