ISO/TR 13115:2011

Non-destructive testing — Methods for absolute calibration of acoustic emission transducers by the reciprocity technique

ISO/TR 13115:2011 describes the method of three-transducer calibration for calibrating frequency responses of absolute sensitivity by means of a reciprocity technique using three reversible acoustic emission transducers of the same kind, the method of two-transducer calibration for calibrating frequency responses of reception sensitivity of an optional acoustic emission transducer by using one acoustic emission transducer, the transmission responses of which have been calibrated by three-transducer calibration, the method for impulse response calibration for calibrating impulse responses of absolute sensitivity through inverse Fourier transform of the frequency responses measured by the three-transducer calibration, and the method for representing the calibration results.

Essais non destructifs — Méthodes d'étalonnage absolu des capteurs d'émission acoustique par la technique de réciprocité

General Information

• Status: Published
• Publication Date: 13-Dec-2011
• ICS: 19.100 - Non-destructive testing
• Technical Committee: ISO/TC 135/SC 9 - Acoustic emission testing
• Drafting Committee: ISO/TC 135/SC 9 - Acoustic emission testing
• Current Stage: 6060 - International Standard published
• Start Date: 12-May-2012
• Completion Date: 14-Dec-2011

Relations

• Consolidates: ISO/TS 13499:2003 - Road vehicles — Multimedia data exchange format for impact tests
• Effective Date: 06-Jun-2022

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 13115
First edition
2011-12-15

Non-destructive testing — Methods for
absolute calibration of acoustic emission
transducers by the reciprocity technique
Essais non destructifs — Méthodes d'étalonnage absolu des capteurs
d'émission acoustique par la technique de réciprocité




Reference number
ISO/TR 13115:2011(E)
©
ISO 2011

---------------------- Page: 1 ----------------------
ISO/TR 13115:2011(E)

COPYRIGHT PROTECTED DOCUMENT


©  ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2011 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TR 13115:2011(E)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Preparation for calibration. 3
4.1 Transfer medium and calibration signal . 3
4.2 Mounting of acoustic emission transducer . 4
4.3 Calculation of reciprocity parameters . 5
5 Method for three-transducer calibration . 6
5.1 Apparatus to be used . 6
5.2 Method of measurement . 6
5.3 Method for determination of absolute sensitivity . 9
6 Method for two-transducer calibration . 9
6.1 Apparatus to be used . 10
6.2 Method of measurement . 10
6.3 Method for determination of absolute sensitivity . 10
7 Method for impulse response calibration . 11
7.1 Apparatus to be used . 11
7.2 Method of measurement . 11
7.3 Method for determination of frequency response . 13
7.4 Method for determination of impulse response . 15
8 Method for representing calibration results . 16
8.1 Representation items for calibration results . 16
8.2 Method for representing frequency response of absolute sensitivity . 16
8.3 Method for representing impulse response of absolute sensitivity . 17
Bibliography . 18

© ISO 2011 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TR 13115:2011(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.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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/TR 13115 was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee
SC 9, Acoustic emission testing.

iv © ISO 2011 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/TR 13115:2011(E)
Introduction
[1]
A standard method for primary calibration of acoustic emission transducers, ISO 12713:1998 , introduced the
seismic surface pulse method for Rayleigh surface wave calibration, wherein the breaking of a glass capillary
is employed for the sound source and a standard capacitive transducer is used for the measurement of
[2]
dynamic displacements of the surface. In ISO 12714:1999 , on secondary calibration of acoustic emission
sensors, a transducer which has been calibrated by the seismic surface pulse method is employed for
comparison of reception sensitivity.
This Technical Report describes the methods for calibrating absolute sensitivity of acoustic emission
transducers, both to Rayleigh surface waves and longitudinal waves, by means of a reciprocity technique.
Since reciprocity parameters have been derived, absolute sensitivity can be determined by purely electrical
measurements without the use of mechanical sound sources or reference transducers.
Procedures of the seismic surface pulse method and reciprocity technique differ from each other; however,
there is a common theoretical basis in the two calibration methods. For the seismic surface pulse method,
theoretical surface displacements were calculated on the basis of Lamb's theory (Reference [7]). For the
reciprocity calibration, reciprocity parameters for the Rayleigh wave calibration were also derived from Lamb's
theory. As for the Rayleigh surface wave calibration, a round robin experiment was carried out in a
collaborative effort between the USA and Japan, and it was ascertained that absolute sensitivities as obtained
by either method agreed well.
The aim of both methods is the same, namely, to establish uniformity of acoustic emission testing, to form a
basis for data correlation, and to provide for the interpretation of results obtained by different laboratories at
different times.
This Technical Report describes methods for three-transducer calibration, two-transducer calibration, and
impulse response calibration, respectively. In three-transducer calibration, three acoustic emission
transducers of the same kind, which are reversible transducers, are prepared to configure three independent
pairs of transmitting and receiving transducers on a solid transfer medium. Transmission signal current and
reception signal voltage are measured on each pair as a function of frequency, and frequency responses of
amplitude of absolute sensitivity both to the Rayleigh surface waves and longitudinal waves are determined on
each transducer. Once three-transducer calibration has been carried out, an optional transducer, which is not
necessarily a reversible transducer, can be calibrated by a relatively simple procedure by using the calibrated
transducer as a reference of transmission or reception. In two-transducer calibration, frequency responses of
amplitude of absolute reception sensitivity are determined on an optional transducer by using one acoustic
emission transducer, the transmission responses of which have been calibrated by the three-transducer
calibration. In addition, by means of three-transducer calibration, impulse responses of each acoustic
emission transducer can also be determined. In the impulse response calibration, frequency responses of
phase angle, in addition to amplitude, of absolute sensitivity are measured by three-transducer calibration on
the basis of complex reciprocity parameters, and impulse responses are determined through inverse Fourier
transform of the frequency responses of amplitude and phase.

