(a) 10 ms Division
(b) 2 ms Division
Figure 2-7: Time Interval Measurement
2.3.4
Phase Difference Measurements
Phase difference or phase angle between two signals can be measured using the dual-trace feature of the
oscillocope, or by operating the oscilloscope in the X-Y mode.
Dual-trace Method
This method works with any type of waveform. In fact, it will often work even if different waveforms are being
compared. This method is effective in measuring large or small differences in phase, at any frequency up to
20 MHz.
To measure phase difference by the dual-trace method, proceed as follows:
1.
Set up the scope as described in 2.3.3 Dual-trace Operation, connecting one signal to the CH 1 IN
connector (24) and the other to the CH 2 IN connector (22).
Note:
At high frequencies use identical and correctly-compensated probes, or equal lengths of the
same type of coaxial cable to ensure equal delay times.
2.
Position the Trigger Source Switch (18) to the channel with the cleanest and most stable trace.
Temporarily move the other channel's trace off the screen by means of it Vertical POSITION control.
3.
Center the stable (trigger source) trace with its Vertical POSITION control, and adjust its amplitude
to exactly 6 vertical divisions by means of its VOLTS/DIV switch and VARIABLE control.
4.
Use the Trigger LEVEL control (9) to ensure that the trace crosses the central horizontal gratitude
line at or near the beginning of the sweep. See Figure 2-10.
5.
Use the TIME/DIV switch (15), A VARIABLE control (12) and the Horizontal POSTION control (10) to
display one cycle o trace over 7.2 divisions. When this is done, each major horizontal division
represents 50, and each minor division represents 10°.
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 and VARIABLE control to adjust its amplitude to
exactly 6 vertical divisions.
7.
The horizontal distance between corresponding points of the waveform is the phase difference. For
example, in the Figure 2-10 illustration the phase difference is 6 minor divisions, or 60°.
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