How is overall vibration level calculated from a spectrum?

The overall (broadband) vibration level is calculated as the root-sum-of-squares (RSS) of individual spectral components: Overall = √(a₁² + a₂² + ... + aₙ²). This applies to RMS amplitudes of individual frequency components.

What is the crest factor?

Crest factor is the ratio of peak value to RMS value. For a pure sine wave, CF = √2 ≈ 1.414. Higher crest factors indicate impulsive events like bearing faults. Normal machinery typically has CF = 2–4; CF > 4 may indicate developing faults.

Should I use peak or RMS amplitudes?

Use RMS amplitudes for overall level calculation. Most vibration analyzers display spectral lines as RMS values. If you have peak values, divide by √2 to convert to RMS before summing.

Why doesn't the overall level equal the sum of components?

Because vibration components at different frequencies are independent and combine as root-sum-of-squares, not arithmetic sum. The RSS method accounts for the statistical independence of different frequency components.

What units should I use?

Any consistent unit works — mm/s RMS for velocity, g RMS for acceleration, or μm for displacement. The key requirement is that all input components use the same unit and measurement type (all RMS or all peak).

Herramienta de ingeniería gratuita — #014

Calculadora de nivel general de vibración

Calcule el nivel general de vibración a partir de los componentes del espectro mediante la raíz de la suma de cuadrados. Ingrese hasta 10 valores de amplitud y un valor pico opcional para el factor de cresta.

Método RSS Factor de cresta Hasta 10 componentes

Resultados

Nivel RMS general

—

Factor de cresta

—

Número de componentes

—

Componente dominante

—

Contribución dominante

—

Raíz de la suma de cuadrados (RSS)

El nivel general de vibración a partir de componentes espectrales independientes es:

Donde a_i son las amplitudes RMS de los componentes espectrales individuales.

Factor de cresta

CF = √2 ≈ 1.414 — Onda sinusoidal pura
CF = 2–4 — Maquinaria normal
CF > 4 — Eventos impulsivos (defectos de rodamiento)
CF > 6 — Impacto severo o holgura mecánica

Ejemplo práctico

Ejemplo: bomba centrífuga

Componentes espectrales (mm/s RMS): 3.2, 1.8, 0.9, 0.4, 0.2

General = √(3.2² + 1.8² + 0.9² + 0.4² + 0.2²) = √(10.24 + 3.24 + 0.81 + 0.16 + 0.04)

General = √14.49 = 3.81 mm/s RMS

Si pico = 8.5 mm/s → CF = 8.5 / 3.81 = 2.23 (normal)

ℹ️ Nota: El componente dominante (1×, por lo general) suele contribuir más al nivel general. Si un componente es mucho mayor que los demás, el nivel general ≈ la amplitud de ese componente.