Research On Capacitance Normalization Model For Electrical Capacitance Tomography System

Electrical Capacitance Tomography(ECT)Technology Process tomography developed in the 1980 s to detect multi-phase flow in industrial pipelines.It is by measuring the capacitance value installed between the electrodes around the measured object,and through the reconstruction algorithm to calculate the visual field distribution of the internal permittivity.ECT technology has the advantages of wide range of application,non-invasive,fast response,non-radiation,easy installation and transportation,low cost and good safety performance.Nowadays,ECT technology has become the focus of research on process parameter inspectors at home and abroad.In the reconstruction of capacitive tomography images,the measured capacitance values need to be normalized.The normalized capacitance model can describe the relationship between the dielectric constant distribution in the measurement area and the measured capacitance.In order to obtain a better reconstructed image,this paper has carried on the thorough research to the capacitance normalization model.The main research contents are as follows:(1)Four commonly used capacitance normalization models are analyzed,namely:parallel,series,Maxwell B?ttcher normalization model,and the simulation results of four common normalized models are compared.The results show that four kinds of normalized models Commonly used normalization model of imaging results are poor,to be further improved.(2)The distribution of multi-phase flow in the field is complicated and changeable,which can not be expressed in parallel or in series.In this paper,ECT image reconstruction based on thresholding normalized binocular model was studied,and the reconstruction effects of thresholds of 10%,15%,20%,25%,30% and 35%were analyzed.The results show that the 25%,30% and 35% threshold normalized model reconstruction images are better than the 10%,15% and 20% threshold normalization models respectively,and the threshold reconstruction effect is the best for different flow patterns it is good.The selection of the scene flow complex and changeable threshold can only be based on the subjective judgment of the operator.(3)Based on the ratio of the minimum distance to the maximum distance between the unit cell and the central electric field line,the weighting factors of the normalized model of the capacitor-capacitor combination are determined and the sensitivity matrix is calculated accordingly.The simulation experiments and static tests are carried out.The results show that the accuracy and shape fidelity of reconstructed images are obviously improved.(4)The adaptive normalization model is studied.The adaptive factor of the model is calculated according to the ratio of the minimum distance to the maximum distance between the cell and the center electric field in the two regions divided by the center electric field lines.The simulation and static experiments show that the reconstructed image quality improve.