EN 12668-2:2001

SLOVENSKI STANDARD
01-junij-2002
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Non-destructive testing - Characterization and verification of ultrasonic examination
equipment - Part 2: Probes
Zerstörungsfreie Prüfung - Charakterisierung und Verifizierung der Ultraschall-
Prüfausrüstung - Teil 2: Prüfköpfe
Essais non destructifs - Caractérisation et vérification de l'appareillage de contrôle par
ultrasons - Partie 2: Traducteurs
Ta slovenski standard je istoveten z: EN 12668-2:2001
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 12668-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2001
ICS 19.100
English version
Non-destructive testing - Characterization and verification of
ultrasonic examination equipment - Part 2: Probes
Essais non destructifs - Caractérisation et vérification de Zerstörungsfreie Prüfung - Charakterisierung und
l'appareillage de contrôle par ultrasons - Partie 2: Verifizierung der Ultraschall-Prüfausrüstung - Teil 2:
Traducteurs Prüfköpfe
This European Standard was approved by CEN on 16 April 2001.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12668-2:2001 E
worldwide for CEN national Members.

Page 2
Contents
page
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms, definitions, symbols and abbreviations.4
4 General requirements for compliance .6
5 Manufacturer's technical specification for probes.6
6 Test equipment .10
6.1 Electronic equipment .10
6.2 Test blocks and other equipment.10
7 Performance requirements for probes .13
7.1 Physical aspects .13
7.2 Radio frequency pulse shape.13
7.3 Pulse spectrum and bandwidth.13
7.4 Relative pulse-echo sensitivity.14
7.5 Distance-amplitude curve .14
7.6 Electrical impedance or static capacitance .15
7.7 Beam parameters for immersion probes.16
7.8 Beam parameters for contact, straight-beam, single-transducer probes.20
7.9 Beam parameters for contact shear wave, angle-beam, single-transducer probes.23
7.10 Beam parameters for contact, straight beam, dual-transducer probes.26
7.11 Beam parameters for contact, shear wave angle beam, dual-transducer probes .28
Annex A (normative) Calculation of nearfield length of non-focusing probes.45
Annex B (informative) Calibration block for angle-beam probes .48

Page 3
Foreword
This European Standard has been prepared by Technical Committee CEN/TC 138, "Non-destructive testing", the
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by November 2001, and conflicting national standards shall be withdrawn at the latest
by November 2001.
This standard consists of the following parts :

EN 12668-1, Non-destructive testing - Characterization and verification of ultrasonic examination equipment -
Part 1: Instruments

EN 12668-2, Non-destructive testing - Characterization and verification of ultrasonic examination equipment -
Part 2: Probes

EN 12668-3, Non-destructive testing - Characterization and verification of ultrasonic examination equipment -
Part 3: Combined equipment
Annex A is normative. Annex B is informative.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,
Switzerland and the United Kingdom.

Page 4
1 Scope
This European standard covers probes used for ultrasonic non-destructive examination in the following categories with
centre frequencies in the range 0,5 MHz to 15 MHz, focusing and without focusing means:
a) single or dual transducer contact probes generating compressional or shear waves ;
b) immersion probes.
Where material dependent ultrasonic values are specified in this standard they are based on steels having an
ultrasonic sound velocity of (5 920 ± 50) m/s for longitudinal waves, and (3 255 ± 30) m/s for transverse waves.
Periodic tests for probes are not included in this standard. Routine tests for the verification of probes using on-site
methods are given in EN 12668-3.
If parameters in addition to those specified in EN 12668-3 are to be verified during the probe's life time, as agreed upon
by the contracting parties, the methods of verification for these additional parameters should be selected from those
given in this standard.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN 1330-4, Non destructive testing - Terminology - Part 4 : Terms used in ultrasonic testing.
EN 12223, Non-destructive testing - Ultrasonic examination - Specification for calibration block No. 1.
EN 12668-1, Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part
1 : Instruments.
EN 12668-3, Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part
3 : Combined equipment.
EN 27963, Welds in steel - Calibration block No. 2 for ultrasonic examination of welds (ISO 7963:1985).
EN ISO 9001, Quality systems - Model for quality assurance in design, development, production, installation and
servicing (ISO 9001:1994).
EN ISO 9002, Quality systems - Model for quality assurance in production, installation and servicing (ISO
9002:1994).
3 Terms, definitions, symbols and abbreviations
For the purposes of this European Standard the terms and definitions given in EN 1330-4 apply, together with the
following terms and definitions.
3.1
dead zone
depth of the zone immediately beneath the coupling surface of the work piece, in which it is not possible to detect a
given reflector
3.2
focal distance; (nearfield length)
point on the acoustical axis where the acoustic pressure is at its maximum

