ISO 16063-41:2011

INTERNATIONAL ISO
STANDARD 16063-41
First edition
2011-08-01


Methods for the calibration of vibration
and shock transducers —
Part 41:
Calibration of laser vibrometers
Méthodes pour l'étalonnage des transducteurs de vibrations et de
chocs —
Partie 41: Étalonnage des vibromètres à laser





Reference number
ISO 16063-41:2011(E)
©
ISO 2011

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ISO 16063-41:2011(E)

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ISO 16063-41:2011(E)
Contents Page
Foreword . iv
1  Scope . 1
2  Normative references . 1
3  Classification of laser vibrometers and principles of test methods . 2
4  Uncertainty of measurement . 4
5  Requirements for apparatus and other conditions . 5
6  Preferred amplitudes and frequencies . 14
7  Common procedure for primary calibration (methods 1, 2 and 3) . 15
8  Method using fringe counting (method 1) . 15
9  Method using minimum-point detection (method 2) . 16
10  Methods using sine approximation: method 3 (homodyne version) and method 3
(heterodyne version) . 18
11  Method using comparison to a reference transducer (method 4) . 20
12  Report of calibration results . 21
Annex A (normative) Uncertainty components in the primary calibration by laser interferometry of
vibration and shock transducers . 31
Annex B (informative) Three versions of method 3 based on laser Doppler velocimetry . 36
Annex C (informative) Example of calculation of measurement uncertainty in calibration of a laser
vibrometer . 40
Annex D (informative) Phase shift calibration of laser vibrometers . 42
Bibliography . 44

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ISO 16063-41:2011(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 16063-41 was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and condition
monitoring, Subcommittee SC 3, Use and calibration of vibration and shock measuring instruments.
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 15: Primary angular vibration calibration by laser interferometry
 Part 21: Vibration calibration by comparison to a reference transducer
 Part 22: Shock calibration by comparison to a reference transducer
 Part 31: Testing of transverse vibration sensitivity
 Part 41: Calibration of laser vibrometers
The following parts are under preparation:
 Part 16: Calibration by Earth's gravitation

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INTERNATIONAL STANDARD ISO 16063-41:2011(E)

Methods for the calibration of vibration and shock
transducers —
Part 41:
Calibration of laser vibrometers
1 Scope
This part of ISO 16063 specifies the instrumentation and procedures for performing primary and secondary
calibrations of rectilinear laser vibrometers in the frequency range typically between 0,4 Hz and 50 kHz. It
specifies the calibration of laser vibrometer standards designated for the calibration of either laser vibrometers
or mechanical vibration transducers in accredited or non-accredited calibration laboratories, as well as the
calibration of laser vibrometers by a laser vibrometer standard or by comparison to a reference transducer
calibrated by laser interferometry. The specification of the instrumentation contains requirements on laser
vibrometer standards.
Rectilinear laser vibrometers can be calibrated in accordance with this part of ISO 16063 if they are designed
as laser optical transducers with, or without, an indicating instrument to sense the motion quantities of
displacement or velocity, and to transform them into proportional (i.e. time-dependent) electrical output signals.
These output signals are typically digital for laser vibrometer standards and usually analogue for laser
vibrometers. The output signal or the reading of a laser vibrometer can be the amplitude and, in addition,
occasionally the phase shift of the motion quantity (acceleration included). In this part of ISO 16063, the
calibration of the modulus of complex sensitivity is explicitly specified (phase calibration is provided in
Annex D).
NOTE Laser vibrometers are available for measuring vibrations having frequencies in the megahertz and gigahertz
ranges. To date, vibration exciters are not available for generating such high frequencies. The calibration of these laser
vibrometers can be estimated by the electrical calibration of their signal processing subsystems utilizing appropriate
synthetic Doppler signals under the following preconditions:
 the optical subsystem of the laser vibrometer to be calibrated has been proven to comply with defined requirements
comparable to those given in 5.5.3;
 synthetic Doppler signals are generated as an equivalent substitute for the output of the photodetectors.
More detailed specifications of this approach (see Reference [25]) lie outside the scope of this part of ISO 16063.
