Research Of Improving The Electrical Capacitance Measurement Circuit Sensitivity Of The Electrical Capacitance Tomography System

Electrical Capacitance Tomography (ECT) is based on the principle that each phase of the multiphase in the pipeline or closed container has different permittivity. The inter-electrodes capacitance data can be measured through the ECT sensor, measurement circuit and data acquisition system. Distributing image of the multiphase in pipeline or container can be displayed by the combination of the capacitance data and image reconstruction algorithm. ECT can be applied to industrial controlling process by extraction of image feature parameters. ECT has been widely used in power, petroleum and chemical engineering in recent years, due to its advantages such as non-intrusive, high speed, safety, widely applicable and simple structure.Tiny capacitance measurement circuit is one of the key technologies of ECT. The improvement of measurement circuit sensitivity causes the increase of sensitivity of the change of the multiphase in the pipeline or closed container and optimizes the accuracy of reconstructed image. Therefore, research of the capacitance measurement circuit sensitivity has great significance. The main research tasks of the thesis which is based on the previous studies are as follow:1. The principle of the ECT and current research status of capacitance measurement circuit are analyzed. Several typical types of capacitance measurement circuits are introduced, and the advantages and disadvantages of these circuits are compared.2. The sensitivity model of measurement circuit is deduced under the practical application conditions, that is to say circuit existing conduction resistance of analog switch and the limited gain of the amplifier and so on. And the relationship between circuit parameters and measurement sensitivity is shown clearly by the model.3. The analysis about the influence of stray capacitance on measurement circuit sensitivity is made by the sensitivity model. The method of phase compensation is presented to improve the capacitance measurement circuit sensitivity and experimental results demonstrate that the circuit sensitivity is effectively improved.4. The analysis about the influence of exciting frequency on measurement circuit sensitivity is made by the sensitivity model. The method of optimal exciting frequency is presented to improve the circuit sensitivity. Experiment results show that the circuit sensitivity is effectively improved. The optimal exciting frequency in different type of application conditions can be calculated by the model.5. ECT hardware including capacitance sensor, the excitation signal source and the measurement circuit are designed and tested. The testing results show that hardware platform satisfies the requirement of ECT system.