ISO 21940-21:2012

Mechanical vibration - Rotor balancing - Part 21: Description and evaluation of balancing machines

ISO 21940-21:2012 specifies requirements for evaluating the performance of machines for balancing rotating components by the following tests: a) test for minimum achievable residual unbalance, Umar test; b) test for unbalance reduction ratio, URR test; c) test for couple unbalance interference on single-plane machines; d) compensator test. These tests are performed during acceptance of a balancing machine and also later on a periodic basis to ensure that the balancing machine is capable of handling the actual balancing tasks. For periodic tests, simplified procedures are specified. Tests for other machine capacities and performance parameters, however, are not contained in ISO 21940-21:2012. For these tests, three types of especially prepared proving rotors are specified, covering a wide range of applications on horizontal and vertical balancing machines. An annex describes recommended modifications of proving rotors prepared in acccordance with ISO 2953:1985. Moreover, ISO 21940-21:2012 stresses the importance attached to the form in which the balancing machine characteristics are specified by the manufacturer. Adoption of the format specified enables users to compare products from different manufacturers. Additionally, in an annex, guidelines are given on the information by which users provide their data and requirements to a balancing machine manufacturer. ISO 21940-21:2012 is applicable to balancing machines that support and rotate rotors with rigid behaviour at balancing speed and that indicate the amounts and angular locations of a required unbalance correction in one or more planes. Therefore it is applicable to rotors with rigid behaviour as well as to rotors with shaft-elastic behaviour balanced in accordance with low-speed balancing procedures. It covers both soft-bearing balancing machines and hard-bearing balancing machines. Technical requirements for such balancing machines are included; however, special features, such as those associated with automatic correction, are excluded. ISO 21940-21:2012 does not specify balancing criteria; such criteria are specified in ISO 1940-1 and ISO 11342 (only low-speed balancing procedures apply).

Vibrations mécaniques — Équilibrage des rotors — Partie 21: Description et évaluation des machines à équilibrer

General Information

• Status: Withdrawn
• Publication Date: 09-Jul-2012
• ICS: 21.120.40 - Balancing and balancing machines
• Technical Committee: ISO/TC 108/SC 2 - Measurement and evaluation of mechanical vibration and shock as applied to machines, vehicles and structures
• Drafting Committee: ISO/TC 108/SC 2/WG 31 - Balancing
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 07-Nov-2022
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 21940-21:2022 - Mechanical vibration - Rotor balancing - Part 21: Description and evaluation of balancing machines
• Effective Date: 23-Apr-2020
• Revises: ISO 2953:1999 - Mechanical vibration - Balancing machines - Description and evaluation
• Effective Date: 08-May-2010

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21940-21
First edition
2012-07-15
Mechanical vibration — Rotor
balancing —
Part 21:
Description and evaluation of balancing
machines
Vibrations mécaniques — Équilibrage des rotors —
Partie 21: Description et évaluation des machines à équilibrer

