17
18.0 GLOSSARY (for vibration purposes)
Acceleration
A scalar quantity that specifies time rate of change of
velocity; expressed in either g‑force (g) or m/sec
2
where 1 g
= 3.86.1 in/sec
2
and 9.8066 m/sec
2
Acceleration
Enveloping
A high‑frequency, filtered data collection method expressed
in gE
Accelerometer
A transducer which converts acceleration motion into an
electrical output
Amplitude
The magnitude of vibratory motion; can be measured as
peak‑to‑peak, zero‑to‑peak, or RMS
Axial
The direction parallel to the axis of rotation
Baseline
Recorded values taken when a machine is known to be
good; the standard to which all additional readings will be
compared
CPM
Unit of frequency measurement — cycles per minute
Displacement
A scalar quantity specifying the change of position of a body
measured from the resting position
Dynamic Force
A force that varies with time
Force
Energy applied to a mass producing a deflection (static
force) or motion (dynamic force)
Frequency
The repetition rate of a periodic event, expressed in cycles
per second (Hz), CPM, RPM, or multiples of running speed
(orders)
g’s
Units of acceleration referenced against the force of gravity
(1 g = 32.1739 ft./sec/sec; 1 g = 9.8066 m/sec/sec)
Gear Mesh
Frequency
A frequency generated by a gear; defined as the number of
gear teeth on a gear times its shaft‑rotating frequency
Hertz (Hz)
A unit of frequency measurement, cycles per second
High‑Pass Filter
A filter that allows only those components above a selected
frequency to pass
