One of the challenges in the field of free field measurements is the transport of the equipment to the location of the measurement. Furthermore, the system needs to be able to conduct a long distance measurement without neglecting the complexity of the object.
The Acoustic Camera as a self-sufficient system can localize and analyse the time and frequency of broad band and narrow band emissions.
In this case, the measurement of noise emissions of a bucket excavator in a coal mine has been performed to reduce noise pollution in a village nearby.
NoiseImage 4: Spectral Analysis , Acoustic Movie
The mobile power supply Slim MPS enables independent usage of the Acoustic Camera for up to 4 hours.
Acoustic analysis of large objects in free field during operation.
Stripping shovel of a coal strip mining.
In order to cover the whole strip mining excavator during the first measurement, the Acoustic Camera was set up at 150 m distance from the noise source. To get a close up of the derrick jib, a second measurement was carried out where the Acoustic Camera was set up at 100 m distance of it.
For a detailed analysis of the upper-side of the jib, a third measurement was done at the bank. The entire measurement session and the main analysis were performed within 3 hours directly on the strip mine.
A high-capacity, portable battery was used as power supply offering a continuous operation of more than 4 hours.
All data was treated with an A–weighting filter in order to minimize the background noise created by wind and other machines nearby the strip mine.
In the first measurement, the powerhouse was identified as the loudest source. The second loudest source was detected during the second measurement at the derrick jib. The measurement shows the main emissions on the redirection at the top of the jib and some reflections on the ground which also adds to the overall noise level in the strip mining.
The third measurement at working level of the bank pointed out that the broad band rattles were emitted by hits caused by the guides of the shovels while running onto the guide block right below the redirection. This phenomenon can be seen in the spectrogram. The detailed analysis of the broad band rattles are calculated from the marked areas of the spectrogram.
The time- and frequency-selective filtering also allows the analysis of the squeaks emitted around 900 Hz. The sources of these emissions are the shovels themselves, squeaking shortly after turning at the redirection, respectively.