Reference number
©
ISO 2012
©  ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
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Tel. + 41 22 749 01 11
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Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword . iv
1  Scope . 1
2  Normative references . 2
3  Terms and definitions . 2
4  Capacity and performance data of the balancing machine . 2
4.1  General . 2
4.2  Data for horizontal balancing machines . 2
4.3  Data for vertical balancing machines . 6
5  Machine features . 10
5.1  Principle of operation . 10
5.2  Arrangement of the machine . 10
5.3  Indicating system . 11
5.4  Plane separation system . 12
5.5  Setting and calibration of indication . 12
5.6  Other devices . 13
6  Minimum achievable residual unbalance . 13
7  Production efficiency . 13
7.1  General . 13
7.2  Time per measuring run. 14
7.3  Unbalance reduction ratio . 14
8  Performance qualifying factors . 14
9  Installation requirements . 15
9.1  General . 15
9.2  Electrical and pneumatic requirements . 15
9.3  Foundation . 15
10  Proving rotors and test masses . 15
10.1  General . 15
10.2  Proving rotors . 15
10.3  Test masses . 17
11  Verification tests . 26
11.1  Requirements for performance and parameter verification . 26
11.2  Duties of manufacturer and user . 26
11.3  Requirement for weighing scale . 27
11.4  Test and rechecks . 27
11.5  Test speed . 27
11.6  Test for minimum achievable residual unbalance, U . 27
mar
11.7  Test for unbalance reduction ratio, URR . 31
11.8  Test for couple unbalance interference on single-plane machines . 40
11.9  Compensator test . 40
11.10  Simplified tests . 41
Annex A (informative) Information provided by the user to the balancing machine manufacturer . 42
Annex B (informative) URR limit diagrams . 47
Annex C (informative) Shafts of outboard proving rotors type C . 50
Annex D (informative) Modifications of proving rotors prepared in accordance with ISO 2953:1985
to this part of ISO 21940 . 52
Bibliography . 53
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 21940-21 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 first edition of ISO 21940-21 cancels and replaces ISO 2953:1999, of which it constitutes an editorial
revision. The main change is that for all definitions, reference is made to ISO 1925. Additionally, the Scope
has been reworded in order to exactly reflect what this part of ISO 21940 is dealing with. Furthermore, some
rough rounding in the numbers given in the Tables has been smoothened, and some Figures drawn more
exactly.
ISO 21940 consists of the following parts, under the general title Mechanical vibration — Rotor balancing:
1)
 Part 1: Introduction
2)
 Part 2: Vocabulary
3)
 Part 11: Procedures and tolerances for rotors with rigid behaviour
4)
 Part 12: Procedures and tolerances for rotors with flexible behaviour
5)
 Part 13: Criteria and safeguards for the in-situ balancing of medium and large rotors

1)
Revision of ISO 19499:2007, Mechanical vibration — Balancing — Guidance on the use and application of balancing
standards
2)
Revision of ISO 1925:2001, Mechanical vibration — Balancing — Vocabulary
3)
Revision of ISO 1940-1:2003 + Cor.1:2005, Mechanical vibration — Balance quality requirements for rotors in a
constant (rigid) state — Part 1: Specification and verification of balance tolerances
4)
Revision of ISO 11342:1998 + Cor.1:2000, Mechanical vibration — Methods and criteria for the mechanical balancing
of flexible rotors
5)
Revision of ISO 20806:2009, Mechanical vibration — Criteria and safeguards for the in-situ balancing of medium and
large rotors
iv © ISO 2012 – All rights reserved

6)
 Part 14: Procedures for assessing balance errors
7)
 Part 21: Description and evaluation of balancing machine
8)
 Part 23: Enclosures and other protective measures for the measuring station of balancing machines
9)
 Part 31: Susceptibility and sensitivity of machines to unbalance
10)
 Part 32: Shaft and fitment key convention

6)
Revision of ISO 1940-2:1997, Mechanical vibration — Balance quality requirements of rigid rotors — Part 2: Balance
errors
7)
Revision of ISO 2953:1999, Mechanical vibration — Balancing machines — Description and evaluation
8)
Revision of ISO 7475:2002, Mechanical vibration — Balancing machines — Enclosures and other protective
measures for the measuring station
9)
Revision of ISO 10814:1996, Mechanical vibration — Susceptibility and sensitivity of machines to unbalance
10)
Revision of ISO 8821:1989, Mechanical vibration — Balancing — Shaft and fitment key convention
INTERNATIONAL STANDARD ISO 21940-21:2012(E)

