A high-performance EIT system

This paper presents the development of a new electrical impedance tomography system for online measurement of two-phase flows with axial velocities up to 10 ms^-1. The system is designed in a modular fashion and can consist of several data acquisition modules and computing modules. The data acquisition module includes a voltage controlled current source with a direct-current-restoration circuit, an equal-width pulse synthesizer unit and a synchronized digital demodulation unit. A new concept of current switching scheme is developed to enhance the ac coupling speed. The computing module includes a digital signal processor (TMS320C6202/6713) with memory, multichannel buffered serial ports and an IEEE1394 communication interface. Several DSP modules can be pipelined for a series of tasks ranging from measurement control to image reconstruction to flow velocity implementation. The performances have been tested and some trial results are reported. A data acquisition speed of 1164 dual-frames (2.383 million data points) per second has been achieved with a root mean square error less than 0.6% at 80 kHz in static test application. An application in the measurement of vertical oil-in-water pipe flow is reported.