Methods for the calibration of vibration and shock transducers — Part 21: Vibration calibration by comparison to a reference transducer

ISO 16063-21:2003 describes the calibration of rectilinear vibration transducers by comparison. Although it mainly describes calibration using direct comparison to a standard calibrated by primary methods, the methods described can be applied between other levels in the calibration hierarchy. ISO 16063-21:2003 specifies procedures for performing calibrations of rectilinear vibration transducers by comparison in the frequency range from 0,4 Hz to 10 kHz. It is primarily intended for those who are required to meet ISO standardized methods for the measurement of vibration under laboratory conditions, where the uncertainty of measurement is relatively small. It can also be used under field conditions, where the uncertainty of measurement may be relatively large. From knowledge of all significant sources of uncertainty affecting the calibration, the expanded uncertainty can be evaluated using the methods given in ISO 16063-21. It also covers the assessment of uncertainties for calibrations performed using a check standard.

Méthodes pour l'étalonnage des transducteurs de vibrations et de chocs — Partie 21: Étalonnage de vibrations par comparaison à un transducteur de référence

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Status
Published
Publication Date
18-Aug-2003
Current Stage
9093 - International Standard confirmed
Start Date
16-Oct-2008
Completion Date
24-Jul-2019
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INTERNATIONAL ISO
STANDARD 16063-21
First edition
2003-08-15
Methods for the calibration of vibration
and shock transducers —
Part 21:
Vibration calibration by comparison to a
reference transducer
Méthodes pour l'étalonnage des transducteurs de vibrations et de
chocs —
Partie 21: Étalonnage de vibrations par comparaison à un transducteur
de référence
Reference number
ISO 16063-21:2003(E)
ISO 2003
---------------------- Page: 1 ----------------------
ISO 16063-21:2003(E)
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ii © ISO 2003 — All rights reserved
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ISO 16063-21:2003(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope...................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Uncertainty of measurement................................................................................................................ 2

4 Requirements for apparatus and environmental conditions............................................................ 3

4.1 General................................................................................................................................................... 3

4.2 Environmental conditions.................................................................................................................... 3

4.3 Reference transducer ........................................................................................................................... 3

4.4 Vibration generation equipment.......................................................................................................... 4

4.5 Voltage measuring instrumentation.................................................................................................... 6

4.6 Distortion measuring instrumentation................................................................................................ 6

4.7 Oscilloscope.......................................................................................................................................... 7

4.8 Phase shift measuring instrumentation ............................................................................................. 7

5 Calibration.............................................................................................................................................. 7

5.1 Preferred amplitudes and frequencies ............................................................................................... 7

5.2 Measurement requirements ................................................................................................................. 7

5.3 Calibration procedure........................................................................................................................... 8

6 Expression of results............................................................................................................................ 8

7 Reporting the calibration results......................................................................................................... 9

Annex A (normative) Expression of uncertainty of measurement in calibration ...................................... 11

Annex B (normative) Definitions of amplitude sign and phase shift between mechanical motion

and vibration transducer electrical output....................................................................................... 20

Annex C (informative) Nomogram for conversion between acceleration, velocity and

displacement ....................................................................................................................................... 22

Annex D (informative) Example of uncertainty calculation.......................................................................... 24

Bibliography ..................................................................................................................................................... 29

© ISO 2003 — All rights reserved iii
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ISO 16063-21:2003(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.

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 16063-21 was prepared by Technical Committee ISO/TC 108, Mechanical vibration and shock,

Subcommittee SC 3, Use and calibration of vibration and shock measuring instruments.

This first edition of ISO 16063-21 cancels and replaces ISO 5347-3:1993, which has been technically revised.

ISO 16063 consists of the following parts, under the general title Methods for the calibration of vibration and

shock transducers:
— Part 1: Basic concepts
— Part 11: Primary vibration calibration by laser interferometry
— Part 12: Primary vibration calibration by the reciprocity method
— Part 13: Primary shock calibration using laser interferometry
— Part 21: Vibration calibration by comparison to a reference transducer

— Part 22: Shock calibration by comparison to an accelerometer, velocity or force transducer

iv © ISO 2003 — All rights reserved
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ISO 16063-21:2003(E)
Introduction

The ISO 16063 series of standards is concerned with methods for the calibration of vibration and shock

transducers under both standard laboratory conditions and in the field.

