Diagnostics of gear units based on spectrum of envelope curve

Diagnostics of gear units

Based on spectrum of envelope curve

In case of occurrence and development of a defect on a rotating element, an amplitude modulation equal to a rotational frequency should be observed in the noise bands connected with the signals induced by such defect. The degree of modulation depends on the level of defect development. The program — envelope curve is used for search and analysis of such faults. This program is implemented as follows.

A user configures a digital filter (appearance of the signal filtering program is shown in Figure 1) — a central filter frequency and filter bandwidth. Then the filter with the preset parameters processes an input stream of digitized data. After the filter circuit a sensor and integrator operates. The output signal after processing can be checked in the form of graph. Figure 2 shows the graphs of signals: original signal, signal after the filter and envelope curve of the vibration pickup’s signal. The bandwidth is equal to 200 Hz, the central filter frequency is 3 kHz — the first gear-meshing frequency.

Diagnostics of Gear Units Based on Spectrum of Envelope Curve

Figure 1

Diagnostics of Gear Units Based on Spectrum of Envelope Curve

Figure 2

Fourier transformation is used to extract a periodic component from the amplitude signal envelope, which results in the spectrum of amplitude envelope. Figure 3 shows the graph of amplitude envelope spectrum. The graph contains a peak at the frequency of about 90 Hz equal to the shaft speed. The high level of this peak shows a great degree of modulation of vibration pickup’s signal at the gear-meshing frequency and therefore it suggests the degree of axial asymmetry of gear pair.

Diagnostics of Gear Units Based on Spectrum of Envelope Curve

Figure 3

The level of amplitude envelope modulation and, hence, the level of envelope spectrum allows judging the degree of defect development and using this method for troubleshooting and output products inspection.

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