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Vol. 100, Issue 1, January 2009, pp.72-84





A New Wide Frequency Band Capacitance Transducer with Application to Measuring Metal Fill Time


Wael DEABES, Mohamed ABDELRAHMAN, and Periasamy K. RAJAN

Electrical and Computer Engineering Department,

Tennessee Technological University, Cookeville, TN 38505, USA

Tel.: (931) 372-6272, fax: (931) 372-3463

E-mail: wadeabes21@tntech.edu



Received: 23 October 2008   /Accepted: 19 January 2009   /Published: 26 January 2009


Abstract: A novel low cost, high frequency circuit for measuring capacitance is proposed in this paper. This new capacitance measuring circuit is able to measure small coupling capacitance variations with high stray-immunity. Hence, it could be used in many potential applications such as measuring the metal fill time in the Lost Foam Casting (LFC) process and Electrical Capacitive Tomography (ECT) system. The proposed circuit is based on differential charging/discharging method using current feedback amplifier and a synchronous demodulation stage. The circuit has a wide high frequency operating range with zero phase shift; hence multiple circuits can work at different frequencies simultaneously to measure the capacitance. The non-ideal characteristic of the circuit has been analyzed and the results verified through LTSpice simulation. Results from the tests on a prototype and a simulation elucidate the practicality of the proposed circuit.


Keywords: Capacitance measurement, Stray-immune, Circuit analysis, Metal fill time


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