152 Troubleshooting and Maintenance Manual
7 Analyzers and Collision Cell
Filaments
Two filaments (Figure 27 and Figure 29) are located on opposite sides of the
outside of the EI ion source. The active filament carries an adjustable AC
emission current. The emission current heats the filament causing it to emit
electrons which ionize the sample molecules. In addition, both filaments have
an adjustable DC bias voltage. The bias voltage determines the energy on the
electrons, usually –70 eV.
The CI ion source has only one filament of a different design from the EI
filaments. A “dummy” filament provides connections for the Filament 2 wires.
The filament is shut off automatically if there is a general instrument
shutdown. Three parameters affect the filaments: filament selection
(Filament), filament emission (Emission) current, and electron energy
(EIEnrgy).
Filament selection
The filament selection parameter (Filament) selects which filament in the ion
source is active. In the CI source, it is always Filament 1.
Since filaments may have some variability, we advise running a tune for each
filament and saving the tune accordingly.
Emission current
The filament emission current (Emission) is variable between 0 and –315 µA,
but should be set to the software default for normal operation.
Electron energy
The electron energy (EIEnrgy) is the amount of energy on the ionizing
electrons. It is determined by the bias voltage; –70 VDC bias on the filament
causes emitted electrons to possess –70 eV (electron volts). This value is
adjustable from –5 to –241 VDC, but for normal operation, set this parameter
to 70.
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