Calculator Inputs
This layout is single-column overall, with responsive input grids: three columns on large screens, two on medium screens, and one on small screens.
Example Data Table
| Case | RPM | n | d (mm) | D (mm) | θ (°) | Expected Use |
|---|---|---|---|---|---|---|
| Pump Motor A | 1800 | 8 | 10 | 50 | 0 | General vibration screening |
| Fan Bearing B | 1480 | 9 | 9.5 | 46 | 10 | Envelope spectrum comparison |
| Gearbox Input C | 2950 | 11 | 7.8 | 38 | 15 | High-speed condition monitoring |
Formula Used
Shaft frequency: \( f_r = \dfrac{RPM}{60} \)
BPFO: \( \dfrac{n}{2} \cdot f_r \cdot \left(1 - \dfrac{d}{D}\cos\theta\right) \)
BPFI: \( \dfrac{n}{2} \cdot f_r \cdot \left(1 + \dfrac{d}{D}\cos\theta\right) \)
BSF: \( \dfrac{D}{2d} \cdot f_r \cdot \left(1 - \left(\dfrac{d}{D}\cos\theta\right)^2\right) \)
FTF: \( \dfrac{1}{2} \cdot f_r \cdot \left(1 - \dfrac{d}{D}\cos\theta\right) \)
Slip-adjusted value: Base frequency × \(1 - \text{slip\%}/100\)
Here, n is the number of rolling elements, d is rolling element diameter, D is pitch diameter, and θ is the contact angle. These formulas are standard first-pass bearing kinematic relations used in vibration analysis and machine condition monitoring.
How to Use This Calculator
- Enter shaft speed in RPM.
- Input the number of rolling elements in the bearing.
- Provide rolling element diameter and pitch diameter in matching units.
- Add contact angle in degrees. Use zero for many radial cases.
- Set harmonics and graph range for spectral review.
- Optionally apply a slip percentage and relative amplitudes.
- Press the calculate button to display results above the form.
- Use CSV or PDF export to save results and harmonic data.
Why these frequencies matter
Bearing defects create repeating vibration events. Each defect type produces a characteristic frequency pattern. Comparing measured spectrum peaks against BPFO, BPFI, BSF, FTF, and their harmonics helps isolate probable outer race, inner race, rolling element, or cage faults before failure becomes severe.
FAQs
1) What does BPFO mean?
BPFO means Ball Pass Frequency Outer race. It estimates how often rolling elements strike or pass a defect on the outer race during each second of operation.
2) What does BPFI mean?
BPFI means Ball Pass Frequency Inner race. It estimates the repetition rate associated with an inner race defect and often appears with sidebands around shaft speed.
3) What is BSF in bearing analysis?
BSF is Ball Spin Frequency. It reflects how quickly a rolling element spins around its own axis and helps identify defects on the balls or rollers.
4) What is FTF?
FTF is Fundamental Train Frequency. It relates to cage rotation and is commonly used to assess cage defects, instability, or lubrication issues.
5) Why is contact angle included?
Contact angle changes the effective kinematics of the rolling elements. As the angle increases, the projected geometry changes and defect frequencies shift accordingly.
6) Are these results exact for every bearing?
No. Real machines may show slip, load changes, lubrication effects, manufacturing tolerances, and measurement noise. These values are strong diagnostic estimates, not perfect spectral matches.
7) Why should I check harmonics?
Defect signatures often appear at integer multiples of the main bearing frequency. Harmonics can be stronger than the base line in envelope or acceleration spectra.
8) Can this tool replace vibration testing?
No. It supports diagnosis by predicting likely frequencies. You still need measured vibration, spectrum analysis, operating context, and maintenance history for confident conclusions.