Definitions and terms
The rate of change of velocity with time (Dv/Dt) usually along a
specific axis, expressed in "g".
The magnitude of variation from a base value (normally zero). It
is used for displacement, velocity or acceleration. Excursion is
double the Amplitude (Peak to peak). The value is useful in the
balancing procedure to reduce the vibration forces generated by
rotation by adjusting a mass in the rotating element.
The particular resonant ferquency at which a damage (or degrading
in performance) to the installation occurs.
The complete sequence of instantaneous values of a periodic event
that occur during one period.
The dissipation of vibratory energy with motion or time. Critical
damping is the value of damping that provides most rapid response
to a step function without overshot.
The vibration motion of a system is said to be forced if it is caused
by some mechanical excitation.
Occurs without forcing, as after a string is plucked.
The reciprocal value of the period. The bestknown unit is Hertz
(Hz), which represents cycles per second. When referreing to vibrators,
cycles per minute or revolutions per minute (r.p.m.) are common.
Impact is a single collision between masses at least one of
which is in motion.
The intergral force within a time window.
The severity of a vibration or shock. Similar to amplitude but without
Isolation is the reduction in severity of motion, usually attained
by proper use of resilient support.
Refers to the ratio of change of acceleration with time (Da/Dt).
The frequency of free vibration of a system.
The variation with time of a quantity, such as force, pressure,
displacement or velocity. Usually some regularity such as sinusoidal
or complex vinration is implied.
The extreme value of a varying quantity measured from the base or
The period of a periodic vibration is the smallest interval of time
in which the vibration repeats itself.
The vibration motion, force or energy of a mechanical system
that results from some mechanical input to that system.
In a true Single-Degree-of-Freedom system resonance exists when
any change of excitation frequency causes a decrease in its response.
Therefore, resonance represents the maximum response of the sprung
mass, if frequency is varied while input force is kept constant.
The temporarily sustained vibration of a mechanical system.
A device to measure the frequency of a vibrating machine. Usually
an extendable spring that can be adjusted to come in resonance at