Gratis tekniskt verktyg #037
Kalkylator för bladpassfrekvens
Calculate the kinematic passage frequency for a known integer blade or vane count and measured shaft speed. Frequency alone does not predict amplitude or identify a fault.
Resultat
BPF-övertoner
| Harmonisk | Frekvens (Hz) | Order (× axel) | Period (ms) |
|---|
Passage frequency
Z is the integer number of recurring rotor elements, n is shaft speed in r/min, and fs is shaft rotational frequency. For a fixed observation point, Z equally recurring elements produce Z passages per revolution. ANSI/AMCA 301-22 gives this same fan blade-pass equation in its sound-rating method (Eq. 5.7).
Övertoner och sidband
The table lists mathematical integer harmonics h·fBPF. Real spectra may contain BPF, harmonics and modulation components, but their presence and amplitude depend on rotor/stator geometry, flow, loading, sensor location, structure and acoustic response. A calculated line is a frequency marker, not a predicted spectral amplitude.
Diagnostic boundary
Do not diagnose from one line. A BPF peak, its harmonics or shaft-spaced sidebands do not uniquely prove clearance error, blade damage, fouling, resonance, recirculation or cavitation. Compare like-for-like operating points with baseline/trend data and use corroborating phase, waveform, pressure, acoustic, process and inspection evidence. Cavitation assessment also requires hydraulic operating and NPSH evidence.
Worked calculation
fs = 2950/60 = 49.1667 Hz
fBPF = 6 × 49.1667 = 295 Hz
Period = 1/295 = 3.3898 ms; 2×BPF = 590 Hz; 3×BPF = 885 Hz.
Sources and standard scope
- ANSI/AMCA Standard 301-22, Eq. 5.7 — fan blade-pass frequency.
- NASA technical report 20030064154 — BPF/harmonics in rotor–stator forced response and modulation context.
- Grundfos cavitation reference — cavitation and NPSH context.
Omfattning: steady shaft speed and one integer count of equally recurring elements. Variable speed smears or sweeps the frequency; nonuniform pitch can create additional components. This calculator is not an ISO severity or acceptance assessment.
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