FEI Quanta FEG 250, Руководство пользователя

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Operating Procedures: Obtaining an Image
5-5
SELECTING VACUUM MODE
When a specimen and appropriate detector(s) are inserted correctly,
close the specimen chamber door and continue the procedure (see
above):
6. In Vacuum module, select the High Vacuum / Low Vacuum /
ESEM radio button.
7. For Low Vacuum / ESEM modes use water or select the desired
gas environment (option) from the drop down list box and the
target pressure that the system pumps to in the
Chamber
Pressure adjuster.
8. In the Vacuum module click on the Pump button. While pumping,
choose the highest specimen point and bring it to the 10 mm WD
(yellow line in an optical quad).
Note:
Under normal operation, the system knows the PLA size for the
detector installed. This allows the system to set automatic
pressure range limits for the aperture installed, thus avoiding
vacuum errors when setting chamber pressure. In some cases the
user is prompted for the PLA size by the PLA Configuration
dialogue.
WA R N I N G !
The system can be damaged by using the Low Vacuum / ESEM
mode without an appropriate PLA. Do not select a PLA Cone
which is not actually mounted onto the objective pole piece.
9. Wait for the vacuum status Pumped , represented in the Status
module at the base of the page by the green icon.
Low Vacuum and ESEM Modes
Which one of these modes is used depends on either the detector
installed or some special conditions (working with the cooling stage
implies ESEM mode for instance).
Purging
The microscope provides automatic sequencing for purging the
specimen chamber according to the settings of
Purge Mode in the
Preferences… / ESEM tab. There may be certain applications (e.g.,
working with a sensitive sample) where the operator needs to change
the purging parameters:
• Select No Purge when purging the specimen chamber is not
desired. The chamber goes to the set pressure directly and the gas
mixture in the chamber slowly changes to the selected gas type.
• Select Automatic to use pre-defined values for Minimum /
Maximum Pressure and Number of cycles . The Purge Settings
displays the actual default values.
• Select Custom to change the Minimum / Maximum Pressure and
the Number of cycles manually using the Custom Edit boxes.
Caution:
The maximum allowed pressure is 200 Pa (1.5 Torr) for all actually
available PLA Cones.