Gene Vogel
EASA Pump & Vibration Specialist
and
Walter Barringer
Mobius Institute, Knoxville, TN

Temperature is hot or cold, pressure may be high or low and a tank may be full or empty. But vibration cannot be adequately described by a single parameter. Vibration is composed of amplitude, frequency and phase. Overall amplitude may be used as a simplistic indicator of machinery condition; much like a noise could be described as loud or soft, even though there is a big difference between the scream of a siren and the roar of a train. And so it is with vibration.

The siren sounds different than the train because they are different frequencies. In the same way, the vibration from a failing rolling element bearing can be distinguished from coupling misalignment. This combination of vibration amplitude and frequency is the most common and useful vibration data for determining machinery condition, and analyzing machinery vibration problems. The phase angle of the vibration plays an important role in dynamic balancing and advanced analysis. The analysis of vibration amplitude and frequency as represented in the vibration spectrum, is the topic of this paper.

This paper covers how to get the vibration spectrum and what it means, including:

• Wave form
• Displacement
• Velocity
• Demodulation

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