Data Acquisition Hardware Design Of An Electrical Resistance Tomographic Measurement System

In this thesis, a tested prototype of data acquisition of an Electrical Resistance Tomographic (ERT) measurement system is presented, according to the principle of adjacent method. It entails the following circuit designs: A measuring current source is formed by a chip of direct digital synthesis (DDS) technology whose amplitude and frequency is programmable. The loading capacity of a traditional dual-opamp structured voltage controlled current source (VCCS) is enhanced by implementing a feedback channel design. A CPLD circuit based electrode selection controller, using the principle of adjacent measurement method, is designed. Such a design permits the flexible modification of ERT measurement strategy but would minimize the hardware change should such modification is necessary. The preamplifier is implemented in such a way that a special filter is embedded in the feedback channel to remove the offset DC voltage as well as reduce the phase error introduced from the direct AC coupling in the forward channel; Other designs include a programmable gain amplifier, a switch demodulator, and a lowpass filter to condition the weak analog signal; The data acquisition circuit is formed by a high speed AD which is found stable with a maximum error of 3LSBs; The measuring device (slave unit) can be controlled by a host computer through a USB interface; A Visual Basic 6.0 based data acquisition software is designed which is able to set the frequency and amplitude of current source,the initial gain of amplifier, the data acquisition speed etc. The tomographic image reconstruction is performed by a COM module that implements the Linear Back Projection (LBP) algorithm. This COM module is integrated into the data acquisition software. The experimental results obtained from a test section that contains 16 electrodes are also described in the thesis. Measurement of signal response with regarding to liquids of different conductivities and phantom (a circular plastic rod) positions are given and analysis is performed accordingly. The prototype is very easy to use and it can supply ERT measurement data for future research work.