Mechanical vibration — Rotor balancing —
Part 21:
Description and evaluation of balancing machines
1 Scope
This part of ISO 21940 specifies requirements for evaluating the performance of machines for balancing
rotating components by the following tests:
a) test for minimum achievable residual unbalance, U test;
mar
b) test for unbalance reduction ratio, URR test;
c) test for couple unbalance interference on single-plane machines;
d) compensator test.
These tests are performed during acceptance of a balancing machine and also later, on a periodic basis, to
ensure that the balancing machine is capable of handling the actual balancing tasks. For periodic tests,
simplified procedures are specified. Tests for other machine capacities and performance parameters, however,
are not contained in this part of ISO 21940.
For these tests, three types of specially prepared proving rotors are specified, covering a wide range of
applications on horizontal and vertical balancing machines. An annex describes recommended modifications
[2]
of proving rotors prepared in acccordance with ISO 2953:1985.
Moreover, this part of ISO 21940 also stresses the importance attached to the form in which the balancing
machine characteristics are specified by the manufacturer. Adoption of the format specified enables users to
compare products from different manufacturers. Additionally, in an annex, guidelines are given on the
information by which users provide their data and requirements to a balancing machine manufacturer.
This part of ISO 21940 is applicable to balancing machines that support and rotate rotors with rigid behaviour
at balancing speed and that indicate the amounts and angular locations of a required unbalance correction in
one or more planes. Therefore, it is applicable to rotors with rigid behaviour as well as to rotors with shaft-
elastic behaviour balanced in accordance with low-speed balancing procedures. It covers both soft-bearing
balancing machines and hard-bearing balancing machines. Technical requirements for such balancing
machines are included; however, special features, such as those associated with automatic correction, are
excluded.
[1]
This part of ISO 21940 does not specify balancing criteria; such criteria are specified in ISO 1940-1 and
[3]
ISO 11342 (only low-speed balancing procedures apply).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
)
ISO 1925, Mechanical vibration — Balancing — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1925 apply.
4 Capacity and performance data of the balancing machine
4.1 General
The manufacturer shall specify the data listed in 4.2 for horizontal or 4.3 for vertical balancing machines, as
applicable, and in a similar format.
NOTE Information provided by the user to the balancing machine manufacturer is summarized in Annex A.
4.2 Data for horizontal balancing machines
4.2.1 Rotor mass and unbalance limitations
4.2.1.1 The maximum mass of a rotor, m, which can be balanced shall be stated over the range of
balancing speeds (n , n , .).
1 2
The maximum moment of inertia of a rotor with respect to the shaft axis, m r , where m is the rotor mass and r
is the radius of gyration, which the machine can accelerate in a stated acceleration time shall be given for the
range of balancing speeds (n , n , .) together with the corresponding cycle rate (see Table 1).
1 2
4.2.1.2 Production efficiency (see Clause 7) shall be stated, as follows.
4.2.1.2.1 Time per measuring run:
a) Time for mechanical adjustment: . s
b) Time for setting indicating system: . s
c) Time for preparation of rotor: . s
d) Average acceleration time: . s
e) Reading time (including time to stabilize): . s
f) Average deceleration time: . s
g) Relating readings to rotor: . s
h) Other necessary time: . s
i) Total time per measuring run [a) to h) in the preceding]: . s

11)
To become ISO 21940-2 when revised.
2 © ISO 2012 – All rights reserved

4.2.1.2.2 Unbalance reduction ratio, URR, for inboard rotors: . %
4.2.1.2.3 Unbalance reduction ratio for outboard rotors: . %
Table 1 — Data for horizontal balancing machines
Manufacturer: . Model: .
Balancing speeds or speed ranges (see also 4.2.3.1) n n n n …
1 2 3 4
maximum, m
max
Rotor mass
kg
(see Note 1)
minimum
Occasional overload force per support

N
(see Note 1)
Maximum negative force per support
N
(see Note 1)
Maximum rotor moment of inertia with respect to the shaft axis
kg·m
(see Note 2)
Cycle rate
(see Note 2)
measurable
Maximum unbalance
g·mm/kg or g·mm
(see Note 3)
permissible
a) For inboard rotors
maximum mass, m
max
Minimum achievable residual
g·mm/kg 0,2 m
max
specific unbalance, e
mar
(see Note 4 and Clause 6)
minimum mass
Corresponding deflection of analogue
maximum mass, m
max
amount-of-unbalance indicator, mm

