# Could someone explain undulation per revolution?

1. Sep 29, 2005

### Watts

Could someone explain undulation per revolution? I would prefer to have a mathematical function defining it also if possible. Can any explain ONE also?

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2. Sep 29, 2005

### FredGarvin

Are you referring to a 1 per rev imbalance in a rotating component?

3. Sep 29, 2005

### Astronuc

Staff Emeritus
Perhaps one needs to distiguish between an undulation caused by - mass imbalance, or deviation in concentricity or roundness - any of which can result in the deviation (undulation) of a component's surface.

Mass imbalance implies a variation in momentum that would cause a part to vibrate during rotation. Similarly concentricity, in which the center (central axis) of a round part is not coincident with the rotating axis, e.g. the axis of a shaft. Now normally, this would like produced one undulation/rotation.

If a part's surface is out-of-round, it could have more than one deviation (from roundness) on the circumference and thus one would measure more than one undulation per full revolution.

Last edited: Sep 29, 2005