Supplementing vibration testing with spectral analysis of the output signal from the ultrasonic detector can be a helpful tool when used for the analysis of bearing and other types of mechanical faults. Some Ultrasonic instruments detect frequencies centered at 40 kHz ± 20 kHz. Others have tunable filters, they are generally all suitable for problem finding in a condition monitoring based reliability regime. The ultrasonic signals are demodulated to produce an audible signal, which are heard using the headphone or viewed using the data collector. The amplitudes of the spectrums not only depend on the severity but also depend on the medium that the signals are traveling through. As a result the data is not easily scalable and therefore difficult to trend. Nevertheless by using the data collector the spectral data can be analyzed and the cause of the machine problem can be determined. The bearing defect frequencies can be heard and their spectrum viewed even by taking the data as much as 10 feet away.

Practically the machine analyst could rapidly scan the machine with the ultrasonic detector and the headset. When an unusual sound from a bearing is detected, then a data collector measurement will provide the analyst with useful data.

Tip excerpted from "Vibration & Ultrasound Technologies: A Possible Integrated Inspection Tool?" by Stuart Courtney, Senior Applications Engineer, SKF Reliability Systems