8.
Adjust the focus control (fig 2-8a) to obtain a clear, well-defined image on
the screen.
The focus of the display may be affected by setting the intensity
control. Therefore, it may be necessary to adjust the focus control a small amount
when the intensity control is changed.
9.
The scale illumination control (fig 2-8a) is directly under the focus
control.
Adjust the scale illumination control so that the graticule lines are
illuminated to desired brightness.
10.
The trace finder control (fig 2-8a) is used to locate a display which exceeds
the scan of the display area.
When you press the trace finder button, the
horizontal and vertical deflection is reduced, and the display is compressed within
the graticule area.
After locating the display, center it by adjusting the
position controls.
11.
There are five modes of operation that can be selected by the mode
switch.
They are channel 1, channel 2, alternate, chopped, and algebraic addition
(fig 2-
8a).
When either channel 1 or channel 2 is selected, only the signal
that is
applied to the respective channel is displayed.
The other three modes
are for
dual-trace operations.
a. When the alternate position is selected, the signal applied to one channel
is presented for one cycle of the horizontal sweep voltage.
Then the signal
applied to the other channel is presented for the next cycle of the sweep voltage.
The scope CRT coating retains the image of the first channel's presentation during
the time the second channel makes its presentation when the sweep rates are
sufficient. Although all sweep rates can be used in the alternate mode, alternate
mode switching becomes visually perceptible at slower sweep speeds.
The chopped
mode is preferred at sweep rates below about 0.5 millisecond per division.
b. In the chopped mode the signals applied to the two channels are
electronically switched on and off to produce a display.
The switching rate is
about 500Hz.
A segment of the signal displayed from channel 1 is displayed for
about one microsecond; then a segment of the next signal from channel 2 is
displayed for the next microsecond.
For most applications the chopped mode
provides the best display at sweep rates slower than about 0.5 millisecond or when
dual-trace single-shot phenomena are to be displayed.
At faster sweep rates the
chopped switching becomes obvious and interferes with the display.
c. The third dual-trace operation is the algebraic addition mode.
When the
algebraic addition mode is selected, the signals from channel 1 and channel 2 are
algebraically added, and the algebraic sum is displayed on the CRT. If you want to
improve the signal-to-noise ratio, you can eliminate part of the noise by using
this mode to display the difference of two signals.
You can do this in the
algebraic addition mode by following these steps.
(1) Apply the signal that contains the desired and undesired signals to
channel 1 input and apply the signal containing only the undesired signal to
channel 2.
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