or 0,2 m
max
Number of digital units
minimum mass
(see Note 4)
b) For outboard rotors
maximum mass, m
max
Minimum achievable residual
g·mm/kg 0,2 m
max
specific unbalance, e
mar
(see Note 4 and Clause 6)
minimum mass
Corresponding deflection of analogue amount-of-
maximum mass, m
max
unbalance indicator, mm
or 0,2 m
max
Number of digital units
minimum mass
(see Note 4)
NOTE 1 The occasional overload force is only stated for the lowest balancing speed. It is the maximum force per support that can be
accommodated by the machine without immediate damage.
The negative force is the static upward force resulting from a rotor having its centre of mass outside the bearing support.
NOTE 2 Cycle rate for a given balancing speed is the number of starts and stops which the machine can perform per hour without
damage to the machine when balancing a rotor of the maximum moment of inertia.
NOTE 3 In general, for rotors with rigid behaviour with two correction planes, one-half of the stated value pertains to each plane; for
disc-shaped rotors, the full stated value holds for one plane.
NOTE 4 Limits for soft-bearing machines are generally stated in gram millimetres per kilogram (specific unbalance, g·mm/kg), since
this value represents a measure of rotor displacement and, therefore, motion of the balancing machine bearings. For hard-bearing
machines, the limits are generally stated in gram millimetres (g·mm), since these machines are usually factory calibrated to indicated
unbalance in such units (see Clause 6). For two-plane machines, this is the result obtained when the minimum achievable residual
unbalance is distributed between the two planes.
4.2.2 Rotor dimensions
4.2.2.1 Adequate envelope drawings of the pedestals and of other obstructions, such as belt-drive
mechanism, shroud mounting pads, thrust arms and tie bars, shall be supplied to enable the user to determine
the maximum rotor envelope that can be accommodated and the tooling or adaptors required.
A combination of large journal diameter and high balancing speed can result in an excessive journal
peripheral speed. The maximum journal peripheral speed shall be stated.
When belt drive is supplied, balancing speeds shall be stated for both the maximum and minimum diameters
over which the belt can drive, or other convenient diameter.
The manufacturer shall state if the axial position of the drive can be adjusted.
4.2.2.2 Rotor envelope limitations shall be stated (see Figure 1).

Key
1 shaft
2 rotor
3 support
4 bed
If the left-hand support is not a mirror image of the right-hand support, separate dimensions shall be shown.
The profile of the belt-drive equipment shall be shown, if applicable.
Figure 1 — Example of a machine support drawing illustrating rotor envelope limitations
4 © ISO 2012 – All rights reserved

4.2.2.3 Rotor diameter:
a) Maximum diameter over bed: . mm
b) Maximum diameter over which belt can drive: . mm
c) Minimum diameter over which belt can drive: . mm
4.2.2.4 Distance between journal centrelines:
a) Maximum: . mm
b) Minimum: . mm
c) Maximum distance from coupling flange to centreline of farthest bearing: . mm
d) Minimum distance from coupling flange to centreline of nearest bearing: . mm
4.2.2.5 Journal diameter:
a) Maximum: . mm
b) Minimum: . mm
Maximum permissible peripheral journal speed . m/s
4.2.2.6 Correction plane limitations (consistent with the statements in 5.4) shall be stated.
4.2.2.7 Correction plane interference ratios (consistent with the statements in 5.4 and based on the
proving rotor) shall be stated.
4.2.3 Drive
4.2.3.1
Balancing speed Rated torque on rotor
r/min N·m
n . .
n . .
n . .
n . .
n . .
n . .
n . .
n . .
or or
steplessly variable steplessly variable
from  . .
to  . .
4.2.3.2 Torque:
a) Zero-speed torque: . % of rated torque on rotor
b) Run-up torque adjustable from . % to . % of rated torque on rotor
c) Peak torque . % of rated torque on rotor
NOTE In most cases, maximum torque is required for accelerating a rotor. However, in the case of a rotor with high
windage or friction loss, maximum torque can be required at balancing speed. When there is axial thrust, it is necessary
that provisions be made to take this into account.
4.2.3.3 Type of drive to rotor: .
EXAMPLES End drive by universal joint driver, end drive by band, belt drive, magnetic field, driven bearing rollers, air
jet.
4.2.3.4 Prime mover (type of motor): .
a) Rated power: . kW
b) Motor speed: . r/min
c) Power supply, voltage/frequency/phase: . / . / .
4.2.3.5 Brake
a) Type of brake: .
b) Braking torque adjustable from . % to . % of rated torque
c) Can the brake be used as a holding device? Yes / No
4.2.3.6 Motor and controls in accordance with the following standard(s): .
4.2.3.7 Speed regulation provided:
Accurate or constant within . % of . r/min, or . r/min
4.2.4 Couple unbalance interference ratio: . g·mm/(g·mm )
NOTE This value is only applicable for single-plane balancing machines. It describes the influence of couple
unbalance in the rotor on the indication of resultant unbalance.
4.2.5 Air pressure requirements: . Pa, . m /s.
4.3 Data for vertical balancing machines
4.3.1 Rotor mass and unbalance limitations
4.3.1.1 The maximum mass of a rotor, m, which can be balanced shall be stated over the range of
balancing speeds (n , n , .).
1 2
, where m is the rotor mass and r
The maximum moment of inertia of a rotor with respect to the shaft axis, m r
is the radius of gyration, which the machine can accelerate in a stated acceleration time shall be given for the
range of balancing speeds (n , n , .) together with the corresponding cycle rate (see Table 2).
1 2
6 © ISO 2012 – All rights reserved

