Schaeffler North America


Catalog | 2015-07
Mounting and Maintenance of Rolling Bearings
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Measurement Methods

Modal Analysis

Modal analysis is a particular form of vibration diagnosis. This method does not examine individual components of a machine but the machine as a whole. The aim is to determine the overall vibration behaviour of the machine. A model of the machine is created on the computer and a large number of measurement points are defined. The machine is then specifically excited to vibration using an impulse hammer. Based on parallel measurement of the excitation and resulting machine vibrations at the various measurement points, a vibration model of the machine can be determined by the computer and presented in three dimensions.


Modal analysis has a wide variety of possible applications:

  • Determination of natural frequencies or resonance frequencies:
    Due to design-related factors such as mass and rigidity, each machine has one or more natural frequencies. If the speed of the motor in a machine is within the range of a natural frequency, extreme vibrations may occur in the machine. With the aid of modal analysis, the Schaeffler vibration experts can submit recommendations for design improvements to the machine.
  • detection of the “soft spot” in a machine:
    If a high level of vibration occurs during initial operation or after a technical modification of a machine, this may be due to a so-called “soft spot”. This is defined as a rigidity problem, often caused by a poor quality connection between two machine parts, for example at a screw connection. For analysis, the measurements are used to produce an animation showing the movements of the machine. Showing the movement of the individual machine parts in relation to each other quickly leads to the “soft spot” in the machine. A joint discussion can be held to prepare proposals for improving the design of the machine.