Installation and Start-Up | 3-39
Sample Conditioning System Optimization
Perform this optimization procedure only after the Optical Bench and
Column temperatures have reached their normal operating tempera-
tures.
Differences in sample stream composition in various applications can
affect the operation of the chromatographic columns that are used to
remove interfering species. As the quantity of ethane and heavier hydro-
carbons in the sample stream increases, the elution time of all gas species
through the Columns tends to decrease.
This change in elution time affects the analyzer’s Column Switch Interval
and Hold Time parameters. These two parameters are factory-set using
stream composition data that was provided for the application. View the
Column Timing dialog box (Figure 3-19) and check to ensure that the pa-
rameters are properly set for the application. Adjust them if necessary.
Column Switch Time Optimization
The first UV-absorbing gas species that elute through the chromato-
graphic columns are hydrogen sulfide (H
2
S), carbonyl sulfide (COS), and
methyl mercaptan (MeSH). Because the Model 933 Analyzer can measure
the concentrations of all three of these species, COS and MeSH do not
interfere with the H
2
S measurement. The concentration reading of each
species is automatically corrected for the presence of the other two com-
pounds. Ethyl mercaptan (EtSH) is the first UV-absorbing species to elute
that interferes with the concentration measurement of the first three spe-
cies.
During normal analyzer operation, while sample gas is flowing through
one absorbing column and concentration measurements are being per-
formed, the other column is being regenerated. Periodically, the columns
are switched before interfering species can elute from the absorbing col-
umn. The Switch Interval is the time Column switch timing cycle. When
the Switch Interval is properly adjusted, the columns switch before EtSH
elutes from the absorbing column.
!
CAUTION
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