Analyzer 7
5977B Series MSD Troubleshooting and Maintenance Manual 201
Other Source Elements
Magnet
The field created by the magnet directs the electrons emitted by the filament
into and across the ionization chamber. The HES magnet assembly is a
permanent magnet with a charge of 650 gauss in the center of the field. The
non-HES and CI source magnet assembly is a permanent magnet with a charge
of 350 gauss in the center of the field.
Repeller
The repeller forms one wall of the ionization chamber. A positive charge on the
repeller pushes positively-charged ions out of the source through a series of
lenses. The repeller voltage is also known as the ion energy, although the ions
only receive about 20% of the repeller energy. The repeller voltage can be
varied from 0 to +42.8 VDC. Some tune programs use a fixed repeller voltage.
Others ramp the repeller voltage to find the optimum setting.
• Setting repeller voltage too low results in poor sensitivity and poor high
mass response.
• Setting repeller voltage too high results in precursors (poor mass filtering)
and poor low mass resolution.
Drawout plate and cylinder
The drawout plate forms another wall of the ionization chamber. The ion beam
passes through the hole in the drawout plate and into the drawout cylinder.
The drawout cylinder is slotted. The slots correspond to slots in the source
body. These slots allow carrier gas and unionized sample molecules or
fragments to be pulled away by the vacuum system. The drawout plate and
drawout cylinder are both at ground potential. These are used in the standard,
inert, and CI ion sources only.
Extractor lens
A voltage is applied to the extractor lens to increase ion focusing through the
source.
To Next Page
Loading...
Need help?
General
