Design And Implementation Of0.003hz～10khz Search Coil Magnetometer

Magnetotelluric(MT) method uses the electromagnetic field as a field source,through the inversion algorithm to calculate the electrical structure of the undergroundmedium, by measuring the electric and magnetic components, calculating the apparentresistivity of the underground medium and phase differences of the electric andmagnetic field. It plays an irreplaceable role in the fields of oil and natural gasexploration, deep geological structure detection, exploration of groundwater resources,earthquake prediction and prevention of geological disasters and so on.At present, most of the domestic development of the magnetic sensor’spreamplifier has poor noise characteristics, many of them use integrated chopperamplifier as preamplifier, and they have greater noise level, higher1/f noise cornerfrequency. There are no domestic commercial sensors and MT instruments. Thus, inour country, Most of the research and field test requirements are addressed by theimport currently, so the geological research is limited. The purpose of this paper is tosolve the key problem of the preamplifier noise performance of the sensor, also, usethe preamplifier in a self-designed sensor, to obtain the satisfying noise characteristicsand transmission characteristics, make contribution for MT equipment in our country.This paper mainly studied the working principle of the chopper amplifier, analyzedthe various factors affecting the noise characteristics theoretically, and put forward theprinciples to select relative devices, designed a chopper preamplifier which is suitablefor electromagnetic sensor, also designed a set of field testing and calibration system,which is convenient for field data acquisition and sensor calibration. The thesismainly completes the following work:1. Understood the basic principles of magnetotelluric method, studied currentsituation of the development of MT sensor at home and abroad, and researched the chopper amplifier noise performance at home and abroad.2. Intensively studied the working principle and the theoretical model of thechopper amplifier, detailed analyzed the effect on the noise characteristics which thecharge injection, clock feed-through and leakage current of the analog switch have.3. According to the research results, the basic principles which should be followedin designing the chopper amplifier is presented, and measured the transmissioncharacteristic of the sensor which used the chopper amplifier, it is proved that thedesign meets the requirements.4. Designed a data acquisition and calibration system based on ARM7, which hasthe features of low power consumption, large storage capacity. The data can be storedin a2GB SD card, and is conveniently processed and analyzed by computer.