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).

免費工程工具 — #014

整體振動等級計算器

使用方根和法（RSS）從頻譜分量計算整體振動級。輸入最多 10 個振幅值，以及用於計算波峰因數的選填峰值。

方根和法（RSS）峰值因數最多 10 個分量

結果

整體 RMS 級

—

峰值因數

—

分量數量

—

主要分量

—

主要貢獻

—

方根和（RSS）

來自獨立頻譜分量的整體振動級為：

其中 a_i 為個別頻譜分量的 RMS 振幅。

峰值因數

CF = √2 ≈ 1.414 — 純正弦波
CF = 2–4 — 正常機械
CF > 4 — 衝擊事件（軸承缺陷）
CF > 6 — 嚴重衝擊或鬆動

實務範例

範例 — 離心泵

頻譜分量（mm/s RMS）： 3.2, 1.8, 0.9, 0.4, 0.2

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

整體 = √14.49 = 3.81 mm/s RMS

若峰值 = 8.5 mm/s → CF = 8.5 / 3.81 = 2.23 （正常）

ℹ️ 注意： 主要分量（通常為 1×）通常對整體級貢獻最大。若某一分量遠大於其他分量，則整體級 ≈ 該分量的振幅。

整體振動級計算器 | 來自頻譜的 RMS

結果

方根和（RSS）

峰值因數

實務範例

商店

支撐

聯絡我們