Application Note

Safety checklist
3 Use a meter that meets
accepted safety standards for
the environment in which it
will be used.
3 Use a meter with fused current
inputs and be sure to check
the fuses before making cur-
rent measurements.
3 Inspect test leads for physical
damage before making a mea-
surement.
3 Use the meter to check conti-
nuity of the test leads.
3 Use only test leads that have
shrouded connectors and fin-
ger guards.
3 Use only meters with recessed
input jacks.
3 Select the proper function and
range for your measurement.
3 Be certain the meter is in good
operating condition.
3 Follow all equipment safety
procedures.
3 Always disconnect the “hot”
(red) test lead first.
3 Don’t work alone.
3 Use a meter that has overload
protection on the ohms func-
tion.
3 When measuring current with-
out a current clamp, turn the
power off before connecting
into the circuit.
3 Be aware of high-current and
high-voltage situations and
use the appropriate equip-
ment, such as high-voltage
probes and high-current
clamps.
Accessories and glossary
DMM accessories
One very important requirement
of a DMM is that it can be used
with a wide variety of acces-
sories. Many accessories are
available that can increase your
DMM’s measurement range and
usefulness, while making your
measurement tasks easier.
High-voltage probes and cur-
rent probes scale down high
voltages and currents to a level
the DMM can safely measure.
Temperature probes convert your
DMM into a handy digital ther-
mometer. RF probes can be used
to measure voltages at high fre-
quencies.
Furthermore, a selection of
test leads, test probes, and test
clips can help you easily connect
your DMM to the circuit. Soft and
hard carrying cases protect your
DMM and conveniently store your
accessories with your DMM.
Glossary
Accuracy. How close the DMM’s
displayed measurement is to the
actual value of the signal being
measured. Expressed as a per-
centage of reading or as a per-
centage of full scale.
Analog meter. An instrument
that uses a needle movement to
display the value of a measured
signal. The user judges the read-
ing based on the position of the
needle on a scale.
Meter ratings and capabilities vary by manufacturer.
Before working with a new meter, be sure to familiar-
ize yourself with all operating and safety procedures for
that meter contained in the users manual.
Independent testing is the key to safety
compliance
How can you tell if you’re getting a genuine
CAT III or CAT II meter? It’s not always easy. It
is possible for a manufacturer to self-certify its
meters as CAT II or CAT III without any inde-
pendent verification. Beware of wording such as
“Designed to meet specifications...” Designer’s
plans are never a substitute for an actual inde-
pendent test. The IEC (International Electro-
technical Commission) develops and proposes
standards, but it is not responsible for enforcing
the standards.
Look for the symbol and listing number of
an independent testing lab such as UL, CSA,
TÜV or other recognized approval agency. That
symbol can only be used if the product success-
fully completed testing to the agency’s standard,
which is based on national/ international stan-
dards. UL 3111, for example, is based on IEC
1010. In an imperfect world, that is the closest
you can come to ensuring that the multimeter
you choose was actually tested for safety.
Annunciator. A symbol that
identifies a selected range or
function.
Average responding DMM. A
DMM that accurately measures
sinusoidal waveforms, while
measuring non-sinusoidal wave-
forms with less accuracy.
Count. A number used to specify
a DMM’s resolution.
Current-shunt. A low-value
resistor in a DMM for measuring
current. The DMM measures the
voltage drop across the current
shunt and, using Ohm’s Law, cal-
culates the value of the current.
DMM, digital multimeter. An
instrument that uses a digital
display to show the value of a
measured signal. DMMs feature
greater durability, resolution, and
far more accuracy than analog
meters.
Non-sinusoidal waveform. A
distorted waveform such as a
pulse train, square waves, tri-
angular waves, sawtooth waves
and spikes.
Resolution. The degree to which
small changes in a measurement
can be displayed.
rms. The equivalent dc value of
an ac waveform.
Sinusoidal waveform. A pure
sine wave without distortion.
True-rms DMM. A DMM that
can accurately measure both
sinusoidal and non-sinusoidal
waveforms.
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6 Fluke Education Partnership Program ABCs of DMMs: Multimeter features and functions explained