长周期大地电磁场源信号采集电路研究

发布时间：2018-05-08 12:51

本文选题：深部地球物理探测 + 长周期大地电磁　；参考：《成都理工大学》2017年硕士论文

【摘要】：长周期大地电磁探测法是重要地球物理探测方法之一,其在资源勘探、环境保护、防灾减灾等方面有着重要的科学意义。上世纪末,众多发达国家纷纷启动以长周期大地电磁测深法为主的深部探测计划,我国于2008年启动“深部探测专项”,以扩大资源的获取空间。目前国内研究长周期大地电磁仪器的主要有中国地质大学(北京)和吉林大学,国内主要使用进口的长周期大地电磁测深系统,国外很多长周期大地电磁系统都严格限制对我国出口,严重制约了我国深部探测计划的进程。“十一五”国家高技术研究计划启动深部矿产资源勘探技术专项,希望突破深部资源勘探技术方面方面的壁障,本论文来源于“863”重大仪器专项——长周期分布式大地电磁观测系统(2014AA06A612)。长周期大电磁信号微弱,信号周期极长,而且需要解决闪烁噪声的影响,因此本论文设计了基于斩波原理器件的长周期大地电磁场源信号采集电路,实现高分辨率、高稳定性、低噪声、低漂移采集电路设计。采集电路分为输入保护电路、输入匹配电路、滤波电路、程控增益电路、模数转换器电路、数模转换器反馈补偿电路和FPGA控制器电路等七部分。数模反馈补偿电路通过数模转换电路和减法电路能够有效补偿前端输入信号的背景场,剩下动态变化的交流分量,然后通过环路中的程控增益控制电路对该交流量进行放大,提高环路增益和信噪比,增大模数转换器的有效分辨率。使用FPGA作为控制器,采用并行处理方式实现多通道信号高精度同步采集和处理。采用堆叠的方式开发了两套样机,按照准校准规范对样机进行校准测试、噪声测试、道间串扰测试和通道一致性测试,同时与LEMI-417系统进行了野外对比实验。使用最小二乘法和一元线性回归方法对样机进行了分段校准,测试表明电场信通道噪声有效值最大为0.4uV,磁场通道噪声有效值最大为0.08nT,样机的道间串扰和通道一致性等指标都达到设计指标要求。野外实验结果表明,使用本论文采集电路研制的LMT仪器获取的资料与LEMI-417系统获取的资料经相同软件处理后,电阻率结果高度一致。
[Abstract]:Long-period magnetotelluric sounding is one of the important geophysical methods, which has important scientific significance in resource exploration, environmental protection, disaster prevention and mitigation. At the end of last century, many developed countries started the deep exploration plan with long period magnetotelluric sounding as the main method. In 2008, our country launched the "deep exploration project" to expand the acquisition space of resources. At present, China University of Geosciences (Beijing) and Jilin University are the main researchers in China, and import longperiod magnetotelluric sounding systems are mainly used in China. Many long period magnetotelluric systems in foreign countries have restricted the export to our country, which seriously restricted the process of our country's deep exploration program. In the 11th Five-Year Plan, the National High Technology Research Plan launched the deep mineral resources exploration technology project, hoping to break through the barrier in deep mineral resources exploration technology. This thesis comes from the long period distributed magnetotelluric observation system (LDCMS), which is an important instrument of "863". The long period large electromagnetic signal is weak, the signal period is very long, and the influence of scintillation noise needs to be solved. Therefore, this paper designs a signal acquisition circuit of long period magnetotelluric field source based on chopper principle, which realizes high resolution and high stability. Low noise, low drift acquisition circuit design. The acquisition circuit is divided into seven parts: input protection circuit, input matching circuit, filter circuit, program-controlled gain circuit, analog-to-digital converter circuit, digital-to-analog converter feedback compensation circuit and FPGA controller circuit. The digital-analog feedback compensation circuit can effectively compensate the background field of the front-end input signal through the digital-analog conversion circuit and the subtraction circuit, leaving the dynamic AC component, and then amplifying the AC quantity through the program-controlled gain control circuit in the loop. The loop gain and signal-to-noise ratio (SNR) are improved, and the effective resolution of A / D converter is increased. FPGA is used as controller and parallel processing method is used to realize high precision synchronous acquisition and processing of multi-channel signals. Two sets of prototypes were developed by stacking method. Calibration test, noise test, inter-channel crosstalk test and channel consistency test were carried out according to the quasi-calibration specification. Field experiments were also carried out with LEMI-417 system. The method of least square and linear regression is used to calibrate the prototype. The test results show that the maximum effective value of the signal channel noise is 0.4uV and the maximum effective value of the magnetic channel noise is 0.08nT. the interchannel crosstalk and channel consistency of the prototype meet the design requirements. The field experiment results show that the data obtained by using the LMT instrument developed in this paper is highly consistent with the data obtained by the LEMI-417 system and processed by the same software.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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