Slow speed bearing monitoring with ultrasound is actually easier than you might think.

Because most high end ultrasound instruments have a wide sensitivity range and frequency tuning, it is possible to listen to the acoustic quality of the bearing, especially at slower speeds.

In extreme slow speed bearing applications (usually less than 25rpm), the bearing will produce little to no ultrasonic noise. In that case, it is important to not only listen to the sound of the bearing, but more importantly to analyze the recorded ultrasound sound file in a spectrum analysis software, focusing on the time wave form to see if there are any anomalies present. If “crackling” or “popping” sounds are present, then there is some indication of a deformity occurring.

In bearing speeds above 25rpm, it is possible to set a baseline decibel level and trend the associated decibel level readings over time.