Leader LBO-516 Instruction Manual - page 29
6. Move the off-screen trace back on the CRT with its vertical
POSITION control, precisely centering it vertically. Use the
associated VOLTS/DIV switch (10) and VARIABLE control
(11) to adjust its amplitude to exactly 6 vertical divisions.
7. The horizontal distance between corresponding points on the
waveform is the phase difference. For example, in the Figure
2-19 illustration the phase difference is 6 minor divisions, or
60°. You can use the X FINE control (30) to align one of the
mid-cycle zero crossings with a graticule calibration to
facilitate this measurement.
8. If the phase difference is less than 50° (one major division),
pull the A VARIABLE (X10 MAG) control (26) outwards
and use the horizontal POSITION control (if needed) to
position the measurement area back on screen. With 1 OX
magnification, each major horizontal division is 5% and each
minor division is 1°.
Lissajous Pattern Method. This method is used primarily
with sine waves. Measurements are possible at frequencies up to 3
MHz, the bandwidth of the horizontal amplifier. However, for
maximum accuracy, measurements of small phase differences
should be limited to below 100 kHz.
To measure phase difference by the Lissajous pattern
method, proceed as follows:
1. Depress the X-Y switch (20).
CAUTION: Reduce the trace intensity, lest the
undetected spot damage the CRT phosphor.
2. Ensure that the CH-2 INV switch (19) is out. This will in-
troduce a 180° error if pushed in.
3. Connect one signal to the CH-1 or X IN connector (14), and
the other signal to the CH-2 or Y IN connector (15).
4. Center the trace vertically with the CH-2 vertical POSITION
control (18), and adjust the CH-2 VOLTS/DIV switch (10)
and VARIABLE control (I1) for a trace height of exactly 6
divisions (the 100% and 0% graticule lines tangent to the
trace).
5. Adjust the CH- 1 VOLTS/DIV control (10) for the largest
possible on-screen display.
6.
Precisely center the trace horizontally with the horizontal
POSITION control (29) or X-FINE control (30).
7. Count the number of divisions subtended by the trace along
the central vertical graticule line (dimension B in Figure 2-
20a). You can now shift the trace vertically with the CH-2 or
Y POSITION control to a major division line for easier
counting.
8. The phase difference (angle T) between the two signals is
equal to the arc sine of dimension B÷A (the Step 7 number
divided by 6). For example, the Step 7 value of the Figure 2-
20a pattern is 2.0. Dividing this by 6 yields .3334, whose arc
sine is 19.5 degrees.
9. The simple formula in Figure 2-20a works for angles less
than 90°. For angles over 90° (leftward tilt), add 90° to the
angle found in Step 7. Figure 2-20b shows the Lissajous
patterns of various phase angles; use this as a guide in de-
termining whether or not to add the additional 90°.
10. The sine-to-angle conversion can be accomplished by using
trig tables or a trig calculator. However, if the sine is
between 0.1 and 1.0, you can use the Figure 2-21
nomograph. Simply lay a ruler on the nomograph so its edge
passes through the cross mark and the number of divisions
measured in Step 7 (B dimension). When this is done the
edge will also intersect the phase-angle column.
2-4-5 Distortion Comparison
The dual-trace feature of the LBO-516 offers a quick method
of checking for distortion caused by a signal-processing device
(such as an amplifier). To do this, proceed as follows:
1. Connect the output of the signal generator (of frequency
suitable to the device under test) to the CH- 1 IN
connector (14) and the input of the device under test
(DUT).
2. Connect the CH-2 IN connector (15) to the output of the
device or its load (see Figure 2-22)
3. Increase the signal to the DUT until the channel 2 trace
or an RMS AC voltmeter indicates the desired output
level.
4. If the DUT has reversed the phase, press the CH-2 INV
pushbutton (19).
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