Research On Digital Demodulation Of Dual-Mode Electrical Tomography System

Dual-mode electrical tomography system including electrical capacitance tomography and electrical resistance tomography in the same system is a PT technology to obtain dielectric constant and electric conductivity of the sensing field. It has the advantages of non-radiant, non-intrusive, rapid response and low cost. Data acquisition are the key links of the technique in the image reconstruction. The method of the demodulation of the signal can be divided to analog demodulation and digital demodulation.The author focuses on the measurement methods and digital demodulation method of dual-mode tomographic system. The following achievements have been obtained:1. The digital hardware system is tested and improved on the basis of the former system including the exciting module, the measurement module and data acquisition module. The amplitude limiter circuit is designed, and the measurement methods were generalized.2. The whole hardware system is controlled by the 6701PA data acquiring card and the data is analysed. The digital demodulation methods are researched, dual-window FFT spectral analysis and parametric demodulation are introduced to the system, and improve the speed and the precision to some extent.3. The error analysis of the digital system is done, including the error introduced by the amplifier and the influence to the result, the error introduced by the digital demodulation, the influence to the result.The standard to choice the feedback resistance, the feedback capacitance and the frenquency of the exciting signals.