Study On Electrical Impedance Tomography For Dredging Application

In dredging project,the parameter detection of the pipeline for mud transportation is important to process control,production efficiency and optimization.And the solid fraction of solid-liquid two-phase flow in pipeline is the key parameter,closely relating to safety and efficiency of the project.At present,ray source densitometers are used in the dredger pipeline to measure the solid fraction.However,the ray source densitometers are expensive,hard to maintenance,and not qualified for requirements of environmental protection.With no pollution and low cost,measuring apparatus based on Electrical Impedance Tomography(EIT)are gradually replacing ray source densitometers as the main measuring device.However,there are still many problems to be solved in the practical application of the electrical measuring instrument.In this paper,the measuring apparatus based on EIT and its application in dredging engineering is studied.The research is conducted in the following three aspects:1)Theoretical derivation is carried out to analyze the nonlinear relationship between the measured value and the background conductivity of two-phase flow.The out-field resistance is speculated to be the key factor causing the nonlinear relationship,which is confirmed by simulation.Then,further study is conducted to analyze the influence of out-field resistance on the measured value and the relationship between the sensitivity of dredging apparatus and the out-field resistance under different background conductivity.The range of value of out-field resistance suitable for application in dredging engineering is proposed.2)Now that the existing equipment not qualified for wide range background conductivity,a set of FPGA-based EIT data acquisition system is designed,which can work within [0.025,3.2](S/m).Circuit design and FPGA firmware programming are the main work,including signal timing,parasitic capacitance,intermittent excitation signal,phase-sensitive demodulation,and functional diversity.In addition,the out-field resistance is set to a proper value.The experimental result shows that the signal-tonoise ratio(SNR)of the system exceeded 62 d B and the sensitivity index under background conductivity of 3.2 S/m exceeded 2%.Therefore,the apparatus is qualified to apply in the dredging engineering.3)Analyzation on the causes of abnormalities is done to solve the problem that the solid fraction is inaccurate due to the exception occurred to measured values.Then,experiments are performed and method of identification of abnormal status and dataprocessing is proposed.The application in dredging engineering proves the effectiveness of the method.After that,method based on frequency domain is proposed to extract the features of the measured data.Experiments show that this method reduces impact of noise,and the accuracy of the calculated solid fraction is higher than that of existing schemes under certain conditions.