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
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