ISO 5348:2021

Mechanical vibration and shock — Mechanical mounting of accelerometers

This document specifies the important technical properties of the different methods for mounting vibration transducers and describes recommended practices. It also shows examples of how accelerometer mounting can influence frequency response and gives examples of how other influences can affect the fidelity of the representation of actual motion in the structure being observed. This document applies to the contacting type of accelerometer which is currently in wide use. It is applicable to both uniaxial and multi-axial transducers. This document can also be applied to velocity transducers. This document enables the user to estimate the limitations of a mounting and consequent potential measurement deviations. Transducer mounting issues are not the only problem that can affect the validity of acceleration measurement. Other such problems include, amongst others: transverse movements, alignment of the transducer, base bending, cable movement, temperature changes, electric and magnetic fields, cable whip and mounting torque. Issues other than mounting and their possible effects are outside the scope of this document.

Vibrations et chocs mécaniques — Fixation mécanique des accéléromètres

General Information

• Status: Published
• Publication Date: 28-Jan-2021
• ICS: 17.160 - Vibrations, shock and vibration measurements
• Technical Committee: ISO/TC 108 - Mechanical vibration, shock and condition monitoring
• Drafting Committee: ISO/TC 108 - Mechanical vibration, shock and condition monitoring
• Current Stage: 6060 - International Standard published
• Start Date: 29-Jan-2021
• Due Date: 22-Mar-2021
• Completion Date: 29-Jan-2021

Relations

• Revises: ISO 5348:1998 - Mechanical vibration and shock — Mechanical mounting of accelerometers
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 5348
Third edition
2021-01
Mechanical vibration and
shock — Mechanical mounting of
accelerometers
Vibrations et chocs mécaniques — Fixation mécanique des
accéléromètres
Reference number
ISO 5348:2021(E)
©
ISO 2021

---------------------- Page: 1 ----------------------
ISO 5348:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 5348:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Basics . 1
5 Characteristics to be specified by manufacturers of accelerometers .4
6 Considerations for selecting a mounting method . 4
6.1 General considerations . 4
6.1.1 Procedures . 4
6.1.2 Conditions . 4
6.2 Specific considerations . 5
6.2.1 Frequency range of operation . 5
6.2.2 Transducer cable . 5
6.3 Determination of the mounted fundamental resonance frequency. 6
6.3.1 General. 6
6.3.2 Vibration excitation method . 6
6.3.3 Shock excitation methods . 7
6.4 Recommendations for particular types of mountings . 8
6.4.1 General. 8
6.4.2 Stud mounting . 9
6.4.3 Adhesive mounting .10
6.4.4 Magnets .13
6.4.5 Quick mount.13
6.4.6 Probe .14
6.4.7 Conical bolting .14
6.4.8 Low-percussion mounting devices for recording human exposure to vibration .15
6.4.9 Mounting by three-point support and ground spikes.15
6.4.10 Wedge anchors .15
6.4.11 Mounting fixtures .15
7 Typical frequency response for various types of mounting .16
8 Further mounting aspects .19
8.1 Base strain sensitivity of an accelerometer .19
8.2 Thermal mounting effects .19
8.3 Electrical ground loops .20
Bibliography .21
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ISO 5348:2021(E)

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 of the voluntary nature of standards, 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 www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and
condition monitoring.
This third edition cancels and replaces the second edition (ISO 5348:1998), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the theory of mass and stiffness influence on the frequency response obtained has been expanded;
— the frequency responses have been replaced by actual measurements and have been made more
comparable;
— the influence of electrical loops has been added.
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.
iv © ISO 2021 – All rights reserved

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ISO 5348:2021(E)

