Controlled balancing worksheet
Trial-Mass Force Screening
Calculate the trial unbalance and synchronous centrifugal-force magnitude created by a proposed trial mass, then compare it with an externally authorized force limit. This worksheet does not choose or certify a safe trial mass.
Proposed mass onlyNo invented ISO formulaExternal limit requiredNo 10%-of-weight rule
Documented input
Screening record
No result. Complete the controlled inputs and submit explicitly.
——
| Cantidad | Calculated value |
|---|---|
| Trial unbalance, Ut | — |
| Angular speed, ω | — |
| Synchronous force magnitude, Ft | — |
| Force / supplied limit | — |
| Force margin (limit − Ft) | — |
| Mass exactly at supplied scalar limit | — |
What the worksheet actually calculates
General mechanics identities
Tút = mt rt
ω = 2πn / 60
Ft = mt rt ω² = Utω²
ω = 2πn / 60
Ft = mt rt ω² = Utω²
Code units are kg, m, s, rad/s and N. The displayed g·mm value is the same trial-unbalance magnitude expressed in workshop units.
Comparison—not approval
R = 100 Ft / Flimit
ΔF = Flimit − Ft
mat limit = Flimit /(rtω²)
ΔF = Flimit − Ft
mat limit = Flimit /(rtω²)
The last value is only the mathematical mass at the supplied scalar limit. It is not a recommended starting mass and may still be unsafe for reasons this worksheet cannot model.
Límite de seguridad: a force below the supplied limit does not prove that a trial run is safe. This calculation cannot validate the attachment, fastener or magnet retention, guarding, rotor/bearing stress, resonances, machine condition, critical-speed passage, sensor range, personnel exclusion zone or shutdown criteria.
Why the former recommendation was removed
- The former expression multiplied rotor mass by invented support-stiffness and vibration-severity coefficients. Those coefficients had no verified primary source, were dimensionally unexplained and could increase the proposed trial mass when vibration was already severe.
- The former automatic cap of trial-mass force at 10% of rotor weight was presented as a safety rule without a verified standard or manufacturer basis. Rotor weight alone cannot establish attachment, bearing, rotor-stress or resonance limits.
- ISO 21940-11:2016 with Amendment 1:2022 addresses procedures and residual-unbalance tolerances for rotors with rigid behaviour. Its public scope does not establish the removed trial-mass formula.
- ISO 21940-13:2012 addresses criteria, safeguards and records for in-situ balancing of medium and large rotors; its public abstract explicitly says it does not give a method for calculating correction masses.
- ISO 1940-1:2003 is withdrawn and replaced by ISO 21940-11:2016. It must not be presented as the current basis for a trial-mass recommendation.
Response adequacy is measured, not predicted here: after a controlled trial run, follow the balancing instrument and approved procedure. The Schenck SmartBalancer 4 manual, for example, instructs the operator to change the test weight if the measured unbalance changes too little or by more than a factor of two. That device-specific workflow is not a universal ISO threshold.
Sources and normative status
| Fuente | Verified use | Límite |
|---|---|---|
| BIPM SI Brochure, 9th edition, version 4.01 (2026) | SI coherent units and general mechanics quantities used in the equations. | These identities are general mechanics, not an ISO trial-mass sizing rule. |
| ISO 21940-11:2016 + Amd 1:2022 | Current public lifecycle; rigid-rotor procedures and residual-unbalance-tolerance scope. | Under systematic review. Exact clauses and amendment changes require licensed controlled copies. |
| ISO 21940-13:2012 | Current confirmed public scope: in-situ balancing criteria, safeguards and records. | The public abstract says correction-mass calculation methods are outside its guidance. |
| Schenck SmartBalancer Eco manual, pp. 16–17 | Official manufacturer example and warning that a suggested trial mass may be unsuitable and could damage the machine. | Instrument-specific; the internal suggestion algorithm is not published there. |
| Schenck SmartBalancer 4 manual, v2.0, §6.2.8 | Official workflow: measure the trial response and adjust a test weight that changes unbalance too little or by more than double. | Device-specific operating guidance; not a universal acceptance rule. |
Clasificación: verified general-mechanics calculation plus comparison with a user-supplied controlled limit. No trial mass is recommended, no 10%-of-rotor-weight rule is applied and no ISO-conformity verdict is produced.
Independent check example
For a proposed 20 g mass at 650 mm and 1001 r/min, Ut = 13,000 g·mm and Ft ≈ 142.84 N. If the authorized external limit is 300 N, this is 47.61% of that supplied limit; it is no thereby certified safe.
Technical revision: 15 July 2026 · English source page · Computational guards: mass ≤ 10⁹ g, radius and speed ≤ 10⁷, force limit ≤ 10¹⁵ N. These are software guards, not equipment ratings.
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