Direct Measurement of Vapor Pressure Fluctuations and Gradients

Abstract

An instrument for direct measurement of vapor pressure and vapor pressure gradient (and similarly for temperature) has been designed and constructed. Thermistors are used as wet-and dry-bulb thermometers in the adjacent arms of a resistance bridge network. The resistance arms and the thermistors in the bridge circuit are theoretically determined by relating the differential equation of the output voltage with the psychrometric differential equation. The output voltage varies linearly with vapor pressure in the range 5–40 mb. Field measurements show fast fluctuations in temperature and vapor pressure gradients. The accuracy of the instrument in the measurement of vapor pressure is about ±1.2% in the working range 0–32C.