Acoustic monitoring of machinery
Monitoring of a machine is performed by an acoustic monitor which acquires, through an acoustic sensor, acoustic signals from a vicinity of a machine, while the machine is operative. A processor calculates a frequency spectrum of a segment of the acquired acoustic signals, determines boundaries of a frequency band to be analyzed and extracts, from the calculated frequency spectrum, a base frequency window in the determined boundaries, and one or more harmonics windows of harmonics of the determined boundaries. For each of the base and harmonic windows a weight based on a distribution of values of frequencies in the windows is determined and a parameter of operation of the machine is calculated as a function of a weighted sum of the base and harmonic windows. The operation of the machine is evaluated responsive to the calculated parameter.
1. A method of monitoring a machine, comprising:
acquiring, by an acoustic sensor, acoustic signals from a vicinity of a machine, while the machine is operative;
calculating, by a processor, a frequency spectrum of a segment of the acquired acoustic signals;
determining boundaries of a frequency band to be analyzed;
extracting, from the calculated frequency spectrum, a base frequency window in the determined boundaries, and one or more harmonics windows of harmonics of the determined boundaries;
determining for each of the base and harmonic windows a weight based on a distribution of values of frequencies in the windows;
calculating a parameter of operation of the machine as a function of a weighted sum of the base and harmonic windows; and
providing feedback on the operation of the machine, responsive to the calculated parameter, on a display coupled to the processor.
2. The method of claim 1 , comprising generating an alert, responsive to a determination that the calculated parameter is outside a predefined range of values for the parameter.
3. The method of claim 1 , comprising generating an alert, responsive to a determination that the calculated parameter is different than a corresponding value reported by a controller of the machine.
4. The method of claim 1 , wherein calculating the operation parameter comprises determining a frequency in the weighted sum of the windows having a maximal power.
5. The method of claim 1 , wherein calculating the operation parameter comprises determining a ratio between power in a segment around a given frequency in the weighted sum of the windows and a measure of power outside the segment.
6. The method of claim 1 , wherein determining a weight for each window comprises determining a frequency-domain entropy of the window.
7. The method of claim 1 , wherein further comprising determining a time until a required maintenance of the machine, as a function of the calculated parameter.
8. The method of claim 1 , further comprising automatically changing an operation state of the machine responsive to the calculated parameter.
9. The method of claim 5 , wherein determining the ratio comprises calculating a numerator of the ratio as a power in frequency segments around an operation frequency of the machine and one or more harmonics of the operation frequency.
10. The method of claim 9 , wherein the operation frequency comprises a frequency corresponding to a time period of a single cog of a gear of the machine.
11. The method of claim 10 , wherein providing the feedback comprises automatically providing an estimate of a time to a required replacement of the gear.
12. The method of claim 9 , wherein the operation frequency comprises a frequency corresponding to an entire cycle of a gear of the machine.
13. The method of claim 12 , wherein providing the feedback comprises determining that the ratio is in a predetermined range and providing an alert of a broken gear cog responsively to the determining.
14. The method of claim 5 , wherein determining the ratio comprises calculating a denominator of the ratio as a power of the entire frequency spectrum.
15. The method of claim 5 , wherein determining the ratio comprises calculating a denominator of the ratio as a power of the frequency spectrum not included in the segments.
16. The method of claim 5 , wherein calculating the frequency spectrum comprises extracting a sample of a given duration from the acquired signals and calculating the frequency spectrum from the extracted sample.
17. The method of claim 16 , wherein extracting the sample comprises extracting at times defined by an electrical timing signal from the machine.
18. An acoustic machine monitor, comprising:
an acoustic sensor for acquiring acoustic signals from a vicinity of a machine, while the machine is operative; and
a processor configured to calculate a frequency spectrum of a segment of the acquired acoustic signals, to determine boundaries of a frequency band to be analyzed, to extract from the calculated frequency spectrum, a base frequency window in the determined boundaries, and one or more harmonics windows of harmonics of the determined boundaries, to determine for each of the base and harmonic windows a weight based on a distribution of values of frequencies in the windows, to calculate a parameter of operation of the machine as a function of a weighted sum of the base and harmonic windows, and to provide feedback on the operation of the machine, responsive to the calculated parameter.
19. The monitor of claim 18 , wherein the processor is configured to generate an alert, responsive to a determination that the calculated parameter is outside a predefined range of values for the parameter.