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Example 5: Application of X-Y Function
Examine the Phase Difference between Signals of two Channels
Example: Test the phase change of the signal after it passes through a circuit network.
Connect the oscilloscope with the circuit and monitor the input and output signals of the circuit.
For the examination of the input and output of the circuit in the form of X-Y coordinate graph, please operate
according to the following steps:
1.
Set the probe menu attenuation coefficient for
10X
and that of the switch in the probe for
10X
.
2.
Connect the probe of channel 1 to the input of the network and that of Channel 2 to the output of the
network.
3.
Push down the
AUTOSET
button, with the oscilloscope turning on the signals of the two channels and
displaying them in the screen.
4.
Adjust the
VOLTS/DIV
knob, making the amplitudes of two signals equal in the rough.
5.
Push down the
DISPLAY
button and recall the
DISP SET
menu.
6.
Press the F3 menu selection button and choose XY for Format. The oscilloscope will display the input and
terminal characteristics of the network in the
Lissajous
graph form.
7.
Adjust the
VOLTS/DIV
and
VERTICAL POSITION
knobs, optimizing the wave form.
8.
With the elliptical oscillogram method adopted, observe and calculate the phase difference
(see Fig. 110).
Fig. 110
Lissajous Graph
Based on the expression
sin =A/B or C/D
, where, 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).
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The signal must be centered
and kept in the horizontal
direction.