OPTO-EDU A63.7069, Instruction Manual

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filament current should not be increased, otherwise, the service life of filament may be
shortened.
❖
Pay attention to the speed of adjustment in order to prolong the filament ’s service life. It is
suggested that at the range of 0A to 2A, the speed of filament adjustment should be controlled
lower than 0.25A/s; at the range of 2A to saturated point, the speed of filament adjustment
should be controlled lower than 0.1A/s.
❖
Beam current value is relevant to the selected HV value, the distance between wehnelt and
anode, and the relative position of filament and wehnelt cap. It is usually recommended to
control at
≤
200 μA . If the beam is too large, the beam size can be controlled by adjusting the
Bias; if it is too small, the filament installation height should be checked. It is suggested that
the filament installation height should be in the range of 0.4-0.7 mm, within this range, the
minimum gradient can be adjusted to 0.1mm.
❖
The vacuum and Filament control are interlocked, so the Filament button can start only
when the vacuum satisfies requirements and V1 valve is opened. The Filament will be cut off
automatically when the vacuum is low.
3.3.5. Brightness and Contrast
❖
Dragging the scroll bar of [Brightness] and [Contrast] on panel with mouse can control the
value of brightness and contrast.

Note: Contrast signal should be added after opening V1 valve in order to avoid damage of
contrast supply and photomultiplier caused by impulse of large voltage.
3.3.6. Condenser Lens
❖
Dragging the scroll bar of [Condenser Lens] on panel to control condenser lens. It is divided
into coarse, fine and tiny adjustment. The step size of coarse adjustment is 10 times larger
than fine adjustment, while the step size of fine adjustment is 10 times larger than tiny
adjustment.
❖
When the current of condenser lens increases, the focal length of lens will be shortened and
the beam spot size on specimen will be smaller. Generally, the larger the lens current, the
smaller the spot size. In order to observe image with high resolution, small spot size should be
adopted, current of condenser lens should be increased until satisfied SNR. Small current of
condenser lens can lead to large spot, and the beam current on the specimen is larger, so the
specimen with weak image signal can be observed.
3.3.7. Condenser Lens Reversal switch
❖
Condenser Lens Reversal means reversal of current of condenser lens. This function can judge
whether the condenser lens is in good alignment. If so, the position of electron beam should