Introduction
The method most commonly used for determining the vibratory motion of a structure or body is
the use of an electromechanical vibration transducer, also called a transducer or a vibration sensor.
These vibration transducers can be divided into the two broad classes: non-contacting and contacting
transducers.
Non-contacting transducers are relative measuring transducers recording a motion in relation to a
fixed space coordinate system. Typical examples are eddy-current probes, optical sensors and laser
vibrometers. These transducers have no direct mechanical contact with the structure and are therefore
not dealt with in this document.
Contacting transducers are mounted onto the structure by mechanical coupling. This includes, for
example, piezoelectric, capacitive and piezoresistive accelerometers as well as seismic velocity
transducers. These absolute measuring transducers record the motion by seismic forces from the space
coordinate system onto which they are mounted. If such a transducer is mounted onto a structure, the
properties of the mounting can significantly influence the frequency response of the structure as well
as the vibration transducer. Very large measurement deviations can occur in case of lack of care in the
mounting property, particularly at high frequencies.
Under certain circumstances the mass, geometry and mounting stiffness of the transducer can directly
influence the measured vibration amplitude of the structure. This effect occurs for example if the
masses of the transducer and the structure are in the same order of magnitude.
This document is concerned with the contacting type of seismic accelerometers and seismic velocity
transducers which are currently in wide use. The concern with using such transducers is that the
mechanical coupling between the accelerometer and the test structure can significantly alter the
response of the accelerometer, the structure or both. This document attempts to isolate parameters of
concern in the selection of a method to mount the accelerometer onto the structure.
In a basic sense, many aspects of velocity transducer mounting are similar to those of accelerometers,
but they are not identical. Please refer to 6.2.1.
This document does not cover geophones.
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INTERNATIONAL STANDARD ISO 5348:2021(E)
Mechanical vibration and shock — Mechanical mounting of
accelerometers
1 Scope
This document specifies the important technical properties of the different methods for mounting
vibration transducers and describes recommended practices. It also shows examples of how
accelerometer mounting can influence frequency response and gives examples of how other influences
can affect the fidelity of the representation of actual motion in the structure being observed.
This document applies to the contacting type of accelerometer which is currently in wide use. It is
applicable to both uniaxial and multi-axial transducers. This document can also be applied to velocity
transducers.
This document enables the user to estimate the limitations of a mounting and consequent potential
measurement deviations.
Transducer mounting issues are not the only problem that can affect the validity of acceleration
measurement. Other such problems include, amongst others: transverse movements, alignment of the
transducer, base bending, cable movement, temperature changes, electric and magnetic fields, cable
whip and mounting torque. Issues other than mounting and their possible effects are outside the scope
of this document.
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 2041, Mechanical vibration, shock and condition monitoring — Vocabulary
ISO 8042, Shock and vibration measurements — Characteristics to be specified for seismic pick-ups
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2041 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Basics
A vibration transducer is mounted on the surface of a structure in motion, as illustrated in the simplified
diagram shown in Figure 1. Under ideal conditions, the vibration transducer supplies an electric signal
at its output which is proportional to the magnitude of the mechanical acceleration input vector, a .
N
The vector a is normally directed to the transducer base and measures the projection of the structure
N
vibration acceleration vector, a , in the direction of the transducer nominal sensitive vectorial axis, a
S N
(measurement direction).
The vibration in the direction of the acceleration vector, a , on the structure is transferred into the
S
measurement direction of the transducer via the mechanical mounting fixture. Frequency-dependent
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ISO 5348:2021(E)

changes of the nominal vibration amplitude, a , of the transducer can occur due to the dynamic
N
properties of the mounting fixture with its mechanical stiffness, damping and the transducer mass. The
mechanical mounting therefore changes the usable frequency range of the transducer with regards to
amplitude and phase for a given accuracy (see 6.2.1). This document is only applicable to the mounting
of accelerometers which are mounted on the surface of the structure in motion, as shown in the
simplified diagram in Figure 1.
Key
a nominal vibration acceleration vector
N
a structure vibration acceleration vector
S
1 electrical connector
2 transducer base
3 transducer
4 mounting fixture
5 structure
Figure 1 — Mounting of an accelerometer
Often, the transducer vibration acceleration vector with the largest sensitivity is not parallel to the
accelerometer nominal axis, as a is perpendicular to its coupling mounting area, as shown in Figure 1.
N
This forms a cross axis sensitivity of the transducer; see ISO 16063-31. Cross axis sensitivity is
maximal in one direction and ideally zero in a direction perpendicular to this in the mounting area. In
some transducers on the market, a red dot marks the minimal cross axis sensitive direction. Mounting
the transducer in this direction minimizes the cross axis sensitive effects of the transducer during a
measurement, if large lateral acceleration magnitudes occur by proper alignment of the transducer.
Figure 2 illustrates the complex vectorial relationship between the structure vibration vector, a ,
S
the accelerometer nominal axis vector, a , the transducer vibration acceleration vector with largest
N
sensitivity, a , and the angles φ, α and α in between them. The elimination of these alignment
T 1 2
deviations usually requires a coordinate transformation. In this consideration, the projection of the
S S S
structure vibration acceleration vector, a = (a , a , a ), to the transducer vibration acceleration
S X Y Z
T T T
vector with largest sensitivity, a = (a , a , a ), forms the output signal, u, of the transducer. But it is
T X Y Z
N N N
the magnitude in the direction of the accelerometer nominal axis vector, a = (a , a , a ), which is of
N X Y Z
interest.
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ISO 5348:2021(E)

