A digital hygrometer using a capacitance-to-frequency converter

A digital hygrometer using a relative humidity sensor is developed. The sensor consists of a polyimide film spin-coated onto a Si substrate. The sensor model for signal processing is first derived which describes the sensor capacitance in terms of relative humidity and temperature in closed form. The interface appropriate for the sensor model is next designed based on a relaxation oscillator. A prototype hygrometer built using a one-chip microcomputer for signal processing and its performance are finally described to demonstrate the validity of the sensor model and interface