As such, the intended user group of this part of ISO 16063 is wide, ranging from metrologists in mechanical

vibration to technicians evaluating the vibration characteristics of a machine or structure, or human exposure

to vibration. The key to the application of this part of ISO 16063 is in the careful detailed specification and

evaluation of measurement uncertainty, i.e. the error budget and computation of expanded uncertainty

associated with the measurement of vibration.

This part of ISO 16063 is particularly intended for those engaged in vibration measurements requiring

traceability to primary national or international standards through a secondary, reference, working or check

standard (portable calibrator intended for field use) as defined in the International vocabulary of basic and

general terms in metrology (VIM). The specifications for the instrumentation and the procedures given are

intended to be used for calibration of rectilinear vibration transducers (with or without signal conditioning) to

obtain the magnitude and (optionally) phase shift of the complex sensitivity at frequencies in the range of

0,4 Hz to 10 kHz.
© ISO 2003 — All rights reserved v
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INTERNATIONAL STANDARD ISO 16063-21:2003(E)
Methods for the calibration of vibration and shock
transducers —
Part 21:
Vibration calibration by comparison to a reference transducer
1 Scope

This part of ISO 16063 describes the calibration of rectilinear vibration transducers by comparison. Although it

mainly describes calibration using direct comparison to a standard calibrated by primary methods, the

methods described can be applied between other levels in the calibration hierarchy.

This part of ISO 16063 specifies procedures for performing calibrations of rectilinear vibration transducers by

comparison in the frequency range from 0,4 Hz to 10 kHz. It is primarily intended for those who are required to

meet ISO standardized methods for the measurement of vibration under laboratory conditions, where the

uncertainty of measurement is relatively small. It can also be used under field conditions, where the

uncertainty of measurement may be relatively large.

From knowledge of all significant sources of uncertainty affecting the calibration, the expanded uncertainty

can be evaluated using the methods given in this part of ISO 16063. It also covers the assessment of

uncertainties for calibrations performed using a check standard.

Comparison calibrations made in accordance with this part of ISO 16063 need to allow for the environmental

conditions of the reference transducer calibration.

NOTE Transducer calibrations made under extreme environmental conditions are covered by other International

Standards.
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 266, Acoustics — Preferred frequencies
ISO 2041:1990, Vibration and shock — Vocabulary

ISO 16063-1:1998, Methods for the calibration of vibration and shock transducers — Part 1: Basic concepts

ISO 16063-11:1999, Methods for the calibration of vibration and shock transducers — Part 11: Primary

vibration calibration by laser interferometry

Guide to the expression of uncertainty in measurement (GUM). BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML,

1993
1) Corrected and reprinted in 1995.
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ISO 16063-21:2003(E)
3 Uncertainty of measurement

3.1 All users of this part of ISO 16063 are expected to make uncertainty budgets according to Annex A to

document their level of uncertainty (see example in Annex D).

To help set up systems fulfilling different requirements two examples are given. System requirements for each

are set up and the attainable uncertainty is given. Example 1 is typical for calibrations under well-controlled

laboratory conditions with the requirement to obtain a high accuracy. Example 2 is typical for calibrations

where less than the highest accuracy can be accepted or where calibration conditions are such that only less

narrow tolerances can be maintained. These two examples will be used throughout this part of ISO 16063.

a) Example 1

The reference transducer is calibrated by primary means and documented uncertainty. The calibration

may be transferred to a working standard for practical reasons. The temperature and other conditions are

kept within narrow limits during the comparison calibration as indicated in the appropriate clauses.

b) Example 2

The reference transducer is not calibrated by primary means, but has a traceable calibration, as defined

in VIM (see [2]), with the corresponding uncertainty documented. The calibration may be transferred to a

working standard for practical reasons. The requirements on other parameters and instruments are

indicated in the appropriate clauses.

3.2 For both examples, the minimum calibration requirement for the reference transducer is calibration

under suitable reference conditions (i.e. frequency, amplitude and temperature). Normally the conditions will

be chosen as indicated in ISO 16063-11.
It is applicable for the following parameters:
Frequency range: 20 Hz to 5 000 Hz, optionally 0,4 Hz to 10 000 Hz (see Note 1)
2 2 2 2
Dynamic range: 10 m/s to 1 000 m/s r.m.s., optionally 0,1 m/s to 1 000 m/s
(frequency dependent)

NOTE The indicated frequency ranges are not mandatory and single-point calibrations are also acceptable.

