ISO 20816-1:2016
(Main)Mechanical vibration — Measurement and evaluation of machine vibration — Part 1: General guidelines
Mechanical vibration — Measurement and evaluation of machine vibration — Part 1: General guidelines
ISO 20816-1:2016 establishes general conditions and procedures for the measurement and evaluation of vibration using measurements made on rotating, non-rotating and non-reciprocating parts of complete machines. It is applicable to measurements of both absolute and relative radial shaft vibration with regard to the monitoring of radial clearances, but excludes axial shaft vibration. The general evaluation criteria, which are presented in terms of both vibration magnitude and change of vibration, relate to both operational monitoring and acceptance testing. They have been provided primarily with regard to securing reliable, safe, long-term operation of the machine while minimizing adverse effects on associated equipment. Guidelines are also presented for setting operational limits. NOTE 1 The evaluation criteria for different classes of machinery will be included in other parts of ISO 20816 when they become available. In the meantime, guidelines are given in Clause 6. NOTE 2 The term "shaft vibration" is used throughout ISO 20816 because, in most cases, measurements are made on machine shafts. However, the ISO 20816 series is also applicable to measurements made on other rotating elements if such elements are found to be more suitable, provided that the guidelines are respected. For the purposes of ISO 20816, operational monitoring is considered to be those vibration measurements made during the normal operation of a machine. The ISO 20816 series permits the use of different measurement quantities and methods, provided that they are well-defined and their limitations are set out, so that the interpretation of the measurements is well-understood. The evaluation criteria relate only to the vibration produced by the machine itself and not the vibration transmitted to it from outside. ISO 20816-1:2016 does not include consideration of torsional vibration. NOTE 3 For torsional vibration, see, for example, ISO 3046‑5, ISO 22266‑1 or VDI 2039.
Vibrations mécaniques — Mesurage et évaluation des vibrations de machines — Partie 1: Lignes directrices générales
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INTERNATIONAL ISO
STANDARD 20816-1
First edition
2016-11-15
Mechanical vibration — Measurement
and evaluation of machine
vibration —
Part 1:
General guidelines
Vibrations mécaniques — Mesurage et évaluation des vibrations de
machines —
Partie 1: Lignes directrices générales
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurements . 2
4.1 General . 2
4.1.1 Overview . 2
4.1.2 Vibration measurements . 2
4.1.3 Frequency range . 2
4.2 Types of measurements . 2
4.2.1 Vibration measurements on non-rotating parts . 2
4.2.2 Relative shaft vibration measurements . 2
4.2.3 Absolute shaft vibration measurements . 3
4.3 Measurement parameters . 3
4.3.1 Measurement quantities . 3
4.3.2 Vibration magnitude . . 4
4.3.3 Vibration severity . . 4
4.4 Measuring positions . 4
4.4.1 Positions for measurements on non-rotating parts . 4
4.4.2 Positions for measurements on rotating shafts . 7
4.5 Machine support structure for acceptance testing . 9
4.5.1 General. 9
4.5.2 In-situ tests . 9
4.5.3 In a test facility .10
4.6 Machine operating conditions .10
4.7 Evaluation of vibration from other sources .10
5 Instrumentation .10
6 Evaluation criteria .11
6.1 General .11
6.1.1 Overview .11
6.1.2 Types of measurement on rotating shafts .11
6.2 Factors affecting evaluation criteria .12
6.3 Types of evaluation criteria .12
6.3.1 General.12
6.3.2 Criterion I: Vibration magnitude at rated speed under steady
operation conditions .12
6.3.3 Criterion II: Change in vibration magnitude .16
6.4 Operational limits .16
6.4.1 General.16
6.4.2 Setting of ALARMS .17
6.4.3 Setting of TRIPS .17
6.5 Additional factors .17
6.5.1 Vibration frequencies and vectors . .17
6.5.2 Vibration sensitivity of the machine .17
6.5.3 Techniques for rolling element bearings .18
Annex A (informative) Explanation of measurement quantities .19
Annex B (informative) Techniques for detection of problems in rolling element bearings .26
Annex C (informative) Guidelines for specification of evaluation criteria for vibration
measured on non-rotating parts and rotating shafts .28
Annex D (informative) Vector analysis of change in vibration .31
Bibliography .33
iv © ISO 2016 – All rights reserved
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 documents 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).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is 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 20816-1 cancels and replaces ISO 7919-1:1996, ISO 10816-1:1995 and
ISO 10816-1:1995/Amd 1:2009 which have been merged and editorially revised.