© ISO 2011 – All rights reserved v

---------------------- Page: 5 ----------------------
TECHNICAL REPORT ISO/TR 13115:2011(E)

Non-destructive testing — Methods for absolute calibration of
acoustic emission transducers by the reciprocity technique
1 Scope
This Technical Report describes the method of three-transducer calibration for calibrating frequency
responses of absolute sensitivity by means of a reciprocity technique using three reversible acoustic emission
transducers of the same kind, the method of two-transducer calibration for calibrating frequency responses of
reception sensitivity of an optional acoustic emission transducer by using one acoustic emission transducer,
the transmission responses of which have been calibrated by three-transducer calibration, the method for
impulse response calibration for calibrating impulse responses of absolute sensitivity through inverse Fourier
transform of the frequency responses measured by the three-transducer calibration, and the method for
representing the calibration results.
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 12716:2001, Non-destructive testing — Acoustic emission inspection — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12716 and the following apply.
3.1
reciprocity technique
calibration method on three reversible acoustic emission transducers of the same kind, wherein transducers
are arranged on a solid transfer medium so that they configure three independent pairs of transmitting and
receiving transducers, and absolute sensitivity is determined only by electrical measurements of transmission
current and reception voltage on each pair
3.2
reversible transducer
transducer which can be used both for transmission and reception
3.3
absolute sensitivity
quantity of reception voltage sensitivity or transmission current response of an acoustic emission transducer
3.4
reception voltage sensitivity
ratio of the open-circuit output voltage of an acoustic emission transducer used for reception to the vertical
component of displacement velocity at the position where the transducer is to be placed
© ISO 2011 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/TR 13115:2011(E)
3.5
transmission current response
ratio of the vertical component of displacement velocity at the index point to the input current of an acoustic
emission transducer used for transmission
3.6
index point
position on the surface of the transfer medium, which is located at the specified distance in the specified
direction from the acoustic emission transducer used for transmission, and used as the reference of
transmission response
3.7
reciprocity parameter
ratio of reception sensitivity to transmission response of an acoustic emission transducer which is a reversible
transducer
3.8
transfer medium
solid block on the surfaces of which transducers are placed in the calibration so that they configure a pair of
transmitting and receiving transducers of the Rayleigh surface waves or longitudinal waves
3.9
calibration signal
electrical voltage signal which is applied to the transmitting transducer in the calibration
3.10
tone burst signal
calibration signal consisting of sinusoidal waves with a specified frequency and a specified period modulated
so that the envelope forms one squared cosine
3.11
calibration frequency
frequency of sinusoidal waves of which a tone burst signal consists
3.12
squared-cosine signal
calibration signal which trigonometrically increases from zero to a maximum and decreases to zero during a
specified period
3.13
Hanning window
cosine-type time window with a specified period, which is used for Fourier transform of transmission and
reception signals measured in the impulse response calibration
3.14
Rayleigh wave calibration
calibration by which sensitivity to Rayleigh surface waves is determined by using Rayleigh waves for
transmission and reception
3.15
longitudinal wave calibration
calibration by which axial sensitivity to longitudinal waves is determined by using longitudinal waves for
transmission and reception
3.16
three-transducer calibration
calibration by a reciprocity technique, wherein frequency responses of amplitude of reception voltage
sensitivity and/or transmission current response are determined on each of the three acoustic emission
transducers
2 © ISO 2011 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/TR 13115:2011(E)
3.17
two-transducer calibration
calibration on an optional acoustic emission transducer which is not necessarily a reversible transducer,
wherein frequency responses of amplitude of reception voltage sensitivity are determined by using one
acoustic emission transducer for transmission, the transmission current response of which has been
determined by three-transducer calibration
3.18
impulse response calibration
calibration on three reversible acoustic emission transducers of the same kind, wherein impulse responses of
reception voltage sensitivity are determined through inverse Fourier transform of the frequency responses of
amplitude and phase of absolute sensitivity measured by three-transducer calibration
4 Preparation for calibration
4.1 Transfer medium and calibration signal
The transfer medium should be made of a material whose density and elastic moduli are as close as possible
to those of the actual object on which acoustic emission transducers are intended for use. In this Technical
Report, carbon steel is principally assumed to be the material of possible objects. While any solid can be used
for the transfer medium, forged steel is most recommended. The transfer medium should undergo ultrasonic
testing in order to assure that detectable flaws or inclusions, which may affect the Rayleigh wave or
longitudinal wave calibration, are not included. Namely, in longitudinal ultrasonic testing at a frequency
between 2 MHz and 5 MHz, the medium should contain no flaws which give a reflection greater than 10 % of
the first back-wall reflection. The planes of the transfer medium, used for the longitudinal wave calibration,
should be parallel within 0,2°.
At the measurement of reception signals in the calibration, discrimination between the direct wave of the
Rayleigh waves or longitudinal waves, which is the object of measurement, and other spurious waves is made
on the basis of the propagation time of each wave. A larger dimension of the medium causes longer
differences in the propagation time between waves, and consequently, the period Tof a tone burst signal used
in three-transducer or two-transducer calibration, or the period T of a Hanning window used in impulse
w
response calibration, can be set longer.
Figure 1 shows examples of setting on the period, T, in seconds, of a tone burst signal or the period, T , in
w
seconds, of a Hanning window in relation to the dimension of a cylindrical transfer medium made of forged
steel. In general, the shape of the medium is not limited to a cylinder. A rectangular medium, for instance, may
be used as long as its volume contains the cylinder.
Figure 2 shows an example of the waveform and frequency spectrum of a tone burst signal with a period, T, in
seconds, and a calibration frequency, f , in hertz.
max
Tone burst signal period or
Diameter Thickness
Hanning window period
T or T
D 
w
m m s
0,4 0,19 0,000 05
0,6 0,38 0,000 1

