Instantaneous Acceleration

An less common unit is based on a concept called "jerk measurement" and is refered to as "Instantaneous Acceleration" in older research papers (some still classified). The concept is in observing the rate of change of acceleration without filtering. Since most FFT analyzers are digitally processing the input signal it is very easy to extract an IA number. The change in acceleration for a fixed period (often 0.0002 seconds) and the absolute values of the highest and lowest values (during a 0.10 second increment) are added creating an IA value. The usefulness of this measurement is best seen in the following example.

A vibration signature with multiple harmonics (unbalance, looseness, misalignment & vane pass) has a small random noise within the data array. The overall signature is shown below.

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Last updated: November 24, 2002