is one of
the most common causes of motor breakdown. NASA has reported that ultrasonic monitoring of
bearings is perhaps the most effective method of detecting the first sign of bearing
failure. What's more, ultrasonic monitoring will detect a problem long before it is
discovered through heat or vibration testing. Bearings nearing failure generate measurable
ultrasonic frequencies before audible or mechanical signals can be detected. Because of
this, ultrasonic detection is the most useful way to monitor incipient bearing failure.
Trending methods using ultrasound are simple and do not require extensive
How To Trend Bearings With Ultrasound
Mechanical movements produce a
wide spectrum of sound. By focusing on a narrow band of high frequencies, the Ultraprobe
detects subtle changes in amplitude and sound quality. It then heterodynes these normally
undetectable sounds down into the audible range where they are observed on a meter (for
trending and comparison purposes) and heard through headphones. Based on research by NASA,
it was established that ultrasonic monitoring provides early warning of bearing failure.
Various stages of bearing failure have been established. An 8-dB gain over baseline
indicates pre-failure or lack of lubrication. A 12-dB increase establishes the very
beginning of the failure mode. A 16-dB gain indicates advanced failure condition while a
35-50 dB gain warns of catastrophic failure.
There are two basic methods for
ultrasonic bearing monitoring: comparative and historical. In order to troubleshoot
bearings or to establish a baseline, it is necessary to compare similar bearings for
potential differences in amplitude and sound quality. To do this, make a reference point
on a bearing housing or use the grease fitting, tune to 30 kHz and reduce the sensitivity
until the bearing reads 20 on the meter. Then compare this base reading to other similar
bearings. A failing bearing will show an increase of 12 dB or higher and will sound rough.
Lack of lubrication will sound smooth but will show an 8-dB gain. Once a series of
bearings have been tested, and a base line set, data is recorded and then compared to
future readings for historical trending and analysis. Additional information regarding
vibration data logging connections is available by contacting us.