Table 2 — Data for vertical balancing machines
Manufacturer: . Model: .
Balancing speeds or speed ranges (see also 4.3.3.1) n n n n …
1 2 3 4
maximum, m
max
Rotor mass
kg
(see Note 1)
minimum
Occasional overload force up to
N
(see Note 1)
Maximum rotor moment of inertia with respect to the shaft axis
kg·m
(see Note 2)
Cycle rate
(see Note 2)
measurable
Maximum unbalance
g·mm/kg or g·mm
(see Note 3)
permissible
maximum mass, m
max
Minimum achievable residual
specific unbalance, e
mar g·mm/kg 0,2 m
max
(see Note 4 and Clause 6)
minimum mass
Corresponding deflection of analogue amount-of-unbalance
maximum mass, m
max
indicator, mm
or
0,2 m
max
Number of digital units
minimum mass
(see Note 4)
NOTE 1 The occasional overload force is only stated for the lowest balancing speed. It is the maximum force that can be
accommodated by the machine without immediate damage.
NOTE 2 Cycle rate for a given balancing speed is the number of starts and stops which the machine can perform per hour without
damage to the machine when balancing a rotor of the maximum moment of inertia.
NOTE 3 In general, for rotors with rigid behaviour with two correction planes, one-half of the state value pertains to each plane; for
disc-shaped rotors, the full stated value holds for one plane.
NOTE 4 Limits for soft-bearing machines are generally stated in gram millimetres per kilogram (specific unbalance, g·mm/kg), since
this value represents a measure of rotor displacement and, therefore, motion of the balancing machine bearings. For hard-bearing
machines, the limits are generally stated in gram millimetres (g·mm), since these machines are usually factory calibrated to indicated
unbalance in such units (see Clause 6). For two-plane machines, this is the result obtained when the minimum achievable residual
unbalance is distributed between the two planes.

4.3.1.2 Production efficiency (see Clause 7) shall be stated, as follows.
4.3.1.2.1 Time per measuring run:
a) Time for mechanical adjustment: . s
b) Time for setting indicating system: . s
c) Time for preparation of rotor: . s
d) Average acceleration time: . s
e) Reading time (including time to stabilize): . s
f) Average deceleration time: . s
g) Relating readings to rotor: . s
h) Other necessary time: . s
i) Total time per measuring run [a) to h) in the preceding]: . s
4.3.1.2.2 Unbalance reduction ratio, URR: . %
4.3.2 Rotor dimensions
4.3.2.1 If the machine is equipped with two or more speeds, the information on rotor dimensions shall be
stated for each speed. If the machine is equipped with steplessly variable balancing speeds, then the
information shall be given in the form of a table, formula or graph.
Adequate drawings of the support surface of the spindle or mounting plate and of obstructions, such as drill
heads and electrical control cabinets, above the mounting plate shall be supplied to enable the user to
determine the maximum rotor envelope that can be accommodated and the tooling or adaptors required.
4.3.2.2 Maximum diameter: . mm
4.3.2.3 Rotor height:
a) Maximum overall height: . mm
b) Maximum height of centre of gravity: . mm
at 100 % of maximum mass: . mm
at 50 % of maximum mass: . mm
at 25 % of maximum mass: . mm
4.3.2.4 Rotor envelope limitations, including machine spindle or mounting plate interface, shall be stated
(see Figure 2).
4.3.2.5 Correction plane limitations (consistent with the statements in 5.4) shall be stated.
4.3.3 Drive
4.3.3.1
Balancing speed Rated torque on rotor
r/min N·m
n . .
n . .
n . .
n . .
n . .
n . .
n . .
n . .
8 © ISO 2012 – All rights reserved