Page 5
3.3
horizontal plane of a sound beam
with angle-beam probes the plane perpendicular to the vertical plane of sound beam including the acoustical axis in
the material
3.4
operating frequency, f ; (centre frequency)
o
in the frequency spectrum of an echo the upper and lower cut-off-frequencies are determined at -6 dB compared to
the maximum amplitude. With these upper and lower frequencies f and f the centre frequency is calculated as :
u l
f  f  f
o u l
3.5
peak-to-peak amplitude, h
maximum deviation between the largest positive and the largest negative cycles of the pulse (see Figure 1)
3.6
probe data sheet
sheet giving information on probe performance which accompanies each probe. The data sheet need not
necessarily be a test certificate of individual probe performance
3.7
pulse duration
time interval over which the modulus of the unrectified pulse amplitude exceeds 10 % of its maximum amplitude, as
shown in Figure 1
3.8
reference side
reference side is the right side of an angle beam probe looking in the direction of the beam, unless otherwise
specified by the manufacturer
3.9
relative bandwidth, f
rel
ratio of the difference of the upper and lower cut-off frequencies f and f and the centre frequency f in percent
u l o
f = [(f - f )/f ]  100 %
rel u l o
3.10
squint angle for straight-beam probes, 
deviation between the axis of the beam and a perpendicular to the coupling surface at the emission point
(see Figure 2)
For angle-beam probes
angle between the sides of the probe housing and the measured beam axis, projected onto the plane of the probe
face (see Figure 3)
3.11
transducer
element in the probe which transforms electrical oscillations to mechanical oscillations and vice versa, in most
cases piezoelectric elements
3.12
vertical plane of a sound beam
with angle-beam probes the plane in which the sound beam axis in the probe wedge and the sound beam axis in
the inspected component both lie

