Free Engineering Tool
Permissible Residual Unbalance Calculator
Calculate permissible residual unbalance for a rigid rotor using ISO 21940-11. Enter rotor mass, maximum service speed, and the specified balance quality grade.
Results
Permissible Specific Unbalance
Per ISO 21940-11, the permissible specific unbalance (eccentricity) is:
- G — balance quality grade (mm/s)
- n — maximum service speed (RPM)
- ω — angular velocity (rad/s)
Total Permissible Residual Unbalance
Where m is rotor mass in kg. Result Uper is in g·mm when eper is in μm and m in kg.
Balance Quality Grades
| Grade | e·ω (mm/s) |
|---|---|
| G0.4 | 0.4 |
| G1.0 | 1.0 |
| G2.5 | 2.5 |
| G6.3 | 6.3 |
| G16 | 16 |
| G40 | 40 |
| G100 | 100 |
| G250 | 250 |
| G630 | 630 |
| G1600 | 1600 |
| G4000 | 4000 |
Practical Example
Given: Rotor mass = 120 kg, Speed = 1500 RPM, Grade = G6.3
ω = 2π × 1500 / 60 = 157.08 rad/s
eper = 6.3 × 1000 / 157.08 = 40.11 μm
Uper = 40.11 × 120 = 4,813 g·mm
Per-plane (2 planes, 50/50): 4,813 / 2 = 2,407 g·mm
⚠️ Note: For disc-like rotors, 50/50 split between planes is acceptable when CG is centered. For long rotors, use the lever rule based on actual CG position relative to correction planes.
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Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