Key
N N N
a accelerometer nominal axis perpendicular to its coupling mounting area (a , a , a )
N X Y Z
S S S
a structure vibration acceleration vector (a , a , a )
S X Y Z
T T T
a transducer vibration acceleration vector with largest sensitivity (a , a , a )
T X Y Z
φ angle between a and a
N T
α angle between a and a
1 N S
α angle between a and a
2 S T
1 axis of minimum cross sensitivity
2 axis of maximum cross sensitivity
3 red dot, assigning minimal cross axis sensitivity axis
4 cross sensitivity vector
NOTE For exact measurement of the structure vibration, the vectors a and a are ideally identical in amount
S N
and direction; see 6.1.1.
Figure 2 — Acceleration vector considerations for mounting the accelerometer
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ISO 5348:2021(E)

5 Characteristics to be specified by manufacturers of accelerometers
The technical characteristics of vibration transducers shall be specified in accordance with ISO 8042
in the data sheet or manual. From a multitude of information items, only a few are relevant for the
mounting of transducers:
a) frequency response under well-defined mounting conditions, range of operation and best possible
mounting;
b) mounting surface of the transducer: dimensions of the mounting surface, mounting options, thread
dimensions, thread depths, sectional view of the mounting surface, material of the mounting
surface, surface finish roughness, surface flatness, hole perpendicularity and tap class;
c) applicable recommended mounting torque and, as an option, the maximum permitted mounting
torque;
d) geometric dimensions of the vibration transducer, including:
— position of the centre of gravity of the vibration transducer as a whole,
— position of the centre of gravity of the seismic mass of the vibration transducer;
e) pertinent mechanical characterisitics of the accelerometer, i.e.:
— total mass of the vibration transducer,
— material of the base,
— maximal transverse sensitivity and frequency at which it was determined;
f) first resonance frequency of the vibration transducer under mounting conditions;
g) temperature limitations of the transducer and the fastening device.
6 Considerations for selecting a mounting method
6.1 General considerations
6.1.1 Procedures
An accelerometer achieves optimal performance only if the following general procedures are followed:
a) The accelerometer shall perform as closely as possible the same motion as the structure at the
accelerometer attachment.
b) The motion of the structure is changed as little as possible by the addition of the accelerometer, for
example, by mass loading and reinforcement in the mounting surface area.
6.1.2 Conditions
In order to achieve the aforementioned ideal conditions, it shall be ensured that:
a) the accelerometer and its mounting are as rigid and firm as possible and the mounting surfaces are
as clean and flat as possible;
b) distortions due to natural vibrations of the mounting are only very small (e.g. symmetrical
mountings shall be aimed at);
c) the mass of the accelerometer and mounting are small in comparison with that of the dynamic
mass of the structure (see ISO 2954).
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ISO 5348:2021(E)

6.2 Specific considerations
6.2.1 Frequency range of operation
The accelerometer shall be used well below its mounted fundamental resonance frequency to prevent
amplitude distortions. In the case of undamped accelerometers (resonance magnification factor, Q,
greater 30 dB) and mounting in accordance with manufacturer’s recommendations, the following limit
frequencies can be used for estimation of the amplitude deviations:
— the amplitude deviations of the transducer are mostly lower than 5 % for up to approximately 20 %
of the resonance frequency of the transducer;
— the amplitude deviations are mostly lower than 10 % for up to approximately 30 % of the resonance
frequency;
— the amplitude deviations are mostly lower than 3 dB for up to approximately 50 % of the resonance
frequency.
NOTE 1 Special measurement methods exist, for example, in the rolling bearing condition monitoring that
operates in the resonance range of the accelerometer.
NOTE 2 For single-shock measurements, deviations of a few percent can be expected if the mounted
fundamental resonance frequency is ten times greater than the inverse of the pulse duration.
NOTE 3 Electrodynamic vibration velocity transducers are mostly used above their resonance frequency.
6.2.2 Transducer cable
Relative movement of the cable to the transducer can lead to incorrect measurement signals, in
particular in the case of stiff cables. Careful clamping and laying of the cables is required to avoid this
problem (see Figure 3).
Loose, moving cables can introduce triboelectric effects for piezoelectric type transducers with charge
output or impose dynamic response on the transducer not consistent with the motion of the tested
surface.
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ISO 5348:2021(E)

