INNOVATIONS ON A QUARTZ-CRYSTAL MICROBALANCE FROST-POINT HYGROMETER

The authors describe a hygrometer based on a quartz crystal (QC) micro balance. The hygrometer is based on frost accumulation rather than ads orption. Previous designs are improved in two ways. First, a radial fl ow geometry makes it possible to quantitatively remove water from an a irstream and therefore measure water vapor by measuring the rate of fr ost accumulation as well as by measuring the frost point. second, a th in-film copper-constantan electrode on the QC measures the temperature of the front surface of the QC while still allowing measurement of th e oscillation frequency. The hygrometer design is appropriate for fros t points between about -100 degrees and -40 degrees C, and a future im plementation could be used on a lightweight balloon or unmanned aerial vehicle payload.