Study And Development On Long-Period Intelligent Magnetotelluric Instrument System

Magnetotelluric sounding is a key geophysical method to study the crust and upper mantle structure,so long period MT instrument is essential during some projects on deep probe,such as "Deep Exploration Technology and Experimentation(Sino Probe)" carried out in China recently.However,China can not make long period MT instrument by itself now and only relies on LMTI(Long-Period MagnetoTelluric Instrument)LEMI-417 imported from Ukraine.In order to solve the problem of the long-period magnetotelluric instrument only relying on imports,the scarcity of these instruments and its low signal resolution,poor human-computer interaction function,Geo-detection Laboratory,Ministry of Education start to develop a set of long-period magnetotelluric instrument fit for this kind of project.Firstly,after summarizing the design principles of the long-period MT,the structure of the several types of modern instruments,and the hardware composition of general MT instrument,an uncomplicated architecture system based on two-stage microcomputer control was proposed and put to use the design of the long-period MT instrument to be developed,which made the instrument easy to carny.Secondly,according to the design principles of long-period MT instrument,such as low power consumption and high accuracy,after studying of the functional structure of several MT instruments used commonly in the wild by our team,analyzing the advantages and disadvantages of each functional structure,the function structure of our long-period magnetotelluric instrument was determined and each circuit module,such as data acquisition module,data storage module and clock module,was developed.Some functions of this instrument are better than LEMI-417,which is used by our team now.Then,the PC software system,consist of GUI module,data acquisition module of PC,data processing module and auxiliary module,was programmed with Microsoft VC++development kit.GUI module can display the collected data with oscilloscope display style and help the user to judge its quality;Data acquisition module of PC realizes PC can store the collected data and analyze it on the spot when PC connects instrument,and thus avoid CF card is inserted or removed repeatedly;Data processing module data provides data correction,data conversion,multi-data comparison display and other functions;auxiliary module can help user save the screen as an image file.The PC software has enriched the function of the instrument greatly.Finally,some experiments for the instrument were done to check it can work normally or not in the laboratory,outdoors and in the fields.The instrument and LEMI-417 were used to acquire magnetotelluric data in the same time period at several measuring sites of the project,such as SinoProbe-01-02 and SinoProbe-02-04.The results show that their time series curves are consistent and the magnetotelluric sounding curves after magnetotelluric data processing are consistent too,which shows the instrument is capable of doing magnetotelluric sounding.