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Practical Solutions to Machinery and Maintenance Vibration Problems

Chapter 1, Basic Information

Section 4, The Most Common Vibration Amplitude Units in Use

Peak-to-Peak is mostly used as basis for displacement units. Most often used in Western Hemisphere. Sometimes used in other parts of the world. Sometimes referred to as "Zero-to-Peak."

Peak is most often used in Western Hemisphere. Sometimes used in other parts of the world. Sometimes referred to as "Zero-to-Peak." Used as a basis for velocity units.

rms refers to terms of "root-mean-square" used to mathematically determine its value. Units used by those who feel that the vibration's "power" is more important than its amplitude based on "Peak." Units are used worldwide but are in more frequent use outside the Western Hemisphere.

Displacement is a distance, usually measured in mils ( 1 mil = 0.001") or in microns
(1 micron = 1 millionth of a meter). Displacement is usually the preferred unit for low frequency vibrations of machines with running speeds of less than 1000 rpm.

Velocity is the rate of change of displacement. It is usually measured as in/sec in the Western Hemisphere and mm/sec in countries using the metric system. Most vibration instruments become less accurate when measuring velocity at frequencies over 60,000 cpm or 1000 Hz. It is still used at most plants for higher frequencies but only with corrections for inaccuracies.

Acceleration is the rate of change of velocity with units of in/sec2 or mm/sec2. It is the preferred unit by those more sophisticated in high frequency vibration analysis, especially for such machine frequencies as are generated by defective rolling element bearings and gearmesh vibration and noise.

Textbook Index


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