Inspection of mechanical equipment with ultrasonic instruments such as an Ultraprobe has many advantages. Ultrasound inspection provides early warning of bearing failure, detects lack of lubrication, prevents over lubrication and can be used on all bearing speeds (high, medium and low). In addition, since ultrasound is a high frequency, short wave signal, it is possible to filter out stray, confusing background noises and focus on the specific item to be inspected. Basic inspection methods are extremely simple and require very little training. For those who require more sophistication, UE Systems offers training courses that range from one-day specialized classes to five-day certifiable courses.

Ultrasonic condition analysis is straightforward. Users of analog instruments can observe sound levels while simultaneously listening to the sound quality.  Digital users have additional options such as both sound and data analysis through specialized software. The more sophisticated digital instruments provide features for comprehensive mechanical or bearing condition monitoring programs including; data logging, software for trending and creation of alarm groups, sound sample recording, spectral analysis of sounds and software with customizable reporting formats.

How Ultrasound Bearing and Mechanical Inspection Works

Mechanical movements produce a wide spectrum of sound. One of the major contributors to excessive stress in machinery is friction.  Ultrasound instruments detect friction.  By focusing on a narrow band of high frequencies, the Ultraprobe detects subtle changes in amplitude and sound quality produced by operating equipment. It then heterodynes these normally undetectable sounds down into the audible range where they are heard through headphones and observed on a display panel for trending, comparison, and analysis.

It has been established that ultrasound 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.  For those who utilize ultrasound spectral analysis, these conditions can often be observed through both FFT and time series analysis.

Ultrasonic Bearing Inspection Method

There are three methods for ultrasonic bearing monitoring: comparative, historical and analytical. In order to note possible deviations that might indicate a potential failure condition or to establish a baseline for future surveys, it is necessary to compare similar bearings to each other for potential differences in amplitude and sound quality. To do this, make a permanent reference point on a bearing housing or use the grease fitting, tune to 30 kHz and adjust the received sound level (in analog instruments this is the "Sensitivity" dial) so that the intensity or decibel level can be observed on the display panel. Then compare this base reading to other similar bearings. 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. Alarm levels can be set to note any bearings in need of corrective action. An 8 dB gain over a baseline with no change in sound quality will indicate possible lubrication starvation. Levels, such as 12 dB or higher can signify a potential failed condition. The analytical approach can be integrated into the comparative or historical process. Sound anomalies can be recorded and analyzed through spectral analysis software.  Some of the advanced instruments have on-board spectral analysis providing the ability to diagnosis issues while performing inspections out in the plant.

Recommended instruments: Ultraprobe 9000, Ultraprobe 10,000, Ultraprobe 15,000