Phase
Shift
Measurements
The
horizontal
control
section
may have
an XY
mode
that
lets you
display
an input
signal
rather
than the
time
base on
the
horizontal
axis.
(On some
digital
oscilloscopes
this is
a
display
mode
setting.)
This
mode of
operation
opens up
a whole
new area
of phase
shift
measurement
techniques.
The
phase of
a wave
is the
amount
of time
that
passes
from the
beginning
of a
cycle to
the
beginning
of the
next
cycle,
measured
in
degrees.
Phase
shift
describes
the
difference
in
timing
between
two
otherwise
identical
periodic
signals.
One
method
for
measuring
phase
shift is
to use
XY mode.
This
involves
inputting
one
signal
into the
vertical
system
as usual
and then
another
signal
into the
horizontal
system.
(This
method
only
works if
both
signals
are sine
waves.)
This set
up is
called
an XY
measurement
because
both the
X and Y
axis are
tracing
voltages.
The
waveform
resulting
from
this
arrangement
is
called a
Lissajous
pattern
(named
for
French
physicist
Jules
Antoine
Lissajous
and
pronounced
LEE-sa-zhoo).
From the
shape of
the
Lissajous
pattern,
you can
tell the
phase
difference
between
the two
signals.
You can
also
tell
their
frequency
ratio.
Figure
shows
below
Lissajous
patterns
for
various
frequency
ratios
and
phase
shifts.
