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9.Demonstration
(8) With the elliptical oscillogram method adopted, observe and calculate the phase
difference (see Figure 9-6).
Figure 9-6 Lissajous Graph
Based on the expression sin (q) =A/B or C/D, thereinto, q is the phase difference
angle, and the definitions of A, B, C, and D are shown as the graph above. As a result,
the phase difference angle can be obtained, namely, q =± arcsin (A/B) or ± arcsin
(C/D). If the principal axis of the ellipse is in the I and III quadrants, the determined
phase difference angel should be in the I and IV quadrants, that is, in the range of
(0 - π /2) or (3π / 2 - 2π). If the principal axis of the ellipse is in the II and IV
quadrants, the determined phase difference angle is in the II and III quadrants, that is,
within the range of (π / 2 - π) or (π - 3π /2).
Example 6: Video Signal Trigger
Observe the video circuit of a television, apply the video trigger and obtain the stable
video output signal display.
Video Field Trigger
For the trigger in the video field, carry out operations according to the following
steps:
(1) Push the Trigger Menu button to display the trigger menu.
(2) Select the first menu item in the bottom menu. Select Single in the right menu.
The signal must be
centered and kept in the
horizontal direction.
136
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