Design of sensor electronics for electrical capacitance tomography

Abstract

The design of the sensor electronics for a tomographic imaging system based on electrical capacitance sensors is described. The performance of the sensor electronics is crucial to the performance of the imaging system. The problems associated with such a measurement process are discussed and solutions to these are described. Test results show that the present design has a resolution of 0.3 femtofarad (For a 12-electrode system imaging an oil/gas flow, this represents a 2% gas void fraction change at the centre of the pipe) with a low noise level of 0.08 fF (rms value), a large dynamic range of 76 dB and a data acquisition speed of 6600 measurements per second. This enables sensors with up to 12 electrodes to be used in a system with a maximum imaging rate of 100 frames per second, and thus provides an improved image resolution over the earlier 8-electrode system and an adequate electrode area to give sufficient measurement sensitivity.

Circulating fluidized bed hydrodynamics experiments for the multiphase fluid dynamics research consortium (MFDRC).

“…The output voltage indicates the current flow in proportion to the feedback resistance R F by Ohm's law. Similar measurement schemes are reported by Huang et al (1992), Williams and York (1999), and Georgakopoulos et al (2001).…”

Virtual Instrument for Online Electrical Capacitance Tomography

“…According to the type of excitation signals being used, ECT can be divided into two categories: AC-based (sine-wave excitation) and charge-discharge-based (square-wave excitation). The former is advantageous in terms of measurement stability and accuracy, whereas the latter has lower circuit complexity (Huang et al, 1992). In recent years, studies have been conducted on sensing principle and circuit optimization to enhance the performances of ECT.…”

Direct imaging of two-phase flows by electrical impedance measurements

“…Problems issued from diffractive or scattering systems can be usually solved by means of algorithms based on moment and pseudo inversion methods (Caorsi et al [5]; Chiu et al [6]). Problems issued from electric sensing systems can be frequently treated with several back-projection methods (Huang et al [7]; Xie et al [8]) and by means of iteration algorithms based on optimization techniques (Isaksen & Nordtvedt [9]), perturbation methods (Kim & Woo [10]; Yorkey et al [11]) or the NewtonRaphson method (Yorkey et al [12]; Abdullah et al [13]). …”

“…• the probe should have a limited measuring volume in order to reduce the longitudinal averaging effect and to increase the resolution in this direction (what restricts the adoption of long longitudinal measuring electrodes such as for instance proposed by Klug & Mayinger [17] and Huang et al [7]). Considering these requirements, the geometry that seemed the most appropriate consists of two stainless steel ring electrodes flush mounted inside the tube, as illustrated in Figure 2.…”