A novel technique to measure two independent components of impedance sensors with a simple relaxation oscillator

A simple interface circuit for impedance measurement based on a relaxation oscillator is presented. The measurement strategy is revealed and the principle of operation is discussed. It is intended for measuring impedance, which can be presented with a capacitor and resistor in series. By means of a four-signal measurement technique a continuous self-calibration is achieved. The output signals for both components of the unknown impedance are time-periods and for calculating their values only one reference capacitor is needed. A measurement setup is presented with which the new method was tested. The experimental results prove that with this new technique very high sensitivity for both components of the measured impedance can be achieved.