a) Accelerometer with axial connector b) Accelerometer with radial connector
Key
1 cable entry — do not stress
2 vibrating surface
3 cable entry — do not stress
4 fix cable to the surface
Figure 3 — Accelerometer with axial and radial connectors
6.3 Determination of the mounted fundamental resonance frequency
6.3.1 General
It is very useful, although difficult at times in practice, to accurately determine the mounted fundamental
resonance frequency of the accelerometer mounted on a structure. The resonance frequency in the
nominal measuring direction can vary widely from that in the lateral direction (which is usually lower).
For multi-axial accelerometers, the resonance frequencies of the axes can vary considerably.
The following methods can be of use in determining the approximate resonance frequency, thus
ensuring that an adequate margin exists between the resonance frequency and test frequency.
6.3.2 Vibration excitation method
A suitable electrodynamic vibration exciter with reference transducer can be used to assess the
influence of the quality of mounting surfaces and materials. For this purpose, the materials under test
are mounted between the armature of the vibration exciter and the transducer and its output signal as
a function of the vibration frequency is measured.
For the method of determining the fundamental (resonance) frequency, see ISO 5347-22 and
ISO 16063-32.
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ISO 5348:2021(E)

6.3.3 Shock excitation methods
For the method of determining the mounted fundamental resonance frequency by shock excitation,
see ISO 16063-32. Beside ISO 16063-32, the following measurement technologies are also in use: the
pendulum impact test, the drop test, a simple hammer blow and breakage of a pencil lead.
In the first case, the accelerometer is attached to a counterweight suspended from a pendulum while a
similarly suspended weight acts as a hammer providing the blow.
In the drop test, the accelerometer is mounted onto a hammer which is guided in its vertical fall onto
a stationary anvil to provide the shock. The mounting of the accelerometer to the weight should be
similar to the test body (actual structure under test) mounting. When it is impossible to represent the
test body by the mass of the hammer or anvil in a realistic way, the weight should be made of the same
material and of sufficient size to be a reasonable representation of the test body in terms of stiffness.
One hammer blow applied near the mounted accelerometer on the actual structure can provide the
necessary information, if structural resonances in the test body can be disregarded.
The accelerometer output signal produced by the shock under suitable conditions has the resonance
frequency superimposed (see Figure 4) in cases where the shock duration, t , is shorter than 5/f ,
S Res
where f is the lowest mounted fundamental resonance frequency of the accelerometer.
Res
Some experimentation is required with the energy of shock (i.e. the height from which the weight is
released) and the stiffness of the impact surface (e.g. steel or lead lined) to obtain a suitable period of
impact for displaying the resonance effects. The lowest resonance should be excited during the shock.
The use of a suitable single-event recorder, for example, a storage oscilloscope, enables the frequency
of the resonance ripple (i.e. of the oscillations) to be determined. These methods are particularly suited
for high frequencies.
When repeated, consistently well-defined shocks can give additional information about the stability of
the mounting.
Key
X time
Y acceleration
1 shock response with resonance ripple
Figure 4 — Accelerometer response to shock at shock duration t < 5/f
S Res
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ISO 5348:2021(E)

A broadband shock response spectrum can be generated by breaking a pencil lead (preferably with a
diameter of 0,5 mm and a hardness of 2H) in the direction of the sensitive axis of the accelerometer
under test in the vicinity of the mounting area. For this purpose, a commercially available mechanical
pencil is equipped with a plastic moulded part which specifies the breaking angle and prevents
bouncing (see ASTM E976). Here the shock duration, t , is shorter than 1/f and the accelerometer
S Res
[16]
under test is excited in its lowest fundamental mounted resonance frequency , as shown in Figure 5.
key
X time
Y acceleromter output signal
a input shock pulse (approx. dirac pulse)
b typical impulse response of an accelerometer (resonance oscillation)
Figure 5 — Accelerometer response to shock (idealized illustration)
6.4 Recommendations for particular types of mountings
6.4.1 General
The mounting surface on the structure shall be carefully examined for smoothness and contamination
and, if necessary, it shall be machined flat. The size of the contact area of magnets, adhesive mounting
pads and other mounting parts should be at least as large as the mounting surface of the transducer. If
possible, any lack of alignment between the sensitive axis of the accelerometer and the measurement
direction shall be kept to a minimum; otherwise this can lead to deviations introduced by angular
deviation and transverse sensitivity. These deviations can be particularly large if the transverse motion
is much greater than the axial motion.
The higher the frequency to be measured, the higher the static mounting force and the stiffness of the
mounting should be.
The masses of the transducer and fastening material and the resonant cable should be as low as possible
in order to minimize the influence on the measurement object.
For vibration measurements on electrical machines, it can be necessary to mount the transducer in an
isolated manner in order to prevent ground loops (see 8.3).
8 © ISO 2021 – All rights reserved