At any given frequency and amplitude of acceleration, velocity or displacement, the dynamic range will be

limited by the noise floor and the amount of distortion produced by the excitation apparatus (if no filtering is

used) or its maximum power. (Techniques are also used to counteract the inherent distortion at large

displacements for spring-controlled exciters by changing the waveform of the input voltage.) Typical maximum

values for electrodynamic vibration exciters designed for the frequency range from 10 Hz to 10 kHz are

2 2

200 m/s to 1000 m/s r.m.s. acceleration, 0,5 m/s to 1 m/s r.m.s. velocity and 5 mm peak displacement. The

lower limits will be set by the noise in the two measurement channels, and by the bandwidth used. Typical

2 2

values used for measurement are 50 m/s to 100 m/s r.m.s. acceleration or 0,1 m/s r.m.s. velocity. For

2 2

calibrators, values between 1 m/s and 10 m/s r.m.s. are normally used. A graph similar to the one shown in

Annex C is useful when considering the ranges covered.

When measurements are performed at the lowest frequencies, the limiting factor is normally displacement. At

2 2

1 Hz, typical values for long-stroke vibrators are 1 m/s to 2 m/s r.m.s. acceleration or 0,1 m/s to 0,3 m/s

r.m.s. velocity.

3.3 The attainable uncertainties (expanded uncertainties calculated using a coverage factor of 2 in

accordance with ISO 16063-1) for the two examples are given in Table 1. In practice, these limits may be

exceeded depending on the uncertainty with which the reference transducer has been calibrated, the

response characteristics of the reference transducer and the transducer to be calibrated, the vibratory

characteristics of the exciter and the instrumentation used in the measurement apparatus. It is the

responsibility of the laboratory or end user to make sure that the reported values of expanded uncertainty are

credible.
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ISO 16063-21:2003(E)

Table 1 — Attainable uncertainties of magnitude and phase shift of the complex sensitivity

Parameter Example 1 Example 2
Magnitude
For accelerometers (0,4 Hz to 1 000 Hz) 1 % 3 %
For accelerometers (1 000 Hz to 2 000 Hz) 2 % 5 %
For accelerometers (2 kHz to 10 kHz) 3 % 10 %
For displacement and velocity transducers (20 Hz to 1 000 Hz) 4 % 6 %
Phase shift
At reference conditions (i.e. the level and frequency at which the 1° 3°
reference transducer was calibrated)
Outside reference conditions 2,5° 5°
Phase shift measurement is not mandatory.

Recommended reference conditions are as follows (from ISO 16063-11:1999, Clause 2):

 frequency in hertz: 160, 80, 40, 16 or 8 (or angular frequency ω in radians per second: 1000, 500, 250, 100 or 50),

 acceleration in metres per second squared (acceleration amplitude or r.m.s. value): 100, 50, 20, 10, 5, 2 or 1.

NOTE The expanded uncertainties given as examples (e.g. 1 %) are based on concrete uncertainty budgets such

as given in Annex D as an example (resulting expanded uncertainty 0,84 %).
4 Requirements for apparatus and environmental conditions
4.1 General
The examples referred to in this clause are those described in Clause 3.

If the recommended specifications listed below are met for each item, the uncertainties given in Clause 3

should be obtainable over the applicable frequency range depending on the uncertainty with which the

reference transducer has been calibrated, and the response characteristics of the reference transducer and

transducer to be calibrated. Other combinations of requirements can, however, lead to the same uncertainty.

Special instrumentation may be required in order to meet the expanded uncertainties given in Clause 3 at

frequencies less than 1 Hz. It is mandatory to document the expanded uncertainty using the methods of

Annex A.
4.2 Environmental conditions
These shall be the following.
Example 1 Example 2
Room temperature (23 ± 5) °C (23 ± 10) °C
Relative humidity 75 % max. 90 % max.
4.3 Reference transducer
This should preferably be calibrated together with the amplifier.
a) Example 1

The transducer shall be calibrated in accordance with suitable primary methods or by comparison against

a transducer calibrated in accordance with suitable primary methods (see ISO 16063-11 or other parts)

with an expanded uncertainty of 0,5 % (magnitude) and 0,5° (phase shift) at selected reference frequency

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ISO 16063-21:2003(E)

and acceleration (the uncertainties are those obtained when calculating expanded uncertainties using a

coverage factor of 2). Higher uncertainty values are accepted at high and low frequencies.

b) Example 2

The transducer shall be calibrated by suitable and known methods with traceability to a primary reference

transducer and an uncertainty of less than 2 % (magnitude) and 2° (phase shift) at selected reference

frequency and acceleration (the uncertainties are those obtained when calculating expanded

uncertainties using a coverage factor of 2). Higher uncertainty values are accepted at high and low

frequencies.

