Vibration-diagnostics engine for reliability engineers: characteristic defect frequencies from bearing geometry — ball pass outer (BPFO), ball pass inner (BPFI), ball spin (BSF) and fundamental train frequency (FTF) — in Hz and shaft orders, with harmonics, ±1× sidebands, a stem-spectrum preview and frequency-vs-speed sensitivity. Preset geometry database for common 62xx/63xx bearings plus full custom entry. Every report with the full audit trail.
SectorCalc SC-024 computes the characteristic defect frequencies of a rolling-element bearing from its internal geometry: how many times per shaft revolution the rolling elements pass a point on the outer race (BPFO), on the inner race (BPFI), the rolling element spin frequency (BSF) and the cage rotational frequency (FTF). A localized defect generates vibration at exactly these kinematic rates — matching them against a measured spectrum is the foundation of bearing condition diagnosis. Results carry a 1–2 % kinematic slip allowance in practice; always confirm bearing geometry from the manufacturer's datasheet before condemning a machine.
The cage rotates at roughly half shaft speed because each element rolls between two races. The exact ratios depend only on three numbers: element count Nb, element diameter Bd, and pitch diameter Pd — plus the contact angle φ for angular-contact and thrust bearings. Note that (Bd/Pd)·cosφ appears in every formula; most deep-groove bearings sit near 0.18–0.23, which is why BPFO always lands at 3–5× and BPFI at 4–7× shaft speed.
All in shaft orders — multiply by n/60 for Hz. A quick sanity identity: BPFO + BPFI = Nb exactly. If your computed pair does not sum to the element count, an input is wrong.
Real defects rarely appear as single lines. An inner-race defect rotates through the load zone, so BPFI is amplitude-modulated at 1× shaft speed — expect BPFO ±0 lines but BPFI flanked by ±1× sidebands. Cage damage modulates at FTF. The engine lists the sideband set for the modulation source you select.
Diagnostic sequence: (1) confirm actual shaft speed with a tachometer — a 2 % speed error shifts every line; (2) look for harmonics: a single BPFO line is early-stage, a harmonic series with raised noise floor is advanced; (3) BPFI with ±1× sidebands is the classic inner-race signature; (4) BSF usually appears with its 2× harmonic and FTF sidebands; (5) sub-synchronous lines near 0.4–0.5× are NOT bearing defects — check looseness, rub or oil whirl.
Elements skid 1–2 % under light load, so measured lines land slightly below the computed values. Preset geometry is catalog-typical; internal geometry varies between manufacturers and series revisions. For a legal-grade diagnosis (warranty claim), pull the exact geometry from the bearing manufacturer's engineering datasheet and re-run with custom entry.
Very likely yes. Rolling-element slip of 1–2 % is normal, especially under light radial load. The pattern (BPFI + harmonics + ±1× sidebands) matters more than the exact frequency match.
A defect on a rolling element hits both races per spin, so the 2×BSF harmonic often dominates over the fundamental. Expect FTF sidebands around it.
At φ = 0°, barely. Under axial load a deep-groove bearing develops 10–20° effective contact angle, shifting BPFO/BPFI by a few tenths of a percent — negligible for diagnosis, but use the real angle for angular-contact (72xx/73xx) or tapered bearings.
No — frequencies tell you WHERE to look in the spectrum, not whether the machine is failing. Severity needs amplitude, trend history, and envelope/demodulation analysis. This tool supplies the kinematic truth table; the diagnosis is yours.
