Vibration: The Three Essential Parameters
Vibration is a complex phenomenon that can be measured in a variety of ways. Three of the most important parameters used to measure vibration are acceleration, velocity, and displacement. Each of these parameters have their own pros and cons, proper use of which can provide unique insight into the nature of vibration. Used correctly, a comprehensive understanding of the phenomenon can be obtained. In this blog post, we will discuss these three parameters in detail, exploring their individual characteristics and how they can be used to decipher vibration.
Acceleration is the rate of change of velocity over time. It is measured in units of meters per second squared (m/s2) or g’s. Acceleration is most effective at detecting impacting and high frequency vibrations. Such examples of potential faults that occur in this range are rolling element bearing and gear faults like deformations on the races or rolling elements, cracked or worn gear teeth, even gear eccentricity or backlash.
Displacement shows the distance between a rotating object and the applicable sensor. Measured in units of millimeters (mm) or mils (thousandths), displacement is most effective in very low frequency vibrations – generally below five times running speed on slow moving machinery. Potential defects that can occur in this range are eccentricity, unbalance, and misalignment among others.
Velocity is the rate of change of displacement over time and is measured in units of millimeters per second (mm/s) or inches per second (in/s or ips). Most commonly used, velocity is typically perceived as a “happy medium” between displacement and acceleration. While displacement is best for measuring very low speed/frequency vibration, and acceleration is best suited for high speed/high frequency vibration, velocity is a well-balanced solution for most speeds and frequencies. Several potential faults can be identified with velocity such as misalignment, unbalance, mechanical looseness, propeller or impeller related vibration, and the list goes on.
In summation, velocity, acceleration, and displacement are three of the most important parameters to consider when measuring vibration. It’s always best to consider what machine you are measuring, what components are contained within that machine, and what are some of the potential faults that could occur. The answers to those questions will help determine which parameter is best suited for the application. Low frequency faults on slow turning machinery would be best identified by displacement, high frequency issues on medium to high speed machinery will most likely present themselves when using acceleration, and if you’re unsure of the particulars, or monitoring a standard piece of machinery, velocity provides a good balance between the two scenarios.
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