Agilent Technologies 5975T LTM GC/MSD, Руководство по устранению неисправностей и техническому обслуживанию

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Analyzer
13
Troubleshooting and Maintenance Guide 203
Filaments
Two filaments ( Figure 31 ) 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 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.
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.
Filament care
Like the filaments in incandescent light bulbs, the ion source
filaments will eventually burn out. Certain practices will reduce
the chance of early failure:
• If you have an optional G3397A Micro-Ion vacuum gauge,
use it to verify that the system has an adequate vacuum
before turning on the analyzer, especially after any
maintenance was performed.