Design Of An Electrical Resistance Tomographic Measurement System With Real Time Phase Compensation

Electrical Resistance Tomography (ERT) is a new measurement technique that can provide on-line process measurement with obvious advantages of process imaging, non-intrusive sensing and relative low cost in addition to its inherent safe operation principle. The technique has long been applied to measure conductive liquid based two-phase flow.In the design of ERT measurement system hardware, it is important to focus on both the measurement accuracy and the speed at which the complete measurement is taken. The work present in this thesis is a modification design on a prototype ERT system designed previously in the lab, aiming at improving both static and dynamic measurement performance achieved with the original system and producing a better design that is more suited to industrial applications. The main contributions and works are as follows:1. The new ERT hardware design has added a phase difference detection and compensation measurement scheme. The system design covers the circuits design on signal generation, electrode selection control, electrode driving, conditioning of analog signal channel, phase difference detection and compensation, A/D conversion and data acquisition. The electrode driving circuits is redesigned to improve the weak signal measurement. The addition of phase detection and compensation circuit reduces the effects of phase variation on demodulation output among the different measurements. The compensation of phase variation could increase the output of demodulation circuit which ultimately would improve imaging.2. In conjunction with the hardware design, developed a Visual Basic GUI based data acquisition software which is able to set the frequency, amplitude and phase of measuring current source and the reference signal, the sampling rate and data points. The software can perform functions such as data collection, storing and on-line imaging using a Linear Back Projection (LBP) algorithm programmed with Visual C++ and OpenGL library.3. In addition to each hardware circuit module debugging, the overall system performance is tested with a 16 electrode testing phantom. Both static and dynamic experiments are performed in the lab. The result shows that the new design has achieved a better performance than its previous prototype with regarding to measurement stability and reliability. Imaging performance under different circumstances are also analyzed and compared according to different experimental setup. It shows that phase compensation based ERT measurement scheme can improve ERT performance.