Development Of Transient Electro-magnetic Receiver Based On DSP And Pocket PC

On the basis of the transient electromagnetic receiver design has beenmade, functional perfect of it was made in this thesis. The new receiver basedon DSP and Pocket PC is mainly composed by four parts: data acquisition unitbased on DSP , synchronous unit, communication unit and Pocket PC whichused as input and output equipment.Transient Electromagnetic methods (TEM) can be called as Time DomainElectromagnetic methods. The measuring equipments of it include two units:transmitter and receiver. Utilizing re-line untouched to ground (big re-line ormagnetism even source) or electricity power touched to ground (electricity-even-source),the transmitter sends the first field, and then the receiver measuresthe induced electromagnetic field (the second field) changed with time whichis created by underground substance. So it can measure the position of under-ground inhomogeneous substance and estimate its scale and electricity capabil-ity. With the development of digital and intellectual receiver, the accretion ofemit power, the use of forward computation and inversion of digital model com-puter, the improvement of explanation level, TEM can resolve a larger rangeof geology problems which almost includes every field of geophysical explo-ration: ore exploration, constitution exploration, hydrogeology and engineeringgeology investigation, environment survey supervising and archaeology and soon.TEM signal quickly decreases in the beginning period and has a largebreadth (from dozens ofμs to hundreds ofμs, the breadth decreases from about10V to mV or evenμV ). In middle and late period, the TEM signal slowlydecreases and has a small breadth (from hundreds ofμs to several ms or even several seconds, the breadth decreases from about mV orμV toμV or nV ).Therefore, the receiver must have the capability of rapid sampling in high den-sity, high resolution and wide dynamic range.In unit of data acquisition based on DSP, the dynamic range of the TEMsignal is greater than 138dB. That is to require the expensive 24bits A/D, butthe speed cannot be satisfied. So, we applies the ?oating point amplificationtechnique in the data acquisition unit, which attains higher signal dynamic rangein lower cost. The ?oating point amplification technique is to magnify the signalwith appropriate value firstly, then to convert the signal with A/D. We can getthe original signal by data processing.The ?oating point amplification includes two main sections, namely thefront acquisition-fast speed 8bits A/D and the rear acquisition-16bits A/D. Weacquire the exponent-code and the tail-code by acquiring the TEM signal, andthen deal with these data with Q24 format. Finally, We can get the original signalon Pocket PC. Utilizing the ?oating point data acquisition not only expand thedynamic range, but also let the signal range entered A/D converter always at halfquantity in the range. Therefore the SNR of quantization will keep accordantapproximately. Use of Q24 data format guarantees the receiver to the actualdynamic range of 138dB, at the same time , effectively decreases the truncationerror caused by division operation.To recognize and correct the singular point caused by the ?oating-pointdesign, and better to preserve the original signal details, we present a methodbased on the first order differential and the quantile distribution diagram method.The tests proved that this method can effectively remove large singular points,and preserve the original signal details.In order to make TEM receiver and transmitter synchronous in practicalwork, the line synchronization and GPS synchronization are adopted in the the-sis.Pocket PC, is used as the input and output part of receiver and named asupper computer in text. This would facilitate the expansion of the receiver datastorage capacity and enhance the receiver portability and ease of use. The userapplication software used .NET Compact framework programming. By using it, users can control data acquisition, pick-up data and draw the transient signals,and the data can be on-site assessment.Communications interface uses RS–232 ensure the data transmission be-tween Pocket PC and DSP stable and reliable, to facilitate the upgrading ofBluetooth wireless communications.To test the receiver performance, we test its noise level and transient elec-tromagnetic signal acquisition capability, and the model test proves its measur-ing capability.At last, the thesis is forward to the future work.