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2. Measurements and analysis of diagnostic signals.

Question 2.5.

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:

  1. 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.

  2. 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.



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