-
The unit of amplitude measurement is
acceleration but the signal is processed differently than a conventional
acceleration signal is.
-
The names for the amplitude unit are
manufacturer specific - they each have their own name and/or acronym for
the unit. A few of the manufacturers are:
-
CSI (Emerson)
uses Peakvue
-
Entek (Rockwell
Automation) uses gSE (spike energy - the original IRD acronym)
-
SKF uses HFD (high
frequency domain) and ESP (envelope signal processing - originally a DI
unit)
-
Filters are used to help process the
signal and focus on any impacts that may be occurring.
-
The filters come in two classes:
-
Envelope filter
- this type of filter sets a frequency 'envelope' that includes a high
frequency (Fmax) and a low frequency (Fmin). Any vibration occurring
outside
that range is filtered out.
-
Hi-Pass filter
- this type of filter eliminates the Fmax but still sets an Fmin filter
below
which all vibration influences are filtered out.
-
Each manufacturer
sets up its own signal processing and filters. Therefore, although they
each provide similar information, they are not directly comparable
in the amplitude realm.
-
The signal processing focuses on the
transient, impact type events (spikes on the time domain signal) that the
FFT process "misses" (it would be more accurate to say "makes more difficult
to find") due to the way it processes the time signal.
-
If there is a consistent period between
impacts (i.e. the impacts are occurring at a regular interval), that period
will be converted into the desired frequency units (Hz or cpm).
-
The intensity of the impacts will also
be assessed. This is related to the size of the impact spike on the signal
versus any background noise occurring.
-
The results are displayed on a spectrum
with amplitude peaks at the frequency(s) they are occurring at.
|