A list of all parts in the ISO 20816 series can be found on the ISO website.
Introduction
Machines are now being operated at increasingly high rotational speeds and loads, as well as more
flexible operation at part and full load, and under increasingly severe operating conditions. This has
become possible, to a large extent, by the more efficient use of materials, although this has sometimes
resulted in there being less margin for design and application errors.
At present, it is not uncommon for continuous operation to be expected and required for 2 years or
3 years between maintenance operations. Consequently, more restrictive requirements are being
specified for operating vibration values of rotating machinery, in order to ensure continued safe and
reliable operation.
This document is a basic document which establishes general guidelines for the measurement and
evaluation of mechanical vibration of machinery, as measured on rotating and on non-rotating (and,
where applicable, non-reciprocating) parts of complete machines, such as shafts or bearing housings.
Recommendations for measurements and evaluation criteria pertaining to specific machine types are
provided in additional parts of ISO 20816 as they become available as a replacement of the relevant
parts of ISO 7919 and ISO 10816. ISO/TR 19201 gives an overview over these and further machinery
vibration standards.
For some machines, measurements made on non-rotating parts are sufficient to characterize adequately
their running conditions with respect to trouble-free operation. There are also types of machine, such as
steam turbines, gas turbines and turbo compressors, all of which can have several modes of vibration in
the service speed range, for which measurements on structural members, such as the bearing housings,
might not adequately characterize the running condition of the machine, although such measurements
are useful. Such machines generally contain flexible rotor shaft systems, and changes in the vibration
condition can be detected more decisively and more sensitively by measurements on the rotating
elements. Machines having relatively stiff and/or heavy casings in comparison to rotor mass are typical
of those classes of machines for which shaft vibration measurements are frequently preferred.
Vibration measurements are used for a number of purposes, ranging from routine operational
monitoring and acceptance tests to advanced experimental testing, as well as diagnostic and analytical
investigations. These various measurement objectives lead to many differences in methods of
interpretation and evaluation. To limit the number of these differences, this document is designed to
provide guidelines primarily for operational monitoring and acceptance tests.
Three primary vibration quantities (displacement, velocity and acceleration) are defined and their
limitations given. Adherence to the guidelines presented should, in most cases, ensure satisfactory
service performance.
vi © ISO 2016 – All rights reserved
INTERNATIONAL STANDARD ISO 20816-1:2016(E)
Mechanical vibration — Measurement and evaluation of
machine vibration —
Part 1:
General guidelines
1 Scope
This document establishes general conditions and procedures for the measurement and evaluation of
vibration using measurements made on rotating, non-rotating and non-reciprocating parts of complete
machines. It is applicable to measurements of both absolute and relative radial shaft vibration with
regard to the monitoring of radial clearances, but excludes axial shaft vibration. The general evaluation
criteria, which are presented in terms of both vibration magnitude and change of vibration, relate to
both operational monitoring and acceptance testing. They have been provided primarily with regard
to securing reliable, safe, long-term operation of the machine while minimizing adverse effects on
associated equipment. Guidelines are also presented for setting operational limits.
NOTE 1 The evaluation criteria for different classes of machinery will be included in other parts of ISO 20816
when they become available. In the meantime, guidelines are given in Clause 6.
NOTE 2 The term “shaft vibration” is used throughout ISO 20816 because, in most cases, measurements
are made on machine shafts. However, the ISO 20816 series is also applicable to measurements made on other
rotating elements if such elements are found to be more suitable, provided that the guidelines are respected.
For the purposes of ISO 20816, operational monitoring is considered to be those vibration measurements
made during the normal operation of a machine. The ISO 20816 series permits the use of different
measurement quantities and methods, provided that they are well-defined and their limitations are set
out, so that the interpretation of the measurements is well-understood.
