Application Note

Application Note
Multimeter measurements
on variable frequency
drives using the new
Fluke 289 DMM
From the Fluke Digital Library @ www.fluke.com/library
In the past, motor repair meant dealing
with traditional three-phase motor failures
that were largely the result of water, dust,
grease, failed bearings, misaligned motor
shafts, or just plain old age. But, motor
repair has changed in a big way with the
introduction of electronically controlled
motors, more commonly referred to as
variable frequency drives (VFD). Drives
present technicians with a unique set of
measurement problems that can vex the
most seasoned pro.
This application note describes the elec-
trical measurements you can make dur-
ing the installation and commissioning of
a drive, as well as other measurements
to aid in diagnosing bad components, and
other conditions that may lead to prema-
ture motor failure in VFDs.
Troubleshooting
philosophy
There are many different ways
to go about troubleshooting an
electrical circuit, and a good
troubleshooter will always find
the problem—eventually. The
trick is to track down the problem
as quickly as possible, keeping
downtime to a minimum.
The most efficient procedure
for troubleshooting is to begin at
the motor, and then systemati-
cally work back toward the elec-
trical source, looking for the most
obvious problems first. A lot of
time and money can be wasted
replacing perfectly good parts
when the problem is nothing
more than a simple loose con-
nection.
Next, take care to make
accurate measurements. Nobody
makes inaccu rate measurements
on purpose of course, but it’s
easier to do than you may think,
especially when working in a
high energy, noisy environment
like that of an VFD. Choosing the
right test tools for troubleshoot-
ing, the drive, the motor, and
the connections is of the utmost
importance. This is especially true
when making voltage, frequency
and current measurements on the
output side of the motor drive.
Until now the only meter on
the market able to make these
measurements accurately was
the Fluke 87V Digital Multimeter.
Fluke has just introduced the next
generation of high performance
Multimeter, the new Fluke 289,
incorporating the same selectable
low pass filter found in the
successful 87V DMM. The filter
allows the meter to make
accurate drive
output
measure-
ments that
will now
agree with
the motor
drive controller
display indica-
tions. No longer
does the technician have to
guess whether the drive is
operating correctly and deliv-
ering the correct voltage, current,
or frequency for a given control
setting.
Drive measurements
Editor’s note: For similar instructions using the
Fluke 87V DMM, reference Fluke article 12345.