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 5348, Mechanical vibration and shock — Mechanical mounting of accelerometers
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
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ISO 16063-41:2011(E)
ISO 16063-21, Methods for the calibration of vibration and shock transducers — Part 21: Vibration calibration
by comparison to a reference transducer
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms
(VIM)
3 Classification of laser vibrometers and principles of test methods
3.1 Classification of laser vibrometers
3.1.1 A laser vibrometer standard (LVS) is a reference standard containing a laser interferometer,
designed and intended to serve as a reference to calibrate laser vibrometers and/or vibration transducers.
NOTE Methods 1, 2, and 3 are applicable to the primary calibration of LVSs.
3.1.2 A laser vibrometer (LV) is a measuring instrument containing a laser interferometer, designed and
intended to perform vibration measurements.
NOTE Methods 1, 2, and 3 are applicable to the primary calibration of LVs, and method 4 is applicable to the
secondary calibration of LVs. The reference accelerometer used for method 4 is calibrated by method 1, 2 or 3. For
specific requirements, see 5.11.
3.1.3 A laser optical transducer is a measurement transducer sensing, by laser light, the motion quantities
of displacement or velocity and transforming these quantities into a proportional time-dependent output signal.
3.2 Principles of test methods
3.2.1 General. Four methods are specified in analogy to ISO 16063-11 (laser interferometry) and
ISO 16063-21 (comparison to a reference transducer), respectively. Methods 1, 3, and 4 provide for
calibrations at preferred displacement amplitudes, velocity amplitudes and acceleration amplitudes at various
frequencies. Method 2 requires calibrations at fixed displacement amplitudes (velocity amplitude and
acceleration amplitude vary with frequency).
For each interferometric method specified in this part of ISO 16063 (see 3.2.2 to 3.2.4), currently a specific
frequency range applies. In fact, the applicability of the particular methods mainly depends on the
displacement or velocity amplitudes measurable within given measurement uncertainties. These, however, not
only depend on the measurement method itself but also on the frequency-dependent properties of the
vibration exciters available. Using adequate vibration exciters to generate sufficient displacement or velocity
amplitudes, the upper frequency limits of all methods can be expanded to 100 kHz and even beyond. The
primary method 3 (see 3.2.4) and the comparison method 4 (see 3.2.5) are applicable at frequencies lower
than 0,4 Hz.
3.2.2 Method 1, the fringe-counting method, is a vibration measurement method using a homodyne
interferometer with a single output (see Note 2) in conjunction with instrumentation for fringe counting of the
interferometer signal. Considering that the displacement corresponding to the distance between two fringes
(intensity maxima or intensity minima) is given by half the wavelength of the principal lines in the emission
spectrum of neon of the He-Ne laser, the displacement amplitude can be calculated from the number of
fringes counted during a given number (e.g. 1 000) of vibration periods.
For details, see Clause 8 and, for further information, ISO 16063-11:1999, B.1.
NOTE 1 Method 1 is applicable to the primary calibration of the laser vibrometer (modulus only) in the frequency range
1 Hz to 800 Hz and, under special conditions, at lower and higher frequencies. In Reference [26], the applicability of
method 1 has been demonstrated at frequencies up to 347 kHz.
NOTE 2 Alternatively, the homodyne interferometer signal from one of the two outputs of a quadrature interferometer
can be used.
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ISO 16063-41:2011(E)
NOTE 3 The electronic fringe counting can be substituted by the signal coincidence method (see References [1] [23]
[24]), which indicates a displacement amplitude of a quarter wavelength, /4, of the laser light (158,2 nm for a red helium-
neon laser). In the general case, the interferometer signal shows relative maxima and minima at the times when the
vibration displacement approaches its positive and negative peak values, respectively. In the discrete case (158,2 nm), the
relative signal maxima and minima approach the same signal level from the negative and positive directions, respectively
(“coincidence”). By observing the interferometer signal as a function of time on an oscilloscope and adjusting the vibration
amplitude to the level where a bright sharp line appears, the discrete amplitude (158,2 nm) is identified. The bright line
varies with time as the initial phase of the interferometer signal varies due to low-frequency motion. In Reference [26], the
applicability of the signal coincidence method has been demonstrated at frequencies up to 160 kHz.
3.2.3 Method 2, the minimum-point method, is a vibration measurement method using a homodyne
interferometer with a single output in conjunction with instrumentation for zero-point detection of a component
of the frequency spectrum of the interferometer signal. Considering the frequency spectrum of the intensity
and adjusting the vibration amplitude to the level at which the component of the same frequency as the
vibration frequency is zero, the displacement amplitude can be calculated from the argument corresponding to
the respective zero point of the Bessel function of the first kind and first order.
