Page 177 - An Introduction To Predictive Maintenance

Vibration Monitoring and Analysis 167
Axial
Bearing cap
Boundary condition
Displacement
Dynamics, operating
Fast Fourier Transform (FFT)
Force
Forcing function
Frequency
Frequency, circular
Frequency, natural
Of, on, around, or along an axis (straight line
about which an object rotates) or center of
rotation.
The protective structure that covers bearings.
Mathematically defined as a requirement to
be met by a solution to a set of differential
equations on a specified set of values of the
independent variables.
The change in distance or position of an
object relative to a reference point, usually
measured in mils.
Deals with the motion of a system under the
influence of forces, especially those that
originate outside the system under consider-
ation.
A mathematical technique used to convert a
time-domain plot into its unique frequency
components.
That influence on a body that causes it to ac-
celerate. Quantitatively, it is a vector equal to
the body’s time rate of change of momentum.
The cause of each discrete frequency
component in a machine-train’s vibration
signature.
Frequency, f, is defined as the number of rep-
etitions of a specific forcing function or
vibration component over a specific unit of
1
time. It is the inverse of the period, , of the
T
vibration and can be expressed in units of
cycles per second (cps) or Hertz (Hz). For
rotating machinery, the frequency is often
expressed in vibrations per minute (vpm).
Another measure of frequency measured in
radians (w = 2p f).
All components have one or more natural
frequencies that can be excited by an energy
source that coincides with, or is in proximity
to, that frequency. The result is a substantial
increase in the amplitude of the natural fre-
quency vibration component, which is
referred to as resonance. Higher levels of