Hello All,
I am coming up the curve on doing condition assessment
on motors by analyzing the modulation of the AC power
source caused by the elements of a running motor; that
is, defects within the motor modulate the current. In
its simplest form, this involves doing a spectral
analyis on both the current and voltage signal and
assessing the dB difference between the two at the
rotating fundamental and harmonics to determine the
condition of the rotor bars... the magnitude of the
delta between voltage and current serves as an
indicator of the condition of the rotor bars. Other
types of motor conditions, such as rotor eccentricity
are apparently more difficult to extract. They are
signals buried in the noise that are not necessarily
at the fundamental and it is necessary to remove the
fundamental and its harmonics.
In literature I have read so far, it is mentioned that
one technique for extracting these "modulated" signals
is to perform an "rms demodulation". Think in terms
of AM modulation and demodulation... only in this case
the carrier is the 50 or 60 Hz power source. This
demodulation, apparently, can be done with front end
hardware or as a dsp technique.
Has anyone had experience in this area. Especially
with algorithms to perform the rms demodulation in
software? I have had no luck in my web or literature
searches.
Regards,
Max Harbor
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