Page 178 - An Introduction To Predictive Maintenance

168 An Introduction to Predictive Maintenance

input energy can cause catastrophic, near
instantaneous failure of the machine or struc-
ture.

Frequency, primary The base frequency referred to in a vibration
analysis that includes vibrations that are har-
monics of the primary frequency.
Gravitational constant The constant of proportionality in the
English system of units, g c , which causes one
pound of mass to produce one pound of force
under the acceleration of gravity, equal to
2
32.17lbm-ft/lbf-sec .
Harmonic motion A periodic motion or vibration that is a sinu-
soidal function of time, that is, motion along
a line given by equation x = a cos(wt +f),
where t is time, a and w are constants, and f
is the phase angle. For example, X = X 0 sin
(wt + f) where X is the displacement, X 0 is
the amplitude, w is the circular frequency,
and f is the phase angle.
Harmonics Multiples of the primary frequency (e.g., 2¥,
3¥).
Hertz Unit of frequency; a periodic oscillation has
a frequency of n hertz if in one second it goes
through n cycles.
Imbalance A condition that can result from a mechani-
cal and/or a force imbalance. Mechanical
imbalance is when there is more weight on
one side of a centerline of a rotor than on the
other. Force imbalance can result when there
is an imbalance of the centripetal forces gen-
erated by rotation and/or when there is an
imbalance between the lift generated by the
rotor and gravity.

Machine element Rotating-machine components, such as
rolling-element bearings, impellers, and
other rotors, that turn with a shaft.
Machine-train A series of machines containing both driver
and driven components.
Maintenance management program A comprehensive program that includes pre-
dictive maintenance techniques to monitor
and analyze critical machines, equipment,