Bearing failure 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 experience.

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.