Abstract
A humidity-temperature sensor module with a frequency output signal was fabricated by integrating a humidity sensor, temperature sensor and measuring circuit on a ceramic substrate. The humidity sensor had a copolymer of ionic and non-ionic monomers as its humidity-sensitive material, and a chip thermistor served as the temperature sensor. The measuring circuit was an astable multivibrator, and the humidity and temperature sensors were used as circuit elements to determine the oscillation frequency. Operation of the humidity-sensing circuit was evaluated on the basis of an analysis of the frequency dependence of the humidity sensor impedance. In the derivation of the humidity-oscillation frequency characteristics from the impedance data, a model that expresses the humidity sensor impedance by the bulk resistance of the humidity-sensitive material gave relatively good agreement with expe The fabricated module offers superior long-term stability. Changes in humidity-oscillation frequency and temperature-oscillation frequency characteristics were less than ±3% r.h. and ±0.1 °C, respectively, after more than two years in an open laboratory atmosphere.
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