Fast, high sensitivity dewpoint hygrometer

Details Fast, high sensitivity dewpoint hygrometer Fast, high sensitivity dewpoint hygrometer

1996-09-18

1998-04-14

Williams, Hezron E.

Measuring and testing

Gas analysis

Moisture content or vapor pressure

73 2904, 73597, 324664, 374 28, G01N 2568, G01W 100

Patent

active

057394164

ABSTRACT:
A dewpoint/frostpoint hygrometer that uses a surface moisture-sensitive sensor as part of an RF oscillator circuit with feedback control of the sensor temperature to maintain equilibrium at the sensor surface between ambient water vapor and condensed water/ice. The invention is preferably implemented using a surface acoustic wave (SAW) device in an RF oscillator circuit configured to generate a condensation-dependent output signal, a temperature sensor to measure the temperature of the SAW device and to distinguish between condensation-dependent and temperature-dependent signals, a temperature regulating device to control the temperature of the SAW device, and a feedback control system configured to keep the condensation-dependent signal nearly constant over time in the presence of time-varying humidity, corrected for temperature. The effect of this response is to heat or cool the surface moisture-sensitive device, which shifts the equilibrium with respect to evaporation and condensation at the surface of the device. The equilibrium temperature under feedback control is a measure of dewpoint or frostpoint.

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