Research On The Prototype Of Deep Distributed Electromagnetic Exploration Receiver

With the rapid development of China's national economy, every walk of life increases demand for mineral resources continuously. But China's mining industry is faced with serious situation that the proved reserves of a large number of mines exhaust gradually and the new deposit is discovered less and less. Many prospecting results in home and abroad show that there is great potential in deep and peripheral areas of the resources crisis mines. Now compared to the foreign countries, there is a wide gap in exploration depth of existing mines. It is very difficult to detect mineral resources by using traditional time-domain electromagnetic exploration equipment in deep and peripheral areas of the resources crisis mines, due to limit depth and poor effect of suppressing transient interference. Single point measurement is chosen because of limited channels, but it is not effective in the wild. Therefore, research on time domain combined with frequency domain distributed electromagnetic detection instrument is the effective way of exploring deep and peripheral resources of crisis mines against the strong noise interference of mines.From the need of anti-interference ability and great depth detection, the paper makes the CSAMT, IP and MT as work methods. At the beginning of the paper, the principles of the previous three methods were studied deeply. Then mastered the design requirement for instrument on the basis of detection methods, meanwhile, borrowed ideas from the advanced technology of the correlation instruments of the world, combined with the actual field experiment and gave field work mode and integral design scheme of the distributed electromagnetic exploration receiver.The deep distributed electromagnetic exploration receiving system is composed of one master control station and twenty four acquisition sub-stations. Under the control of the master control station, the sub-stations achieve the functions of parameters setting-up, data acquiring and uploading data to the master control station and so on. The main control station has 8 acquisition channels, three of which measure mutual orthogonal three-component magnetic field signal while the other five channels measure electric field signal. Every acquisition sub-station has two acquisition channels which take charge of measuring electric field signal. The receiving system adopts master-slave distributed network topology structure. The central processing unit of master control station is a industrial computer and the acquisition sub-station adopts 16 bits ultra-low power consumption MSP430 series MCU to be its control core. Every station is connected by shielding twisted pair wires and the communication protocol adopts RS485 balanced transmission standard.In this paper, three key technologies of receiving system were researched deeply, including broadband and large dynamic range signal conditioning technology, delta-sigma analog-digital conversion technology and synchronous control technology of distributed system. In order to realize broadband weak signal detection under the strong noise interference background, low-noise differential amplifier and programmable anti-aliasing filter were designed respectively in the front-end of analog conditioning circuit and analog-to-digital converter. Meanwhile, notch filter for 50Hz was added into analog channel to inhibit the power line interference. In order to solve the problem how to amplify large dynamic range signal and obtain a suitable resolution in the entire measurement range, the main amplifying circuit adopted multi-stage programmable gain amplifier. Through signal pre-sampling, the factor of main amplifier was determined according to the magnitude of the signal. The whole analog channel parameters were set automatically under program control.Based on theΔ-ΣADC technology, the data acquisition module of receiving system was designed and implemented used 24-bit high-precisionΔ-ΣADC ADS1252.Field programmable gate array technique was used in the design of interfacing circuit between analog-to-digital converter and large-capacity non-volatile random access memory and other digital circuits which reduce the size of the system hardware and make upgrade and maintenance easily. The paper operated synchronous mode of ADS1252 by starting the conversion synchronously and reading the data time-sharing.The paper analyzed the advantages and disadvantages of domestic electrical instruments synchronous manner. designed software synchronization, communications line synchronization and GPS+OCXO synchronization according to different precision requirements of three kinds of deep electromagnetic exploration methods. A variety of synchronization modes made receiving system work with various transmitting systems easily which improved flexibility and reliability of receiving system.In order to verify the receiving system, system performance test, the flume comparison experiment for TIP and the RC model experiment for CSAMT were completed .Performance test for system included short circuit noise test, resolution test, notch filter performance test and channel consistency test . These tests and results proved that the system is feasible and accurate by analyzing results. Finally, the works of the thesis were summarized, in order to perfect the system, some suggestions in further design and research were given.