A digital hygrometer using a polyimide film relative humidity sensor

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