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 with 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.
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.
