IRD Mechanalysis have developed “Spike Energy” to detect rolling element bearing condition in its very early stage. “Spike Energy” detects low amplitude transient impacts generated within the ultrasonic frequency range by microscopic surface flaws in rolling element bearings and gears.

As the vibrations are at very high frequencies, circuit utilizes an acceleration signal and a high pass filter to filter out low frequencies. A true Peak-to-Peak value detecting circuit is incorporated as these signals have low RMS values. The acceleration signal processed via a high pass filter and a peak detection circuit produces a numerical value which is the product of the number and amplitude (intensity) of the impacts in a unit of time. This is Spike Energy.

There are four failure stages in a bearing:

Stage 1: Microscopic Flaw, Only seen in ‘Spike Energy’

Stage 2: Size of Flaw increases, natural frequency of bearing appears in Zone C

Stage 3: Bearing Defect frequencies appear in Zone B

Stage 4: Size of Flaw keeps increasing, Spike Energy may actually decline

Spike Energy gives earliest indications in the ultrasonic range. It may first appear at about 0.25 gSE or lower in the first stage which will gradually increase. Slight defects and ensuing impacts begin to ring bearing component natural frequencies. These frequencies occur in the range of 30k-120k CPM. At the end of stage 2, sideband frequencies appear above and below natural frequency. Spike Energy grows from 0.25 to 0.50 gSE. Wear is now visible and may extend around the periphery of the bearing. Spike Energy increases to between 0.5 -1.0. Discreet bearing defect frequencies disappear and are replaced by random broad band vibration in the form of a noise floor. Towards the end, even the amplitude at 1 X RPM is affected. High frequency noise floor amplitudes and Spike Energy may in fact decrease at this stage. Just prior to failure gSE may rise to high levels. 

Readings need to be directly taken on bearing, minimise interfaces. For consistency between measurements always use the same accelerometer. Transducer mounting makes a difference and hence follow mounting suggested in IRD manual. Spike energy or shock pulse propagate through structure at the speed of sound in steel (16000 ft/sec). Energy is lost at interfaces of two material (60 to 80%). PLEASE KEEP ULTRASONIC TRANSDUCER AS CLOSE TO THE BEARING AS POSSIBLE. As ultrasonic energy is localized it is easier to isolate the bearing with problem.

IRD Model IRD811 and IRD811D meters have Spike Energy measurement facility.

IRD Mechanalysis Training programme VT2 and CAT 2 (Vibration Technology Level 2) discusses Spike Energy in greater details.

Note: Some companies use high pass filter and check vibration acceleration and call it vibration spikes or high frequency defects. This signal is just a filtered acceleration and does not indicate the true bearing condition. This is due to the fact that bearings in their nascent stage of deterioration emit very low signals in the ultrasonic range which is lost in the filtered signature carpet.