The evaluation criteria relate only to the vibration produced by the machine itself and not the vibration
transmitted to it from outside.
This document does not include consideration of torsional vibration.
NOTE 3 For torsional vibration, see, for example, ISO 3046-5, ISO 22266-1 or VDI 2039.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 2954, Mechanical vibration of rotating and reciprocating machinery — Requirements for instruments
for measuring vibration severity
ISO 5348, Mechanical vibration and shock — Mechanical mounting of accelerometers
ISO 10817-1, Rotating shaft vibration measuring systems — Part 1: Relative and absolute sensing of radial
vibration
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
4 Measurements
4.1 General
4.1.1 Overview
This clause describes the measurements, procedures and operating conditions recommended for
assessing machine vibration. The guidelines given permit the evaluation of vibration in accordance
with the general criteria and principles given in Clause 6.
4.1.2 Vibration measurements
It is common practice to measure vibration on non-rotating parts or to measure relative shaft vibration,
or both. The measurement type for the protection system is normally based on the experience from the
machine manufacturer.
4.1.3 Frequency range
The measurement of vibration shall be broad band, so that the frequency spectrum of the machine is
adequately covered.
The frequency range depends on the type of machine being considered (e.g. the frequency range
necessary to assess the integrity of rolling element bearings should include frequencies higher than
those on machines with fluid-film bearings only).
Guidelines for instrumentation frequency ranges for specific machine classes are given in the
appropriate parts of ISO 20816.
NOTE 1 In the past, broad-band measurements in the range 10 Hz to 1 000 Hz were the intended metric for
full-load acceptance testing. This might not meet the requirements of a condition monitoring scheme and might
need to be modified for the purposes of vibration monitoring and diagnostics.
NOTE 2 Vibration condition monitoring and diagnostics of machines are described in ISO 13373.
On certain equipment, e.g. gearboxes and rolling element bearings, it can be appropriate to use a
different frequency range for acceptance purposes.
4.2 Types of measurements
4.2.1 Vibration measurements on non-rotating parts
Vibration measurements on non-rotating parts are generally carried out with a seismic transducer
which senses the absolute velocity or acceleration of structure parts on which it is mounted (e.g. the
bearing housing).
4.2.2 Relative shaft vibration measurements
Relative shaft vibration measurements are generally carried out with a non-contacting transducer
which senses the vibratory displacement between the shaft and a structural member on which it is
mounted (e.g. the bearing housing).
2 © ISO 2016 – All rights reserved
4.2.3 Absolute shaft vibration measurements
Absolute shaft vibration measurements are carried out by one of the following methods:
a) by a shaft-riding probe on which a seismic transducer (velocity type or accelerometer) is mounted
so that it measures absolute shaft vibration directly;
b) by a non-contacting transducer which measures relative shaft vibration in combination with a
seismic transducer (velocity type or accelerometer) which measures the support vibration. Both
transducers shall be mounted close together so that they undergo the same absolute motion in the
direction of measurement. Their conditioned outputs are summed to provide a measurement of the
absolute shaft motion.
NOTE In order to avoid incorrect results, it is important to ensure that the same datum time reference be
used for the outputs from both the seismic and non-contacting transducers.
4.3 Measurement parameters
4.3.1 Measurement quantities
For the purposes of this document, the following measurement quantities can be used:
a) vibration displacement, measured in micrometres;
b) vibration velocity, measured in millimetres per second;
c) vibration acceleration, measured in metres per square second.
The use, application and limitations of these quantities are discussed in Clause 6.
Generally, there is no simple relationship between broad-band acceleration, velocity and displacement;
nor is there between peak (0–p), peak-to-peak (p–p), root-mean-square (r.m.s.) and average values of
vibration. The reasons for this are briefly discussed in A.1, which also defines some precise relationships
between the above quantities when the harmonic content of the vibration waveform is known.
In order to avoid confusion and to ensure correct interpretation, it is important at all times to identify
–6
clearly the measurement quantity and its unit, e.g. peak-to-peak displacement in µm (1 µm = 10 m),
r.m.s. velocity in mm/s.
