Performing Constant-Speed Bearing Fault Detection (Sound and Vibration Measurement Suite)
December 2007
NI Part Number:
372416A-01
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The following example demonstrates how to use the OAT Envelope Detection VI to perform constant-speed bearing fault detection.
The bearing under test has eight balls as the rolling elements. The diameter of each ball is 0.2813 inches, and the pitch diameter is 1.1228 inches. The contact angle between the ball and the race is 0 degrees. The rotational speed of the bearing is 1,234 RPM. You can use these parameters to calculate the characteristic frequencies of the bearing, as shown in the following table.
| Characteristic Bearing Frequency | Value |
|---|---|
| Fundamental train frequency | 7.7 Hz |
| Ball spin frequency | 38.48 Hz |
| Outer race frequency | 61.6 Hz |
| Inner race frequency | 102.9 Hz |
An accelerometer mounted on the bearing casing measures the vibration signal of the bearing. The following front panel shows the power spectrum of the vibration signal.
Because the rotational speed is constant and the vibration signal is on only one channel, use the Waveform Output 1 Channel instance of the OAT Envelope Detection VI to perform envelope detection on the bearing. In the front panel above, noise dominates the frequency band below 3000 Hz. Therefore, select a frequency in the middle frequency range as the center frequency. In this example, set the center frequency [Hz] input to 4800, and set the span [Hz] input to 500. Run the OAT Envelope Detection VI to acquire the envelope signal of the vibration signal.
Use the SVFA Power Spectrum VI to compute the frequency power spectrum of the resulting envelope signal, as shown in the following front panel.
Notice that the Frequency power spectrum of envelope signal plot contains a peak around 60.7 Hz. This value is similar to the outer race frequency of 61.6 Hz. The Frequency power spectrum of envelope signal plot also contains a peak at a harmonic, around 121.4 Hz, of twice the characteristic frequency. From these peaks, you can identify an outer race fault on the bearing. The actual outer race frequency is slightly different from the calculated frequency because of slippage.
Refer to the Envelope Detection Constant Speed (Offline) VI in the labview\examples\Order Analysis\Fault Analysis directory for an example of using the OAT Envelope Detection VI to perform constant-speed bearing fault detection.