Fluke 8012A - Page 31

10
Hz, the update rate
slows
and
follows
the
input signal. For
frequencies between 0.5 Hz
and
0.3 Hz, the
display
may
not
be stable. For frequencies below 0.3 Hz,
the
display
shows
0.000
Hz.
For most frequency measurements,
turn
the rotary
switch
to
theVsetting, connectt he meterto
the signal being measured,
and then press
C~*~)
button. Connecting the meter to
the
signal
before
pressing
Hz will normally allow
the
meter to
autorange
to
an
appropriate
range, but the minimum input
signal required to trigger
the frequency counter
varies,
depending on
the range and frequency
(see
Specifications).
If the input
signal is below the
trigger
level,
frequency
measurements will
not be taken. If your readings
are
unstable,
the input signal may
be
near
the trigger level for
that range. You can
usually correct this by selecting a
lower
range.
In
the
Frequency Counter mode,
the range (displayed
in
the lower-ri ght co rner
of the
LCD)
will
only change when
you
press the
(/mngF)
button.
If your readings seem to be
a
multiple of
what you expected,
your
input
signal may have
distortion or ringing.
(For
example, electronic motor controls distort both
voltage and
current waveforms.)
Select a
higher
input range if
you
suspect
multiple
triggering. An alternative
is
to
turn
the rotary
switch
to
the'v or
m"v
setting, which will
shift the trigger level
from 0V to
a positive voltage that changes with
each range. In
general,
the lowest frequency
displayed
is
the correct
one.
APPLICATIONS
Measuring
Frequency
In
the Frequency Counter
mode, the input range acts
like
an
attenuator,
the
V
function
ac-couples
the
input
signal, and
the V and m'v functions
dc-couple the input signal. The V
function is
optimized for triggering
on
logic
and switching
signals. The 4V
dc range
is
optimized to
trigger
on all
common 5V
logic
families (triggers
at
1.7V
±
0.1V).
High
frequency
logic
signals
may
require the
use
of the 400 mV
ac
range. The
40V
dc range is optimized to
trigger
on automotive
switching signals (triggers
at
4V
±1V). All
ranges
in
the
V
function trigger at
approximately 10%
of range, exceptforthe
4V range.
Frequency
measurements can
be
made
on current inputs. The
inputs
are
always dc-coupled.
The triggering characteristics
are shown
in Table 5.
Table 5. Frequency Counter Operation With Current
Inputs
INPUT
RANGE
APPROXIMATE
SENSITIVITY
(0.5
Hz-20 kHz)
APPROXIMATE
TRIGGER LEVEL
AC
CURRENT
DC
CURRENT
fiA
300
//A 0/iA
400
fjA
mA
30
mA
mA
40 mA
A
3A
OA
4A
25