NOTE Vibration is a vector quantity and therefore, when comparing two different values, it can be necessary
to consider the phase angle between them (see Annex D).
Generally, it can be stated that the preferred measurement quantity for the measurement of vibration
of non-rotating parts is r.m.s. velocity while the preferred measurement quantity for the measurement
of shaft vibration is peak-to-peak displacement.
Since this document applies to both relative and absolute shaft vibration measurements, displacement
is further defined as follows:
— relative displacement which is the vibratory displacement of the shaft with reference to support
structure, such as a bearing housing or machine casing;
— absolute displacement which is the vibratory displacement of the shaft with reference to an inertial
reference system.
It should be clearly indicated whether displacement values are relative or absolute.
Relative and absolute displacements are further defined by several different displacement quantities,
each of which is now in widespread use. These include the following:
maximum vibratory displacement in the plane of measurement, measured from time-
S
max
integrated mean position, see Formula (A.10);
peak-to-peak vibratory displacement in the direction of measurement defined as
S
(p–p)
S = max [S , S ];
(p–p) A(p–p) B(p–p)
S maximum peak-to-peak vibratory displacement in the plane of measurement.
(p–p)max
Any of these displacement quantities may be used for the measurement of shaft vibration. However,
the quantities shall be clearly identified so as to ensure correct interpretation of the measurements in
terms of the criteria of Clause 6. The relationships between these quantities are shown in Figure A.3.
4.3.2 Vibration magnitude
The result of measurements made with an instrument which complies with the requirements of
Clause 5 is called the vibration magnitude at a specific measuring position and direction.
It is common practice, based on experience, when evaluating broad-band vibration of rotating
machinery to consider the r.m.s. value of vibration velocity, since this can be related to the vibration
energy. However, other quantities such as displacement or acceleration and peak values instead of r.m.s.
values may be preferred. In this case, alternative criteria, which are not necessarily simply related to
criteria based on r.m.s. values, are required.
For shaft vibration measurement, it is common practice to consider peak-to-peak values.
4.3.3 Vibration severity
Normally, measurements are made at various measuring positions and in one, two or three measuring
directions, leading to a set of different vibration magnitude values. The maximum broad-band
magnitude value measured under agreed machine support and operating conditions is defined as the
vibration severity.
For most machine types, one value of vibration severity characterizes the vibratory state of that
machine. However, for some machines, this approach can be inadequate and the vibration severity
should then be assessed independently for measurement positions at a number of locations.
4.4 Measuring positions
4.4.1 Positions for measurements on non-rotating parts
Measurements on non-rotating parts should be taken on the bearings, bearing support housing or
other structural parts which significantly respond to the dynamic forces transmitted from the rotating
elements at the bearing locations and characterize the overall vibration of the machine. Typical
measurement locations are shown in Figure 1 to Figure 5.
To determine the vibrational behaviour at each measuring position, it is necessary to take measurements
in three mutually perpendicular directions. The full complement of measurements represented in
Figure 1 to Figure 5 is generally only required for acceptance testing.
The requirement for operational monitoring is usually met by performing one or both measurements in
the radial direction (i.e. normally in the horizontal transverse and/or vertical directions). These can be
supplemented by a measurement of the vibration in the axial direction, but are to be evaluated only on
thrust bearings. The latter can be of significance at thrust bearing locations where direct axial dynamic
forces are transmitted.
Detailed recommendations for specific machine types are provided in the additional parts of ISO 20816.
4 © ISO 2016 – All rights reserved
Figure 1 — Measuring points for pedestal bearings
Figure 2 — Measuring points for housing-type bearings
Figure 3 — Measuring points for small electrical machines
Figure 4 — Measuring points for reciprocating engines close to the bearing locations
Figure 5 — Measuring points for vertical machine sets
6 © ISO 2016 – All rights reserved
4.4.2 Positions for measurements on rotating shafts
4.4.2.1 General
For the measurements on rotating shafts, it is desirable to locate transducers at positions such that
the lateral movement of the shaft at points of importance can be assessed. It is recommended that, for
both relative and absolute measurements, two transducers be located at, or adjacent to, each machine
bearing, see Figure 6. They should be radially mounted in the same transverse plane perpendicular
to the shaft axis or as close as practicable, with their axes within ±5° of a radial line. It is preferable to
mount both transducers 90° ± 5° apart on the same bearing half and the positions chosen should be the
same at each bearing. See Figure 7.
