PN 305200901, Rev YT
Dewpoint Conversions
The 3050-OLV Analyzer is capable of outputting the moisture concentration in
units of dewpoint (Centigrade or Fahrenheit). Dewpoint values are calculated
from the moisture concentration measurements (PPMV) and the sample (i.e.,
process) pressure. For temperatures below 0 °C the 3050-OLV uses equations
to determine the water vapor pressure over ice, rather than over super-cooled
water. Thus, the 3050-OLV reports a “frostpoint” temperature, which is consis-
tent 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 the
rst 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 “frostpoint”
temperature will be higher than the “dewpoint” temperature, the exact mag-
nitude of the dierence will be a function of both the pressure and dewpoint/
frostpoint temperature.
A second consideration, when using the 3050-OLV Analyzer to calculate
dewpoint/frostpoint temperatures, is the sample (i.e., the process) pressure.
The range of process pressures allowed by the 3050-OLV is restricted for many
sample gases. Many gases liquefy at relatively low pressures, so calculating a
dewpoint/frostpoint temperature for these compounds has no value. There-
fore, the 3050-OLV is designed to report an error condition (i.e., process-pres-
sure alarm), to alert the user of conditions that result in ambiguous dewpoint/
frostpoint values.
Denition of Natural Gas
The composition of natural gas streams varies greatly from application to
application. Normally, the methane content of these gas streams is approxi-
mately 90 %, and the concentration of the heavier hydrocarbons falls o with
increasing molecular weight. Because the 3050-OLV Analyzer uses a thermal
mass ow meter as part of its ow control system, it is necessary to dene
the composition of the gas stream to calculate the appropriate Flow Control
parameters. A methane content of 80–90 % has been used to dene the Flow
Control parameters for the “natural gas” listed in the 3050-OLV Analyzer Gas
List (Figure 1-3). If the methane content is above 95 %, AMETEK recommends
selecting methane from the Gas List. In the event that the methane content is
below 80 %, please contact AMETEK for instructions on selecting the appropri-
ate gas from the listing.
Overview | 1-5
To Next Page
Loading...
Need help?
General