For details, see Clause 9 and, for further information, ISO 16063-11:1999, B.2.
NOTE 1 Method 2 can be used for modulus calibration in the frequency range 800 Hz to 10 kHz with an electro-
dynamic vibration exciter, and up to 50 kHz and higher with a vibration exciter for large vibration amplitudes, preferably a
piezo-electric vibration exciter. In Reference [27], the applicability of method 2 has been demonstrated at frequencies up
to 50 kHz.
NOTE 2 For displacement amplitudes smaller than that of the first minimum point (193 nm for the J Bessel function,
1
121 nm for the J Bessel function), the Bessel function ratio method (e.g. see Reference [22]) can be applied if the
0
uncertainty requirements of Clause 4 are complied with.
3.2.4 Method 3, the sine-approximation method, is a vibration measurement method using a homodyne
or heterodyne interferometer with two electrical outputs in quadrature (i.e. phase-shifted by 90°) in conjunction
with instrumentation for signal sampling and processing. A sine approximation of an equidistant sequence of
calculated displacement or velocity values leads to the amplitude and the initial phase shift of the respective
vibration quantity.
For details, see Clause 10 and, for further information, ISO 16063-11:1999, B.3.
NOTE Method 3 can be used for modulus and phase calibration if the laser vibrometer provides both measurement
capabilities. Method 3 in the homodyne or heterodyne interferometer version provides calibrations in the frequency range
0,4 Hz to 50 kHz or wider. In Reference [26], the applicability of method 3 has been demonstrated at frequencies up to
347 kHz.
3.2.5 Method 4, the comparison to a reference transducer, is a vibration measurement method using a
reference accelerometer calibrated by a suitable primary method (laser interferometry) or secondary method
(comparison to a reference transducer), see 5.11. The acceleration amplitude, aˆ , is calculated using the
equation
1
auˆˆ
S
a,R
where
S is the acceleration sensitivity (magnitude) of the reference accelerometer;
a,R
uˆ is the amplitude of the accelerometer output during laser vibrometer calibration.
For the calculation of the displacement and velocity amplitudes and other details, see Clause 11.
NOTE 1 Method 4 is applicable to the calibration of laser vibrometers (magnitude and phase) in a frequency range
0,4 Hz to 50 kHz or wider. For frequencies higher than 5 kHz, the reference transducer shall be calibrated by laser
interferometry (see 5.11). The frequency range of method 4 is limited to the frequency range over which the reference
transducer was calibrated.
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ISO 16063-41:2011(E)
NOTE 2 Vibration calibration of transducers by comparison to a reference transducer is specified in detail in
ISO 16063-21. The same method can be used for calibration of laser vibrometers operated as laser optical transducers
(see 3.1.3).
4 Uncertainty of measurement
All users of this part of ISO 16063 are expected to make uncertainty budgets in accordance with Annex A to
document their uncertainty.
NOTE 1 The uncertainty of measurement is expressed as the expanded measurement uncertainty in accordance with
ISO 16063-1 (referred to in short as uncertainty).
As this part of ISO 16063 covers three measurands (displacement, velocity and acceleration) in wide
amplitude and frequency ranges with different accuracy requirements and different performances of the
devices to be calibrated (laser vibrometer standards and laser vibrometers), the uncertainty of measurement
may range from small to relatively large values. 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.
Two examples are given in order to help set up systems that fulfil different uncertainty requirements. System
requirements for each are set up and the attainable uncertainty is given. Example 1 is applicable to
calibrations performed under well-controlled laboratory conditions resulting in relatively small uncertainties.
Example 2 is applicable to calibrations in which relatively large uncertainties can be accepted or where
calibration conditions are such that only less narrow tolerances can be maintained. These two examples are
used throughout this part of ISO 16063.
EXAMPLE 1
A laser vibrometer standard is calibrated by primary means (method 1, 2 or 3 as specified in this part of ISO 16063) with
documented small uncertainty. The temperature and other conditions are kept within narrow limits during the calibration as
indicated in the appropriate clauses.
Figures 1 to 4 show examples for the calibration equipment applicable to fulfil high accuracy requirements represented by
Example 1.
EXAMPLE 2
A laser vibrometer is calibrated using a laser vibrometer standard calibrated according to Example 1.