1,2 0,76 0,000 2
Figure 1 — Dimension of transfer medium and setting of period T or T
w
© ISO 2011 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO/TR 13115:2011(E)
H
T
t
f
2 f 2
max
f   - f   +
max max
T T

Key
H amplitude
f frequency
f maximum calibration frequency
max
T period
t time
Figure 2 — Waveform and frequency spectrum of a tone burst signal
4.2 Mounting of acoustic emission transducer
Sensitivity of acoustic emission transducers depends on the mounting method, namely, the contact pressure,
couplant, and surface roughness of the object. The contact surface pressure of the transducers under
calibration should be not less than 0,1 MPa, and machine oil is recommended as the couplant for use on steel.
The surfaces of the transfer medium, on which acoustic emission transducers are mounted in calibration,
should have a root mean square surface roughness value R, in metres, so that Condition (1) is satisfied:
20
R (1)
f
max
where f is the maximum frequency, in hertz, of calibration.
max
The distance between the transmitting and receiving transducers on the transfer medium should be so set that
each transducer is located in a far field of the mating transducer. In Rayleigh wave calibration, the distance, r ,
R
in metres, should be set so that Condition (2) is satisfied:
f
max 2
rd (2)
R
c
R
In longitudinal wave calibration, the distance, r , in metres, should be set so that Condition (3) is satisfied:
L
f
max 2
rd (3)
L
c
L
where
d is the diameter, in metres, of the transducer element,
c , c are propagation velocities, in metres per second, of Rayleigh and longitudinal waves in the
R L
transfer medium, respectively.
The propagation velocities are given by Equations (4) and (5):
4 © ISO 2011 – All rights reserved

---------------------- Page: 9 ----------------------
ISO/TR 13115:2011(E)
1/ 2

1 E
c  (4)

R
Y 21



1/ 2

1 E

c  (5)

