Agilent Technologies 5975C TAD VL MSD, Руководство по устранению неисправностей и техническому обслуживанию

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204 5975 Series MSD Troubleshooting and Maintenance Manual
7
Analyzer
Filaments
Two filaments ( Figure 46 ) 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.
Sometimes, one EI filament will give better performance than the other. 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.