The Value of Operating Deflection Shape (ODS)

By Maki Onari

Over the last 25 years at MSI, ODS testing has been an essential and powerful troubleshooting tool that has helped MSI’s engineers and technicians identify the root cause of high vibration on any rotating machinery, as well as nearby stationary equipment. MSI incorporates this testing method in most of our specialized field testing and troubleshooting projects, regardless of how simple or complex the vibration issue at hand. Typically, ODS testing uncovers mechanical or hydraulic issues that one way or the other could participate in the root cause of the problem, and that you might miss with traditional vibration testing.

With ODS you are able to see a 3D animation of your rotating machinery system at a given frequency (i.e. 1x running speed, vane pass frequency, etc.). You can also include rotor vibration using radial and axial proximity probe data from sensors mounted on the bearing housings.

The following is a short list of example machinery problems that ODS testing is able to help identify:

  • The exact location with the highest vibration amplitude at a given frequency
  • The weakest component that could be shifting a structural natural frequency near an excitation source
  • Soft-foot or separation between parts that should be “connected”
  • Determination of approximate mode shapes of key natural frequencies
  • Cracks if vibration data is taken with detail (across the crack)
  • Components under excessive alternating bending or torsional load
  • Rotor imbalance
  • Angular and/or offset misalignment

Depending on the complexity of the problem/ equipment (system), ODS testing can be time-consuming and requires a large number of measurement locations with well documented tracking of the location of each roving accelerometer and its orientation (triax accelerometers).

ODS works best during steady state operation of the machine (frequency domain), but it can be used for mechanical issues during transient events (time domain). However, transient ODS requires a large number of vibration sensors to record data simultaneously in a short period of time. For more information about ODS techniques click here or get in touch with one of the MSI team members today.

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