Key
1 rotor 4 spindle 7 lower correction plane
2 adaptor 5 upper correction plane 8 mounting holes for adaptor
3 protractor 6 centre of mass plane 9 spigot diameter
Figure 2 — Example of vertical machine mounting interface illustrating rotor envelope limitations
4.3.3.2 Torque:
a) Zero-speed torque: . % of rated torque on rotor
b) Run-up torque adjustable from . % to . % of rated torque on rotor
c) Peak torque: . % of rated torque on rotor
NOTE In most cases, maximum torque is required for accelerating a rotor. However, in the case of rotors with high
windage or friction loss, maximum torque can be required at balancing speed.
4.3.3.3 Prime mover (type of motor): .
a) Rated power: . kW
b) Motor speed: . r/min
c) Power supply, voltage/frequency/phase: . / . / .
4.3.3.4 Brake
a) Type of brake: .
b) Braking torque adjustable from . % to . % of rated torque
c) Can the brake be used as a holding device? Yes / No
4.3.3.5 Motor and controls in accordance with the following standard(s): .
4.3.3.6 Speed regulation provided:
Accurate or constant within . % of . r/min, or . r/min
4.3.4 Couple unbalance interference ratio: . g·mm/(g·mm )
NOTE This value is only applicable for single-plane balancing machines. It describes the influence of couple
unbalance in the rotor on the indication of resultant unbalance.
4.3.5 Air pressure requirements: . Pa, . m /s.
5 Machine features
5.1 Principle of operation
An adequate description of the principle of operation of the balancing machine shall be given, e.g. motion
measuring, force measuring, resonance, compensation.
5.2 Arrangement of the machine
5.2.1 The manufacturer shall describe the general configuration of the balancing machine and the principal
features of design, e.g.:
 horizontal or vertical axis of rotation;
 soft- or hard-bearing suspension system;
 resonance-type machine with mechanical compensator.
5.2.2 The manufacturer shall provide details of the following, as applicable.
5.2.2.1 Components designed to support the rotor, e.g.:
 vee blocks;
 open rollers;
 plain half bearings;
 closed ball, roller or plain bearings;
 devices to accommodate rotors in their service bearings;
 devices to accommodate complete units.
Details of bearing lubrication requirements shall be given, where applicable.
5.2.2.2 The mechanical adjustment and functioning of the means provided to take up axial thrust from the
rotor (horizontal machines only).
5.2.2.3 Type(s) of transducers used to sense unbalance effects.
5.2.2.4 The drive and its control.
10 © ISO 2012 – All rights reserved

