Documented criterion required — no ISO tolerance generation
Documented Flexible-Rotor Criterion Arithmetic Check
Compare one measured balance quantity with one documented limit that already applies to the same rotor,mode or tolerance plane,speed,state and quantity definition.
Arithmetic comparison
Arithmetic only
margin=documented−measured
f=n/60; ω=2πn/60
“Within entered limit” means only that one entered number does not exceed another entered number on the declared same basis. It is not an ISO acceptance result or proof of satisfactory running behaviour.
ISO21940-12 flexible-rotor scope
ISO21940-12:2016,edition1,was confirmed in2025 and remains current. It presents typical flexible-rotor configurations,balancing procedures,final-state assessment methods and guidelines for balance-quality criteria. ISO states that it is not an acceptance specification,that structural resonances are outside its scope,and that its industrial experience may not apply directly to specialized equipment. Edition2 is under development and will replace the2016 edition when published.
Why the former formulas were removed
ISO21940-11:2016 সাথে Amendment1:2022 covers rotors with rigid behaviour and explicitly excludes flexible behaviour. Therefore its G-grade residual-unbalance relation cannot be relabelled as a flexible-rotor modal tolerance. No official source was found for dividing that result equally by “modes+1” or prescribing “modes+2” correction planes universally.
ISO21940-14:2012+Amd1:2022 addresses identifying,assessing and accounting for balance-measurement errors;edition2 is under development. This page does not implement its closed procedures.
Not evaluated: rotor category,modal decomposition,mode shapes,modal mass,influence coefficients,critical speeds,run-up/coast-down response,correction-plane effectiveness,thermal state,assembly state,repeatability,measurement errors,structural resonance,operating vibration or specialized-equipment requirements.
