4Operating in EI Mode
90 5977B Series MSD Operating Manual
Pumping Down
The DS or 7890B GC control panel helps you pumpdown the MSD. The process
is primarily automated. After you turn on the MSD by pressing the On/Off
switch, close the analyzer door, and close the vent valve once you hear hissing
(while pressing on the sideplate), the MSD pumps down by itself. The Agilent
MassHunter GC/MS Acquisition software monitors and displays system status
during pumpdown. When the pressure is low enough, the program turns on
the ion source and mass filter heaters and prompts you to turn on the
GC/MSD interface heater. The MSD will shut down if it cannot pumpdown
correctly.
Using the menus or MSD monitors, the DS can display:
• Motor speed for turbo pump MSDs (percent spin speed)
• Foreline pressure for diffusion pump MSDs
• Analyzer chamber pressure (vacuum) for MSDs with the optional G3397B
Micro-Ion Gauge Controller
The 7890A+ and 7890B GC control panels also display this data.
Controlling Temperatures
MSD temperatures are controlled through the DS. The MSD has independent
heaters and temperature sensors for the ion source and quadrupole mass
filter. You can adjust the setpoints, and view these temperatures from the DS
or from the 7890B GC control panel.
Normally, the GC/MSD interface heater is powered and controlled by the
Thermal Aux #2 heated zone of the GC. The GC/MSD interface temperature
can be set and monitored from the DS or from the 7890B GC control panel.
Controlling Column Flow
Carrier gas flow is controlled by inlet pressure in the GC. Set the column mode
to Constant Pressure to maintain a constant inlet pressure, and the column flow
will decrease as the GC oven temperature increases. With EPC and the column
mode set to Constant Flow, the same column flow is maintained regardless of
temperature.
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