Application Note

3 Fluke Corporation Seven ways to use your troubleshooting superpowers for good
#2 Tracking down motor trouble
During your regular scheduled maintenance check
of critical motors in your plant, you perform a
vibration screening using the Fluke 805 Vibration
Tester. You find a motor that gives an indication of
an internal issue. You connect three wireless CNX
modules and begin monitoring all three phases of
motor current over the course of the week.
While the modules are collecting data, you
make a quick check for hot spots from time to time
with the VT02. Early in the week, you see that the
motor has begun to generate moderate heat at the
drive shaft. By the end of the week, the sides of
the motor appear hot. A quick check with the 805
shows that overall vibration is satisfactory and the
bearings are rated “good” on the severity scale.
Ruling out a mechanical issue, it’s time to search
for an electrical problem.
At the end of the week, you wirelessly down-
load the logged data to the SW3000 software on
your laptop using the Fluke CNX PC Adapter. You
discover from the data that the motor current is
high based on its load. You suspect that this exces-
sive current draw is due to an internal problem in
the motor. It may be time to take the motor offline
and do an insulation resistance test. You can use a
Fluke insulation resistance tester to test the wind-
ing insulation to ground and discover the problem.
You remove the motor from service and replace it
with a different motor while the bad motor is refur-
bished and rewound at a rebuild facility.
#3 Troubleshooting a rooftop
HVAC system
A rooftop air conditioner trips the breaker and
shuts down after only 30 minutes of operation.
Yet at restart, it operates within manufacturer’s
specifications. After it has been running a few
minutes, you check bearings, belts and couplings
for vibration using the Fluke 805. All components
are rated “satisfactory” on the severity scale.
Next you use the VT02 to check around for hot
spots. You check the motor itself to see if the sides
are hot, which would implicate the windings. You
then check the output of the belt the motor is driv-
ing. While you didn’t see vibration on the motor
side with the Fluke 805, the belt may have insu-
lated the motor from a mechanical problem at the
fan. Possibly the fan bearing is damaged, putting
strain on the motor.
You use the VT02 to check motor functions,
driven-device functions (such as the fan bearing)
and the output temperature of the cooled, moving
air. Nothing looks excessive, so it’s time to do some
monitoring.
With the unit continuing to operate, you attach
wireless CNX current modules to the incoming
power legs and a wireless CNX current clamp
module at the load.
Start with an inrush test on motor startup. Use
the “inrush” function on the flex clamps to see if
inrush current to the motor falls within range for
the motor ratings. If the measurement is accept-
able you can then connect multiple current and
voltage modules, letting them log readings from
startup until the system shuts down.
The wireless modules give you a way to watch
for issues without somebody “living” on the roof.
You can check the live readings from a comfortable
position within 20 meters/60 feet of the modules.
Meanwhile, each module collects time-stamped
measurements, the critical information you’ll need
for a proper diagnosis.
When you download the data later, it reveals
a large current variance, an increase in amperage,
and an over-heating condition, all with time
stamps. You diagnose a drive component issue.
The repair can be completed after hours. The
system is back up and running quickly, and every-
one keeps cool.