Tektronix 5441 Instruction Manual page 35

Channel 1, or left
Channel 2, or center
plug-in (reference) plug-in
50%
Amplitude
level
-
L I
,
-
1
I
.
I
I I
k ~ o r i z o n t a l I
I
distance
*!
Fig. 2-10. Measuring time difference between two pulses.
Multi-trace Phase Difference Measurement
Phase comparison between two or more signals of the
same frequency can be made using a dual-trace plug-in or
two single-trace plug-ins. This method of phase difference
measurement can be used up to the frequency limit of the
vertical system. To make the comparison, use the following
procedure.
1. Set the input coupling switches of the amplifier chan-
nels to either ac or dc.
2. Set the Display switch on the time-base unit to either
Chop or Alt. In general, Chop is more suitable for low-
frequency signals and the Alt position is more suitable for
high-frequency signals. More information on determining the
mode is given under Vertical Display Mode in this section.
3. Set the vertical plug-in triggering switches to trigger
the display on channel 1 (or left plug-in) and channel 2 (or
center plug-in).
4. Connect the reference signal to the channel 1 input
connector and comparison signal to the channel 2 (or center
plug-in) input connector. The reference signal should pre-
cede the comparison signal in time. Use coaxial cables or
probes that have similar time-delay characteristics to con-
nect the signals to the input connectors.
5. If the signals are of opposite polarity invert the chan-
nel 2 (or center plug-in). (Signals may be of opposite polarity
due to 180" phase difference; if so, take this into account in
the final calculation.)
Operating Information-5441lR5441
6. Set the VoltsIDiv switches and the variable Volts/Div
controls so the displays are equal and about five divisions in
amplitude.
7. Set the time-base triggering controls to obtain a sta-
ble display. Set the SeclDiv switch to a sweep rate that
displays about one cycle of the waveform.
8. Move the waveforms to the center of the graticule
with the vertical Position controls.
9. Turn the variable SeclDiv control until one cycle of the
reference signal (channel 1, or left plug-in) occupies exactly
eight divisions between the second and tenth vertical lines
of the graticule (see Fig. 2-1 1). Each division of the graticule
represents 45" of the cycle (360"
t
8 div
=
45'Idivision).
The sweep rate can be stated in terms of degrees as
45'ldiv.
Channel 1, or left
Channel 2, or center
plug-in (reference) plug-in (lagging)
1
I
I I
I 8 Divisions I
I ( 3 6 0 " ) ' I I
Fig. 2-11. Measuring phase difference.
10. Measure the horizontal difference between corre-
sponding points on the waveforms.
11. Multiply the measured distance (in divisions) by
45"/div (sweep rate) to obtain the exact amount of phase
difference.
EXAMPLE: Assume a horizontal difference of 0.6 div
with a sweep rate of 45"Idiv as shown in Fig. 2-1 1. Use the
following formula.
horizontal sweep rate
Phase
=
difference X (degrees1
=
(6) (45')
=
27'
Difference
(divisions) division)
The phase difference is 27".
REV MAY 1982