Allied Radio Knight KG-640 Посібник оператора - Сторінка 10

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HOW
TO
MEASURE
AC
CURRENT
The AC voltage ranges may also be used to measure AC current
at power line frequencies. This is accomplished by inserting a
low value resistance of sufficient wattage in the current path
and reading the voltage across
it. Since the value of the re-
sistance and the voltage drop are known,
the current can be
calculated by the following formula:
E
(volts)
I (Amperes) =
-
R
(ohms)
[] Place
the black test lead into the jack marked
—COM.
Place the red test lead into the jack marked
VOA.
[] Set the selector switch to the ACV
range that will provide
a reading at the right hand side of the scale. Always start
at the highest range and work your way
down
until you
can read at the right hand
side of the scale.
[] Make
a break in the circuit in which the current
is to be
measured.
[] Insert a resistor of known
value and sufficient wattage
in
the circuit.
[] Measure the voltage drop across the resistor, adjusting the
selector switch to read at the right hand side of the scale.
[_] Calculate the current using the Ohm's Law formula
(above).
HOW
TO
MEASURE
OUTPUT
VOLTS
When
it becomes
necessary to measure
an AC voltage that is
superimposed
on a DC
voltage, the OUTPUT
circuit of your
meter should be used. In the OUTPUT
position, a capacitor is
used to block the DC
current
from
reaching
the meter.
The
meter will then indicate the correct AC
voltage.
((] Plug the black test lead into the jack marked —COM
and
the red test lead into the jack marked
OUTPUT.
[] Proceed
as
indicated
under
HOW
TO
MEASURE
AC
VOLTAGES.
DO NOT
EXCEED
600 VOLTS!
NOTE:
Since the 2000
and 4000
volt AC
ranges
require
a
separate input jack, the blocking capacitor,
necessary for out-
put measurement
is not connected in the meter circuit. These
ranges
cannot
be used
for output
measurements
unless
an
external DC blocking capacitor with a rating of 4 KV is used.
When
AC voltages are measured
with the output circuit, the
impedance
of the DC
blocking
capacitor
will have
an
effect
on the accuracy of the meter reading. The
error which occurs
varies with the frequency
of the applied voltage. The higher
the frequency the smaller this error will be.