Page 6
4 General requirements for compliance
A probe complies with this standard if it satisfies the following conditions:
a) the probe shall meet the technical requirements of this standard ;
b) the probe carries a unique serial number, showing operating frequency, transducer size, angle, and wave
mode, or a permanent reference number from which this information can be traced ;
c) a data sheet is available for the appropriate type and series of probes which gives the performance in
accordance with clause 5 of this standard.
The quality of probes will be assured in one of the following ways :
a) where a large number of identical probes are manufactured under a quality management system, e.g.
EN ISO 9001 and EN ISO 9002, measurements are made on a statistically selected number of probes. The
manufacturer supplies a data sheet which includes the values of the specified parameters with tolerances ;
b) by issuing a declaration of conformity quoting the results of measurements made on an individual probe. This
is suitable where only a small number of probes of each type is manufactured or where probes are required for
special applications.
5 Manufacturer's technical specification for probes
Table 1 gives the list of information to be reported by a manufacturer in a data sheet for all probes within the scope of
this standard (I = Information, M = Measurement, C = Calculation). The data sheet shall also contain information
concerning the instrument used for the test, its settings and coupling conditions etc.
The manufacturer shall also state the operating temperature range of the probe, and any special conditions for storage
or protection during transport.
The supplier and the customer can agree where necessary to preclude some of the information and/or include some
other details not included in Table 1.
For probes intended for use at elevated temperatures the manufacturer shall provide information on the maximum
operating temperature in relation to the time of use, and the effect of temperature on the sensitivity and on the beam
angle.
Page 7
Table 1 — List of information to be given in a data sheet
Category of probe
Contact Immersion
Straight beam Angle beam Straight
Information Compressional Shear Compressional Shear Compressional
to be given Single Double Single Single Double Single Double Single
non-f. focus. non-f. focus. non-f. non-f. focus. non-f. focus. non-f. focus. non-f. focus. non-f. focus.
Manufacturer's name I I I I I I I I I I I I I I I
Type of probe I I I I I I I I I I I I I I I
Weight & size of probe I I I I I I I I I I I I I I I
Type of connectors I I I I I I I I I I I I I I I
TR connect. interchangeable I I I I I I
Material of transducers I I I I I I I I I I I I I I I
Shape & size of transducers I I I I I I I I I I I I I I I
Material of wedge, delay I I I I I I I I I I I I
Material of wear plate I
Wear allowance I I I I I I I I I I I I
I = Information ;
M = Measurement ;
C = Calculation
continued
Page 8
Table 1 (continued)
Category of probe
Contact Immersion
Straight beam Angle beam Straight
Parameters to be Compressional Shear Compressional Shear Compressional
measured or calculated Single Double Single Single Double Single Double Single
non-f. focus. non-f. focus. non-f. non-f. focus. non-f. focus. non-f. focus. non-f. focus. non-f. focus.
Cross talk damping M M M M M M
Pulse shape (time & frequency) M M M M M M M M M M M M M M M
Centre frequency, band width M M M M M M M M M M M M M M M
Pulse-echo sensitivity M M M M M M M M M M M M M M M
Distance-amplitude curve M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C
Impedance, static capacitance M M M M M M M M M M M M M M M
I = Information ;
M = Measurement ;
C = Calculation ;
M,C = Measurement or calculation
continued
Page 9
Table 1 (concluded)
Category of probe
Contact Immersion
Straight beam Angle beam Straight
Parameters to be Compressional Shear Compressional Shear Compressional
measured or calculated Single Double Single Single Double Single Double Single
non-f. focus. non-f. focus. non-f. non-f. focus. non-f. focus. non-f. focus. non-f. focus. non-f. focus.
Probe index MMM M M M M M
Beam angle MMM M M M M M
Angles of divergence M M M M M
Beam axis offset M M M M M M M M M M M M M
Squint angle M M M M M M M M M M M M M
Focal distance, nearfield M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C M,C
Focal width M M M M M MMM M M M M M M M
Focal length M M M M M M M M M M M M M M M
Physical aspects M M M M M M M M M M M M M M M
I = Information ;
M = Measurement ;
C = Calculation ;
M,C = Measurement or calculation
Non-f. = non-focusing
Page 10
6 Test equipment
6.1 Electronic equipment
The ultrasonic instrument (or laboratory pulser/receiver) used for the tests specified in clause 7 shall be of the type
designated on the probe data sheet, and shall comply with EN 12268-1 as applicable. Where more than one type of
ultrasonic instrument is designated the tests shall be repeated with each of the additional designated types.
Testing shall be carried out with the probe cables and electrical matching devices, specified on the probe data sheet
for use with the particular type of ultrasonic instrument.
NOTE Probe leads more than about 2 m long could have significant effect on probe performance.
In addition to the ultrasonic instrument or laboratory pulser/receiver the items of equipment essential to assess
probes in accordance with this standard are as follows :
a) an oscilloscope with a minimum bandwith of 100 MHz ;
b) a frequency spectrum analyzer with a minimum bandwith of 100 MHz, or an oscilloscope/digitizer capable of
performing Discrete Fourier Transforms (DFT) ;
c) an impedance analyzer.
The following additional equipment is optional :
For contact probes only :
d) an electromagnetic-acoustic probe (EMA) and receiver ;
e) a plotter to plot directivity diagrams.
For immersion probes only :
f) hydrophone receiver with an active diameter less than two times the central ultrasonic wavelength
of the probe under test but not less than 0,5 mm. The bandwidth of the amplifier should be higher
than the bandwidth of the probe under test.
6.2 Test blocks and other equipment
The following test blocks shall be used to carry out the specified range of tests, for contact probes only :
a) semi-cylinders with different radii (R) in the range from 12 mm to 200 mm steps of R 2 are recommended.
Steel quality is as defined in EN 27963. The thickness of each block shall be equal to or larger than it's
radius, up to a maximum thickness of 100 mm ;
b) steel blocks with parallel faces and side-drilled holes of 3 mm diameter as shown in Figure 4 a). The
dimensions of the blocks shall meet the following requirements :

length, l, height, h, and width, w, shall be such that the sides of the blocks shall not interfere with the
ultrasonic beam ;

depths of the holes, d , d , . shall be such that at least 3 holes shall fall outside the near field ;
1 2

the distance between the holes, s, shall be such that the amplitude profile across the holes shows an
amplitude drop of at least 26 dB between two adjacent holes ;

steel quality is as defined in EN 27963.