L
112
 


where
E is the Young modulus, in newtons per square metre, of the transfer medium;
 is the Poisson ratio of the transfer medium;
 is the density, in kilograms per cubic metre, of the transfer medium;
Y is a constant which depends on the Poisson ratio.
Table 1 shows the numerical values of Y.
4.3 Calculation of reciprocity parameters
Reciprocity parameters, essential both for three-transducer calibration and the impulse-response calibration,
are dependent not on the transducer design but on the mode of waves, constants of the medium, and
definition of sensitivity. Amplitude |H (f)| and phase angle H (f) of the reciprocity parameter for Rayleigh
R R
wave calibration are given at a frequency, f, in hertz, by Equations (6) and (7), respectively:
1/ 2

12
Hf 2f k X (6)


RR
Ekr
RR

Hfkr (7)

RRR
4
where
2f
k 
R
c
R
X is a constant which depends on the Poisson ratio. Table 1 also shows the numerical values of X.
Amplitude |H (f)| and phase angle H (f) of the reciprocity parameter for longitudinal wave calibration are
L L
given at a frequency, f, in hertz, by Equations (8) and (9), respectively:
11 2
 
Hf  2f (8)

L
Er1

L

Hfkr (9)

LLL
2
where
2f
k 
L
c
L
© ISO 2011 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO/TR 13115:2011(E)
Table 1 — Numerical values of constants X and Y
 X Y
0,00 0,284 4 1,144 1
0,25 0,183 5 1,087 7
0,26 0,180 0 1,085 7
0,27 0,176 5 1,083 8
0,28 0,173 1 1,082 0
0,29 0,169 7 1,080 1
0,30 0,166 4 1,078 3
0,31 0,163 1 1,076 5
0,32 0,159 8 1,074 7
0,33 0,156 6 1,073 0
0,34 0,153 5 1,071 2
0,35 0,150 4 1,069 5

5 Method for three-transducer calibration
The method for three-transducer calibration of acoustic emission transducers consists of the measurement of
transmission current and reception voltage in Rayleigh wave calibration and/or longitudinal wave calibration,
and determination of absolute sensitivity. In three-transducer calibration, a tone burst signal with a period, T, in
seconds, and a calibration frequency, f, in hertz, should be used for the calibration signal. The method for
each procedure is as stated below.
5.1 Apparatus to be used
a) Three acoustic emission transducers T , T and T to be calibrated, which are reversible transducers.
1 2 3
b) Calibration signal generator.
c) Transfer medium.
d) Current probe.
e) Waveform display.
5.2 Method of measurement
5.2.1 Measurement in Rayleigh wave calibration
As illustrated in Figure 3, three independent pairs of transmitting and receiving transducers should be
configured by means of the three acoustic emission transducers under calibration. Figure 4 shows the
instrumentation setup and transducer arrangement for the measurement of Rayleigh wave calibration, where
both the transmitting and receiving transducers in each pair are mounted at a distance, r , in metres, apart
R
from each other on the same plane of the transfer medium. As illustrated in Figure 5, magnitudes of the
transmission current, |I (f)|, in amperes, and reception voltage, |U (f)|, in volts, corresponding to the direct
R R
Rayleigh wave should be measured on each pair. Measured values of the magnitudes are summarized in
Table 2.
6 © ISO 2011 – All rights reserved

---------------------- Page: 11 ----------------------
ISO/TR 13115:2011(E)
1
AB
I U
T T
12 1 2 12
2
I U
23 T2 T3 23
3
I U
31 T T 31
3 1

Key
A transmitting transducers I , I , I currents
12 23 31
B receiving transducers U , U , U voltages
12 23 31
T , T , T transducers 1, 2, 3 pairs of transducers
1 2 3
Figure 3 — Three independent pairs of transmitting and receiving transducers
1
2
6
35
r
R
4

Key
1 calibration signal generator 5 receiving transducer
2 current probe 6 waveform display
3 transmitting transducer
4 transfer medium r distance in Rayleigh wave calibration
R
Figure 4 — Instrumentation setup and transducer arrangement for Rayleigh wave calibration
t
t

Key
I(f) transmission current
U(f) reception voltage
t time
Figure 5 — Measurement of transmission current and reception voltage
© ISO 2011 – All rights reserved 7

U( f )
I( f )

---------------------- Page: 12 ----------------------
ISO/TR 13115:2011(E)
Table 2 — Measured values of transmission current and reception voltage
in Rayleigh wave calibration
Pair Transmission transducer Current Reception transducer Voltage
1 T |I (f)| T |U (f)|
1 R12 2 R12
2 T |I (f)| T |U (f)|
2 R23 3 R23
3 T |I (f)| T |U (f)|
3 R31 1 R31

