Operating Deflection Shape (ODS), Bump Tests and Modal Analysis are three tools at the disposal of Plant Engineering and Predictive Maintenance Teams. Each test has its unique purpose and benefit. I have found that many of our customers are unaware of the three tests and/or are confused by their application and purpose.
Let’s start by defining each test…
Bump Test… also known as an impact test, a structure or object is struck with an excitation force such as a soft faced hammer, while measuring the vibration response. When properly excited, the object will respond to the excitation and vibrate at one or more natural frequencies.
Operating Deflection Shape… is an analytical tool where amplitude and phase measurements are collected, normalized and plotted to obtain a visual of how each point “moves” relative to the others. In some cases, software is available to display the movement in an animation format that enhances the analytical process.
Modal… an object is excited with an external force such as a calibrated force hammer or shaker, and the response of the object is measured simultaneously via cross-channel measurements. Excited natural frequencies will incur an amplification of the response and utilizing data generated by a transfer function (system output/system input), amplitude and phase measurements can be animated to display the movement of the object at its natural frequency.
Over the next several months, our newsletter and will focus on these three test as we believe their use will improve the reliability of the rotating machinery assets at your plant.
If you would like to learn how to complete ODS studies, please consider attending our next ODS Class . It will be held in Houston, Texas (25-27 September)