How to Analyze Variable-Speed Machines

Vibration analysis testing is an essential technique used to diagnose and monitor the health of variable speed machines. A variable speed machine is a type of machine that can operate at varying speeds depending on the requirements of the application. Unlike fixed-speed machines, which operate at a constant speed, variable-speed machines can adjust their speed to match the load or process demand, resulting in increased energy efficiency, improved process control, and reduced wear and tear.

Variable-speed machines are used extensively in various industries, such as manufacturing, aerospace, and transportation. The vibrations that these machines produce can provide valuable information about the condition of their components, such as bearings, gears, and shafts. There are three primary ways to perform vibration analysis testing for variable speed machines, which we will discuss in detail below.

Use Order Tracking
Order tracking is a powerful tool that allows you to identify specific frequencies that are associated with different components in the machine. Order tracking works by tracking the rotational speed of the machine and synchronizing the vibration signals with the machine's rotation. This enables you to isolate the vibration signals associated with specific components and diagnose any issues that may be present. Order tracking allows the analyst to vary sampling rate with speed, often using a tachometer signal along with the accelerometer.

Use Waterfall Plot
A waterfall plot is another technique that can be used to analyze vibration signals in variable-speed machines. A waterfall plot is a graphical representation of the frequency spectrum of a vibration signal over time. It is created by stacking multiple spectra on top of each other, with each spectrum representing a different time period. This enables you to identify changes in the vibration signals over time and diagnose any issues that may be present.

Set Series of Standards
Collect various measurements after defining different speeds and conditions for each measurement. These levels can be used as a reference point to diagnose any issues that may be present. Establishing historical vibration data on machinery is extremely important in order to be able to trend faults over time.  

This blog was written in conjunction with Aly Attia, MDI