National foreword

This British Standard is the UK implementation of ISO 21940‑14:2026. It supersedes BS ISO 21940‑14:2012+A1:2022, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee GME/21/5, Vibration of machines, vehicles and structures.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2026.

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO document should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

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This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and condition monitoring, Subcommittee SC 2, Measurement and evaluation of mechanical vibration and shock as applied to machines, vehicles and structures.

This second edition cancels and replaces the first edition (ISO 21940-14:2012), which has been technically revised. It also incorporates the Amendment ISO 21940-14:2012/Amd.1:2022.

The main changes are as follows:

the extension of the term “error” to "deviations" of the rotor’s state of assembly on the balancing machine from the fully assembled rotor in service.

A list of all parts in the ISO 21940 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

The balance quality of a rotor is assessed in accordance with the requirements of ISO 21940-11 [1] or ISO 21940-12 [2] by measurements taken on the rotor. These measurements can contain errors which originate from a number of sources. Where those errors are significant, they should be taken into account when defining the required balance quality of the rotor.

ISO 21940-11 [1] and ISO 21940-12 [2] do not consider balancing errors in detail. Therefore this document gives examples of typical errors that can occur and provides recommended procedures for their evaluation.

1 Scope

This document specifies the requirements for

identifying errors in the unbalance measuring process of a rotor including all factors similar to errors in their effect on the balancing precision,
assessing the identified errors, and
taking errors into account in preparation and realization of the balancing process and in the evaluation of the residual unbalance.

For the main typical errors this document lists the methods for their reduction in Annex A.

2 Normative references

3 Terms and definitions

4 Balance error sources

4.1 General

4.2 Examples of systematic errors

4.3 Examples of randomly variable errors

4.4 Examples of scalar errors

5 Balance error assessment

5.1 General

5.2 Balance errors caused by balancing equipment and instrumentation

5.3 Balance errors caused by component radial and axial runout

5.4 Balance errors caused by deviation of the rotor configuration on the balancing machine from the configuration at service

5.5 Assessment of balancing operation errors

5.6 Experimental assessment of randomly variable and scalar errors

5.7 Experimental assessment of systematic errors

6 Combined error evaluation

7 Balance criteria

8 Accounting for measurement errors in the balance quality verification process

Bibliography