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recommended for those situations in which it may be considered safer to inspect electrical apparatus at
a distance. The UWC-10 is extremely directional and will locate the exact site of an electrical discharge.
Another accessory is the LRM-10- Long Range Module which also increases the detection distance of
the Ultraprobe. The basic difference is that the LRM is a one-hand operation but has a slightly wider
detection area (11º) versus the UWC 10 (5º).
Monitoring bearing wear
Ultrasonic inspection and monitoring of bearings is by far the most reliable method for detecting incipient
bearing failure. The ultrasonic warning appears prior to a rise in temperature or an increase in low fre-
quency vibration levels. Ultrasonic inspection of bearings is useful in recognizing:
a. The beginning of fatigue failure.
b. Brinelling of bearing surfaces.
c. Flooding of or lack of lubricant
In ball bearings, as the metal in the raceway, roller or ball bearing begins to fatigue, a subtle deformation
begins to occur. This deforming of the metal will produce irregular surfaces, which will cause an increase
in the emission of ultrasonic sound waves. Changes in amplitude from the original reading is indication of
incipient bearing failure. When a reading exceeds any previous reading by 12 dB, it can be assumed that
the bearing has entered the beginning of the failure mode.
This information was originally discovered through experimentation performed by NASA on ball bearings.
In tests performed while monitoring bearings at frequencies ranging from 24 through 50 kHz, they found
that the changes in amplitude indicate incipient (the onset of bearing failure before any other indicators
including heat and vibration changes. An ultrasonic system based on detection and analysis of modula-
tions of bearing resonance frequencies can provide subtle detection capability; whereas conventional
methods are incapable of detecting very slight faults. As a ball passes over a pit or fault in the race sur-
face, it produces an impact. A structural resonance of one of the bearing components vibrates or „rings“
by this repetitive impact. The sound produced is observed as an increase in amplitude in the monitored
ultrasonic frequencies of the bearing.
Brinelling of bearing surfaces will produce a similar increase in amplitude due to the flattening process as
the balls get out of round. These flat spots also produce a repetitive ringing that is detected as an in-
crease in amplitude of monitored frequencies.
The ultrasonic frequencies detected by the Ultraprobe are reproduced as audible sounds. This “hetero-
dyned“ signal can greatly assist a user in determining bearing problems. When listening, it is
recommended that a user become familiar with the sounds of a good bearing. A good bearing is heard
as a rushing or hissing noise. Crackling or rough sounds indicate a bearing in the failure stage. In certain
cases a damaged ball can be heard as a clicking sound whereas a high intensity, uniform rough sound
may indicate a damaged race or uniform ball damage. Loud rushing sounds similar to the rushing sound
of a good bearing only slightly rougher, can indicate lack of lubrication. Short
duration increases in the sound level with „rough“ or „scratchy“ components indicate a rolling
element hitting a „flat“ spot and sliding on the bearing surfaces rather than rotating. If this condition is
detected, more frequent examinations should be scheduled
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