What is minimum detectable unbalance (Umin)?

Umin is the smallest unbalance that a balancing machine can reliably detect and display. It depends on the machine type, sensor sensitivity, display resolution, rotor mass, and balancing speed. A lower Umin means better sensitivity.

What is the difference between soft and hard bearing balancing machines?

Soft bearing machines operate below the first critical speed of the rotor-bearing system, measuring displacement. Hard bearing machines operate well below critical speed with stiff supports, measuring force. Hard bearing machines are generally faster to set up but may have slightly lower sensitivity for light rotors.

How does rotor mass affect achievable balance grade?

For a given Umin, a heavier rotor will have a better (lower) achievable residual specific unbalance (e = Umin/m). This means heavier rotors can potentially achieve better balance grades on the same machine.

What balance grades can typical machines achieve?

High-quality industrial balancing machines typically achieve G1.0 to G2.5. Laboratory-grade machines can achieve G0.4 or better. The achievable grade also depends on rotor speed — higher speeds make finer grades easier to achieve.

How is machine sensitivity verified per ISO 21940-21?

Machine sensitivity is verified by placing a known test unbalance on a proving (test) rotor and confirming the machine can detect and display it correctly. The test is repeated at different angular positions and the results must be within specified tolerances, following the Umar and URR test procedures of ISO 21940-21 (formerly ISO 2953).

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動平衡機靈敏度計算器

依據 ISO 21940-21（前 ISO 2953）計算軟支承或硬支承動平衡機的最小可檢出殘餘不平衡 (Umin) 與可達平衡等級。

ISO 21940-21Umin軟支承 / 硬支承

結果

最小可檢出殘餘不平衡 (Umin)

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剩餘比不平衡 (eper)

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可達平衡等級

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不平衡減小率 (URR)

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工作轉速 ω

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最小可檢出殘餘不平衡

動平衡機的最小可檢出殘餘不平衡 (Umin) 取決於感測器靈敏度、電子噪聲底噪與顯示解析度：

可達平衡等級

其中 ω 為 工作轉速 （非動平衡轉速）下的角速度。

實用規則： Umin 應遠低於允許殘餘不平衡 (Uper) — 通常不超過約 10% — 以免測量不確定度主導結果。動平衡機本身依據 ISO 21940-21（前 ISO 2953）進行描述與評估，該標準定義了最小可達殘餘不平衡 (Umar) 與不平衡衰減比 (URR) 測試。

平衡機靈敏度計算機 | ISO 21940-21

結果

最小可檢出殘餘不平衡

可達平衡等級

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