5 Operating in CI Mode ď€
128 5977B Series MSD Operating Manual
2 In the Operations area, select admit a reagent gas for the current tune file.
The system evacuates the gas lines for 6 minutes, then turns on the selected
gas (A or B). This is to reduce cross-mixing of the gases in the lines.
3 Enter the reagent gas flow setpoint in the Flow field. This value is entered as
a percentage of maximum flow rate. The recommended flow is 20% for a PCI
source and 40% for an NCI source.
The flow control hardware remembers the flow setting for each gas. When
either gas is selected, the control board automatically sets the same flow
that was used for that gas the last time.
4 To begin reagent gas flow, select Shutoff CI.
The system turns off the present gas flow while leaving the shutoff valve
open. (See Figure 42 on page 129.) This is to remove any residual gas in the
lines. Typical evacuation time is 6 minutes and then the shutoff valve is
closed.
The CI flow control module
The CI reagent gas flow control module regulates the flow of reagent gas into
the CI GC/MSD interface. The flow module consists of a MFC, gas select valves,
CI calibration valve, shutoff valve, control electronics, and plumbing. (See
Figure 42 and Table 13 on page 129.)
The back panel provides Swagelok inlet fittings for methane (CH4) and one
OTHER reagent gas. The software refers to them as Gas A and Gas B,
respectively. If you are not using a second reagent gas, cap the OTHER fitting to
prevent accidental admission of air to the analyzer. Supply reagent gases at
25 to 30 psi (170 to 205 kPa).
The shutoff valve prevents contamination of the flow control module by
atmosphere while the MSD is vented or by PFTBA during EI operation.
When a CI system is installed along with a JetClean system, the MFC is shared
by both systems. By design, its use is restricted to one of these systems at a
time. In this case, the Gas B supply is dedicated to hydrogen used for source
cleaning. For detailed information on the JetClean system refer to the
JetClean Operating manual installed on your PC along with this manual.
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