Bearing Vibration Frequency Inputs
Example Data Table
| Machine | Shaft RPM | Elements | Ball Dia. (mm) | Pitch Dia. (mm) | Contact Angle (°) | Slip (%) |
|---|---|---|---|---|---|---|
| Pump Drive A | 1800 | 8 | 10 | 50 | 0 | 0 |
| Fan Assembly B | 1450 | 9 | 11 | 58 | 15 | 1.5 |
| Gearbox Input C | 2960 | 10 | 9 | 46 | 20 | 2.0 |
Formula Used
This calculator estimates common bearing defect frequencies for vibration analysis. Shaft frequency converts shaft speed from RPM to Hz first.
fr = RPM / 60
FTF = 0.5 × fr × (1 - (Bd / Pd) × cosθ)
BPFO = (N / 2) × fr × (1 - (Bd / Pd) × cosθ)
BPFI = (N / 2) × fr × (1 + (Bd / Pd) × cosθ)
BSF = (Pd / (2 × Bd)) × fr × (1 - ((Bd / Pd) × cosθ)^2)
Here, fr is shaft frequency, N is rolling element count, Bd is rolling element diameter, Pd is pitch diameter, and θ is contact angle. Slip correction scales the result when measured systems deviate slightly.
How to Use This Calculator
- Enter shaft speed in RPM.
- Provide the number of rolling elements.
- Enter rolling element diameter and pitch diameter.
- Set the contact angle from bearing geometry.
- Choose how many harmonics you want listed.
- Add slip correction if field measurements require adjustment.
- Press Calculate Frequencies to view results above the form.
- Use the CSV or PDF buttons to export results.
FAQs
1. What does this calculator measure?
It estimates bearing characteristic frequencies used in vibration diagnostics. These frequencies help identify outer race, inner race, ball spin, and cage defects.
2. Why is shaft speed converted to Hz?
Vibration spectra are commonly analyzed in Hertz. Converting RPM to Hz makes defect frequencies easier to compare with FFT peaks and measured vibration data.
3. What is BPFO?
BPFO means Ball Pass Frequency Outer race. Strong peaks near this value often indicate damage or repeated impacts on the outer race path.
4. What is BPFI?
BPFI means Ball Pass Frequency Inner race. Peaks near BPFI can suggest inner race defects, especially when sidebands appear around running speed.
5. What is BSF?
BSF means Ball Spin Frequency. It relates to rolling element spin and can indicate ball or roller defects when harmonics or modulation patterns appear.
6. What is FTF?
FTF means Fundamental Train Frequency. It represents cage rotation and is useful when diagnosing cage looseness, wear, or instability.
7. Why would I use slip correction?
Real machines may not match ideal geometry perfectly. Slip correction lets you tune calculated frequencies closer to observed spectral peaks from field data.
8. Are these values exact fault confirmations?
No. They are diagnostic targets. Always compare them with measured spectra, harmonics, sidebands, load conditions, and supporting inspection evidence.