Design And Implementation Of Data Acquisition System Based On DSP For Electrical Capacitance Tomography

Electrical capacitance tomography (ECT) technique is a kind of process tomography (PT) technique based on the sensitive principle of capacitance. The technique with its advantages such as no radiation, no invasion, high speed of response, simple structure, low cost, wide application range, better safety and so on has now being a most important technique of two-phase flow parameter measurement. But there is a long distance in practical application and there are some problems and difficulties in system design and application. So there is a lot of work to be done in order to use the technique in the industry as soon as possible.This dissertation is based on the study of 12-electrode electrical capacitance tomography system for oil-water two-phase measurement. The characteristics, the operation principles, and the structure of ECT system are studied. Low capacitance measurement circuit is designed according to the data from finite element analysis. Phase sensitivity demodulation is used in the system for restricting noise interference. The influence of coupling capacitance to the measurement system is analyzed. A model of coupling capacitance compensation is proposed, and is built using hardwire and software of real time compensation. A circuit of electrode-chosen is designed, and electrodes share the C/V converting circuit and signal generator. The system used the controllable differential circuit to carry on direct current compensation, used PGA differentiator control filter circuit output direct current signal, DSP conveyed data to the computer by Serial port. The experimental results show that the method is practicable to the measurement of small capacitance.