Design Of Dual Frequency Induced Polarization Receiver Based On FPGA

Induced polarization method is one of the most effective geophysical prospectingmethods to look for metal deposits. It is one of the electrical prospecting method basedon the difference of the physical and electrochemical effects. It reflect the effect ofunderground rock and ore in the artificial electric field.Two electrodes are placed to observe the potential difference of the surface whenwe current the rock and ore stone. Even when the size of the emission current does notchange, the potential difference between the electrodes get grow, after reaching acertain time interval, measuring the potential difference tends to a saturation value.Also, when the power supply current is disconnected, the measured potential differenceinformation will also change, the numerical size decreases continuously, after reach acertain length of time, potential difference value tending to zero. The phenomenon ofpotential difference vale changes over time no matter the power supply or not, is calledthe induced polarization effect or IP. It is a kind of electrochemical polarization effectabout the aqueous solution of rock and ore.Dual-frequency IP method are two different frequency square wave excitationcurrent of current superposition, into the superposition of the electric current into theground, underground IP field will make potential information contained in these twokinds of frequency components, if you receive this potential information is processedby instrument, you can get low frequency and high frequency electrical potentialdifference at a time. Due to dual frequency IP method does not need to be at the secondpotential difference measurement, power supply current compared to time domain canbe much smaller, so the dual-frequency IP instruments can light a lot. Midway throughthe dual-frequency IP measurement doesn’t need variable frequency operation, it canreduce half of the measuring time and can improve the detection efficiency of theinstrument. In dual frequency IP measurement, power supply current is the same, soaccidental factors for low or high frequency electrical potential difference value are thesame, calculate the difference of the low frequency voltage and high frequency electrical potential difference, so the accidental factors may offset each other, this canimprove the precision of the instrument.This paper design the dual-frequency IP receiver based on FPGA in the aspect ofhardware circuit mainly includes power circuit, signal modulation circuit, A/Dconversion circuit, FPGA and MCU control circuit design. In the FPGA programmingcompleted the PLL control module and decoder module, A/D module, FFT module andFIFO module design work. Implementation in the single-chip microcomputerinstrument and PC communication between PDA and the PDA control display software,the application of LabVIEW in the design work to complete the control of the receiverDual-frequency IP receiver based on FPGA, after receives the acquisitiondifferential signal input acquisition circuit, signal conditioning and A/D collectionmodule, the digital signal transmission to the FPGA circuit, FPGA FFT calculation twodifferent frequency component of frequency information, respectively two kinds offrequency information through the MCU and communication protocol, bluetoothwireless transmission module is connected to a serial port to transmission data to thePDA. Application LabVIEW in PDA to processing data depending on the amplitudefrequency and phase difference resulting from the data processing, the LabVIEWcontrol panel shows the result value. While indicating abnormal points the results ofthe two values have significant difference. Depending on the amplitude frequency andphase difference value of each measurement point value will be stored in the memoryof PDA. When the measurement is over, all the results of the measurement point valuecan figure up in the PC to display the trend and observed anomaly positionmeasurement results.After the receiver design is completed, experiments in the laboratory give noabnormal point data values and the measured experimental can refer to this value to seethe abnormal. Through the analysis of experimental results, verifies the accuracy andstability of design of dual frequency induced polarization receiver based on FPGA.