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Trending Bearing Wear with Ultrasonic Detection

Establish a Route-Based Method of Data Collection

Today’s ultrasonic instruments allow greater flexibility than instruments from only a few years ago.  Smaller, more powerful electronic components allow for complex data storage and two-way communications with PC’s.  Proper acoustic vibration monitoring means establishing a route-based method of data collection similar to that of your vibration routes.  Establish routes or groups of machines in a logical sequence and identify asset names to each measurement point for storage, trending, and time-based graphical representation of bearing condition.

Measured Value (dBmV) and its Correlation to Condition

At the outset, the goal is to establish a baseline or normal operating range for each bearing to be checked.  Throughout the life of a bearing its ultrasonic level should remain relatively constant (+/- 3 or 4 dBmV).  As the condition of the bearing changes, increases in acoustic energy due to either lubrication breakdown or structural breakdown will be observed.  Increases correspond with an elevated reading (dBmV) on the instrument.  Trending acoustic energy with data logger software allows the user to accurately predict when lubrication should be applied to a bearing, and when the bearing itself is entering early failure stages.  Remember, trending acoustic vibration warns us of the earliest signs of change in a bearing.  Diligent use of the information gathered results in better lubrication practices and extended bearing life.  The desired result is a much larger window through which to schedule repairs and change outs.

To optimise ultrasonic inspection techniques it is essential to listen to the bearings; not just read the values on the display.  Listening to the ultrasound of a bearing provides significant qualitative information that correlates to the measured values.  A low, muffled smooth noise associated to stable values indicates a normal functioning bearing.  A strident high-pitched noise indicates a lack of lubrication, an overload or a rotation speed beyond spec of the bearing.  A crackling noise associated to unstable or high dB values indicates faults, wear or loose metal particles in the lubricant.  Ultrasonic detectors provide an excellent quantitative measurement via the digital display, but do not ignore the qualitative information provided by the headphone output.