Phase Difference - Tektronix 2213A Instruction Manual

Phase Difference

In a similar manner to "Time Difference Between Two
Time-Related Pulses" phase comparison between two sig­
nals of the same frequency can be made using the dual­
trace feature of the 2213A. This method of phase difference
measurement can be used up to the frequency limit of the
vertical deflection system. To make a phase comparison,
use the following procedure:
1. Preset instrument controls and obtain a baseline
trace, then set the INT switch to CH 1.
2. Set both Input Coupling switches to the same posi­
tion, depending on the type of input coupling desired.
3. Using either probes or cables with equal time delays,
connect a known reference signal to the Channel 1 input
and the unknown signal to the Channel 2 input.
4. Select BOTH VERTICAL MODE; then select either
ALT or CHOP, depending on the frequency of input signals.
The reference signal should precede the comparison signal
in time.
5. If the two signals are of opposite polarity, press in
the Channel 2 INVERT button to invert the Channel 2
display.
6. Set both VOLTS/DIV switches and both Variable
controls so the displays are equal in amplitude.
7. Adjust the TRIGGER LEVEL control for a stable
display.
8. Set the SEC/DIV switch to a sweep speed which
displays about one full cycle on the waveforms.
9. Position the displays and adjust the SEC/DIV Vari­
able control so that one reference-signal cycle occupies ex­
actly 8 horizontal graticule divisions at the 50% rise-time
points (see Figure 4-8). Each division of the graticule now
represents 45° of the cycle (360°
horizontal graticule calibration can be stated as 45o /per
division.
10. Measure the horizontal difference between cor­
responding points on the waveforms at a common horizon­
tal graticule line (50% of rise time) and calculate the phase
difference using the following formula:
- 8 divisions), and Jthe
h
Operating Procedures— 2213A Operators
CHANNEL 1 CHANNEL 2
Figure 4-8. Phase difference.
Phase horizontal
Difference = difference
(divisions)
Example: The horizontal difference is 0.6 division with a
graticule calibration of 45° per division as shown in Fig­
ure 4-8.
Substituting the given values into the phase difference
formula:
Phase difference = 0.6 div x 45°/div = 27°.
More accurate phase measurements can be made by us­
ing the X I0 Magnifier function to increase the sweep speed
without changing the SEC/DIV Variable control setting.
EXAMPLE: If the sweep speed were increased 10 times
with the magnifier (X I0 Magnifier button out), the magni­
fied horizontal graticule calibration would be 45°/division
divided by 10 (or 4.5°/division). Figure 4-9 shows the
same signals illustrated in Figure 4-8, but magnifying the
displays results in a horizontal difference of 6 divisions
between the two signals.
Substituting the given values in the phase difference
formula:
Phase difference = 6 div x 4.5°/div = 27°.
MEASURE
TIM E FROM
® TO ( | )
HORIZONTAL
DIFFERENCE
C4207-19
horizontal
graticule
x
calibration
(deg/div)