Heathkit IO-4550 - Page 15

([—— Se FSV So
HORIZONTAL
af LINE
“O,
B.,
W.
VERTICAL
TANGENT LINE
Figure 8
Typical Lissajous patterns are shown in Figure 8. The
Pattern depends upon the relative amplitudes, frequencies,
and phase of the two voltages. The frequency ratio can be
figured from the formula:
fx Th (f)
x= Ty
Where f, is the unknown frequency, Th is the number of
loops which touch the horizontal tangent line; Tv is the
number of loops which touch the vertical tangent line; f is
the known frequency.
When using Lissajous figures, it is good practice to have the
figure rotating slowly rather than remain stationary. This
eliminates the possibility of an error in counting the tangent
points. If the pattern is stationary, a double image may be
formed. In such cases, the end of the trace should be
counted as one-half a tangent point rather than a full point.
This condition may occur when neither frequency can be
varied.
Example 5
Phase Measurements (X-Y Function)
It is sometimes necessary to determine the phase
relationship between two AC voltages of the same
frequency. This can be accomplished quite easily by
applying one of the voltages to the horizontal input and the
other voltage to the vertical input. The phase relationship
can be estimated from Figure 9.
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0°,
360°
30°,
330°
60°,
300°
90°,
270°
120°,
240°
150°,
210°
180°
Figure
9
NOTE: For proper displays, the horizontal amplifier gain
must be set to equal the vertical amplifier gain.
To calculate the phase relationship, use the -following
formula:
A
Sin 6 -B , where @ is the phase angle.
As shown in Figure 10, distance A is measured from the X
axis to the intercept point of the trace and the Y axis. The
distance to B represents the height of the pattern above the
X axis. The axes of the ellipse must pass through the point
0.
Y AXIS
Figure 10