Switchless charge-discharge circuit for electrical capacitance tomography

The main factor limiting the performance of electrical capacitance tomography (ECT) is an extremely low value of inter-electrode capacitances. The charge-discharge circuit is a well suited circuit for a small capacitance measurement due to its immunity to noise and stray capacitance, although it has a problem associated with a charge injected by the analogue switches, which results in a dc offset. This paper presents a new diode-based circuit for capacitance measurement in which a charge transfer method is realized without switches. The circuit was built and tested in one channel configuration with 16 multiplexed electrodes. The performance of the elaborated circuit and a comparison with a classic charge-discharge circuit are presented. The elaborated circuit can be used for sensors with inter-electrode capacitances not lower than 10 fF. The presented approach allows us to obtain a similar performance to the classic charge-discharge circuit, but has a simplified design. A lack of the need to synchronize the analogue switches in the transmitter and the receiver part of this circuit could be a desirable feature in the design of measurement systems integrated with electrodes.

[1]  W. Smolik,et al.  Elektryczny tomograf pojemnościowy IREna , 2009 .

[2]  Wuqiang Yang,et al.  New AC-based capacitance tomography system , 1999 .

[3]  Wuqiang Yang,et al.  Design of electrical capacitance tomography sensors , 2010 .

[4]  Wuqiang Yang,et al.  Hardware design of electrical capacitance tomography systems , 1996 .

[5]  William R B Lionheart,et al.  The Reconstruction Problem , 2017 .

[6]  FuQun Shao,et al.  A method for measuring low capacitance for tomography , 1999 .

[7]  T. A. York,et al.  An AC-based capacitance measuring circuit for tomography systems and its silicon chip design , 1995 .

[8]  Philip Williams,et al.  Evaluation of Integrated Electrodes for Electrical Capacitance Tomography , 1999 .

[9]  M. S. Beck,et al.  Capacitance-based tomographic flow imaging system , 1988 .

[10]  Maurice Beck,et al.  REVIEW ARTICLE: Electronic transducers for industrial measurement of low value capacitances , 1988 .

[11]  Lijun Xu,et al.  A Digital Switching Demodulator for Electrical Capacitance Tomography , 2013, IEEE Transactions on Instrumentation and Measurement.

[12]  Robert X. Gao,et al.  A new sensing method for Electrical Capacitance Tomography , 2010, 2010 IEEE Instrumentation & Measurement Technology Conference Proceedings.

[13]  Trevor York,et al.  A miniature electrical capacitance tomograph , 2006 .

[14]  Lijun Xu,et al.  A recursive least squares-based demodulator for electrical tomography. , 2013, The Review of scientific instruments.

[15]  F T Kühn,et al.  Design of an active-differentiator-based capacitance transducer for electrical capacitance tomography , 1997 .

[16]  P. Brzeski,et al.  Multichannel capacitance tomograph for dynamic process imaging , 2003 .

[17]  Wuqiang Yang,et al.  CAPACITANCE TOMOGRAPHY SENSOR WITHOUT CMOS SWITCHES , 1997 .

[18]  Waldemar T. Smolik,et al.  Single-shot charge-discharge circuit for dynamic electrical capacitance tomography , 2012 .

[19]  R. F. Mudde,et al.  A Fast Active Differentiator Capacitance Transducer for Electrical Capacitance Tomography , 1999 .