Tektronix 5103N

Operating
Instructions—
5103N
Fig.
2-8.
High-resolution
phase-difference
measurement with in-
creased sweep rate.
High
Resolution
Phase
Measurements
More accurate
dual-trace
phase
measurements
can
be
made by
increasing
the
sweep
rate (without
changing the
Variable
Seconds/Div
control
setting). One
of the easiest
ways to
increase the
sweep
rate is
with the SWP MAG
(10X) button on
the
time-base
unit. The
magnified
sweep
rate is
automatically
indicated
by
the
knob-skirt scale-
factor
readout.
EXAMPLE:
If the
sweep
rate
were increased 10
times
with the
magnifier,
the
magnified
sweep rate
would be
45°/
division-^
10=
4.5°/division.
Fig.
2-8
shows the
same sig-
nals as
used in
Fig. 2-7,
but
with
the
SWP
MAG button
pushed in. With a
horizontal
difference
of
six
divisions, the
phase
difference is:
horizontal
magnified
Phase
Difference
=
difference
X sweep
rate
(divisions)
(degrees/division)
(6)
(4.5°)
=
27°
The phase
difference is
27°.
X-Y
Phase
Measurements
The
X-Y
phase
measurement
method can
also be used
to
measure the
phase
difference
between
two
signals
of the
same
frequency.
The
phase
angle is
determined
from the
Lissajous
pattern as
outlined
in
the
following
steps:
1.
Insert
an
amplifier
plug-in
unit into
one
of
the
verti-
cal
plug-in
compartments
and an
amplifier
of the
same
type
into the
horizontal
plug-in
compartment.
Fig.
2-9.
Phase
difference measurement from an X-Y
display.
2.
Connect a
signal to
the input
connector
of
each
plug-
in
and select the
desired input
coupling.
3.
Position
the display
to the
center
of
the
screen and
adjust
the Volts/Div
switches to
produce a
display six
divi-
sions
vertically
(Y) and six
divisions
horizontally (X).
4.
Center
the
display in relation to
the center
vertical
graticule line.
Measure the
distances A and
B
as
shown in
Fig.
2-9.
Distance
B
is
the vertical
measurement
between
the
two points
where the trace
crosses the center vertical
line. Distance A
is the
maximum vertical
amplitude
of the
display.
5.
Divide
B
by A
to
obtain the sine
of
the phase
angle
(T>)
between the
two signals. The
angle can then
be
obtained from a
trigonometric
table.
If
the display
appears
as a
diagonal
straight line, the
two signals
are either in
phase
(tilted upper
right to
lower
left),
or
180°
out
of
phase
(tilted
upper
left
to
lower right).
If the display is a
circle,
the
signals are
90°
out
of phase. Fig.
2-10
shows
the
Lissajous
displays produced
between
0°
and
360°.
Notice
that
above
180°
phase
shift, the
resultant display
is
the
same as at
some lower
angle.
EXAMPLE:
Assume a
display
as
shown
in Fig.
2-9
where A is
6
divisions and
B
is
0.4 division.
Using the
formula:
Sine
=
-
7
-
=
=
0.0660
A
6
From
the
trigonometric
tables
(or slide
rule):
$
=
arcsin 0.0660
=
3.78°
2-11