Agilent Technologies 5977B Series, Troubleshooting And Maintenance Manual

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Analyzer
7
5977B Series MSD Troubleshooting and Maintenance Manual 199
Filaments
For an HES two filaments are located within the ion source mount of the EI
ion source. For a non-HES, two filaments 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 for a non-HES source and 120eV for the HES.
The CI ion source has only one filament of a different design from the
standard or extractor EI filaments. A dummy filament provides connections
for the Filament 2 wire.
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 ion source, it is always Filament 1.
Sometimes, one EI filament will give better performance than the other does.
To select the better of the two filaments, run two autotunes, one with each
filament. Use the filament that gives the best results.
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 for a non-HES source and 120 for the HES.