Electrical capacitance tomography
ACECT system
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ACECT system

System hardware

The ACECT system employs an AC-based capacitance measuring circuit with high-frequency sinusoidal excitation and phase-sensitive demodulation (PSD). This circuit can measure the change in capacitance as small as 0.0001 pF accurately at high speeds, and the system can acquire image data at 140 frames per second from a 12-electrode sensor. The circuit can measure both capacitance and loss conductance by means of PSD. Because of the DDS signal generators used, the excitation frequency is programmable, providing spectroscopic measurement. In addition, the hardware design allows any electrode combination, offering flexibility in setting up different excitation patterns. 

A journal paper describing the design of the system hardware was awarded the 2000 IEE Ayrton Premium. It has been confirmed experimentally that the ACECT system has 4 times better signal-to-noise ratio (SNR), 40% higher data acquisition rate and 3 times faster on-line image reconstruction rate than the charge/discharge ECT system.

The ACECT system consists of three main units: (1) an electronics box complying with the Eurocase and Eurocard standard, which can hold up to 16 measuring channels, (2) a desktop PC with a PCI data acquisition board or a laptop PC with a PCMCIA data acquisition card, and (3) a 12-electrode demonstration sensor. 

System software

The system software is written in Visual C++ and implements two main functions: (1) control of the operation of hardware and (2) image reconstruction. It employs 32-bit programming. The following picture shows the Windows user interface.

Two image reconstruction algorithms are mostly used: (1) linear back-projection (LBP) and (2) Landweber iteration. Both algorithms offer real-time image reconstruction. The following pictures show images of a plastic rod in air. Clearly, a much clearer image can be generated by the Landweber iterative algorithm with 10 iterations than LBP.

The system software has been designed in such a way that users can incorporate their own image reconstruction algorithm into the system as a plug-in unit for their specific applications. Therefore, the system is a powerful and flexible tool, and can be used for advanced research into industrial process tomography. The system can also work with a twin-plane ECT sensor. The picture below shows a screen shot of twin-plane operation.

To download the specification of the ACECT system, click here.

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