5.3 Indicating system
5.3.1 General
A balancing machine shall have means to determine the amount of unbalance and its angular location; such
means shall be described, e.g.:
 wattmetric indicating system;
 voltmetric indicating system with phase-sensitive rectifier (including systems with frequency conversion);
 voltmetric system with stroboscope and filter;
 voltmetric indicating system with marking of angular position on the rotor itself;
 compensator with mechanical or electrical indication.
5.3.2 Amount indicators
The manufacturer shall describe the means of amount indication provided, e.g.:
 wattmetric or voltmetric component meters;
 wattmetric or voltmetric amount meters;
 wattmetric or voltmetric vector meters;
 mechanical or optical indicators;
 analogue or digital readout.
5.3.3 Angle indicators
The manufacturer shall describe the means of angle indication provided, e.g.:
 wattmetric or voltmetric component meters;
 wattmetric or voltmetric vector meters;
 direct angle indication in degrees on a scale meter;
 oscilloscope, stroboscopic indicators;
 mechanical or optical indicators;
 analogue or digital readout.
5.3.4 Operation of the indicating system
The manufacturer shall describe the procedure by which readings are obtained, taking into account at least
the following aspects.
a) How many measuring runs are required to obtain:
 the two readings for single-plane balancing?
 the four readings for two-plane balancing?
b) Is an indicator provided for each reading or is it necessary to switch over for each reading?
c) Are readings retained after the end of the measuring run?
d) Is an individual plus-and-minus switch provided for each plane which permits the indication of a heavy or
light spot?
5.4 Plane separation system
5.4.1 This subclause is not applicable to single-plane balancing machines, for which see 5.4.2.
The manufacturer shall state whether plane separation is provided. If it is provided, at least the following
details shall be given.
a) How is it operated for single rotors of a type not previously balanced?
b) How is it operated for single rotors in a series, with identical dimensions and mass?
c) The limits of rotor geometry over which plane separation is effective shall be defined with the
effectiveness stated on the basis of the correction plane interference ratio, stating the following:
 the ratio of bearing distance to plane distance for which plane separation is effective;
 whether either or both correction planes can be between or outside the bearings;
 whether the centre of mass can be between or outside the two selected correction planes or
bearings.
d) Whether the indicator system can also be used to measure directly resultant unbalance and couple
unbalance.
5.4.2 For single-plane horizontal or vertical machines, the manufacturer shall state to what extent the
machine is able to suppress effects of couple unbalance (see 11.8).
5.5 Setting and calibration of indication
5.5.1 General
The manufacturer shall describe the means of setting and calibration and the means provided for checking
these.
The manufacturer shall state whether setting is possible for indication in any desired unit, whether practical
correction units or unbalance units.
The manufacturer shall state the number of runs required for calibrating the balancing machine:
 for single-plane balancing;
 for two-plane balancing.
The manufacturer shall state the maximum permissible change, in percentage terms, in repeatability of speed
during calibration and operation.
5.5.2 Soft-bearing machines
The manufacturer shall state how calibration is accomplished on the first rotor of a particular mass and
configuration (e.g. whether the rotor has to be balanced by a trial-and-error procedure or whether a
compensator is provided, whether calibration masses are required), and whether total or partial recalibration is
required when changing the balancing speed.
If a compensator is provided, the limits of initial unbalance, of rotor geometry and speed for which
compensation is effective shall be stated.
12 © ISO 2012 – All rights reserved

5.5.3 Hard-bearing machines
The manufacturer shall state whether the balancing machine is permanently calibrated and can be set
according to the rotor or whether it requires calibration by the user for different balancing speeds, rotor
masses and dimensions.
5.6 Other devices
Special devices which influence the efficient functioning of the balancing machine shall be described in detail,
e.g.:
 indication in components of an arbitrary coordinate system;
 indication of unbalance resolved into components located in limited sectors in more than two correction
planes;
 correction devices;
 devices to correlate the measured angle or amount of unbalance with the rotor;
 suitable output for connection to a computer, printer or other peripherals.
6 Minimum achievable residual unbalance
The minimum residual unbalance that can be achieved with a balancing machine shall be specified in terms of
specific unbalance, in gram millimetres per kilogram (g·mm/kg), together with the corresponding
amount-of-unbalance indication.
This minimum achievable residual specific unbalance, e , shall be stated for the full range of rotor masses
mar
and balancing speeds of the machine.
In achieving the stated residual unbalance, the manufacturer shall consider whether the accuracy of the
following is adequate for this purpose:
 amount indication;
 angle indication;
 plane separation;
 scale multiplier;
 drive, bearings, etc.
It should be noted that the stated minimum achievable residual unbalance value applies to the balancing
machine as delivered, but if out-of-round journals, excessively heavy or loose adaptors, or other tooling are
employed by the user, the minimum achievable residual unbalance can be affected.
7 Production efficiency
7.1 General
Production efficiency is the ability of the machine to assist the operator in balancing a rotor to a given residual
unbalance in the shortest possible time. It shall be assessed by using a proving rotor or, alternatively, a test
rotor to be specified by the user.
To find the production rate for a specific rotor (number of pieces per time or the reciprocal of the floor-to-floor
time), the time per measuring run, the necessary number of runs, the time for loading, unbalance correction
and unloading have to be taken into cons
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