The reference transducer may be of the so-called back-to-back type meant for direct mounting of the

transducer to be calibrated on top of it in a so-called back-to-back configuration (see Figure 1). It may also be

a transducer with normal mounting provisions used underneath a fixture in line with the transducer to be

calibrated. It is not recommended to mount the two transducers side by side as rocking motions will often be

present, causing large errors in many circumstances. For calibrators, the reference transducer may be an

integral part of a moving element.

Subclauses 4.4 to 4.8 specify characteristics of apparatus that contribute to the uncertainty of measurement.

4.4 Vibration generation equipment
This shall fulfil the requirements given in Table 2.
Table 2 — Vibration generation equipment
Parameter Unit Example 1 Example 2
Frequency uncertainty % u 0,1 u 0,2
% of reading over the
Frequency stability 0,1 0,2
measurement period
% of reading over the
Acceleration amplitude stability 0,1 0,3
measurement period
Total harmonic distortion at
% u 5 u 10
frequencies > 20 Hz
Total harmonic distortion over the
% u 10 u 20
whole frequency range
u 10 at f u 1 kHz
Transverse, bending and rocking
acceleration
u 30 at f > 1 kHz
Hum and noise ( f W 10 Hz) dB below full output W 50 W 40
Hum and noise ( f < 10 Hz) dB below full output W 20 W 10

The hum and noise will only be important when inside the measurement bandwidth used. For every

combination of frequency, acceleration and load that is used during calibration, the magnitude of the

transverse, bending and rocking accelerations, hum and noise shall be consistent with the uncertainties given

in Clause 3.

Static or dynamic base strain introduced to the transducer from the attachment surfaces shall not unduly

influence the calibration result.

All mounting surfaces between any two transducers compared shall have flatness and roughness

specifications suitable for the purpose. If the highest frequency range is used, strict tolerances are necessary.

The surface on which the transducer is to be mounted shall have a roughness value, expressed as the

arithmetical mean deviation Ra of < 1 µm. The flatness shall be such that the surface is contained between

two parallel planes 5 µm apart, over the area corresponding to the maximum mounting surface of any

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ISO 16063-21:2003(E)

transducer to be calibrated. The drilled and tapped hole for connecting the transducer shall have a

perpendicularly tolerance to the surface of < 10 µm, i.e. the centreline of the hole shall be contained in a

cylindrical zone with 10 µm diameter and a height equal to the hole depth.

The mounting surface of the vibration exciter should be perpendicular to the direction of motion. Any deviation

from perpendicularity should be taken into account in the uncertainty budget, see Annex A.

Key
1 exciter 5 reference transducer 8 distortion meter for occasional checks

2 amplifiers 6 transducer to be calibrated 9 oscilloscope for visual inspection (optional)

3 power amplifier 7 voltmeter 10 phase meter (optional)
4 frequency generator and indicator

Figure 1 — Example of a measuring system for vibration calibration by comparison to a

reference transducer

NOTE 1 Multisine, sine or random generators can be used in conjunction with frequency analysers. Typically Fast

Fourier Transform (FFT) analysers are used for random and multisine signals and Single-Sine Correlation or Frequency

Response Analysers (FRA) are used for single-sine signals. The distortion is then normally of no importance. Therefore

analysers are normally preferred instead of broadband r.m.s. voltmeters which, although fundamentally more accurate, are

sensitive to distortion and other signals at frequencies differing from the measurement frequency. Measurement of

coherence can be used to estimate whether or not the signal-to-noise ratio and the linearity of the transducers are within

well-defined limits when spectral averaging is used. With random excitation and 64 averages a minimum coherence limit

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ISO 16063-21:2003(E)

of 0,98 will ensure that the errors due to signal-to-noise ratio and linearity are less than 0,9 % for a dual channel

measurement. In rare cases, broadband excitation can, however, create unwanted (transverse) vibration or output signals

at a measuring frequency due to non-linear behaviour of shaker or transducer at other frequencies.

NOTE 2 The items in 4.3 and 4.4 may be integrated into a calibrator.
4.5 Voltage measuring instrumentation
Two alternative set-ups are considered.

a) A single voltmeter measuring true r.m.s. at transducer amplifier output is used. The outputs from the

reference transducer and the transducer to be calibrated are measured consecutively and the reference

transducer output at least twice. This equipment shall fulfil the requirements given in Table 3.

