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Zeroing the Analyzer
The Zero process is used to correct any offsets in the sample system. By com-
paring the two (2) Zero readings (Reference and Sample) with the internally
generated "Zero" gas, any offset can be Zeroed out. This is done by measuring
the Zero offset frequency and storing it in memory. This offset is then subtract-
ed from ∆ƒ before the sample moisture concentration is calculated.
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 3050-AMS uses equations to determine the water vapor pressure over
ice, rather than over super-cooled water. Thus, the 3050-AMS reports a frost-
point temperature consistent with the physical form of the condensed phase
in a real process stream.
Another consideration, when using the 3050-AMS Analyzer to calculate dew/
frost point temperatures, is the sample or process pressure. The range of pro-
cess pressures allowed by the 3050-AMS 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 3050-AMS is
designed to report an error condition, the process pressure alarm, to alert the
user to conditions that result in ambiguous dew/frost point values.
1-8 | 3050-AMS Moisture Analyzer
AMETEK recommends performing a Zero every 24 hours for the first
month of operation. After this start-up period, the analyzer will have
dried down sufficiently to increase the Zeroing interval to one (1)
week. AMETEK recommends that the duration of the Zero cycle be set
to 120 (i.e., 2 hours).
Water in super-cooled liquid state will only exist as a transient species, as
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 305804902, Rev A
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