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Absolute and differential measurement of water vapor supersaturation using a commercial thin-film sensor

Chng, C. K. and Yu, H. and Libbrecht, Kenneth G. (2000) Absolute and differential measurement of water vapor supersaturation using a commercial thin-film sensor. Review of Scientific Instruments, 71 (1). pp. 266-270. ISSN 0034-6748. doi:10.1063/1.1150192.

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We describe a technique for measuring the water vapor supersaturation of normal air over a temperature range of –40<~T<~0 °C. The measurements use an inexpensive commercial hygrometer which is based on a thin-film capacitive sensor. The time required for the sensor to reach equilibrium was found to increase exponentially with decreasing sensor temperature, exceeding 2 min for T = –30 °C; however, the water vapor sensitivity of the device remained high down to this temperature. After calibrating our measurement procedure, we found residual scatter in the data corresponding to an uncertainty in the absolute water vapor pressure of about ±15%. This scatter was due mainly to long-term drift, which appeared to be intrinsic to the capacitive thin-film sensor. The origin of this drift is not clear, but it effectively limits the applicability of this instrument for absolute measurements. We also found, however, that the high sensitivity of the thin-film sensor makes it rather well suited for differential measurements. By comparing supersaturated and saturated air at the same temperature we obtained a relative measurement uncertainty of about ±1.5%, an order of magnitude better than the absolute measurements.

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Libbrecht, Kenneth G.0000-0002-8744-3298
Additional Information:©2000 American Institute of Physics. (Received 2 September 1999; accepted 17 September 1999) The authors acknowledge financial support from the Summer Undergraduate Research Fellowship program of the California Institute of Technology.
Subject Keywords:humidity measurement; vapour pressure measurement; measurement uncertainty; water; hygrometers; capacitive sensors; low-temperature techniques
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Record Number:CaltechAUTHORS:CHNrsi00
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6918
Deposited By: Archive Administrator
Deposited On:02 Jan 2007
Last Modified:08 Nov 2021 20:38

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