Modal and ODS analysis

In the process of diagnosing rotating machinery, it is unavoidable to do some structural vibration analysis as well. Most often this is done by performing ODS (Operating Deflection Shape) Analysis or Modal Analysis.

An operating deflection shape shows the deformation of a structure at a specific frequency or during a time waveform playback. ODS shows the response of a structure to both resonant and forced vibration, and is generally very representative of the real world data. ODS evaluation can be particularly useful in the analysis of rotating equipment where internally generated forces can be high.

Modal analysis is similar to ODS in that deformation of the structure can be viewed, but it is primarily concerned with resonance frequencies (or natural frequencies) of a structure. Modal analysis is typically performed as a vibration exciter by exciting the structure with a known force and measuring the response of the structure at many locations using accelerometers. The measured frequency response functions are analyzed to determine the modal parameters.