Datastick’s Peaking Value and IFactor Metrics:
Putting Meaningful Numbers on Damaging Vibration Characteristics

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Over the past few years, computer software and hardware has progressed enormously, but the methods used in vibration analysis have not changed — until now. Datastick has developed advanced “intelligent” enhancements to reveal vital information that is contained in vibration measurements.

One of the parameters used to estimate the high frequency energy in a vibration signal is the comparison of the energy in the highest peaks to the overall vibration energy. Generally such a measurement is a “peak factor” and there are several ways to derive such a value.

Traditionally, the most commonly used peak factor used in vibration analysis is “Crest Factor.” Crest factor is the maximum peak value of a waveform divided by the RMS value of that waveform signal. This metric can sometimes be misleading in that it can be significantly swayed by other factors such as the overall dynamic force vibration level, and does not in any way reflect the total amount of damaging peaking energy.

Datastick has developed two new metrics that are much more useful in condition assessment and trending. They are called Peaking and Impact Factor and they are exclusively available in DAART™ — Datastick Advanced Analysis and Reporting Toolkit.

Peaking Value: A More Accurate and Useful Metric than Crest Factor

Peaking Valueis one of the advanced signal-processing metrics Datastick has developed for detecting and tracking the development of high frequency impulse energy buried in a machine vibration signal.

Peaking reflects the amount of impact energy (both random and periodic) within the high-frequency content contained in excessive peak spikes (that portion in excess of a natural peak over the RMS level) in the vibration. In other words, Peaking reflects the sum magnitude (volume in ‘g’s) of peak spiking (random and periodic) within the high-frequency content of a vibration signal.

According to extensive laboratory testing, it is more reliable to use Peaking Value to track (trend) a situation like roller bearing defects than to use a straight high-frequency acceleration level or an enhanced Crest Factor (modified, pre- or post-processed). In other words, using Peaking is a convenient and reliable method of detection, quantifying, and tracking of developing situations where an acceleration signal contains shock waves or other impulse events.

Impact Factor (IFactor): Putting a Numerical Value on Periodic Impact Noise

IFactor is an index that reliably reflects the proportion of your vibration signal that is made up of periodic bursts of Impulse energy or impacts. IFactor measures the kind of energy that comes from bearing damage, which is commonly revealed in the form of FFT “haystacks.” Haystacks are normally indicators of bearing damage and are graphic representations of the noise generated by the damaged area of the bearing passing through the load zone of the bearing. IFactor is expressed in a scale of 0 to approximately 4, although extreme impact noise can result in an IFactor higher than 4.

The major usefulness of the IFactor is to make it easier to monitor the type of energy produced by bearing faults.

The IFactor can be compared to Crest Factor to illustrate its nature. Crest Factor is the ratio between any high peak value and the overall RMS level of the signal. In contrast, IFactor scales the total Impulse/Impact type energy specifically found in periodic busts, as compared to the overall RMS of the acceleration signal.

Crest Factor simply characterizes the time domain signal. It does not specifically differentiate or quantify any type of energy. IFactor favors the periodic impact energy typical of bearing defects.

How IFactor differs from Peaking

Peaking is a result of signal processing done directly with the time domain waveform alone and equally reflects continuous and burst sets of peaks. In other words, it includes random peak energy and periodic peak energy. It is expressed as a level of g RMS. Peaking is calculated and displayed along with time-domain waveform graphs.

IFactor is an index that reflects the proportion of your vibration signal that comes from periodic bursts of impulse energy or impacts. IFactor is calculated and displayed along with FFT graphs transformed from time domain data.

Additionally, a high IFactor indicates that a demodulation graph should yield significant results, whereas a high Peaking level does not necessarily indicate that.

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