When evaluating machinery and equipment it is useful to know their
classification range and group type. There are four machine groups
and classification ranges recognized internationally (ISO 2372 and
VDI 2056). The limits for vibration severity (mm/s) are shown in the
GROUP K – Small Machinery up to 15KW (for example, production
GROUP M – Medium-sized Machinery up to 75KW (for example, electrical
motors without special foundations)
GROUP G – Large Machinery on Heavy Foundations
GROUP T – Large Turbo Machinery on Special Foundations
Relative Sensitivity Table (ISO 2954)
Vibration: Vibration is an oscillation or repetitive motion of an
object around an equilibrium position.
Displacement: Displacement is the peak-to-peak distance from a
reference position, or equilibrium point, of an object under test.
Peak Amplitude: Peak –to-peak amplitude is the displacement of an
object (see above). It can be thought of as the distance from the
maximum positive deviation point to the maximum negative deviation
point with respect to an object’s equilibrium position.
Velocity: Velocity is the rate of change of displacement. Velocity
is measured in inches/second (mm/second) units.
Acceleration: Acceleration is the rate of change of velocity. Units
of measure for Acceleration is feet per second squared (meters per
Peak Amplitude: Maximum deviation of an object from its equilibrium
RMS: Root Mean Square Amplitude (RMS) is the square root of the
average of the squared values of a waveform. The RMS amplitude of
vibration is 0.707 times the peak amplitude value The RMS value of a
vibration signal is an important measure of its amplitude.