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Outputs
True Peak Acceleration
Details: This is the highest acceleration value captured within the sampling window.
The acceleration signal used for this output is high pass filtered at 250 Hz.
Best Uses: This is the best and most commonly used method for early detection of bearing wear for fixed
speed machinery. The peak capture and high pass filtering provide values that strongly correlate to the
severity of cracks, spalling or brinelling. The short pulse cause by these faults has low energy compared
to the overall broadband vibration, and therefore would typically get lost in a traditional RMS
measurement.
RMS Acceleration
Details: This is the arithmetic average of all values captured within the sampling window.
The acceleration signal used for this output is high pass filtered at 2500 Hz.
Best Uses: RMS Acceleration can be used when it is preferred to run a bearing close to failure before
raising an alarm. It is also helpful for processes which involve violent impacting and short, high-amplitude
pulses that can transfer through the machinery to the bearing. In these cases, using the RMS
Acceleration output avoids false trips caused by these high-energy, short duration vibrations. The True
Peak Acceleration output may increase greatly with one of these impacts, but the RMS Acceleration will
not significantly increase.
Compensated Peak Acceleration (Peak Acceleration with Correction)
Details: This is a normalized ratio of the acceleration of impacts within the bearing to the linear speed of
the rolling element passing over a defect. This uses the speed and diameter of the bearing that were
programmed into the sensor to determine the linear velocity of the rolling element. The output is a unit-
less severity scale from 1 to 16.
The acceleration signals used for this output are high pass filtered at 250 Hz.
Best Uses: Compensated Peak Acceleration is most helpful for when the user has various size and speed
machinery for which they would like to monitor the rolling element bearings. By normalizing the output
using the shock pulse method described above, the values will be similar for machines with the same
bearing condition, even if these machines vary greatly in size and speed. Therefore a single alarm limit
can be set in the control system for all monitored bearings across different pieces of machinery.
Crest Factor
Details: This is the ratio of True Peak to RMS Acceleration. Therefore this value increases as the
amplitude of high-frequency impacts in the bearing increase compared to the amplitude of broadband
overall vibration. The output is a unit-less severity scale from 1 to 16. The acceleration signals used for
this output are high pass filtered at 250 Hz.
Best Uses: Crest Factor is better suited for variable speed machinery because the ratio of Peak to RMS
acceleration should not vary much at different speeds. This is due to the fact that both will increase as
speed increases; however, only True Peak Acceleration will increase if the fault severity increases in the
early stages of bearing failure. Please note that once the bearing condition is poor enough, the fault
vibrations will actually start to cause the RMS Acceleration value to increase, and therefore the Crest
Factor starts to decrease as the condition gets worse. Trending this Crest Factor value can capture that
decrease and still provide accurate awareness of the bearing condition. If you are not able to trend these
values or would like a similar output that always increases as bearing condition worsens, consider using
the Crest output described below.