Page 11
c) steel blocks with inclined faces with a notch as shown in Figure 4 b), and steel blocks with hemispherical
holes as in Figures 4 c) and 4 d). Steel quality is as defined in EN 27963. These blocks are used to measure
the beam divergence in the vertical and horizontal plane respectively ;
d) an alternative steel block to measure index point, beam angle and beam divergence for angle beam probes
is given in annex A ;
e) ruler ;
f) feeler gauges starting at 0,05 mm.
NOTE Not all blocks are required if only special kinds of probes are to be checked, e.g. blocks to measure the index
point and beam angle are not necessary if only straight-beam probes have to be measured.
For testing immersion probes the following reflectors and additional equipment shall be used :
g) a steel ball or semi-spherical ended rod with smooth reflective surface. For each frequency range the
diameter of ball or rod to be used is given in Table 2.
Table 2 — Steel ball (rod) diameters for different frequencies
d
Probe centre frequency Diameter of ball or rod
(MHz) (mm)
3 < f  15 d  3
0,5  f 33 < d  5
h) a large plane and flat reflector target. The target's lateral size shall be at least ten times wider than the
diameter of the beam of the probe under test at the end of focal zone, as defined in 7.7.2.2.
Thickness is at least five times the wave length of the probe under test, calculated using the velocity of
ultrasound in the material of the target.
i) immersion tank equipped with a manual or automatic scanning bridge with five free axes :

three linear axes X, Y, Z ;

two angular axes  and .
j) Automatic recording means: If the amplitudes of ultrasonic signals are recorded automatically, then it is the
responsibility of the manufacturer to ensure that the system has sufficient accuracy. In particular
consideration shall be given to the effects of the system bandwidth, spatial resolution, data processing and
data storage on the accuracy of the results.
Throughout this standard the coordinate system shown in Figures 12 and 13 is used.
The scanning mechanism used with the immersion tank should be able to maintain alignment between the target
and the probe in the X and Y directions, i.e. within ± 0,1 mm for 100 mm distance in the Z direction.
The temperature of the water in the immersion tank shall be maintained at (20 ± 2) °C during the beam
characterization of immersion transducers described in 7.7.
Care shall be taken about the influence of sound attenuation in water, which, at high frequencies, causes a downshift
of the echo frequency when using broadband probes.
Table 3 shows the relation between frequency downshift and water path.

Page 12
Table 3 — Frequency downshift in percent of centre frequency fo depending on total water path length, for relative bandwidths (b.w.) 50 % and 100 %
b.w. Total water path in mm
f
o
MHz % 10 20 30 40 50 60 70 80 90 100 150 200 250 300 350 400
5 50 000000111 1122233
100 011122233 35679 10 11
10 50 011122233 35679 10 11
100 13456789 10 11 16 21 24 28 31 34
15 50 112344566 7 10 13 15 18 20 23
100 3 6 8 10 13 15 17 19 21 23 30 37 42 47 50 54
20 50 13456789 10 11 16 21 24 28 31 34
100 51013172124272932 34445156616467
25 50 24679 11 12 14 15 17 23 29 34 38 41 45
100 71420242933363942 45556267707476
30 50 3 6 8 10 13 15 17 19 21 23 30 37 42 47 50 54
100 10 19 26 32 37 41 45 48 51 54 64 70 74 78 80 82

