2. Measurements and analysis of diagnostic signals.
Is it possible to increase the monitoring and diagnostics
systems' efficiency by using directional microphones for remote noise
measurements at least in the measurement points that have no access for direct
vibration measurements? The question was asked by the employees of maintenance
teams of October railway (Russia).
The question is answered by
Alexej V. Barkov:
Yes, it is, but only partly. There will be a loss of
information in this case that is determined by the following main reasons:
A high level of acoustical interference caused by multiple
reflection of the audio waves. This interference will be more severe when
the weak vibration sources, and hence the noise, are measured when in the
compartment there are other powerful sources of noise.
It is impossible to measure the noise in the nearest zone of the source (pseudonoise
and pseudovibration) that gives the main volume of information about the
incipient defects. Here the pseudonoise and pseudoviabrartion means the
noise and vibration components that can be identified just near the source,
when the distance is less than the quarter of the vibroacoustical wave, but
on larger distances they are absent because of the mutual compensation of
oscillations generated in different points of the source.
However, the mentioned causes do not limit the possibilities of using the
directional microphones in monitoring systems that are not intended to
detect all the main defects on their incipient stage of development.
Nowadays many R&D works are made in the field of using the directional
microphones in monitoring systems especially for transport vehicle
monitoring during its movement, and mainly on the railways.