A single transducer may be used at each measurement plane in place of the more typical pair of
orthogonal transducers if it is known to provide adequate information about the shaft vibration.
It is recommended that special measurements be made in order to determine the total non-vibration
runout, which is caused by shaft surface metallurgical non-homogeneities, local residual magnetism
and shaft mechanical runout. It should be noted that, for anisotropic rotors such as, for example, two-
pole generators, the effect of gravity can cause a false runout signal.
Key
1 to signal processing
2 signal conditioning units
3 non-contacting transducers
4 shaft
5 bearing housings
6 bearings
Figure 6 — Measuring points for measurements on rotating shafts
Key
1 to signal processing
2 signal conditioning units
3 shaft
4 non-contacting transducers
Figure 7 — Mounting of non-contacting probes for the measurement of shaft relative vibration
4.4.2.2 Positions for relative shaft vibration measurements
Relative vibration transducers of the non-contacting type are normally mounted in tapped holes
in the bearing housing or by rigid brackets adjacent to the bearing housing or bearing shell. Where
the transducers are mounted in the bearing, they should be located so as not to interfere with the
lubrication pressure wedge. However, special arrangements for mounting transducers in other axial
locations may be made, but different vibration criteria for assessment will then have to be used. For
bracket-mounted transducers, the bracket shall be free from natural frequencies which adversely affect
the capability of the transducer to measure the relative shaft vibration.
The surface of the shaft at the location of the transducer, taking into account the total axial float of the
shaft under all thermal conditions, shall be smooth and free from any geometric discontinuities (such
as keyways, lubrication passages and threads), metallurgical non-homogeneities and local residual
magnetism which can cause false signals. In some circumstances, an electroplated or metallized shaft
surface may be acceptable, but it should be noted that the calibration can be different. It is recommended
that the total combined electrical and mechanical runout, as measured by the transducer, does not
exceed 25 % of the allowable vibration displacement, specified in accordance with 6.3.2.2, or 6 μm,
whichever is greater. For measurements made on machines already in service, where provision was not
originally made for shaft vibration measurements, it can be necessary to use other runout criteria.
4.4.2.3 Positions for absolute shaft vibration measurements using combined seismic and
non-contacting relative vibration transducers
If a combination of seismic and non-contacting relative vibration transducers is used, the absolute shaft
vibration is obtained by
a) integrating the signal from the seismic transducer to convert the acceleration or velocity output to
displacement, and
b) summing the displacement outputs from both transducers.
NOTE 1 In order to avoid incorrect results, it is important to ensure that the same datum time reference is
used for the outputs from both the seismic and non-contacting transducers.
8 © ISO 2016 – All rights reserved
The mounting and other requirements for the non-contacting transducer are as specified in 4.4.2.2.
In addition, the seismic transducer shall be rigidly mounted to the machine structure (e.g. the bearing
housing) close to the non-contacting transducer so that both transducers undergo the same absolute
vibration of the support structure in the direction of measurement. The sensitive axes of the non-
contacting and seismic transducers shall be parallel, so that their summed, conditioned signals result in
an accurate measure of the absolute shaft vibration. See Figure 8.
NOTE 2 Information on mounting accelerometers for seismic measurements is given in ISO 5348.
NOTE 3 In the past, absolute shaft vibration measurements have also been performed using a shaft-riding
mechanism with a seismic transducer.
Key
1 to signal processing
2 signal conditioning units
3 shaft
4 non-contacting transducers
5 seismic transducers
Figure 8 — Mounting of non-contacting and seismic probes for the measurement of shaft
absolute vibration
4.5 Machine support structure for acceptance testing
4.5.1 General
The acceptance criteria should be agreed between the customer and manufacturer.
4.5.2 In-situ tests
When acceptance is carried out in situ, the support structure shall be that supplied for the machine.
