Pumping Down; Controlling Temperatures; Controlling Column Flow - Agilent Technologies G7035A Operation Manual

3
Operating in Electron Ionization (EI) Mode

Pumping Down

The data system or local control panel 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.
Using the menus or MS monitors, the data system 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
The LCP can also display these data.

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. For the 7820 Series GC's, the heater is
either connected to the rear inlet thermal zone for single inlet models or is
connected to the manual valve thermal zone for dual inlet models. The
GC/MSD interface temperature can be set and monitored from the data
system or from the GC.

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.
56
Micro-Ion Gauge Controller
5977 Series MSD Operation Manual