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November - December 2019
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15
and ultrasonic stress waves. ese techniques apply to measure-
ments from various sensors, including a piezoelectric accelerometer,
microphone and radio-wave antenna. Each of the graphs includes
an orange and blue plot. e abscissa (Y-axis) is the signal strength
in millivolts (mV), and the ordinate (X-axis) is the time in seconds.
e area below the orange line is the total ultrasonic peak energy
above 20 kilohertz (kHz), while the area between the blue line and
the orange line represents the total sonic peak energy between 500
hertz (Hz) and 20 kHz. e ultrasonic energy below the orange
line is related to friction and turbulence. e sonic energy between
the blue and orange lines is associated with the compression energy
transfer reflecting work done by force through distance or pressure
through volume.
CAPITALIZING ON YOUR EFFORTS
Now that you have a better understanding of common failure
mechanisms (abrasion, corrosion, fatigue, adhesion, erosion,
cavitation, electrical discharge and deposition), as well as what
can be done to prevent them, it is important to remember that
each mechanism has contributing factors, affects different types
of equipment and requires proactive measures. By employing
non-intrusive monitoring techniques such as sonic and ultrasonic
stress-wave analysis, you can begin capitalizing on your preventive
efforts for greater reliability.
ML
Figure 5. Airborne stress waves from erosion
Figure 8. Microphone and radio-wave sensors detect
stress waves from a sparking electrical discharge
originating from a 120-volt source. Sparking events are
more common than arcing events for electrical
equipment 480 volts and below.
Figure 6. Radio stress waves from a partial
electrical discharge
Figure 7. Sonic and ultrasonic event stress waves
using microphone and radio-wave sensors to monitor
a continuous plasma and arcing electrical discharge
ML
