A Electrical Capacitance Tomography System Based On FPGA And AD5933

As a tomography technology based on electromagnetic field sensitive principledeveloped in the1980s, Electrical Tomography (ET) has attracted wide attention fromresearchers at home and abroad for its no radiation, non-invasive, fast response, lowcost, and visualization.Being a kind of Electrical Tomography technology, Electrical CapacitanceTomography (ECT) technology, researching on the sensitive field permittivitydistribution, can be widely used in the detection and control of industrial processes,and has a very attractive application prospect.The ECT technology has already begun the transition from the laboratory toindustrial applications after decades of development, and technical theories andtechnical supports are also matured and improved. Then, with the deepening of thetechnical applications of ECT, more and more requirements are proposed, whichinclude not only faster data acquisition speed, higher accuracy of data collection,better quality of image reconstruction, but also intensive, portable and low powerconsumption. In order to meet the development requirements of the new situation, aswell as broaden the application range of ECT system, new exploration and research isconducted based on the original ECT system and a new ECT system based on FPGAand AD5933has been developed.The AD5933is a low power, integrated impedance spectroscopy measurementchip, packaged in a16-lead SSOP. The chip combines some modules, such as a directdigital frequency synthesizer, a low-pass filter, analog-to-digital converter and adigital-to-analog converter, and can directly output the impedance of the measuredmedium by I~2C bus. In the ECT system, the FPGA with multiple AD5933chipsperform together, and one AD5933chip is responsible for one electrode. Theelectrode state is determined by the "T" type switch and the measurement data finalupload to the host computer by RS232serial for image reconstruction.The I~2C bus module and the RS232serial communication module areprogrammed by VHDL to achieve the communication between the FPGA andAD5933as well as the host computer, and the system flow is controlled by anembedded8-bit microprocessor PicoBlaze in FPGA. The signal-to-noise ratio of the system is up to70dB tested by some experiments, and the data acquisition speedvaries from electrode numbers. In the ECT system with8electrodes the dataacquisition can reach about110frames per second, with12electrodes about75frames per second, and with16electrodes about56per second. Finally, the ECTsystem based on FPGA and AD5933system has small size, low power consumption,and can be applied in such occasions that require less real-time and have certainrequirements on the system size and power consumption.