Page 13
7 Performance requirements for probes
7.1 Physical aspects
7.1.1 Method
Visually inspect the outside of the probe for correct identification and assembly and for physical damage which can
influence its' current or future reliability. In particular for contact probes measure the flatness of the contact surface of
the probe using a ruler and feeler gauges.
7.1.2 Acceptance criterion
For flat faced probes, over the whole probe face the gap shall not be larger than 0,05 mm.
7.2 Radio frequency pulse shape
7.2.1 Method
The amplitude and pulse duration of the echo is determined with a measurement setup as in Figure 5 (contact probe)
or Figure 13 (immersion) :
a) for contact probes with a single transducer the echo out of a semi-cylinder is used whose radius is larger than
1,5 of the nearfield length of the probe or within the focal range of focused probes ;
b) for dual-transducer probes a semi-cylinder is used whose radius is nearest to the focal point of the probe ;
c) for immersion probes a large flat reflector is used at the focal distance for focused probes or at more than 1 of
the nearfield length for flat transducers.
The pulser setting shall be recorded, and the peak-to-peak amplitude of the transmitter pulse shall be measured. It is
recommended to plot the transmitter pulse shape and it is preferable that the plot of the transmitter pulse be included in
the results of this test.
7.2.2 Acceptance criterion
The pulse duration shall not deviate by more than ± 10 % from the manufacturer's specification.
7.3 Pulse spectrum and bandwidth
7.3.1 Method
Use the same blocks and the same setup is used as in 7.2. Gate the reflector echo and determine the frequency
spectrum using a spectrum analyzer or a Discrete Fourier Transform.
Spurious echoes from the probe's wedge, housing, damping block, etc. are not to be analyzed together with the echo
from the reference block. The gate has to be twice the pulse duration as a minimum and centered on the maximum of
the pulse.
The lower and upper frequencies for a - 6 dB drop of echo amplitude have to be measured. For immersion technique
the values shall be corrected according to Table 3.
From these upper and lower frequencies f and f the centre frequency f is calculated :
u l o
f  f  f (1)
o u l
Page 14
The bandwidth is :
f = f – f (2)
u l
and the relative bandwidth is calculated, in percentage, as :
f = (f / f )  100 (3)
rel o
7.3.2 Acceptance criteria
The centre frequency has to be within ± 10 % of the frequency quoted in the data sheet.
The - 6 dB bandwidth has to be within ± 15 % of the nominal bandwidth. If the spectrum between f and f has more
l u
than one maximum, the amplitude difference between adjacent minima and maxima shall not exceed 3 dB.
For broadband probes with a relative bandwidth exceeding 100 %, the lower frequency shall not be higher than
f + 10 %, and the upper frequency shall not be lower than f - 10 %.
l u
7.4 Relative pulse-echo sensitivity
7.4.1 Method
Set the ultrasonic instrument to separate pulser/receiver mode. Relative pulse-echo sensitivity is defined as :
S = 20 log (V /V ) (4)
rel 10 e a
where V is the peak-to-peak voltage of the echo from a specified reflector, preferable flat, before amplification and V is
e a
the peak-to-peak voltage applied to the probe as measured in 7.2.
Probe sensitivity comparisons made with different types of ultrasonic instruments can vary, because the probe
sensitivity is influenced by the coupling conditions and by the impedances of pulser, probe, cable and receiver.
Therefore, these parameters have to be specified in the data sheet.
7.4.2 Acceptance criterion
The relative pulse-echo sensitivity shall be within ± 3 dB of the manufacturer's specification.
7.5 Distance-amplitude curve
7.5.1 Method
The amplitude of ultrasonic pulses varies with distance from the probe. Therefore, to evaluate echos of reflectors, for all
kinds of probes, distance-amplitude curves are needed using the reflectors in Table 4.
Table 4 — Reflectors for distance-amplitude curves
Contact Immersion
Disk shaped reflectors Flat bottom holes Flat ended rod
Cylindrical reflectors Side drilled holes Cylindrical rod
Spherical Hemispherical bottom hole Hemispherical ended rod or ball
Disk-shaped reflectors, side-drilled holes and hemispherical bottom holes are used as equivalent reflectors when using
contact probes. With immersion probes usually a small-sized steel ball is used to measure a distance-amplitude curve
(see 7.7.2). For dual-transducer probes the separation layer shall be perpendicular to the side-drilled holes.

Page 15
Using a series of reflectors of constant size but at different distances to the probe the received echo amplitudes are
plotted against distance. At least 8 measurement points on each curve shall be available. The distances used shall
cover the focal range of focusing probes or the range including the nearfield length of non-focusing probes.
Distances and amplitudes are determined on the calibrated screen of an ultrasonic instrument mentioned in the data
sheet.
To generate a noise curve, at each position of a maximized reflector echo the difference between noise and the
reflector echo is determined by increasing the gain until the noise reaches the former height of the reflector echo.
If it is not possible to increase the gain by such an amount, the difference can be estimated.
If, e.g. the reflector echo was at 40 % of full screen height, then the noise at :

20 % means an additional difference of 6 dB ;

10 % means an additional difference of 12 dB ;