In this case, it is important to ensure that all the major components of the machine and structure are
installed when the test is carried out.
Valid comparisons of vibration for machines of the same type but on different foundations or sub-
foundations can only be made if the foundations concerned have similar dynamic characteristics.
4.5.3 In a test facility
There are many classes of machines for which, because of economic or other reasons, acceptance is
carried out on a test bed which can have different support structure characteristics from those at the
site. The support structure can significantly affect the measured vibration and every attempt should be
made to ensure that the natural frequencies of the complete test arrangement do not coincide with the
rotational frequencies of the machine or with any of its significant harmonics.
The test arrangement normally meets these requirements if the vibration magnitude measured in the
horizontal and vertical directions at the machine feet, or at the base frame near the bearing support or
stator feet, does not exceed 50 % of the vibration magnitude measured in the same measuring direction
at that bearing. Additionally, the test arrangement shall not cause a substantial change in any of the
major resonance frequencies.
If a significant support resonance is present during acceptance test and it cannot be eliminated, the
vibration acceptance may have to be carried out on the fully installed machine in situ.
For some classes of machines (e.g. small electrical machinery), acceptance tests can be carried out
when machines are supported by a resilient system (see, for example, IEC 60034-14). In this case, all
the rigid-body mode frequencies of the machine on its support system shall be less than one-half of the
lowest significant excitation frequency of the machine. Appropriate support conditions can be achieved
by mounting the machine on a resilient support baseplate or by free suspension on a soft spring.
4.6 Machine operating conditions
Shaft vibration measurements shall be made after achieving contractually agreed normal operating
conditions (speed, load, temperature, pressure, etc.). Additional vibration measurements that may be
taken under other conditions are not applicable for evaluation in accordance with Clause 6.
4.7 Evaluation of vibration from other sources
If the measured vibration magnitude exceeds the recommended limit, it can then be necessary to take
measurements of environmental vibration with the machine shut down to ensure that this is not making
a significant contribution to the observed vibration. Where possible, steps should be taken to reduce the
magnitude of environmental vibration if it is greater than one-third of the recommended limits.
5 Instrumentation
The instrumentation used shall be designed to operate satisfactorily in the environment for which it
is to be used, for example, with respect to temperature and humidity. Specification for instruments for
measuring vibration severity is given in ISO 2954 and instruments for measuring shaft vibration are
specified in ISO 10817-1.
Particular attention shall be given to ensure that the vibration transducer is correctly mounted and
that its presence does not affect the vibration response characteristics of the machine. Specifications
for mounting accelerometers are given in ISO 5348, which, in principle, are applicable also to velocity
transducers.
Modern instrumentation can provide multiple methods to deliver a measurement value. The acceptance
criteria here are based on r.m.s. velocity in mm/s for measurements on non-rotating parts and peak-
to-peak displacement in micrometres for measurements on rotating parts. The acceptance criteria
may be scaled suitably to match the units in common use at the site, using the same assumptions as
programmed into the distributed control systems.
It is desirable that the measurement system has provision for on-line calibration of the readout
instrumentation and, in addition, has suitable isolated outputs to permit further analysis as required.
10 © ISO 2016 – All rights reserved
6 Evaluation criteria
6.1 General
6.1.1 Overview
This clause specifies general criteria and principles for the evaluation of machine vibration. The
evaluation criteria relate to both operational monitoring and acceptance testing, and they apply only to
the vibration produced by the machine itself and not the vibration transmitted from outside.
The specification of evaluation criteria for machine vibration is dependent upon a wide range of
factors and the criteria adopted vary significantly for different types of machine and, in some cases,
for different rotors in the same coupled line. It is important, therefore, to ensure that valid criteria are
adopted for a particular machine and that the criteria which relate to a certain type of machine are not
erroneously applied to other types.
EXAMPLE Evaluation criteria for a high-speed compressor operating in a petrochemical plant are likely to
be different from those for large turbo-generators.
This clause establishes a basis for specifying evaluation criteria for measurements on non-rotating
parts, as well as on rotating shafts. No attempt has been made to specify vibration values. If the
procedures of both kinds of measurements are applicable, the one which is more restrictive shall
generally apply. Specific criteria for different classes and types of machinery are given in the relevant
parts of ISO 20816.
