Measuring Duty Cycle - Fluke 8010A User Manual

APPLICATIONS
Measuring Duty Cycle
Measuring Duty Cycle
Duty Cycle
(or
duty
factor)
is
an
alternate
Frequency Counter
mode
that displays, in
percent, the time the
input signal
is
above
the
trigger level (or
below
the
trigger level
if
the negative
trigger
slope
is
selected).
The Duty Cycle
mode
is
optimized
for
measuring
the
on
or
off
time
of logic
or switching controls.
Many
industrial control
systems
(electronic fuel injection
in
automobiles,
for
example)
are pulse-width modulated, and
duty cycle
measurements
provide
a
quick
check on
their
performance.
For
logic level signals,
use
the
4V dc
range. For
1
2V
switching
signals
in
automobiles, use the
40V
dc
range.
For sine waves,
use
the
most
sensitive
range you can
without
getting
double
triggering.
(Normally,
a
clean
signal
can be up
to
ten times the
amplitude
of
the
range you
are
on.)
Duty cycle
measurements
can
also
be used as an
indication
of potential triggering
prob-
lems on
sine
wave
or
near
sine
wave
signals.
If
you do
not
measure
approximately
50%
duty cycle,
you
may
have a
dis-
torted
waveform.
In
Duty Cycle (and Frequency Counter) mode, the slope
(or
edge) on which the counter
triggers
is
selected
by pressing
C "ii
)
.
The
slope selected
is
indicated
by a + or
-
annunciator
in
the
lower-left
corner
of
the
LCD.
The waveform
shown
in
Figure
4 represents
the duty cycle
measurement
of
a
typical
logic signal.
+
SLOPE
TRIGGER POINT
30%
+SLOPE
-SLOPE
TRIGGER
POINT
70%
-SLOPE
100%
26
Figure
4.
Duty Cycle
Measurement
of
Typical Logic Signal