For both examples, the minimum calibration requirement on the reference transducer is a calibration at
suitable reference conditions (i.e. frequency, amplitude and temperature). Normally, the conditions are chosen
as indicated in Clause 5.
The typical attainable uncertainties specified in Table 3 are applicable for the parameters specified in Table 1.
Table 1 — Typical frequency and amplitude ranges of displacement, velocity and acceleration
Frequency range: 0,4 Hz to 50 kHz
Dynamic range (amplitude):
 displacement  1 nm to 1 m
 velocity  0,1 mm/s to 1 m/s (frequency-dependent)
2 2
 acceleration  0,1 m/s to 20 km/s (frequency-dependent)
NOTE The indicated ranges are not mandatory, and calibrations performed at a single point or in smaller ranges of frequency,
amplitude or both are also acceptable.
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ISO 16063-41:2011(E)
At any given frequency and amplitude of acceleration, velocity or displacement, the dynamic range is limited
by the noise floor and the amount of distortion produced by the vibration generation equipment (if no filtering is
used) or its maximum power. In the case of spring-controlled vibration exciters, specific techniques may be
used to compensate for inherent distortion occurring at large displacements by using an appropriate non-
sinusoidal voltage at the input of the power amplifier. Typical frequency ranges and maximum vibration
amplitude ranges of electro-dynamic and piezo-electric vibration exciters are given in 5.3.
The uncertainty components of the calibration methods characterized in Table 2 are specified in Annex A.
Table 2 — Applicability of calibration methods influencing the uncertainty of measurement
Characterization of method
Marking of method
(Optical transducer/signal treatment)
Method 1 Homodyne interferometer (single output signal/fringe counting)
Method 2 Homodyne interferometer (single output signal/spectral analysis)
Method 3 (homodyne) Homodyne interferometer (two output signals in quadrature/sine approximation)
Method 3 (heterodyne) Heterodyne interferometer (output with frequency offset/sine approximation)
Method 4 Comparison to a reference transducer calibrated by method 1, 2 or 3
NOTE 2 Calibrations shall be traceable to a national measurement standard of the SI unit of acceleration, velocity or
displacement and be performed by a competent laboratory, e.g. one that is in compliance with ISO/IEC 17025
(Reference [21]).
Typical uncertainties that are attainable for Example 1 and Example 2 given above are specified in Table 3.
In practice, these uncertainty values may be exceeded or even smaller uncertainties may be achieved
depending on the performance of the calibration apparatus and the quantities influencing the calibration result.
It is the responsibility of the laboratory or end user to make sure that the reported values of expanded
uncertainty are credible. This can be achieved by evaluating the expanded measurement uncertainty in
accordance with Annex A and ISO 16063-1:1998, Annex A.
Table 3 — Typical attainable uncertainties
Frequency range Example 1 Example 2
0,4 Hz to 1 Hz 0,25 % 1 %
1 Hz to 5 kHz 0,25 % 0,5 %
5 kHz to 10 kHz 0,3 % 1 %
10 kHz to 20 kHz 0,5 % 3 %
20 kHz to 50 kHz 1 % 5 %
NOTE The expanded uncertainties given as examples (e.g. 0,5 % at 20 kHz) are based on concrete uncertainty budgets
established in accordance with Annex A.
5 Requirements for apparatus and other conditions
5.1 General
This clause gives recommended specifications for the apparatus necessary to fulfil the scope of Clause 1 and
to obtain the uncertainties of Clause 4.
If desired, systems covering parts of the ranges may be used, and normally different systems (e.g. exciters)
should be used to cover different parts of the frequency and amplitude ranges.
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ISO 16063-41:2011(E)
NOTE The apparatus specified in this clause covers all devices and instruments required for any of the four
calibration methods specified in this part of ISO 16063. The assignment to a given method is indicated.
The examples referred to in this clause are those described in Clause 4.
If the recommended specifications listed below are met for each item, the uncertainties given in Clause 4
should be obtainable over the applicable frequency range. Special instrumentation may be required in order to
meet the expanded uncertainties given in Clause 4 at frequencies less than 1 Hz and higher than 10 kHz. It is
mandatory to document the expanded uncertainty using the methods of Annex A.
5.2 Environmental conditions
The calibration shall be carried out under the ambient conditions contained in Table 4.
Table 4 — Ambient conditions
Influence quantity Example 1 Example 2
Room temperature (23  3) °C (23  5) °C
Relative humidity 75 % max. 90 % max.