The criteria presented in this clause are applicable only to the vibration due to excitation from the
rotating elements. The criteria are not applicable to the evaluation of the electromagnetic vibration
excited at twice the line frequency (i.e. twice the electrical system frequency) and transmitted from the
generator stator core to the bearings.
6.1.2 Types of measurement on rotating shafts
6.1.2.1 There are two principal factors by which shaft vibration is judged:
a) absolute vibration of the shaft;
b) vibration of the shaft relative to the structural elements.
6.1.2.2 If the evaluation criterion is the change in shaft vibration, then
a) when the vibration of the structure, on which the shaft-relative transducer is mounted, is small (i.e.
less than 20 % of the relative shaft vibration), either the relative shaft vibration or absolute shaft
vibration may be used as a measure of shaft vibration, and
b) when the vibration of the structure, on which the shaft-relative transducer is mounted, is 20 % or
more of the relative shaft vibration, the absolute shaft vibration shall be measured and, if found to
be larger than the relative shaft vibration, it shall be used as the measure of shaft vibration.
6.1.2.3 If the evaluation criterion is the dynamic load on the bearing, the relative shaft vibration shall
be used as the measure of shaft vibration.
6.1.2.4 If the evaluation criterion is stator/rotor clearance, then
a) when the vibration of the structure, on which the shaft-relative transducer is mounted, is small
(i.e. less than 20 % of the relative shaft vibration), the relative shaft vibration shall be used as a
measure of clearance absorption, and
b) when the vibration of the structure, on which the shaft-relative transducer is mounted, is 20 % or
more of the relative shaft vibration, the relative shaft vibration measurement may still be used as a
measure of clearance absorption unless the vibration of the structure, on which the shaft-relative
transducer is mounted, is not representative of the total stator vibration. In this latter case, special
measurements are required.
6.1.2.5 The shaft vibration associated with a particular evaluation range depends on the size and mass
of the vibrating body, the characteristics of the mounting system and the output and use of the machine.
It is therefore necessary to take into account the various purposes and circumstances concerned when
specifying different ranges of shaft vibration for a specific class of machinery. Where appropriate,
reference should be made to the product specification.
6.2 Factors affecting evaluation criteria
There are a wide range of different factors which need to be taken into account when specifying
evaluation criteria for vibration measurements. Amongst these are the following:
a) the purpose for which the measurement is made (e.g. the requirement for ensuring that running
clearances are maintained is, in general, different from that if the avoidance of excessive dynamic
load on the bearing is the main concern);
b) the type of measurement made (vibration of non-rotating parts, relative or absolute shaft vibration);
c) the quantities measured (see Annex A);
d) the positions where the measurements are made;
e) the rotational speed of the shaft;
f) the bearing type, clearance and diameter;
g) the function, output and size of the machine;
h) the stiffness of the bearings, pedestals and foundations;
i) the rotor mass and stiffness.
Clearly, this wide range of factors makes it impossible to define unique evaluation criteria which can be
applied to all machines. Different criteria, which have been derived from operational experience, are
necessary for different machines, but at best, they can only be regarded as guidelines and there will be
occasions where machines will operate safely and satisfactorily outside any general recommendations
or are unable to operate despite vibration values are well within guideline values.
6.3 Types of evaluation criteria
6.3.1 General
Two evaluation criteria are used to assess vibration severity on various classes of machines. One
criterion considers the magnitude of observed broad-band vibration; the second considers changes in
magnitude, irrespective of whether they are increases or decreases.
6.3.2 Criterion I: Vibration magnitude at rated speed under steady operation conditions
6.3.2.1 Non-rotating parts
For non-rotating parts, this criterion is concerned with defining limits for absolute vibration magnitude
consistent with acceptable dynamic loads on the bearings and acceptable vibration transmission into
the support structure and foundation. The maximum vibration magnitude observed at each bearing
or pedestal is assessed against four evaluation zones established from international experience. This
maximum magnitude of vibration measured is defined as the vibration severity (see 4.3.3).
12 © ISO 2016 – All rights reserved
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