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The Prototype Development Of Transmitter/Receiver Separate MRS Instrumentation

Posted on:2013-04-21Degree:MasterType:Thesis
Country:ChinaCandidate:Z ZhangFull Text:PDF
GTID:2232330371483092Subject:Measuring and Testing Technology and Instruments
Abstract/Summary:PDF Full Text Request
The method of magnetic resonance sounding is used to detect groundwater, it isthe only non-destructive geophysical new method which can detect groundwaterdirectly in the world. In this method, the coil on the ground is used to transmitalternating current, this alternating current generates an alternating electromagneticfield which is perpendicular to the ground, so the hydrogen nuclei betweengeomagnetic field and the alternating electromagnetic field have a transition ofZeeman energy levels (that is resonance), when the alternating electromagnetic fieldis removed, the hydrogen nuclei will transit to low energy level spontaneously inaccordance with the exponential law and release electromagnetic waves with a certainfrequency,receiving the electromagnetic waves (MRS signal) using a coil, then thegroundwater information of the testing site can be calculated using sampled MRSsignals. At present, France, China and Russia have developed commercial MRSinstruments, these instruments complete transmission and reception using the samecoil, which has the following effects on instrument: The horizontal resolution ofdetection results is too low. The electromagnetic compatibility design of high-powertransmission and weak signal detection is complicate, and the ability ofanti-interference is poor. In combination with the research of domestic and foreignMRS methods and the latest development of instruments, the overall program oftransmitter/receiver separate MRS instrumentation prototype is proposed based on thelaw of electromagnetic induction, and the development of prototype is completed,finally, the accuracy and effectiveness of the prototype is proved by a field applicationexample.The completed prototype of transmitter/receiver separate MRS detector includesthe following technologies: Transmitter/receiver separate technology. High-power excitation technology. Weak signal detection technology. Full-wave acquisitiontechnology of MRS signal. Improving detection signal to noise ratio technology.The overall design of transmitter/receiver separate MRS detector is introducedin the second chapter. The technology of transmitter/receiver separation is completedbased on MRS principles and the law of electromagnetic induction, then the completeseparation is realized by using programmable logic devices to control reed relays.High-power transmission is used to excite groundwater,and the adjustment andacquisition of signal is completed by receiving part. The transmitter and receiver areall work orderly under the control of PC control software.The measurement technology on transmitter/receiver separation is introduced inthe third chapter, in addition, the separation technology of prototype,thetransmission technology, the circuit design of received signal after separating, thefull-wave acquisition and noise reduction technology are all introduced in detail inpoint of hardware. The separation technology is completed by using programmablelogic devices to control reed relays accurately and fastly. The transmission technologyof MRS detector is realized based on a H bridge circuit which is composed of highpower IGBT and LC series resonant circuit (L is transmitting coil, C is harmoniccapacitor box), then the alternating current flowing through the H bridge circuit underthe control of MRS timing, so the alternating electromagnetic field which isperpendicular to the constant geomagnetic field is generated according to right handlaw. The receiving circuit of MRS signal after separating the transmitter and receiverincludes frequency selection circuit, low-noise amplifier circuit and programmablefilter amplifier circuit. The envelope detection technology of MRS signal is used byexisting MRS instrument, which calculates the initial phase of MRS signal will has agreat error when the signal to noise ratio is low, therefore the full-wave acquisitiontechnology is used in the separate MRS prototype. Finally, the normalized digitalorthogonal detection technology which is used to process MRS signal is introduced,this technology can improve the detection SNR of MRS signal.The software design of MRS system is introduced in the fourth chapter,including the whole timing design based on state machine, the timing and software design of sampling system, the flow chart of PC program design and so on. Timing ofthe whole MRS system is to transform MRS principles into the core of MRSinstrument, which is designed by top-down method based on state machine. As for theclock signal, the high-precision125MHz crystal oscillator is adopted, which completethe whole timing design precisely and skillfully.The tests of system performance and results analysis are introduced in the fifthchapter, including LC series resonant test, the switch test of transmitter/receiverseparate relay, the test of full-wave acquisition system, the test of the whole MRSsystem both in laboratory and in the field, and the results is analysed in detail. Theresults show that the prototype of transmitter/receiver separate MRS detector candetect groundwater accurately.Summary of the paper is described in the sixth chapter, and the suggestions offurther design and research about transmitter/receiver separate MRS detector isproposed.The results of laboratory and field test proved that it feasible and effective for theprototype of transmitter/receiver separate MRS detector to detect groundwater, thefurther research include one transmitter with many receiver coil, setting some receivercoil that receive noise only, increasing the turns of receiver coil and so on, thesemethods can improve the horizontal resolution, reduce noise of reference coil andincrease the strength of signal.
Keywords/Search Tags:magnetic resonance sounding, transmitter/receiver separation, anti-interference, full-wave data acquisition
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