Development of Control and Data Acquisition Circuit for Electrical Capacitance Tomography

Accurate measurement and visualization of fluid distribution in cryogenic transfer lines are critical for optimizing performance and safety. Electrical capacitance tomography (ECT) is attractive for such diagnostics because it can infer liquid–vapour distribution from permittivity changes without optical access. This paper reports the first-stage development of a control and data-acquisition (DAQ) front-end for an 8-electrode ECT sensor intended for liquid-nitrogen (LN2) two-phase flow studies. Mutual capacitances are acquired sequentially (n(n-1)/2 pairs) using a low-parasitic relay matrix and a high-resolution capacitance-to-digital converter (TI FDC1004Q) with CAPDAC offset compensation and active shield drive. Guard electrodes on the flexible-PCB sensor and shielded lead routing are used to suppress cable parasitics and electromagnetic interference, enabling stable measurement of sub-picofarad capacitances in a dynamic, noisy environment. The microcontroller performs I2C control, timing/averaging, and data framing, while a LabVIEW interface executes electrode-pair sequencing, live display, and logging. Calibration/normalization and a permittivity-to-void-fraction estimation approach for LN2 flows are outlined; detailed reconstruction and cryogenic flow images are reported separately..