Power Cepstrum – A Power Cepstrum is the
result of taking the inverse Fourier transform of
the logarithm of the spectrum of a signal. A
Power Cepstrum converts the power spectrum
values and converts them to decibels, then
performs a FFT on the shape to produce
another spectrum. With a Power Cepstrum,
both negative and positive values display. A
Power Cepstrum contains information about
rate of change in the different spectrum bands.
It has higher, more obvious peaks, which makes
it easier for the analyst to identify, giving a
better insight into the repetition of both signals.
Power Spectrum - The squared values
(amplitude) of a spectrum (squaring of every
spectrum amplitude). When creating a power
spectrum, the units modify to the original units
and are squared (
2
).
Probe - An eddy-current sensor, although
sometimes used to describe any vibration
sensor.
Probe Gap - The physical distance between the
face of an eddy probe tip and the observed
surface. The distance can be expressed in
terms of displacement (mils, micrometers) or in
terms of voltage (millivolts), which is the value of
the (negative) dc output signal and is an
electronic representation of the physical gap
distance. Standard polarity convention dictates
that a decreasing gap results in an increasing
(less negative) output signal; increasing gap
produces a decreasing (more negative) output
signal.
Radial - Direction perpendicular to the shaft
centerline.
Radial Position -The average location, relative
to the radial bearing centerline, of the shaft
dynamic motion.
Radial Vibration - Vibration which is
perpendicular to a shaft's centerline.
Resonance - The condition of vibration
amplitude and phase change response caused
by a corresponding system sensitivity to a
particular forcing frequency. A resonance is
typically identified by a substantial amplitude
increase, and related phase shift.
RMS - The square root of the sum of a set of
squared instantaneous values.
ROUTE - A measurement POINT collection
sequence.
Run Up/Run Down - The monitoring of
machinery conditions during a start up or shut
down process.
Sensitivity - The ratio of magnitude of an
output to the magnitude of a quantity
measured. Also the smallest input signal to
which an instrument can respond.
Sensor - A transducer which senses and
converts a physical phenomenon to an analog
electrical signal.
Setpoint - (See alarm setpoint.)
Signal Analysis - Process of extracting
information about a signal's behavior in the time
domain and/or frequency domain. Describes
the entire process of filtering, sampling,
digitizing, computation, and display of results in
a meaningful format.
Spectrum - A display of discrete frequencies
and their amplitudes.
Spectrum Analyzer - An instrument which
displays the frequency spectrum of an input
signal.
Thermocouple - A temperature sensing device
comprised of two dissimilar metal wires which,
when thermally affected (heated or cooled),
produce a change in electrical potential.
Time Domain - A dynamic amplitude vs. time
graph.
Time Waveform - (See Waveform.)
Transducer - A device which translates a
physical quantity into an electrical output.
Trend - The measurement of a variable vs.
time.
Trigger - Any event which can be used as a
timing reference.
Upload - Transferring data from the measuring
device to the host computer.
Vibration - The behavior of a machine's
mechanical components as they react to
internal or external forces. Magnitude of cyclic
motion; may be expressed as acceleration,
velocity, or displacement. Defined by frequency
and timebased components.
Waveform - A presentation or display of the
instantaneous amplitude of a signal as a
function of time.
SKF Microlog - GX Series Glossary - 3
User Manual
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