Belt Frequency
Why is 2× belt frequency often the dominant peak in vibration spectra?
Because belt defects (e.g., cracks, seam issues) typically cause impacts twice per revolution of the belt loop—once at each pulley—amplifying the 2× harmonic.
How does belt natural frequency differ from belt pass frequency?
Belt pass frequency is the forcing frequency (rate of a point passing a fixed point); natural frequency is the belt’s inherent transverse vibration mode determined by tension span length and mass, used to calculate tension via T = 4f²l²m.
Can belt frequency be used for timing belts vs. V-belts?
For timing (synchronous) belts, frequency is often Pulley RPM × teeth count (mesh frequency); for V-belts, use (π × D × RPM) / L; terms are frequently confused, so distinguish belt natural, mesh, and defect frequencies.
Belt Frequency, also known as belt pass frequency or belt rate, is the rate at which a specific point on a belt loop passes a fixed reference point. It is calculated as the belt's linear speed divided by its total length and is always sub-synchronous, meaning it is less than the RPM of either the motor or driven sheave. The formula is Belt Frequency (Hz) = (π × D × RPM) / L, where D is the pitch diameter of the sheave, L is the belt length, and RPM is the sheave speed.
In shop floor maintenance, belt frequency is used in vibration analysis and motor current signature analysis (MCSA) to detect belt-related faults. Peaks at 1× belt frequency and harmonics, especially 2× belt frequency, indicate issues like misalignment, tension loss, or belt damage. In CMMS systems, belt frequency is tracked as a diagnostic threshold for predictive maintenance alerts. Technicians verify belt tension by measuring the belt's natural frequency using a tachometer or Clavis meter and adjusting until it matches the target frequency to prevent resonance. When belt frequency is present, technicians first check tension and sheave alignment, then inspect for defective belts, eccentric sheaves, or bad belt seams.
Misaligned sheaves cause uneven loading, premature wear, and high-amplitude peaks at belt frequency and harmonics.
Excessive or improper tension: too loose leads to slippage and resonance; too tight increases bearing load and accelerates wear, shifting natural frequency and exciting resonance.
Eccentric sheaves or defective belt seams generate periodic impacts detectable as belt frequency peaks, often mistaken for unbalance due to proximity to 1× turning speed.