Preventing Bearing Failure Using Ultrasound

UE Systems has a wide range of instruments, both analogic and digital, which are perfect for bearing inspection and bearing condition monitoring using Ultrasound technology. These will allow maintenance professionals to get an early warning of bearing failures and to act on it, avoiding equipment downtime.


There are many advantages in using Ultrasonic inspection in mechanical equipment:

  • Early warning of bearing failure
  • Detects lack of lubrication
  • Prevents over lubrication
  • 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 test point. Basic inspection methods are extremely simple and require very little training.


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:

  • Viewing decibel levels
  • Data logging
  • Data analysis and trending through specialized software
  • Creation of alarm groups
  • Sound sample recording
  • Spectral analysis of sounds

How Does It Work?

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, an Ultrasound instrument 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
  • 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.

Typical ultrasound inspections include: bearings (it has proven to be very effective on low-speed bearings), pumps, motors, conveyors, gear & gear boxes, couplings, fans, compressors, robots….

Ultrasonic Bearing Inspection Method

There are three methods for ultrasonic bearing monitoring:

  • Comparative
  • Historical
  • Analytical

In order to note possible deviations that might indicate a possible failure condition or to establish a baseline for future surveys, compare similar bearings to each other for 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 so that the intensity or decibel level can be observed on the display panel.


Then compare this base reading to other similar bearings, while listening for any sound quality anomalies. 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. High and low 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 a need to lubricate due to depleted lubricant. Levels such as 16 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 analysed 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 UE Systems instruments for bearing inspection and lubrication: