Fluke 117 User Manual

New Fluke 117 Digital

Multimeter drives the

ghosts out of the attic

(and the electric circuits)

As an electrician, Eldon
Walstad’s job can be like that

Testing
Functions

Case
Study

Tool: Fluke 117 Electrician’s
Multimeter

Profile: Eldon Walstad,
Rodgers Electric

Measurements: High impedance for
troubleshooting sensitive electronic or
control circuits, and low impedance for
detecting ghost voltages

of a radar operator when it
comes to detecting the invisible.
He has to be able to determine
what is real and what is not,
and separate what is dangerous
from what only appears to be.
Now Walstad has a new tool
that can help him make those
critical decisions—the Fluke 117
Digital Multimeter (DMM).

In an average week Wals­tad, a journeyman electrician
with Rodgers Electric in Everett,
WA., handles all kinds of issues
related to electrical installa­tion, maintenance and repair. A
frequent challenge is to deter­mine why a device isn’t operat­ing, and track down the faulty
contact, fuse, relay or broken
wire that’s preventing current
from flowing.

But occasionally a digital
multimeter will show voltage
present, even on a circuit that
should not be energized. Is it
real and potentially danger­ous voltage, or merely “ghost
voltage” caused by capacitive
coupling between energized
wiring and adjacent unused
wiring?

“The other day I had a situ­ation where I had 73 volts
showing up on a circuit,” says
Walstad, a second-generation
electrician with more than 30
years experience. The circuit in
question: a control circuit on a
concrete transfer cart used to
move material from the mixer to
the molds in a factory making
precast concrete light poles. In

Application Note

the wet, dirty plant environ­ment, the potential problems
were many. “It should have
been either 110 volts, or
nothing.”

Hunting down the ghosts

In the past, tracking down such
a voltage indication could send
the technician off on a time­wasting wild goose chase, look­ing for a problem connection
that was never there. He could
ferret out the ghost voltage with
a low-impedance analog meter
or a solenoid tester, or ‘wiggy’ ­but that would require packing
or fetching an extra tool.

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

But Walstad had extra help.
The Fluke 117 Digital Multi­meter he was using that day
has dual impedance capabil­ity; incorporating both regular
high impedance test capabilities
and low impedance functions
for detecting ghost voltages.
By switching to the meter’s
Auto-V/LoZ (low impedance)
test setting, Walstad could see
instantly that the 73 volts was
only a ghost. “It saved me a trip
back to the truck to get another
meter,” Walstad says.

Ghost voltage can
look real

Ghost voltages are caused when
energized circuits and non­energized wiring are located in
close proximity to each other,
such as in the same conduit or
raceway. This condition forms a
capacitor and allows capacitive
coupling between the energized
wiring and the adjacent unused
wiring.

When you place your multi­meter leads between the open
circuit and the neutral conduc­tor, you effectively complete
the circuit through the input
of the multimeter. The capaci­tance between the connected,
hot conductor and the floating
conductor forms a voltage
divider in conjunction with the
multimeter input impedance.
The multimeter then measures
and displays the resulting volt­age value.

Most digital multimeters
today have an input impedance
that’s high enough to show
this ghost voltage, giving a false
impression of a live conductor.
The meter is actually measuring
voltage coupled into the discon­nected conductor. But at times,
these voltages can be 80-85 %
of what the “hard” voltage
should be. If not recognized as
a ghost voltage, additional time,
effort and money will be lost
troubleshooting circuit problems.

How impedance affects
testing

Most digital multimeters for
testing industrial, electrical and
electronic systems have high
impedance input circuits greater
than 1 megohm. This means
that when the DMM is placed
across a circuit for a measure­ment, it will have little impact
on circuit performance. This is
the desired effect for most volt­age measurement applications,
and is especially important for
sensitive electronics or control
circuits.

Older troubleshooting tools
such as analog multimeters
and solenoid testers gener­ally have low impedance input
circuitry around 10 kilohms or
less. While these tools aren’t
fooled by ghost voltages, they
should only be used for testing
power circuits or other circuits
where the low impedance
will not negatively impact or
alter circuit performance. They
rarely comply with the current
IEC 61010 safety standards
and North American regulatory
requirements.

The best of both worlds

With dual impedance meters,
technicians can safely trouble­shoot sensitive electronic or
control circuits, as well as
circuits that may contain ghost
voltages, and can more reliably
determine whether voltage is
present on a circuit.

On the Fluke 114, 116 and
117 DMMs, the meter’s regu­lar Vac and Vdc switch posi­tions are high impedance. Use
these switch positions for most
troubleshooting scenarios and
especially on sensitive elec­tronic loads.

The Fluke low impedance
function is called Auto-V/LoZ.

Auto-V stands for automatic

•

volts. This feature automati­cally determines whether the
measured signal is ac volt­age or dc voltage, selects the
correct function and range,
and displays the correct infor­mation.

LoZ stands for Low Imped-

•

ance (Z). This feature presents
a low impedance input to
the circuit under test. This
reduces the possibility of
false readings due to ghost
voltages and improves
accuracy when testing to
determine absence or pres­ence of voltage.

2 Fluke Corporation New Fluke 117 Digital Multimeter drives the ghosts out of the attic

Use the Auto-V/LoZ switch
position on the DMM when
readings are suspect (ghost
voltages may be present) or
when testing for the presence
of voltage. When the leads are
placed on an open circuit that
contains a ghost voltage, the
low input impedance will cause
the ghost voltage to dissipate
and the meter will display a
reading near zero volts indicat­ing no voltage present. When
the leads are placed on a live
circuit, however, the input
senses the presence of “hard”
voltage and then displays the
actual voltage present.

Non-contact voltage
detection

The Fluke 117 DMM also
includes the built-in VoltAlert™
non-contact voltage func­tion. Located on the top of the
meter above the LCD display,
it’s another feature handy for
detecting the invisible. The
VoltAlert function detects the
presence of ac voltage, sounds
an audible tone and activates
a red LED indicator light on the
top center of the LCD display.
Using this feature before
making a contact measurement
can add an extra layer of safety.
Users should, of course, still
test for the presence of voltage
using test leads with the meter
in the volts setting.

Four user groups,
four meters

The new Fluke DMMs include
four distinct models, each aimed
at a specific group of users. The
114 Electrical Multimeter is
ideal for electrical troubleshoot­ing and straightforward ‘go/no
go’ testing in the residential
electrical setting, and also is
designed for use in electric util­ity applications to test circuits
before turning power back on
at the meter. The 115 Multi­meter is optimized for electrical
and electronic testing by field
service technicians. The 116
Multimeter features temperature
and microamps measurements
useful for heating, ventilation,
air conditioning and refrigera­tion (HVAC/R) technicians. And
the 117 Electrician’s Multime­ter tested by Eldon Walstad is
designed for commercial electri­cians. All are rated for use in
600 V CAT III environments,
and all except the 115 include
the LoZ low impedance test
capability.

“I like it,” Walstad says of
the 117. “When you’re trying
to prove something, you’ve got
to know whether you’ve got
real power there or not. If you
think you’ve got power but
don’t, then you can go off in a
different direction trying to find
problems when you really need
to be back here working on
something. You’re not wander­ing aimlessly, looking for it.”

And there are no ghosts
in sight.

Fluke. Keeping your world
up and running.™

3 Fluke Corporation New Fluke 117 Digital Multimeter drives the ghosts out of the attic

Fluke Corporation
PO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands

For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa [phone] or
Fax [phone]
In Canada (800)-36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com

©2006 Fluke Corporation. All rights reserved.
Printed in U.S.A. 9/2006 2747091 A-EN-N Rev A