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Publisher Summary This chapter discusses the major measurement techniques, which are available. The three states—gas, liquid, and solid—are discussed. In addition, many commercial instruments measure some parameter, which changes reproducibly with moisture concentration, and these instruments must be regularly calibrated by the user. The chapter concludes with a discussion of the major calibration techniques, which the average user must be willing to employ when using such instruments. Although water vapor is not an ideal gas for most hygrometry purposes, to gain an understanding of the units involved, it is sufficient to assume that water vapor does behave ideally. The basic unit of moisture in a gas against which other units can readily be referred is vapor pressure, and Dalton's Law of Partial Pressures can be assumed to hold if the saturated vapor pressure is not exceeded. In environmental applications, the unit often used is relative humidity, which is the ratio in percent of the actual vapor pressure in a gas to the saturation vapor pressure of water at that temperature. It is therefore temperature-dependent, but is independent of the pressure of the carrier gas. |