Care shall be taken that external vibration and noise do not affect the quality of the measurements.
5.3 Vibration generation equipment
5.3.1 General
Vibration generation equipment shall fulfil the requirements listed in Table 5.
Table 5 — Requirements on vibration generation equipment
Disturbing influence Unit Example 1 Example 2
Frequency uncertainty % 0,1 0,2
Frequency instability over the measurement period % of reading 0,1 0,2
Acceleration amplitude instability over the measurement
% of reading 0,1 0,3
period
Total harmonic distortion of the acceleration signal at
% 5 10
frequencies 20 Hz
Total harmonic distortion over the whole frequency range % 10 20
10 at f  1 kHz
Transverse, bending and rocking acceleration %
30 at f  1 kHz
Hum and noise ( f  10 Hz) level below full output signal dB 50 40
Hum and noise ( f  10 Hz) level below full output signal dB 20 10
The hum and noise influences are only important when present inside the measurement bandwidth used. For
every combination of frequency and vibration amplitude (acceleration, velocity or displacement) used during
calibration, the magnitude of the transverse, bending and rocking accelerations, hum and noise shall be
consistent with the uncertainties given in Clause 4.
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ISO 16063-41:2011(E)
5.3.2 Electro-dynamic vibration exciter
Typical maximum vibration amplitudes for electro-dynamic vibration exciters designed for the frequency range
2
from 10 Hz to 10 kHz are 5 mm displacement amplitude, 0,5 m/s to 1 m/s velocity amplitude and 200 m/s to
2
1 km/s acceleration amplitude. When measurements are performed at the lowest frequencies, the limiting
factor is normally displacement. At 1 Hz, typical values for long-stroke vibration exciters are 80 mm
2
displacement amplitude, 0,5 m/s velocity amplitude and 1 m/s acceleration amplitude. Using resonance
2
effects, electro-dynamic vibration exciters attain large vibration amplitudes in the range of 200 m/s up to
2
5 km/s at frequencies up to 50 kHz, but only with risk of damage to, or destruction of, the exciter.
5.3.3 Piezo-electric vibration exciter
Large vibration amplitudes at high frequencies (1 kHz to 50 kHz or higher) can be generated by piezo-electric
vibration exciters.
NOTE For method 2 (minimum-point method based on using the J Bessel function), a displacement amplitude of at
1
least 193,0 nm needs to be generated in order to obtain minimum point No. 1. At a frequency of 50 kHz, this displacement
2
amplitude corresponds to an acceleration amplitude of approximately 19 km/s .
5.4 Seismic block(s) for vibration exciter and laser interferometer
The vibration exciter and the interferometer shall be mounted on the same heavy block or on two different
heavy blocks so as to prevent relative motion due to ground motion, or to prevent the reaction of the vibration
exciter's support structure from excessively influencing the calibration results.
When a common seismic block is used, it should have a mass of at least 2 000 times that of the moving mass.
This criterion results in a vibration of the interferometer induced by the motion of the exciter that is less than
0,05 % of the amplitude of vibration of the exciter. If the mass of the seismic block is smaller than 2 000 times
that of the moving mass, the motion of the seismic block generated by the vibration exciter shall be taken into
account.
When a common seismic block is used, it is further recommended to mount the vibrometer(s) on an additional
block which is vibrationally isolated from said seismic block by another set of damped springs (see Figure 6).
To suppress the disturbing effects of ground motion, the seismic block(s) should be isolated by damped
springs designed to reduce the uncertainty component due to these effects to less than 0,1 %.
5.5 Interferometer system
5.5.1 Common requirements for methods 1, 2 and 3
The interferometer system consists of a laser optical tranducer (briefly referred to as interferometer) and an
electronic signal decoding subsystem.
The interferometer as laser optical transducer shall transform
 a displacement s(t) at the input of the interferometer into a proportional phase shift  (t) of the
M
interferometer output signal, or
 the velocity v(t) at the input of the interferometer into a proportional frequency shift f (t) (Doppler
D
frequency) of the interferometer output signal.
For both transformations, a homodyne or a heterodyne interferometer (see Figures 2, 3, 4, 5 and 7) may be
used.
For methods 1 and 2, an interferometer shall be used with a photodetector to sense the interferometric
intensity modulation caused by the motion generated by the vibration exciter. The frequency response of the
photodetector shall cover the highest Doppler frequency expected. A common Michelson interferometer with a
sin
...