The Truth Behind Misalignment Vibration Spectra of Rotating Machinery

A shaft centerline diagram is a plot used in the vibration analysis of journal bearings. It is also called a shaft average centerline diagram. The purpose of this graph is to display the average position of the rotor in the bearing. In short, for different bearing types, there is an expected or “normal” position of the shaft in the bearing. If this position changes, it can indicate a problem.

Infrared thermography is the science of seeing heat. Thermal imagers have the ability to produce a visual representation of thermal patterns as heating systems’ components are identified and recorded. Maintenance strategies are then planned and carried out before system breakdowns occur.

A vibration test and analysis guide is a simple book or electronic document that contains a variety of information about the machine. Information should include: A simple schematic of the machine with test points identified, instructions for testing the machine (especially if loads and speeds must be manipulated or verified), name plate information and a simple schematic of internal components. This information is invaluable for conducting a proper diagnosis of the machine.

To be able to truly evaluate the effectiveness of an infrared predictive maintenance program there must be an understanding of the relationship between the equipment that is to be inspected and the problems that are found and repaired. Too often the focus is on only the infrared images that the camera produces while the solutions that the data produced from the program can provide get lost. It all boils down to a simple but fundamental law that is expressed by the equation E = IR8 which focuses on measuring the effectiveness of the overall infrared program as well as on each of the individual components that contribute to its success.

When performing condition monitoring tasks, don’t just rely on expensive condition monitoring tools. You would be surprised at the unusual and simple tools that can be used. 

Costly oversights occur repeatedly despite thoughtful planning dedicated to maximizing the operation and lifespan of the motor. One unsettling realization is that testing, considered part and parcel of preventive maintenance, is not preventing anything because there is nothing to indicate that analyzing the data was even considered. This is a major pitfall and a classic example of a gap in a company’s motor management program.

Are harmonics real or just an artifact or result of processing the waveform through the FFT? This is a question that comes up a lot among vibration analysts, or anyone working with signals and signal processing.