Front-End Circuit Modeling for Low-Z Capacitance Measurement Applications

Applications like electrical capacitance tomography (ECT) rely on capacitance measurements with a good signal to noise ratio. In Low-Z measurement circuitry the measurement frequency can be directly used to increase the signal amplitudes. Simple front-end circuit models consider the behavior of all components by means of lumped capacitors. However, for higher system frequencies and long instrumentation lines, transmission line effects can appear. In this paper we develop a front-end circuit model for Low-Z capacitance measurement systems, which considers wave propagation effects due to transmission lines. We demonstrate the applicability of our modelling approach by means of measurements and show further, that the transmission line characteristic can be used to extend the operational limits of the measurement system by means of pre tuning techniques.