Study On Data Acquisition System Based On DSP For Electrical Capacitance Tomography

Multiphase flow system is a complex, nonlinear system. There are interface effect and relative velocity between these multiphase flow. That cause the difficult of measurement of multiphase flow; Electrical capacitance tomography technique (ECT) is a kind of process tomography technique (PT) 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 still a lot of work to be done for practical use of the technique, for example: low capacitance measuring, improving the anti-interference ability and so on.The object of this dissertation is on the research of 12-electrode Electrical Capacitance Tomography system. The main topic is data acquisition; The paper introduce the basic principles of tomography, the system constitution, the basic feature, developing status and the process tomography based on various sensing technique. It also analyzes the principle and proposes the mathematical model of sensitivity field, discusses the peculiar advantages and research status of the technique. A set of circuit about electrode-chosen can reduce the complication is designed, which could measure couple-capacitance and other noise interference by software in the system; Adopted a method of alternating current measurement capacitance in order to accurately measure the low capacitance ,and used high precision operation amplifier OPA627,can realize the circuit of C/V, not only can adjust the signal, but also validly measure the low capacitance; Make use of cosine signal whose frequency is 500K Hz to trigger the electrode of capacitance, as a result, the signal of coming from the sensor of capacitance is modulated , and make the flowing measurement is easy and accurate; Phase sensitivity demodulation is used in the system for restricting noisy interference; A model of coupling capacitance compensation is proposed, and is built using hardware and software of real time compensation; A DSP based data acquiring system has been developed, which can advance the speed of data acquisition and processing, also communicate with upper computer expediently and fleetly in real time after analyzing the feasibility and rationality of using RS232.