Figure 2-11: Dual-Trace Method of Phase Measurement
6.
Precisely center the trace horizontally with the Horizontal POSITION control (10).
7.
Count the number of divisions subtended by the trace along the central vertical gratitude line
(dimension B). You can now shift the trace vertically with CH 2 POSITION control to a major division
line for easier counting.
8.
The phase difference (angle z) between the two signals is equal to the arc sine of dimension A ÷ B
(the Step 7 number divided by 6). For example, the Step 7 value of the figure 2-9 a pattern is 2.
Dividing this by 6 yields .3334, whose arcsine is 19.5°.
9.
The simple formula in Figure 2-9 a works for angles less than 90°. For angles over 90° (leftward tilt),
and 90° to the angle flound in Step 7.
Figure 2-9 b shows the Lissajous patterns of various phase angles; use this as guide in determining
wether or not to add the additional 90°.
Note:
The sine-to-angle conversion can be accomplished by using trig tables or a trig calculator.
2.3.5 Risetime
Measurement
Risetime is the time for the leading edge of a pulse to rise from 10 % to 90 % of the total pulse amplitude.
Falltime is the time required for the trailing edge of a pulse to drop form 90 % of total pulse amplitude to 10
%. Risetime and falltime, which may be collectively called transition time, are measured in essentially the
same manner.
To measure rise and fall time, proceed as follows:
1.
Connect the pulse to be measured to the CH 1-IN connector (24), and set the AC/GND/DC switch
(25) to AC.
2.
Adjust the TIME/DIV switch (15) to display about 2 cycles of the pulse. Make certain the VAR switch
(12) is rotated fully clockwise.
3.
Center the pulse vertically with the cannel 1 Vertical Position control (4).
4.
Adjust the channel 1 VOLTS/DIV switch (26) to make the positive pulse peak exceed the 100 %
gratitude line, and the negative pulse peak exceed the 0 % line, then rotate the VARIABLE control
(27) counterclockwise until the positive and negative pulse peeks rest exactly on the 100 % and 0 %
gratitude lines (See Figure 2.12).
5.
Use the Horizontal POSITION control (10) to shift the trace so the leading edge passes through the
intersection of the 10 % and central vertical gratitude lines.
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