Introduction
The spectrum of a gearbox signal will
usually consist of a number of harmonic families. These harmonic families originate from the different
shafts and ball-bearings in the gearbox, and from the tooth meshing frequencies of the gears. The gears
usually have numbers of teeth equal
to prime numbers. This is an advantage as it causes wear to be spread
out more evenly on the teeth of the
gears, but it is also an advantage
from a measurement point of view, as
it means that the different harmonic
families will usually not overlap. On
the other hand, there can often be
several harmonic families, and it can
be difficult to separate them in the
spectrum. Cepstrum is a practical
tool that makes it easy to find these
different harmonic families, and the
individual families can be monitored
for changes that might indicate that
something is wrong.
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