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ISO 5348:2021(E)

The condition of the mounting surface and method of mounting should be stated in reports.
In order to meet the manufacturer's specification, the recommended mounting method for the
transducer should be used.
Table 1 provides an overview of criteria for the selection of mounting methods, based on best practices.
Table 1 — Criteria for the selection of mounting methods
Attachment Resonance frequency Static strength Temperature resist- Importance of sur-
fidelity ance face preparation
Stud or
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 5348
ISO/TC 108
Mechanical vibration and
Secretariat: ANSI
shock — Mechanical mounting of
Voting begins on:
2020­10­16 accelerometers
Voting terminates on:
Vibrations et chocs mécaniques — Fixation mécanique des
2020­12­11
accéléromètres
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 5348:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020

---------------------- Page: 1 ----------------------
ISO/FDIS 5348:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 5348:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Basics . 1
5 Characteristics to be specified by manufacturers of accelerometers .4
6 Considerations for selecting a mounting method . 4
6.1 General considerations . 4
6.1.1 Procedures . 4
6.1.2 Conditions . 4
6.2 Specific considerations . 5
6.2.1 Frequency range of operation . 5
6.2.2 Transducer cable . 5
6.3 Determination of the mounted fundamental resonance frequency. 6
6.3.1 General. 6
6.3.2 Vibration excitation method . 6
6.3.3 Shock excitation methods . 6
6.4 Recommendations for particular types of mountings . 8
6.4.1 General. 8
6.4.2 Stud mounting . 9
6.4.3 Adhesive mounting .10
6.4.4 Magnets .12
6.4.5 Quick mount.13
6.4.6 Probe .13
6.4.7 Conical bolting .13
6.4.8 Low-percussion mounting devices for recording human exposure to vibration .14
6.4.9 Mounting by three-point support and ground spikes.14
6.4.10 Wedge anchors .14
6.4.11 Mounting fixtures .14
7 Typical frequency response for various types of mounting .15
8 Further mounting aspects .18
8.1 Base strain sensitivity of an accelerometer .18
8.2 Thermal mounting effects .18
8.3 Electrical ground loops .19
Bibliography .20
© ISO 2020 – All rights reserved iii

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ISO/FDIS 5348:2020(E)

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 non­governmental, 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 of the voluntary nature of standards, 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 www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and
condition monitoring.
This third edition cancels and replaces the second edition (ISO 5348:1998), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the theory of mass and stiffness influence on the frequency response obtained has been expanded;
— the frequency responses have been replaced by actual measurements and have been made more
comparable;
— the influence of electrical loops has been added.
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.
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 5348:2020(E)

Introduction
The method most commonly used for determining the vibratory motion of a structure or body is
the use of an electromechanical vibration transducer, also called a transducer or a vibration sensor.
These vibration transducers can be divided into the two broad classes: non­contacting and contacting
transducers.
Non­contacting transducers are relative measuring transducers recording a motion in relation to a
fixed space coordinate system. Typical examples are eddy-current probes, optical sensors and laser
vibrometers. These transducers have no direct mechanical contact with the structure and are therefore
not dealt with in this document.
Contacting transducers are mounted onto the structure by mechanical coupling. This includes, for
example, piezoelectric, capacitive and piezoresistive accelerometers as well as seismic velocity
transducers. These absolute measuring transducers record the motion by seismic forces from the space
coordinate system onto which they are mounted. If such a transducer is mounted onto a structure, the
properties of the mounting can significantly influence the frequency response of the structure as well
as the vibration transducer. Very large measurement deviations can occur in case of lack of care in the
mounting property, particularly at high frequencies.
Under certain circumstances the mass, geometry and mounting stiffness of the transducer can directly
influence the measured vibration amplitude of the structure. This effect occurs for example if the
masses of the transducer and the structure are in the same order of magnitude.
This document is concerned with the contacting type of seismic accelerometers and seismic velocity
transducers which are currently in wide use. The concern with using such transducers is that the
mechanical coupling between the accelerometer and the test structure can significantly alter the
response of the accelerometer, the structure or both. This document attempts to isolate parameters of
concern in the selection of a method to mount the accelerometer onto the structure.
In a basic sense, many aspects of velocity transducer mounting are similar to those of accelerometers,
but they are not identical. Please refer to 6.2.1.
This document does not cover geophones.
© ISO 2020 – All rights reserved v

