Development Of Electromagnetic Transmitter Based On FPGA

Electromagnetic prospecting generally includes the resistivity method, thecharging method, the natural electrical field method, the polarization method and theelectromagnetic induction method. Resistivity method includes the resistivity profilingmethod， the resistivity sounding method and the high density resistivity method.Induced polarization method includes time domain method and frequency domainpolarization method. Electromagnetic induction method includes electromagneticprofiling method, the frequency domain electromagnetic sounding method, theartificial source electromagnetic sounding method, and the transient electromagneticmethod. These methods provided a theoretical basis for the manufacturing of electricalinstruments. The use of electromagnetic prospecting instruments for petroleum, naturalgas, ground water and geothermal mineral resources is carried out both at home andabroad for many years, and the effect is significant.The article analyzed the characteristics of several current typical andrepresentative electromagnetic instruments and researched the advantages anddisadvantages of their transmitters which are based on electromagnetic prospecting,and then developed the transmitter which is based on FPGA. The design of transmittersatisfies the using demand of various geophysical methods, which can output the single polarity square wave, double polarity square wave of50%duty and100%duty, and thepseudo random waves of three times, five times and dual frequency wave.The mainly work of this transmitter includes four parts, which are power supplyfor the controlling system, transmitter controlling board, bridge driving signalcontrolling board and the detection board for voltage and current. In the power supplypart of control system, the article actualized each output of voltage in the condition of220V AC input and12V DC input. The output voltage included positive12V, analogpositive and negative5V, digital positive5V,3.3V and1.5V and positive5V forconstant temperature crystal oscillator. In the controlling circuit of transmitter, eachpart of bridge driving signal is generated by the method MCU plus FPGA. In thebridge driving signal, the control part generated two groups of conduction byalternation which is used to drive IGBT gate. The design of detection of voltage andcurrent include preceding stage amplify, detection circuit, voltage-frequency transformcircuit and isolation circuit.After the design of transmitter, we tested the transmit wave, transmit power andtransmit frequency, and finally verified the performance indicators of this transmitterhad reached the expected requirements.