Table 3 — Voltage measuring instrumentation — Single voltmeter
Parameter Unit Example 1 Example 2
Frequency range Hz 1 to 10 000 1 to 10 000
% of reading for max.
Maximum deviation from linearity 0,1 0,3
difference in signal levels
Maximum deviation between two
consecutive reference transducer % 0,1 0,3
measurements

NOTE The last row describes the repeatability of the measurement. This includes more than the voltmeter repeatability but is

treated here as a general requirement.

b) An instrument measuring voltage ratio between transducer amplifier outputs is used. This equipment shall

have the characteristics specified in Table 4.
Table 4 — Voltage measuring instrumentations
Parameter Unit Example 1 Example 2
Frequency range Hz 1 to 10 000 1 to 10 000
Maximum uncertainty % 0,2 0,5
4.6 Distortion measuring instrumentation

Distortion measuring instrumentation (limited use, see Note) capable of measuring total harmonic distortion of

1 % to 10 % shall have the characteristics specified in Table 5.
Table 5 — Distortion measuring instrumentation
Parameter Unit Example 1 Example 2
Frequency range Hz 1 to 50 000 1 to 50 000
Maximum uncertainty % of reading 10 10

NOTE Distortion measurement is only needed for sine calibration and is not included in the standard procedure. It is used to

check the performance of the vibration generating equipment initially and then only with suitable intervals or in case of doubt.

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ISO 16063-21:2003(E)
4.7 Oscilloscope

An oscilloscope or similar display may be used for examining the waveforms of the transducer signals.

Its use is strongly recommended but not mandatory.
4.8 Phase shift measuring instrumentation
This equipment shall have the characteristics specified in Table 6.
Table 6 — Phase shift measuring
Parameter Unit Example 1 Example 2
Frequency range Hz 1 to 10 000 1 to 10 000
Maximum uncertainty ° (degree) 0,2 0,5
5 Calibration
5.1 Preferred amplitudes and frequencies

Six frequencies, each with associated acceleration (amplitude or r.m.s. value) and equally covering the

transducer range, should preferably be chosen from the following series.
a) Acceleration (m/s ):
 1, 2, 5, 10 or their multiples of ten.
If broadband signals are used, these values are the total r.m.s. values.
b) Frequency:
 selected from standardized one-third-octave frequency series (see ISO 266).

If broadband signals are used, the desired range should be covered in one or more calibrations.

Values chosen should preferably be the same as those used in the reference transducer calibration. If the

transducer is to be calibrated at frequencies and accelerations other than those at which the reference has

been calibrated, the characteristics of the reference transducer should be assessed at those frequencies and

accelerations. The resulting uncertainty component shall be taken into account in the uncertainty budget (see

Annex A).
5.2 Measurement requirements

When a calibration is to be performed using a new set-up or a new transducer, it is good practice to carry out

the calibration more than once to ensure sufficient repeatability.

It is important to ensure that cable motion and base strain do not appreciably affect the measurement results,

particularly at low frequencies. Altering the attachment of the cable, the mounting of the transducer, or both,

and noting changes in the measurement results or harmonic distortion may be used to evaluate effects due to

these causes. If the measured sensitivity or distortion does not change significantly when compared to the

uncertainty in the calibration, then these influences may be neglected. The mounting conditions of the

transducer should also be repeatable. This can be verified by remounting the transducer several times and

measuring the sensitivity after each successive attachment of the transducer.

If the transducer under test is not being calibrated in combination with an associated signal conditioner or

amplifier, then the gain and frequency response (i.e. magnitude and, if needed, phase shift) of the complex

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ISO 16063-21:2003(E)

sensitivity of the signal conditioner or amplifier used with the transducer under test should be determined in a

traceable fashion at all measurement frequencies. The sensitivity and frequency response of the reference

(transducer plus amplifier) shall also be determined in a traceable fashion at all measurement frequencies.

If any variations, significant compared to the desired uncertainty, are found in the above tests, these should be

quantified by making a sufficiently large number of repeated measurements to get a good estimate of the

variance. This shall then be included in the final uncertainty statement. This is especially important if the

measurement is not made at the frequencies and amplitudes at which the reference transducer was calibrated.

5.3 Calibration procedure

The surfaces of the reference transducer (or fixture) and the transducer to be calibrated shall be examined to

verify that they are free from burrs, etc. and that they comply with the manufacturer’s flatness specifications

and the specifications of Clause 4.

Mount the reference transducer (see 4.4) and the transducer to be calibrated back-to-back or in-l

...

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