Tektronix 442, Instruction Manual

Page: 31 / 170

Operating Instructions—442 Service
Multi-Trace Phase Difference Measurements
Phase comparison between two signals of the same
frequency can be made using the dual-trace feature of the
442. This method of phase difference measurement can be
used up to the frequency limit of the vertical system. To
make a phase comparison measurement, use the follow­
ing procedure:
1. Set the Input Coupling switches (AC-GND-DC) to
the AC or DC position, depending on the type of coupling
desired.
EXAMPLE: Assume a horizontal difference of 0.6
division with a horizontal graticule calibration of
45°/division as shown in Figure 2-17. Using the formula:
Phase Difference =
horizontal
difference X
(divisions)
horizontal graticule calibration
(degrees/div)
Substituting the given values:
Phase Difference = 0.6 X 45°
2. Set the VERT MODE switches to either CHOP or
ALT. In general, the CHOP mode is more suitable for low-
frequency signals while the ALT mode ismoresuitablefor
high-frequency signals.
3. Connect the reference signal to the Channel 1 input
connector and the comparison signal to the Channel 2
input connector. The reference signal should precede the
comparison signal in time. Use coaxial cables or probes
that have equal time delay to connect signalstothe input
connectors.
4. Set the VOLTS/DIV switches and VAR controls so
the displays are equal and about 5 divisions in amplitude.
5. Set the Triggering controls to obtain a stable
display. 6
6. Set the SEC/DIV switch to a sweep rate which
displays about one full cycle of each waveform over 10
graticule divisions.
The phase difference is 27°.
Figure 2-17. Measuring phase difference.
7. Use the Channel 1 and Channel 2 POSITION
controls to center the waveforms around the center
horizontal graticule line.
8. Turn the SEC/DIV VAR control until one cycle of
reference signal (Channel 1) occupies exactly 8 divisions
between the second and tenth graticule lines (see Figure
2-17). Each division of graticule represents 45° of the
cycle (360° -
h
8 divisions = 45°/ division). The horizontal
graticule calibration can be stated in terms of degrees as
45°/division.
9. Measure the horizontal difference between the
corresponding points on the waveforms.
X-Y Phase Measurement
The X-Y phase measurement method can be used to
measure the phase difference between two signals of the
same frequency. This method provides an alternate
method of measurement for signal frequencies up to
2 MHz. However, abovethisfrequencytheinherent phase
difference between vertical and horizontal systems makes
accurate phase measurement difficult. In this mode, one
of the sinewave signals provides the horizontal deflection
(X) while the other signal provides the vertical deflection
(Y) . The phase angle between the two signals can be
determined from the lissajous pattern as follows:
1. Connect one of the sinewave signalstothe Channel
1 or X connector; and the other signal tothe Channel 2 or Y
input connector.
10. Multiply the measured distance by 45°/division to
obtain the exact amount of phase difference.
2. Set the TRIGGERING SOURCE switch to X-Y and
the VERT MODE switch to CH 2 or X-Y.
2 -1 6
REV A MAY 1980