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 5348:2020(E)
Mechanical vibration and shock — Mechanical mounting of
accelerometers
1 Scope
This document specifies the important technical properties of the different methods for mounting
vibration transducers and describes recommended practices. It also shows examples of how
accelerometer mounting can influence frequency response and gives examples of how other influences
can affect the fidelity of the representation of actual motion in the structure being observed.
This document applies to the contacting type of accelerometer which is currently in wide use. It
is applicable to both uniaxial and multi-axial transducers. This document also applies to velocity
transducers.
This document enables the user to estimate the limitations of a mounting and consequent potential
measurement deviations.
NOTE Transducer mounting issues are not the only problem that can affect the validity of acceleration
measurement. Other such problems include, amongst others: transverse movements, alignment of the transducer,
base bending, cable movement, temperature changes, electric and magnetic fields, cable whip and mounting torque.
Issues other than mounting and their possible effects are outside the scope of this document.
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 2041, Mechanical vibration, shock and condition monitoring — Vocabulary
ISO 8042, Shock and vibration measurements — Characteristics to be specified for seismic pick-ups
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2041 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Basics
A vibration transducer is mounted on the surface of a structure in motion, as illustrated in the simplified
diagram shown in Figure 1. Under ideal conditions, the vibration transducer supplies an electric signal
at its output which is proportional to the magnitude of the mechanical acceleration input vector, a .
N
The vector a is normally directed to the transducer base and measures the projection of the structure
N
vibration acceleration vector, a , in the direction of the transducer nominal sensitive vectorial axis, a
S N
(measurement direction).
The vibration in the direction of the acceleration vector, a , on the structure is transferred into the
S
measurement direction of the transducer via the mechanical mounting fixture. Frequency-dependent
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changes of the nominal vibration amplitude, a , of the transducer can occur due to the dynamic
N
properties of the mounting fixture with its mechanical stiffness, damping and the transducer mass. The
mechanical mounting therefore changes the usable frequency range of the transducer with regards to
amplitude and phase for a given accuracy (see 6.2.1). This document is only applicable to the mounting
of accelerometers which are mounted on the surface of the structure in motion, as shown in the
simplified diagram in Figure 1.
Key
a nominal vibration acceleration vector
N
a structure vibration acceleration vector
S
1 electrical connector
2 transducer base
3 transducer
4 mounting fixture
5 structure
Figure 1 — Mounting of an accelerometer
Often, the transducer vibration acceleration vector with the largest sensitivity is not parallel to the
accelerometer nominal axis, as a is perpendicular to its coupling mounting area, as shown in Figure 1.
N
This forms a cross axis sensitivity of the transducer; see ISO 16063-31. Cross axis sensitivity is
maximal in one direction and ideally zero in a direction perpendicular to this in the mounting area. In
some transducers on the market, a red dot marks the minimal cross axis sensitive direction. Mounting
the transducer in this direction minimizes the cross axis sensitive effects of the transducer during a
measurement, if large lateral acceleration magnitudes occur by proper alignment of the transducer.
Figure 2 illustrates the complex vectorial relationship between the structure vibration vector, a ,
S
the accelerometer nominal axis vector, a , the transducer vibration acceleration vector with largest
N
sensitivity, a , and the angles φ, α and α in between them. The elimination of these alignment
T 1 2
deviations usually requires a coordinate transformation. In this consideration, the projection of the
S S S
structure vibration acceleration vector, a = (a , a , a ), to the transducer vibration acceleration
S X Y Z
T T T
vector with largest sensitivity, a = (a , a , a ), forms the output signal, u, of the transducer. But it is
T X Y Z
N N N
the magnitude in the direction of the accelerometer nominal axis vector, a = (a , a , a ), which is of
N X Y Z
interest.
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Key
N N N
a accelerometer nominal axis perpendicular to its coupling mounting area (a , a , a )
N X Y Z
S S S
a structure vibration acceleration vector (a , a , a )
S X Y Z
T T T
a transducer vibration acceleration vector with largest sensitivity (a , a , a )
T X Y Z
φ angle between a and a
N T
α angle between a and a
1 N S
α angle between a and a
2 S T
1 axis of minimum cross sensitivity
2 axis of maximum cross sensitivity
