Application Note

2 Fluke Corporation Clamp Meter ABCs
would produce 0.001 amps or 1
milliamp of current at the input
of the meter. With this technique,
much larger currents can be
easily measured by increasing the
number of turns in the secondary.
Clamp meters measure any
combination of alternating and
direct current. This includes static
dc and charging dc as well as ac.
Clamp meters measure dc current
using Hall effect sensors. A Hall
effect sensor, basically a kind of
magnetometer, can sense the
strength of an applied magnetic
flux. Unlike a simple inductive
sensor, the Hall effect sensor will
work when the applied magnetic
flux is static, not changing. It will
work for alternating magnetic
fields as well. A clamp meter
contains a toroidal iron core that
clamps together with a Hall effect
chip in the gap between the
two halves, so that the induced
magnetic flux from the
current-carrying wire is
channeled through it.
Choosing your
clamp meter
Buying a clamp meter not
only requires looking at
specifications, but also looking
at features, functions, and the
overall value represented by a
meter’s design and the care taken
in its production.
Reliability, especially under
tough conditions, is more impor-
tant than ever. Fluke’s design
engineers make a point of
building these test tools not only
electrically, but also mechanically,
robust. By the time Fluke clamp
meters are ready to be tossed into
toolcases, they’ve undergone a
rigorous testing and evaluation
program.
User safety should be a primary
consideration in choosing a
clamp meter—or any other piece
of electrical test equipment. Fluke
not only designs its clamp meters
to the latest electrical standards,
but each clamp meter is indepen-
dently tested and then listed by
certified testing labs such as CSA,
TÜV, etc. Only with these certi-
fications can you be assured an
electrical tester meets these new
safety standards.
Using a clamp meter in
difficult situations
Electricians and technicians
often need to use clamp meters
in less-than-ideal situations.
The newest clamp meters use
the iFlex
™ flexible current probe
to enable measuring where it’s
difficult to access—for example,
tight cabinets, bundled wires, or
awkward conductors.
When it’s necessary to measure
remotely, a clamp meter with a
detachable display (such as the
Fluke 381) makes it possible to
see the display at a location other
than where the measurement
is being taken. This means one
person—not two—can take the
measurement.
Resolution, digits and
counts
Resolution refers to how fine a
measurement a meter can make.
By knowing the resolution of a
meter, you can determine if it’s
possible to see a small change
in the measured signal. For
example, if the clamp meter has
a resolution of 0.1 amp on a 600
amp range, it’s possible to see a
change of 0.1 amp while reading
100 amps.
You wouldn’t buy a ruler marked
in one-inch segments if you had
to measure down to one-quarter
inch. Similarly, you must choose a
meter that can display the
resolution you need to see in
your measurements.
Use a flexible current probe for situations like this, where large conductors make it difficult
to use the clamp meter jaws.