A Linear Front-End Circuit for Offset-Affected Grounded Capacitive Sensors

Abstract

The paper proposes a simple linear front-end circuit for grounded-type capacitive sensors. The front-end basically uses the capacitance sensor in the vertical branch of a T-network. Further, the circuit conditions the sensor using a simple circuit to obtain a linear indication of the variable part (measurand) of the capacitive sensor. The novel design of the circuit ensures that the final output is independent of the offset capacitance. The functionality of the proposed circuit is verified first using simulation studies. Further, a hardware model of the circuit was developed and tested in the laboratory. Tests were carried out for different offset capacitances and different values of variable capacitances. The circuit was found to work well as expected and the worst-case non-linearity observed in experimentation was 0.1%.