Design Of Three-dimensional Electrical Resistance Tomography System Based On FPGA And DSP

ERT(Electrical Resistance Tomography)is a technology with the characteristic of non-invasion,low price and quick response,which is one of the heated study objects in the field of multiphase flow measurement.The 3-dimension ERT system makes it possible that the 3-dimension information of the measured object can be collected,solving the problem that the 3-dimension parameters such as geometrical shape,relative position,space distribution and other information are always in shortage for collecting in the 2-dimension ERT system,having highly important research value.However,the 3-dimension ERT system has lots problems like low accuracy and bad instantaneity in common,causing the image quality is lowered heavily.In this thesis,making the 3-dimension ERT measure system as the research object,in order to improve the instantaneity,load capacity,and accuracy of ERT system data collection,the optimization design of 3-dimension ERT system is accomplished based on existing work,with features such as the faint border measured voltage,the wide dynamic range and the low signal-to-noise ratio of detected signals.In addition,the ERT system test platform is built to realize the collection of the 3-dimension information of the measured object,completing related experiments and analysis.The main research work of this thesis are as following points,(1)In terms of features of 3-dimension ERT system as large quantities of data collection,quickly processing data,complicated switch logic of the electrode plate and complicated structure of image reconstruction algorithm,the design scheme is presented based on FPGA and DSP,fulfilling the requirements of instantaneity and stability that the single control method fail to realize.Front-end data processing and underlying logic control is mainly completed by FPGA,and DSP is responsible for realizing functions as data transmission,complicated image algorithm and communication with the upper computer.With above two control methods'advantages,the best control can come true.(2)To solve the problems of measured signal too faint between adjacent and interface electrode plates,system collection too difficult,the 3-D simulation model of ERT sensor is constructed with EIDORS.After analyzing impacts of different excitation current on the electrode plate measured voltage,the method of increasing the electrode plate border voltage by enhancing the excitation current is locked.Meanwhile,the analysis to the parameter influences on the reconstruction image quality such as the quantity and the width of the electrode plate is completed,and the sensor structure of 3-layer and 16-electrode is determined at last.(3)To solve the problem that the load capacity of the traditional voltage-controlled current source is so weak that cannot fulfill 3-dimension ERT measurement requirements,the voltage-controlled current source is studied and designed based on Howland topological structure circuit by analyzing performance characteristic of the standard Howland current sources and improving it to fulfill the requirement of voltage-controlled current source performance that the system demands.Meanwhile,aiming at the problems that the process of actual debugging the Howland current source is complicated as well as difficult and its performance is interfered by itself and the outside,the analysis of the improved Howland current source parameter characteristics and the key factors influencing its performance is made during the research,completing the voltage-controlled current source design focusing on the AD8620 voltage-controlled operational amplifier.(4)To solve the problems of measured signal too faint and dynamic range too wide of the 3-dimension ERT system,reaching the goal of high accuracy,the design of the electrode plate selector module,the preamplifier module,PGA amplifier module,band-pass filter,A/D transfer module and other modules is completed.In terms of the high accuracy requirement of output excitation signal from 3-dimension ERT system,the design of the signal excitation source is completed based on FPGA,realizing the accurate control to the output signal amplitude and phase and assuring the accuracy of signal demodulation.(5)For the demodulation of the traditional analog multiplier fails to detect data in real time and accurately,analyzing the phase sensitive demodulation means of ERT system,the means of orthogonal sequence numerical demodulation is presented and designed,obtaining the real-time detection and highly measured accuracy.ERT software control system is designed based on the design of the hardware measure system,including FPGA program,DSP program,USB communication module and the upper computer data processing and display platform based on LabVIEW.After building the 3-dimension ERT system experiment platform,the assembly and debugging to the hardware system and the coding and test to the software system are accomplished.In addition,tests such as the stability of the excitation source signal,load capacity of voltage control current source and the consistency of the system measure channel are completed.After experimental verification,this system can realize the effective and quick collection of 2-dimension and 3-dimension information,reaching the data collecting speed of 100 frame/s and100 frame/s.The load capacity of the voltage-controlled current source is 3988.2 k?,fulfilling the requirement of 3k? that demanded by 3-dimension ERT system.(The fluctuation of output current is less than 1%.)...