Tech Briefs Magazine - October 2021 - ST-15

condition monitoring has become an
important part of factory operations.
Sometimes referred to as Smart Factory,
Industrial IoT (IIoT), or Industry 4.0, factories
are adding sensors and analytical systems
that keep tabs on the health of the
manufacturing equipment.
Condition monitoring is the process of
outfitting equipment with sensors that can
identify significant parametric changes
indicative of an imminent fault or failure.
These systems look for two things. First: Is
the machine operating outside of its
design parameters, requiring a quick
response? Second: What are the long-term
trends of critical parameters for predicting
when the machine will need maintenance,
repair, or replacement.
Factory Electric Motors
One of the most ubiquitous machines
in factories is the electric motor.
It's estimated
there are 300 million motors running
in manufacturing facilities around
the globe today. They provide the power
to fabricate, assemble, and move products
in a factory. The failure of a single
motor can bring a production line to a
grinding halt, costing $10,000s per hour.
Condition monitoring sensors and analytics
give an early warning of problems.
Treating these problems quickly results in
a lower cost of maintenance, fewer disruptions
in process flow, and improved
safety for the equipment operators.
The health of any motor can be determined
by monitoring three operating
parameters:
* Vibration - measured with an
accelerometer.
* Temperature - measured with a contact
type temperature sensor.
* Current - measured with an inductive
or shunt type current sensor.
Accelerometers provide data regarding
the motor's mechanical health.
Temp -
erature sensors provide data regarding
both mechanical and electrical health,
and current sensors look at the electrical
health. Sensors can also provide data
regarding the condition of equipment and
tools attached to the motor.
Accelerometers
All rotating motors have an armature
that's suspended by bearings and rotates
at various speeds. The armatures are balanced
so as not to vibrate while rotating.
However, an unbalanced or damaged
armature creates vibration that can
affect bearings. If the vibrations are at
resonant frequencies of other equipSensor
Technology, October 2021
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Level and Flow | Automation | Proximity Sensing | Inventory Control
ment attached to the motor, damage can
be severe and quick. Vibration frequency
from a motor coincides with the
motor RPM and typically ranges from a
few Hz to 4 kHz. Accelerometers are
suited for measuring these vibrations.
Accelerometers are also used as contact
microphones that listen for high frequency
noise (squeal) from bearings where
lubrication has been depleted. These frequencies
range from 5kHz to 15kHz.
Piezoelectric accelerometers work well
because they have a broad frequency
response that covers both frequency
ranges with a single device.
Typically, a Fast Fourier Transform
(FFT) is used to analyze the signal. The
FFT data shows each frequency band of
vibration and its intensity. Figure 2 indicates
the natural vibration frequencies
and amplitudes of a typical motor.
New motors have natural vibration frequencies
that are recorded and used as a
baseline to compare to data taken later
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Tech Briefs Magazine - October 2021

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