3 red dot, assigning minimal cross axis sensitivity axis
4 cross sensitivity vector
NOTE For exact measurement of the structure vibration, the vectors a and a are ideally identical in amount
S N
and direction; see 6.1.1.
Figure 2 — Acceleration vector considerations for mounting the accelerometer
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5 Characteristics to be specified by manufacturers of accelerometers
The technical characteristics of vibration transducers shall be specified in accordance with ISO 8042
in the data sheet or manual. From a multitude of information items, only a few are relevant for the
mounting of transducers:
a) frequency response under well-defined mounting conditions, range of operation and best possible
mounting;
b) mounting surface of the transducer: dimensions of the mounting surface, mounting options, thread
dimensions, thread depths, sectional view of the mounting surface, material of the mounting
surface, surface finish roughness, surface flatness, hole perpendicularity and tap class;
c) applicable recommended mounting torque and, as an option, the maximum permitted mounting
torque;
d) geometric dimensions of the vibration transducer, including:
— position of the centre of gravity of the vibration transducer as a whole,
— position of the centre of gravity of the seismic mass of the vibration transducer;
e) pertinent mechanical characterisitics of the accelerometer, i.e.:
— total mass of the vibration transducer,
— material of the base,
— maximal transverse sensitivity and frequency at which it was determined;
f) first resonance frequency of the vibration transducer under mounting conditions;
g) temperature limitations of the transducer and the fastening device.
6 Considerations for selecting a mounting method
6.1 General considerations
6.1.1 Procedures
An accelerometer achieves optimal performance only if the following general procedures are followed:
a) The accelerometer shall perform as closely as possible the same motion as the structure at the
accelerometer attachment.
b) The motion of the structure is changed as little as possible by the addition of the accelerometer, for
example, by mass loading and reinforcement in the mounting surface area.
6.1.2 Conditions
In order to achieve the aforementioned ideal conditions, it shall be ensured that:
a) the accelerometer and its mounting are as rigid and firm as possible and the mounting surfaces are
as clean and flat as possible;
b) distortions due to natural vibrations of the mounting are only very small (e.g. symmetrical
mountings shall be aimed at);
c) the mass of the accelerometer and mounting are small in comparison with that of the dynamic
mass of the structure (see ISO 2954).
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6.2 Specific considerations
6.2.1 Frequency range of operation
The accelerometer shall be used well below its mounted fundamental resonance frequency to prevent
amplitude distortions. In the case of undamped accelerometers (resonance magnification factor, Q,
greater 30 dB) and mounting in accordance with manufacturer’s recommendations, the following limit
frequencies can be used for estimation of the amplitude deviations:
— the amplitude deviations of the transducer are mostly lower than 5 % for up to approximately 20 %
of the resonance frequency of the transducer;
— the amplitude deviations are mostly lower than 10 % for up to approximately 30 % of the resonance
frequency;
— the amplitude deviations are mostly lower than 3 dB for up to approximately 50 % of the resonance
frequency.
NOTE 1 Special measurement methods exist, for example, in the rolling bearing condition monitoring that
operates in the resonance range of the accelerometer.
NOTE 2 For single-shock measurements, deviations of a few percent can be expected if the mounted
fundamental resonance frequency is ten times greater than the inverse of the pulse duration.
NOTE 3 Electrodynamic vibration velocity transducers are mostly used above their resonance frequency.
6.2.2 Transducer cable
Relative movement of the cable to the transducer can lead to incorrect measurement signals, in
particular in the case of stiff cables. Careful clamping and laying of the cables is required to avoid this
problem (see Figure 3).
Loose, moving cables can introduce triboelectric effects for piezoelectric type transducers with charge
output or impose dynamic response on the transducer not consistent with the motion of the tested
surface.
a) Accelerometer with axial connector b) Accelerometer with radial connector
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Key
1 cable entry — do not stress
2 vibrating surface
3 cable entry — do not stress
4 fix cable to the surface
Figure 3 — Accelerometer with axial and radial connectors
6.3 Determination of the mounted fundamental resonance frequency
6.3.1 General
It is very useful, although difficult at times in practice, to accurately determine the mounted fundamental
resonance frequency of the accelerometer mounted on a structure. The resonance frequency in the
nominal measuring direction can vary widely from that in the lateral direction (which is usually lower).
