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The novel balanced adsorption quartz hygrometer, which is very useful for practical application, is described. Specifically, the principles of operation, the fabrication and application of the component sensor, and experimental results on the effect of hardeners used for the sensor on frequency-humidity characteristics, sorption mechanism of epoxy resin film, humidity characteristics, response time, and aging effect are discussed. The hygrometer consists essentially ofm aas s sensitive AT-cut crystal, which is coated with epoxy resin film and placed in an oven maintained at a temperature slightly higher than room temperature. The hygrometer is capable of exhibiting linear frequency- humidity characteristics and very small hysteresis, since, by dint of the oven, both the adsorption and desorption of moisture on the epoxy resin film are brought quickly into equilibrium. The hygrometer has been found by use of a climatic chamber to work at 22- 46°C and absolute humidities 0-63 g/m3 with accuracies ±4 percent RH (22°C) and ±1 percent (34 and 46°C). The hygrometer allows us to calculate readily the relative humidity from room temperature, if simultaneously measured.
Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on (Volume:34 , Issue: 2 )
Date of Publication: March 1987