Accurate level measurement based on capacitive differential pressure sensing

In this paper, a capacitive differential pressure sensor is characterized as a liquid level measurement system. The sensor is configured as a first-order low pass filter. Different operating frequencies have been defined and a DFT based feedback loop is proposed in addition to eliminate the impact of interferences at predefined operating frequency. The phase-sensitive demodulation of the signal is performed using a single-tone DFT algorithm, acquiring both excitation and output signals. Each signal is acquired at 10 MSPS and the DFT is computed on 8000 samples. The sensitivity of the proposed instrument is 40ppm/mm with very good linearity and error as low as ±0.3 mm. The measurement characterization of the sensor indicates good performances as lowcost level measurement system.