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D C voltages are measured as displacements of the bright
line through the V . I N P U T DC terminal (13). A DC voltage
displayed on the C R T is directly read as its effective value.
Sensitivity (V/cm) x A cm = Voltage (V)
Fig. 3 DC voltage measurement
MEASUREMENT WITH LISSAJOUS' FIGURES
1.
Frequency measurement
Lissajous' figures are often used as a means of measuring
frequencies of
signals.
For measurement, first set the
S W E E P R A N G E (6) to the E X T position and connect a
signal generator between the G N D (7) and H. I N P U T (8).
Adjust the horizontal
amplitude
Next, apply a signal of unknown frequency to the A C
terminal (1) and the G N D terminal ( 2 ) . Adjust the vertical
amplitude to about 4 ~ 6 cm.
As the signal generator is slowly controlled for continuous
change in the frequency, the following patterns will appear
at certain frequencies (see Fig. 4 ) . As a rule, when the
pattern is a straight line or a true circle, it means that the
unkown frequency is equal to the frequency of the signal
generator.
The displayed Lissajours' figure will only become stationary
when one of the frequencies is an integral multiple of the
other. Therefore, the unknown frequency can be obtained
by calculation.
2.
Measurement of phase difference
A s in the case of the preceding item, Frequency Measure-
ment, when two signals of the same frequency are applied
to H. I N P U T and V . I N P U T (for example, R and L signals
in stereo mode), the pattern on the C R T screen becomes a
straight line slanting from the upper right to the lower left if
they are in the same phase. As the signals become out of
phase, the Lissajous' figure gets more like a circle and when
the signals reach a state of 90° phase difference, then the
pattern becomes a true circle. In measuring and calculating
phase differences we designate the horizontal amplitude as
" X " and the horizontal excursion of the Lissajous' figure as
" x " . T h e phase difference e is then found from:
e =
Sin
x / X
to about
4 ~ 6 cm.
Also in this measurement, phase difference between the
horizontal and vertical circuits of the oscilloscope itself can
be set to " z e r o " over a range up to approximately 2kHz by
turning H. C A I N (10) to the maximum clockwise position.
It should be noted that a measurement with a frequency
above 2 k H z will cause an error in the phase. T h e frequency
range in which the phase difference between V and H is
" z e r o "
position of the H. G A I N ( 1 0 ) .
i : l
I :
2
( v
: H )
Fig. 4 Frequency measurement with Lissajous' figure
is reduced down
to about 500 Hz at the
Fig. 5 Phase measurement with Lissajous' figure
2 : l
(v
: H)
3 : 2
( v : H)
1/2
7
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