Digital Ert System Design Based On Fpga And Dsp

As a new measurement technique based on electromagnetic field theory, Electrical Tomography (ET) has broad developing prospects in the field of industrial application and clinical diagnosis, for its features such as non-intrusive, good safety, simple structure, rapid response and real-time visualization.Electrical Resistance Tomography (ERT) is one kind of ET technologies. It is based on different conductivity for different media, the electrical conductivity distribution inside the measured sensitive field is measured, and then media distribution inside the measured field can be calculated. So ERT aims at measuring two-phase flow in which conductive medium is taken as continuous phase.The ERT system used to adopt analogue filters and associated demodulation, which limited the speed and precision of the system. Moreover, a system built with analogue devices is hard to be upgraded or expanded. In order to improve the speed and precision of the ERT system, a digital ERT system is designed in this paper. The following research work is carried out in this dissertation.1. By comparing DSP and FPGA, the author determined the digital design program of ERT system. As the host controller, DSP is in charge of data read, imaging algorithms and communication with the computer. As the association controller, FPGA is in charge of logical controls of the system, excitation signal generation, data acquisition and phase sensitivity demodulation (PSD).2. In this system, a direct digital synthesizer integrated within FPGA, together with high-speed digital analog converter (DAC) and voltage-congtrolled current source (VCCS) based on AD844, produces current excitation with adjustable frequency, phase and amplitude.3. In order to overcome the shortcomings of the analogue filters, the author designed two kind of digital phase sensitivity demodulation.4. A series of performance tests show that the system has a good channel uniformity and high precision.