Liquid level measurement through capacitive pressure sensor

Property of fluid and material compatibility limit the level sensor's fabrication, dynamic range and accuracy. Piezoresistive pressure sensing elements with media compatible diaphragm are limited in low pressure dynamic. In contrast, capacitive pressure sensing elements provide better solution in terms of dynamic range. In this paper, liquid level measurement is realized through a capacitive differential pressure sensor. A custom digital synchronous detection is implemented in order to optimize the measurement performances, gaining a sensitivity of 40 ppm/mm. Different operating frequencies have been defined and a DFT based feedback loop is proposed in addition to eliminate the impact of interferences at predefined frequency. The sensor characterization indicates linear response. The maximum error is limited to 0.3 mm in range of 0-200 mm as level displacement.