Acceleration
A vector quantity that specifies rate of change of velocity.
Accelerometer
A sensor whose electrical output is proportional to acceleration.
Charge amplifier
An amplifier whose output voltage is proportional to the output charge from a
piezoelectric transducer. Has the advantage that voltage output is not affected
by length of connecting cable from the transducer.
Compliance
The ease with which a system may be displaced or compressed for a given force.
The reciprocal of stiffness.
Critical damping
The minimum viscous damping that will allow a displaced system to return to its
original position without oscillation
Displacement
A vector quantity that specifies the change of position of a body. Usually
measured from the rest position.
Damping
Any means of dissipating vibration energy within a vibrating system.
Damping ratio
Ratio of actual damping to critical damping, at a resonant frequency.
Degree of freedom
In a mechanical system, equals the minimum number of independent co-ordinates
required to completely define the position of all parts of the system at any
instant of time.
Dynamic mass
Ratio of applied force to resulting acceleration during simple harmonic motion.
Dynamic modulus
Ratio of stress to strain under vibratory conditions.
Excitation
An external force or motion applied to a system that causes the system to
respond in same way.
Force
Retardation Agency which gives a mass an acceleration.
Impact
Excitation of a structure with a force pulse e.g. using an Impact Hammer.
Impulse
Well defined pulse. Periodic impulse is repeated impulses.
Integrator
An electrical frequency filter used to convert a vibratory acceleration signal
to one whose amplitude is proportional to velocity or displacement.
Jerk
A vector quantity that specifies time rate of change of acceleration.
Mechanical impedance
Ratio of applied force to resulting velocity during simple harmonic excitation.,
Called driving point impedance if force and velocity are measured at the same
point, otherwise called transfer impedance.
Mobility
Mechanical admittance. Inverse of mechanical impedance.
Modal analysis
A process of determining the mode shapes and associated parameters, natural
frequency and damping.
Natural frequency
The frequency at which a resiliently mounted mass will vibrate when set into
free
vibration.
Periodic vibration
An oscillatory motion whose amplitude pattern repeats after fixed increments of
time.
Random vibration
A vibration whose instantaneous amplitude is not specified at any instant of
time. Instantaneous amplitude can only be defined statistically by a probability
distribution function which gives the fraction of the total time that the
amplitude lies within specified amplitude intervals. Pseudo, or Periodic and
Burst random are special forms.
Resonance
Conditions of peak vibratory response where a small change in excitation
frequency causes a decrease in system response.
Response
Motion or other output resulting from an excitation, under specified conditions.
Shock
Rapid transient transmission of mechanical energy.
Simple harmonic motion
A periodic motion whose displacement varies as a sinusoidal function of time.
Stiffness
Ratio of the change in force to the corresponding change in displacement of an
elastic element.
Transmissibility
Ratio of the amplitude response of a system in steady state vibration to the
excitation amplitude.
Velocity
A vector quantity that specifies time rate of change of displacement.
Vibration isolator
A resilient support that reduces transmissibility.
Vibration meter
An instrument for measuring oscillatory displacement, velocity or acceleration.
Vibration severity
A criteria for predicting the hazard related to specific machine vibration
levels.
Voltage preamplifier
A preamplifier which produces an output voltage proportional to the input
voltage from a piezoelectric accelerometer. Input voltage depends upon cable
capacitance.
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