pdf  Operational Modal Testing

When troubleshooting fan vibration issues, it is helpful to know the dominant mode shapes that are being excited. A useful tool for doing this is Operation Deflection Shape (ODS) testing. In this method, vibration readings are taken off the fan using accelerometers while it is running. These levels can then be imported into a 3-D model of the fan.

By plugging in the actual vibration levels from the fan, it is possible to animate the vibration and see the mode shape that is being excited. This information is effective in determining if the vibration will cause early failures and reduce the life of the fan assembly.