For multi-axial accelerometers, the resonance frequencies of the axes can vary considerably.
The following methods can be of use in determining the approximate resonance frequency, thus
ensuring that an adequate margin exists between the resonance frequency and test frequency.
6.3.2 Vibration excitation method
A suitable electrodynamic vibration exciter with reference transducer can be used to assess the
influence of the quality of mounting surfaces and materials. For this purpose, the materials under test
are mounted between the armature of the vibration exciter and the transducer and its output signal as
a function of the vibration frequency is measured.
For the method of determining the fundamental (resonance) frequency, see ISO 5347-22 and
ISO 16063­32.
6.3.3 Shock excitation methods
For the method of determining the mounted fundamental resonance frequency by shock excitation,
see ISO 16063­32. Beside ISO 16063­32, the following measurement technologies are also in use: the
pendulum impact test, the drop test, a simple hammer blow and breakage of a pencil lead.
In the first case, the accelerometer is attached to a counterweight suspended from a pendulum while a
similarly suspended weight acts as a hammer providing the blow.
In the drop test, the accelerometer is mounted onto a hammer which is guided in its vertical fall onto
a stationary anvil to provide the shock. The mounting of the accelerometer to the weight should be
similar to the test body (actual structure under test) mounting. When it is impossible to represent the
test body by the mass of the hammer or anvil in a realistic way, the weight should be made of the same
material and of sufficient size to be a reasonable representation of the test body in terms of stiffness.
One hammer blow applied near the mounted accelerometer on the actual structure can provide the
necessary information, if structural resonances in the test body can be disregarded.
The accelerometer output signal produced by the shock under suitable conditions has the resonance
frequency superimposed (see Figure 4) in cases where the shock duration, t , is shorter than 5/f ,
S Res
where f is the lowest mounted fundamental resonance frequency of the accelerometer.
Res
Some experimentation is required with the energy of shock (i.e. the height from which the weight is
released) and the stiffness of the impact surface (e.g. steel or lead lined) to obtain a suitable period of
impact for displaying the resonance effects. The lowest resonance should be excited during the shock.
The use of a suitable single-event recorder, for example, a storage oscilloscope, enables the frequency
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of the resonance ripple (i.e. of the oscillations) to be determined. These methods are particularly suited
for high frequencies.
When repeated, consistently well-defined shocks can give additional information about the stability of
the mounting.
Key
X time
Y acceleration
1 shock response with resonance ripple
Figure 4 — Accelerometer response to shock at shock duration t < 5/f
S Res
A broadband shock response spectrum can be generated by breaking a pencil lead (preferably with a
diameter of 0,5 mm and a hardness of 2H) in the direction of the sensitive axis of the accelerometer
under test in the vicinity of the mounting area. For this purpose, a commercially available mechanical
pencil is equipped with a plastic moulded part which specifies the breaking angle and prevents
bouncing (see ASTM E976). Here the shock duration, t , is shorter than 1/f and the accelerometer
S Res
[16]
under test is excited in its lowest fundamental mounted resonance frequency , as shown in Figure 5.
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key
X time
Y acceleromter output signal
a input shock pulse (approx. dirac pulse)
b typical impulse response of an accelerometer (resonance oscillation)
Figure 5 — Accelerometer response to shock (idealized illustration)
6.4 Recommendations for particular types of mountings
6.4.1 General
The mounting surface on the structure shall be carefully examined for smoothness and contamination
and, if necessary, it shall be machined flat. The size of the contact area of magnets, adhesive mounting
pads and other mounting parts should be at least as large as the mounting surface of the transducer. If
possible, any lack of alignment between the sensitive axis of the accelerometer and the measurement
direction shall be kept to a minimum; otherwise this can lead to deviations introduced by angular
deviation and transverse sensitivity. These deviations can be particularly large if the transverse motion
is much greater than the axial motion.
The higher the frequency to be measured, the higher the static mounting force and the stiffness of the
mounting should be.
The masses of the transducer and fastening material and the resonant cable should be as low as possible
in order to minimize the influence on the measurement object.
For vibration measurements on electrical machines, it can be necessary to mount the transducer in an
isolated manner in order to p
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