Electronic circuits for capacitive pressure sensors

Three different electronic circuits for characterizing the commercially available Orthoflex Hercules capacitive pressure sensors over the pressure range of 0-2 MPa are discussed. A portable microprocessor-based system is used to measure the pressure between the foot and the shoe. Two of the circuits, the frequency-to-voltage converter and the phase-locked-loop circuits, have the advantages of simplicity of design and higher bit resolution over counter-type circuits, but they have higher component counts, resulting in greater current consumption and less pressure monitoring time. The counter circuit, though more complex in design, does not have a voltage ripple at the output stage, which compensates for the error due to its poorer bit resolution