Operating in Electron Ionization (EI) Mode 3
5975/5977 Series MSD Operation Manual 65
Pumping Down
The data system helps you pump down the MSD. The process is mostly
automated. Once you close the vent valve and turn on the main power switch
(while pressing on the sideplate), the MSD pumps down by itself. The data
system 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 pump down correctly.
From the Instrument Status Dashboard, OpenLAB CDS can display:
• Motor speed for turbo pump MSDs (percent spin speed)
• Foreline pressure for diffusion pump MSDs
• Analyzer chamber pressure (vacuum) for MSDs equipped with the optional
Micro-Ion Gauge Controller (G3397A for the 5975 and G3397B for the
5977).
Controlling Temperatures
MSD temperatures are controlled through the data system. 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 data system or from the local 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 data system or from the 7890B GC control
panel.
Controlling Column Flow
Carrier gas flow is controlled by inlet pressure in the GC. For a given inlet
pressure, column flow will decrease as the GC oven temperature increases.
With electronic pneumatic control (EPC) and the column mode set to Constant
Flow, the same column flow is maintained regardless of temperature.
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