Performing Variable-Speed Bearing Fault Detection (Sound and Vibration Measurement Suite)
December 2007
NI Part Number:
372416A-01
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You can use the OAT Envelope Detection VI to perform variable-speed bearing fault detection, for example in a run-up test. When the rotational speed of a bearing varies, the characteristic frequencies change in proportion to the rotational frequency. The characteristic orders are constant values because they are functions of the geometric parameters of the bearing. Therefore, use the characteristic orders to perform variable-speed bearing fault detection.
Use the same parameters of the ball diameter, pitch diameter, and contact angle as in the constant-speed test to calculate the characteristic orders of the bearing, as shown in the following table.
| Characteristic Order | Value |
|---|---|
| Fundamental train order | 0.375 |
| Ball spin order | 1.871 |
| Outer race order | 2.998 |
| Inner race order | 5.002 |
In this run-up test, the shaft speed increases from 860 RPM to 1,450 RPM. Because the rotational speed is variable and the vibration signal is on only one channel, use the Even-Angle Signal Output 1 Channel instance of the OAT Envelope Detection VI to calculate the even-angle envelope signal of the vibration signal. For rolling-element bearing fault detection, always set the unit of the center frequency/order input to Hz. In this example, set the value of the center frequency/order input to 4800. Set the span [Order] input to 20. Then run the VI to acquire the envelope signal of the vibration signal.
Use the OAT Order Power Spectrum VI to compute the order power spectrum of the resulting even-angle envelope signal, as shown in the following front panel.
Notice that the Order power spectrum of envelope signal plot contains a peak around the 2.95th order. This value is similar to the outer race order of 2.998. The Order power spectrum of envelope signal plot also contains a peak at a harmonic, around the 5.9th order, of the characteristic order. From these peaks, you can identify an outer race fault on the bearing. The actual outer race order is slightly different from the calculated order because of slippage.
Refer to the Envelope Detection Variable Speed (Offline) VI in the labview\examples\Order Analysis\Fault Analysis directory for an example of using the OAT Envelope Detection VI to perform variable-speed bearing fault detection.