An approach to accurately measuring capacitance with a distorted sinusoidal stimulus signal

In order to obtain an accurate measurement result of individual or capacitive sensors' capacitances, it generally requires the stimulus signal with distortion as low as possible. However, it is difficult for an industrial capacitive sensor to generate such a low distorted stimulus signal in the sensor due to the cost and space limits of the sensor. On the basis of a self-balance capacitance voltage converter, a method for obtaining the accurate measurement results of a capacitance with distorted sinusoidal stimulus signals is presented in this paper. By controlling the capacitance-voltage converter using DSP, two sets of the sampling data corresponding to the distorted stimulus signal with the different amplitudes are obtained. The relationship between the measured capacitance and the root mean squares (RMS) of two sampling data sets is established. Analytical results show that the relationship can totally cancel the influence of the high order harmonics of the stimulus signal on the measurement result of the capacitance. Experimental results verify the effectiveness of the proposed method.