| 摘要 |
<p>Dewpoint/frostpoint hygrometer (1) using surface moisture-sensitive sensor as part of an RF oscillator circuit with feedback control of the sensor temperature to maintain equilibrium at sensor surface between ambient water vapor and condensed water/ice. The invention is preferably implemented using a surface acoustic wave (SAW) device (32) and RF oscillator (36) in RF oscillator circuit (35) configured to generate a condensation-dependent output signal, a temperature sensor (60) to measure temperature of the SAW device and distinguish between condensation-dependent and temperature-dependent signals, a temperature regulating device such as thermoelectric cooler (30) that controls temperature of the SAW device, and a feedback control system (5) with voltage-sensing circuit (64) and current amplifier (22) configured to keep condensation-dependent signal nearly constant over time in the presence of time-varying humidity, as corrected for temperature. This response effects to heat or cool the surface moisture-sensitive device, thereby shifting equilibrium with respect to evaporation and condensation on surface of device. The equilibrium temperature under feedback control is a measure of dewpoint or frostpoint.</p> |