5 % means an additional difference of 18 dB
to the difference given by the attenuator readings.
The noise curve is measured with the reflector removed and the surface of the probe cleaned from couplant.
A diagram showing at least one distance-amplitude curve shall be available for each probe type, attached to the
manufacturer's data sheet. This diagram shall also include a distance-noise curve.
Figure 6 a) shows an example of different distance-amplitude curves for disk-shaped reflectors, calculated for disk-
shaped reflectors in steel (distance-gain-size diagram - DGS-diagram). Figure 6 b) shows an example of a measured
distance-amplitude curve for a 3 mm side-drilled hole.
7.5.2 Acceptance criterion
Within the focal range the dB-difference of a specified reflector echo, e.g. a 3 mm side-drilled hole, to the noise level
shall not be lower than the manufacturer's specification by more than 3 dB.
7.6 Electrical impedance or static capacitance
7.6.1 Method
For probes with an electrical matching circuit, e.g. induction coils in parallel or in series to the transducer, there is no
frequency interval with constant impedance or phase. Therefore the complete impedance/phase curve is necessary to
characterize these probes.
The impedance of the probe is determined with a network analyzer or an impedance/gain/phase analyzer as described
in EN 12668-1. The probe is to be connected directly to the analyzer with its fixed cable or, if the cable is removable,
with a cable not longer than 100 mm. Contact probes are coupled to a calibration block. Immersion probes are used in
immersion.
An impedance modulus and phase curve is plotted against frequency within an interval symmetrical to the centre
frequency of the probe.
For probes without electrical matching circuits the capacitance is calculated from the measured impedance/phase
curve by an impedance/gain/phase analyzer.
At frequencies below 30 % of the centre frequency of the probe the capacitance is nearly constant (capacity of the
transducer - static capacitance).

Page 16
7.6.2 Acceptance criteria
The measured modulus and the measured phase, or the static capacitance, shall be within ± 20 % of the
manufacturer's specification.
7.7 Beam parameters for immersion probes
7.7.1 General
The measurement technique consists of studying the probe acoustic beam in water, using a target. This target is a
small, almost point source reflector, or a hydrophone receiver. The beam parameters are determined by scanning the
reflector or hydrophone relative to the beam, either by moving the target or the probe.
If the target is a reflector, echo-mode is used. Both transmitter and receiver characteristics of the probe are verified. If
the target is a hydrophone, transmission mode is used, and then only the transmitting characteristics of the probe are
verified.
The same reflector or hydrophone shall be used for all the beam parameter measurements associated with one
particular probe.
Small variations in the measured position of maximum responses occur as measured by a hydrophone or different
reflector types. Consequently, for reasons of repeatability, the equipment and the parameters of the target used shall
be recorded with the results.
Targets are listed in 6.1 f) and 6.2 g).
Settings of the ultrasonic instrument or pulser receiver (pulse energy, damping, bandwidth, gain) shall be the same as
those defined in 7.2. However, if the settings are changed during the measurement (gain for example), the new values
shall be recorded on the result sheet.
In the following paragraphs two methods are proposed for beam measurement. They differ only in the methods used to
record the measurement results :
a) direct measurement of specific beam parameters :

 the first technique, described in 7.7.2, is based on direct readings at specific points within the beam
(see Figures 7 to 11) ;
b) measurements performed with an automated scanning system :