5.2.2 Measurement in longitudinal wave calibration
As illustrated in Figure 3, three independent pairs of transmitting and receiving transducers should be
configured by means of the three acoustic emission transducers under calibration. Figure 6 shows the
instrumentation setup and transducer arrangement for the measurement of longitudinal wave calibration,
where the transmitting and receiving transducers in each pair are mounted with their central axes coinciding
on the planes of the transfer medium, parallel to each other with a separation, r , in metres. As illustrated in
L
Figure 5, magnitudes of the transmission current, |I (f)|, in amperes, and reception voltage, |U (f)|, in volts,
L L
corresponding to the direct longitudinal wave should be measured on each pair. Measured values of the
magnitudes are summarized in Table 3.
1
2
6
3
4
5

Key
1 calibration signal generator 5 receiving transducer
2 current probe 6 waveform display
3 transmitting transducer
4 transfer medium r distance in longitudinal wave calibration
L
Figure 6 — Instrumentation setup and transducer arrangement for longitudinal wave calibration
Table 3 — Measured values of transmission current and reception voltage in
Rayleigh wave calibration
Pair Transmission transducer Current Reception transducer Voltage
1 T |I (f)| T |U (f)|
1 L12 2 L12
2 T |I (f)| T |U (f)|
2 L23 3 L23
3 T |I (f)| T |U (f)|
3 L31 1 L31

8 © ISO 2011 – All rights reserved

r
L

---------------------- Page: 13 ----------------------
ISO/TR 13115:2011(E)
5.3 Method for determination of absolute sensitivity
5.3.1 Determination of absolute sensitivity in Rayleigh wave calibration
As for the acoustic emission transducer T , for instance, reception voltage sensitivity |M (f)|, in volt seconds
1 R1
per metre, and transmission current response |S (f)|, metres per second ampere, at a calibration frequency, f,
R1
in hertz, should be determined in Rayleigh wave calibration by Equations (10) and (11), respectively, using the
measured values summarized in Table 2:
1/ 2

Uf I f U f
  
R12 R23 R31
1
 
Mf  (10)

R1

Hf I f U f I f
   
R R12 R23 R31

1/ 2

Uf I f U f
  
R12 R23 R31
 
Sf H f (11)
 
R1 R
 
If U f I f
  
R12 R23 R31

where the index point as the reference of the transmission response is located at the position of the receiving
transducer in the Rayleigh wave calibration. Similar equations also hold for acoustic emission transducers T
2
and T .
3
5.3.2 Determination of absolute sensitivity in longitudinal wave calibration
As for the acoustic emission transducer T1, for instance, reception voltage sensitivity, |M (f)|, in volt seconds
L1
per metre, and transmission current response, |S (f)|, in metres per second ampere, at a calibration
L1
frequency, f, in hertz, should be determined in longitudinal wave calibration by Equations (12) and (13),
respectively, using the measured values summarized in Table 3:
1/ 2

Uf I f U f
  
1 L12 L23 L31
 
Mf  (12)

L1
 
Hf I f U f I f
   
L L12 L23 L31

1/ 2

Uf I f U f
  
L12 L23 L31
 
Sf  H f (13)
 
L1 L
 
If U f I f
  
L12 L23 L31

where the index point as the reference of the transmission response is located at the position of the receiving
transducer in the longitudinal wave calibration. Similar equations also hold for acoustic emission transducers
T and T .
2 3
6 Method for two-transducer calibration
The method for two-transducer calibration of acoustic emission transducers consists of the measurement of
transmission current and reception voltage in Rayleigh wave calibration and/or longitudinal wave calibration,
and determination of absolute sensitivities. In two-transducer calibration, a tone burst signal with a period, T,
in seconds, and a calibration frequency, f , in hertz should be used for the calibration signal. The method
max
for each procedure is as stated below.
© ISO 2011 – All rights reserved 9

---------------------- Page: 14 ----------------------
ISO/TR 13115:2011(E)
6.1 Apparatus to be used
a) Optional acoustic emission transducer to be calibrated, which is either a reversible or nonreversible
transducer.
b) One acoustic emission transducer, the transmission current response of which has been determined by
three-transducer calibration.
c) Calibration signal generator.
d) Transfer medium.
e) Current probe.
f) Waveform display.
6.2 Method of measurement
6.2.1 Measurement in Rayleigh wave calibration
Figure 4 shows the instrumentation setup and transducer arrangement for the measurement of Rayleigh wave
calibration, where one acoustic emission transducer, the Rayleigh-wave transmission current response of
which has been determined by three-transducer calibration, is used for transmission and an optional acoustic
emission transducer under calibration is used for reception. The transmitting and r
...