30
5. Then set the CH 1 VOLTS/DIV knob (12) to
obtain the largest possible image.
6. Use the X position knob (25) to set the hori-
zontal sweep so that the image is centred.
7. Count the DIVs along the vertical centre line
(dimension "A" in the figure on the next
page).
8. The phase displacement (phase angle phi)
between the two signals equals the arc sin of
A divided by B --> PHI = sin-1 x A/B.
Example: In the figure, the counted DIVs =
2.0, divided by 6 DIV this gives 0.334, the arc
sin of this gives a phase angle phi = 19.5.
9. The simple formula in para. 8 only applies up
to a phase angle of 90º. For an angle > 90º
(left-sloping ellipse), add 90º to the calculated
angle. The figure below shows a few Lissajous
patterns having various phase angles. Use
these patterns for guidance when deciding
whether or not to add 90º.
Fig. 18
2.3.6 Measurement of rise time
The rise time is the time which the amplifier
needs in order to track the amplitude of an ideal
square-wave step change from 10% to 90%. The
fall time is the time the amplifier needs to track
the amplitude from 90% to 10%.
To determine the rise time or fall time, proceed
as follows:
1. Connect the measuring signal to CH 1 and set
the AC/GND/DC switch to AC.
2. Set the time-base sweep (TIME/DIV) so that
two cycles of the signal can be viewed on the
screen. Make sure that the VARIABLE knob
(24) is at the right-hand stop and pushed in.
3. Adjust the Volts/Div knob and the CH 1 POS-
ITION knob so that the top of the signal
touches the 100% marker line and the bot-
tom touches the 0% line. If this adjustment
cannot be obtained using only the VOLTS/DIV
knob, turn the VARIABLE knob (14) to the left.
4. Use the X position knob (25) to adjust the
rising edge of the signal so that it passes
through the point where the 10% line inter-
sects the vertical centre line (see figure on
next page).
5. If the rising edge is very steep and a short rise
time can be expected, the image can be
expanded by a factor of 10 by pulling out
the VARIABLE knob (24). Then repeat the pro-
cedure described under heading 4.
6. Count the DIVs between the 10% intersection
and the point at which the rising edge inter-
sects the 90% marker line.
7. Multiply the number of DIVs by the setting of
the TIME/DIV knob. If the PULL x 10 knob was
pulled out to expand the signal, divide the
result by 10.
Example: In the bottom figure (next page),
the 3.6 DIVs read off multiplied by a TIME/DIV
setting of 1 µs (= 100 ns) divided by 10 give a
rise time of 360 ns.
8. To measure the fall time, adopt the same pro-
cedure as when determining the rise time, but
with the difference that the falling edge of
the signal passes through the point where the
10% line intersects the vertical centre line.
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