  the second technique, described in 7.7.3, is based on automated collection of data during scanning.
The results are displayed as a C-scan image. A copy of this image shall be provided with the test results.
This copy shall include a scale of the acoustic levels defined in 7.7.3.
Before performing beam measurements described in the following paragraph, the squint angle shall be compensated
for, by setting the beam axis perpendicular to the XY-plane as shown on Figures 12 and 13. This operation is
performed by adjusting both angles  and  of the probe holder to maximize the echo from a flat target in the XY-
plane.
7.7.2 Beam profile - measurements performed directly on the beam
7.7.2.1 General
Ultrasonic echo peak voltage is recorded using two methods. Either one of the following methods shall be used to
record the ultrasonic peak echo voltage :
a) manually recording the amplitude displayed on an oscilloscope ;
b) automatically recording the amplitude on a paper recorder, plotter or equivalent, synchronized to scanner
movements.
Page 17
In this last case, focal distance, focal length, focal width, transverse profile and beam divergence are deducted from the
graphs obtained.
Figure 12 b) shows the equipment setup used when the target is a reflector and Figure 13 shows the equipment used
when the target is a hydrophone.
The focal distance and focal length are measured from axial profiles and the focal width and beam divergence are
measured from transverse profiles.
7.7.2.2 Axial profile - focal distance and length of the focal zone
7.7.2.2.1 Method
Place the target on the probe axis and place the target and probe in contact. The coordinate of the front face of the
probe or its acoustic lens is Z , see Figure 14.
Move the target (or probe) on Z-axis, increasing probe-target distance. Find the distance at which the signal is
maximized.
Adjust the X- and Y-position to further maximize the signal amplitude. The distance coordinate is Z and the voltage
p
is V .
p
The focal distance is given as :
F = |Z - Z | (5)
D p 0
Find the limits of the focal zone by increasing and reducing the distance between the probe and the reflector to find the
two points where V is reduced by 6 dB, if a reflector is used, or by 3 dB, if a hydrophone is used. Z and Z are the
p L1 L2
coordinates of these points on the Z-axis.
The length of focal zone is given by :
F = |Z - Z | (6)
L L2 L1
7.7.2.2.2 Acceptance criterion
Focal distance and focal length shall be within ± 15 % of the manufacturer's specifications.
7.7.2.3 Transverse profile - focal width
7.7.2.3.1 Method
Use the same set up and same mechanical settings as in 7.7.2.2. Place the target at the focal point of probe, as found
in 7.7.2.2.
To measure the focal width in the X direction move the probe (or hydrophone) in the X direction and find the two points
X and X , where the amplitude from the target has decreased by 6 dB (by 3 dB when a hydrophone is used).
1 2
To measure the focal width in the Y direction return the X-axis to the focal point and repeat the measurement, but this
time move in the Y direction to find the two points Y and Y , where the amplitude of the signal from the target
1 2
decreased by 6 dB (by 3 dB when a hydrophone is used).
The focal widths on X-axis and on Y-axis at focal point are given by the differences :
W = |X - X | (7)
X1 2 1
W = |Y - Y |
Y1 2 1
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7.7.2.3.2 Acceptance criterion
The focal widths shall be within ± 15 % of the manufacturer's specifications.
7.7.2.4 Transverse profile - beam divergence
7.7.2.4.1 Method
The beam divergence is only required for probes that have no artificial focusing means, such as acoustic lenses or
curved piezoelectric elements. The beam divergence is deduced from the measurement of the beam width, as defined
in 7.7.2.3 but measured in the far field.
The measurement shall be performed as follows :
a) first measure the beam widths W and W at focal distance as described in 7.7.2.3 ;
X1 Y1
b) place the target (or probe) at the end of the focal zone (Z ), as measured in 7.7.2.2.
L2
Record X' , X' and Y' , Y' , the target (or probe) positions on X-axis and on Y-axis where the peak voltage decreases
1 2 1 2
of 6 dB (reflector) or 3 dB (hydrophone) from the maximum value V , which is obtained on beam axis.
L
The beam widths at the end of the focal zone are given by :
W = |X' - X' | (8)
X2 2 1
W = |Y' - Y' |
Y2 2 1
The beam divergence in X and Y direction is calculated using the following equations :

= arctan[(W -W )/2(Z -Z )] (9)
X X2 X1 L2 p

= arctan[(W -W )/2(Z -Z )]
Y Y2 Y1 L2 p
7.7.2.4.2 Acceptance criterion
The angles of divergence shall not differ from the manufacturer's specified values by either ± 10 % or by 1°, whichever
is the larger.
7.7.3 Beam profile - measurements made using an automated scanning system
7.7.3.1 General
The ultrasonic echo peak voltage is recorded during an automatic scan of the probe (or the reflector) in different planes.
The variations of amplitude, related to position shall be recorded under the following conditions :
a) the sensitivity, amplitude resolution of data processing, motion speed and motion resolution shall be sufficient
to avoid any loss of information.
The system shall have sufficient dynamic range to collect the high amplitude signals (obtained at the focal
point) without saturation and the low amplitude signals with a sufficient signal-to-noise ratio.
b) the maximum peak voltage V , detected at the focal point, defines the 0 dB level. The coding used for the
p
0 dB, - 3 dB, - 6 dB, - 12 dB levels shall appear on a scale on the scan recording.
The verification is based on performing three scans :
a) one scan in XZ- or YZ-plane including the beam axis gives the focal distance, and focal length ;

