S1 and S2 level earthquakes are designations you might encounter…

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Asked: May 31, 20232023-05-31T19:07:19+05:30 2023-05-31T19:07:19+05:30In: Vibration Analysis

When to use displacement, velocity and acceleration?

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Peter · Answer 1 · 2023-05-31T19:20:48+05:30

Displacement is used to express vibration severity when the vibration frequency is less than 600 CPM (Cycles Per Minute) or 10Hz. Because the dominant mode of equipment failure at low range frequency is stress. The displacement or deflection of an object is directly proportional to stress.
- $\sigma = E \epsilon$ (From Hook’s Law)
- $\sigma = E \, \frac{\delta L}{L}$
- $\sigma \, \alpha \,\delta L$ ( $\delta L \,$ represent the displacement of an object from its mean equilibrium position)
Velocity is used to express vibration severity when the vibration frequency is in the range of 600 to 120,000 CPM or 10 to 2000 Hz. Because the dominant mode of equipment failure at medium-range frequencies is fatigue. Fatigue is a function of displacement-magnitude and its frequency. Velocity is also a function of displacement and time (Time=1/Frequency). Since velocity is the indicator of fatigue, velocity is used to express the vibration severity at medium-range frequencies.
Acceleration is used to express the vibration severity when the vibration frequency is greater than 120,000 CPM or 2000 Hz. Because the dominant mode of failure at high frequencies is due to force. From Newton’s second law of motion, force is expressed as the product of mass and acceleration. Acceleration is proportional to the force. Indirectly, acceleration is representing the force. Generally, faults in the bearings occur at high frequencies.