Dew/Frost Point Measurements - Ametek 5830 User Manual

Dew/Frost Point Measurements

Dew point values are calculated from the moisture concentration measure-
ments (PPMV) and the sample or process pressure. For temperatures below
0 °C, the 5830 uses equations to determine the water vapor pressure over ice,
rather than over super-cooled water. Thus, the 5830 reports a frost-point tem-
perature consistent with the physical form of the condensed phase in a real
process stream.
• Water in super-cooled liquid state will only exist as a transient species, as
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Another consideration, when using the 5830 Moisture Analyzer to calculate
dew/frost point temperatures, is the sample or process pressure. The range
of process pressures allowed by the 5830 is restricted for many sample gases.
Many gases liquefy at relatively low pressures, so calculating a dew/frost point
temperature for these compounds has no value. Therefore, the 5830 is de-
signed to report an error condition, the process pressure alarm, to alert the
user to conditions that result in ambiguous dew/frost point values.
1-10 | 5830 Moisture Analyzer
the first bit of condensate starts to form on a smooth-chilled surface (i.e.,
the true method of measuring a dew point).
Given more time, the dew layer will turn to ice if the temperature is below
the freezing point.
While the frost-point temperature will be higher than the dew point tem-
perature, the exact magnitude of the difference will be a function of both
the pressure and dew/frost point temperature.
PN 583054901, Rev YA