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b) two scans in transverse plane XY at the focal distance and at the end of the focal zone. These scans give the
focal width and the beam widths in X and Y direction. The beam divergence is calculated from the beam
widths measured in the XY-plane.
7.7.3.2 Beam profile by scanning means - focal distance and focal length
7.7.3.2.1 Method
Use the same set up as described on Figure 12 b) when the target is a reflector, and Figure 13 when the target is a
hydrophone.
The focal distance and the focal length are deduced from the scans in the plane containing the beam axis.
Adjust the position of the scanner so that :
a) its motion plane contains the beam axis ;
b) the XZ- or YZ-plane covered by the scanning is wide enough to include the end of the focal zone, and the two
points of transverse axes (X and Y) where the amplitude is 6 dB (reflector) or 3 dB (hydrophone) lower than on
the beam axis.
From the C-scan images the following measurements are made :
a) the focal distance F , as defined in 7.7.2.2 ;
D
b) the focal length F , as defined in 7.7.2.2.
L
An example of this plot is given in Figure 15.
7.7.3.2.2 Acceptance criteria
Focal distance and focal length shall be within ± 15 % of the manufacturer's specification.
7.7.3.3 Beam profile by scanning means - focal width and beam divergence
7.7.3.3.1 Method
The mechanical setup is the same as in 7.7.3.2 and described in Figures 12 b) and 13.
The first scan is performed at the focal distance. The scanner is adjusted as follows :
a) adjust the Z-axis of the scanner so that the target is at the focal point, as it was determined in 7.7.3.2. The
scanner displacements are in the XY plane containing the focal point, and perpendicular to the beam axis.
b) adjust the XY scanning area to include the positions where the amplitudes drop by 20 dB from V if using a
p
reflector, or by 10 dB if a hydrophone is used.
At the focal distance, W and W are the diameters of the zones measured in the X or Y direction where the
X1 Y1
displayed amplitudes are 6 dB (reflector) or 3 dB (hydrophone) lower than the value V measured on the beam axis
p
(see Figure 16 for an example).
The second scan is performed at the end of the focal zone. The mechanical set up and the bridge adjustment are the
same as for the previous scanning, except that the target is placed at the end of the focal zone (Z ), defined in 7.7.3.2.
L2
From the image the focal widths W and W are measured by the same method used to determine W and W at
X2 Y2 X1 Y1
the focal distance.
The angles of divergence in the X and Y direction are obtained by the same calculations used in 7.7.2.4.

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7.7.3.3.2 Acceptance criteria
The angles of divergence shall not differ from the manufacturer's specified values by either ± 10 % or by ± 1°,
whichever is the larger.
The focal widths shall be within ± 15 % of the manufacturer's specification.
7.8 Beam parameters for contact, straight-beam, single-transducer probes
7.8.1 General
The procedures given in this clause are for probes with flat contact surfaces only. Probes with profiled shoes can only
be evaluated on reference blocks having the same curvature as the sample the probe shoe was fitted to.
7.8.2 Beam divergence and side lobes
7.8.2.1 Methods
Different methods can be used to measure the directivity pattern:
a) using electromagnetic-acoustic (EMA) receivers
The probe is coupled to a semi-cylinder (see Figure 17).
The EMA receiver measures the received signal when scanning the cylindrical surface of the block.
The signal amplitude is plotted against the scanning angle of the EMA receiver. The plot shall include the main
lobe and the adjacent side lobes. The angles for the -3 dB positions of the main lobe give the divergence
angles (Figure 17).
The angles of divergence have to be measured in two perpendicular planes.
For rectangular transducers these planes shall be parallel to the larger side (a) and the smaller side (b) of the
transducer.
b) using reference blocks with side-drilled holes
Test blocks with plane parallel sides containing 3 mm side-drilled holes at various distances, as shown in
Figure 4 a), can be used to determine the angles of divergence and the side lobes in the two perpendicular
planes.
For each hole the position of the probe to receive the maximum echo and for the forward and backward
position of the -6 dB drop and side lobe positions are marked in a final plot.
The straight line through the marks of the maximum echo together with the normal to the surface of the block
gives the beam angle. The straight lines fitted to the edge points of the beam together with the beam angle
gives the -6 dB divergence angles.
Note the change in echo amplitude in relation to probe movement as the beam is scanned over each hole in
turn.
If a side lobe is detected in the amplitude profile from two or more holes, maximize the side lobe and plot its
position in relation to that of the main lobe. Also record the amplitude of the side lobe in relation to that of the
main lobe.
c) using reference blocks with hemispherical holes
Test blocks with plan parallel sides containing 10 mm hemispherical holes at various distances, as shown in
Figure 4 c) can be used to determine the angles of divergence in two perpendicular planes. For each hole,
mark in the final plot the position of the probe to receive the maximum echo and for the forward and backward
position of the -6 dB drop.
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