INTERNATIONAL STANDARD ISO 20339 First edition 2017-03 Non-destructive testing — Equipment for eddy current examination — Array probe characteristics and verification Essais non destructifs — Appareillage pour examen par courants de Foucault — Caractéristiques des capteurs multiéléments et vérifications Reference number ISO 20339:2017(E) © ISO 2017 ISO 20339:2017(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2017, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii © ISO 2017 – All rights reserved ISO 20339:2017(E) Contents Page Foreword v Scope Normative references Terms and definitions Probe and interconnecting elements characteristics 4.1 General characteristics 4.1.1 Application 4.1.3 Interconnecting elements f 4.1.6 Environmental conditions 4.2 Electrical characteristics 4.3 Functional characteristics Verification f Measurement of electrical and functional characteristics of an array probe 6.1 Electrical characteristics 6.1.1 General 6.1.2 Measurement conditions 6.1.3 Impedance of coil elements 6.1.4 Impedance of a pattern 6.1.5 Channel assignment — Sequencing 6.1.6 Cross-talk 6.2 Functional characteristics 6.2.1 General 6.2.2 Measurement conditions Surface array probes 7.1 Reference blocks 7.2 Probe motion 7.3 Reference signal — Normalization ff f 10 7.5 Response to a slot 11 7.6 Response to a hole 12 7.7 Length of coverage 12 12 7.9 Minimum slot length for constant probe response 13 7.10 Lift-off effect 13 7.11 Effect of probe clearance on slot response 13 7.12 Effective depth of detection of a sub-surface slot 14 7.13 Resolution 14 7.14 Defective element or pattern 14 Coaxial array probes 14 8.1 General conditions 14 8.2 Reference blocks 14 8.3 Reference signal 16 8.4 Absence of defective elements 17 f f 17 8.6 End effect 17 8.7 Length of coverage 17 f 18 Pro b e typ es Phys ical characteris tics S a ety Level o verificatio ns C haracteris tics to b e verified 7.4 E dge e 7.8 Variatio n in s ens itivity b etween p atterns 8.5 Po s itio n mark o 8.8 H o mo geneity o ect (meas urab le in the cas e o © ISO 2017 – All rights reserved the p ro b e (mainly s imp le geo metry, e g metal s heets , dis ks ) o r p o s itio ning) axial res p o ns e iii ISO 20339:2017(E) Eccentricity e ffect 19 8.10 Fill effect 19 8.11 Effective depth of penetration 19 8.12 Effective depth of detection under ligament 19 8.9 Influence o f interconnecting elements 19 iv © ISO 2017 – All rights reserved Annex A (informative) Simulation of surface probe resolution 20 ISO 20339:2017(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f 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 o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the voluntary nature o f standards, the meaning o f ISO specific terms and expressions related to formity assessment, as well as in formation about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso org/iso/foreword html This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee SC 4, Eddy current testing © ISO 2017 – All rights reserved v INTERNATIONAL STANDARD ISO 20339:2017(E) Non-destructive testing — Equipment for eddy current examination — Array probe characteristics and verification Scope This c ument identi fie s the func tiona l ch arac teri s tics i ntercon ne c ti ng elements and provide s me tho d s for of e ddy c u rrent array prob e s and thei r thei r me as u rement a nd veri fic ation T he eva luation o f the s e charac teri s tics p erm its a wel l- defi ne d de s crip tion a nd comp arabi l ity o f e ddy c u rrent array prob e s Where relevant, this document gives recommendations for acceptance criteria for the characteristics Normative references T he fol lowi ng c u ments are re ferre d to i n the tex t i n s uch a way th at s ome or a l l o f thei r content s titute s re qu i rements o f th i s c u ment For date d re ference s , on ly the e d ition cite d appl ie s For u ndate d re ference s , the late s t e d ition o f the re ference d c ument (i nclud i ng a ny amend ments) appl ie s ISO 12718, Non-destructive testing — Eddy current testing — Vocabulary ISO 15548-1, Non-destructive testing — Equipment for eddy current examination — Part 1: Instrument characteristics and verification ISO 15548-2:2013, Non-destructive testing — Equipment for eddy current examination — Part 2: Probe characteristics and verification Terms and definitions For the pu r p o s e s o f th i s c u ment, the term s and defi n ition s given i n I S O 71 and the fol lowi ng apply ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at http://www.iso org/obp — IEC Electropedia: available at http://www.electropedia org/ 3.1 element s i ngle phys ic a l comp onent s uch a s a coi l, a GM R or a H a l l prob e wh ich has a b as ic or reception fu nc tion o f exc itation 3.2 pattern s i ngle phys ic a l a nd ele c tron ic a rrangement o f s i mu lta ne ou sly ac tive elements 3.3 sequencing ch ronolo g y o f the ac tivation o f p attern s 3.4 threshold lowe s t accep table s en s itivity va lue defi ne d i n an appl ic ation c ument © ISO 2017 – All rights reserved ISO 20339:2017(E) Probe and interconnecting elements characteristics 4.1 General characteristics 4.1.1 Application P rob e s a nd application i ntercon ne c ti ng elements a re s ele c te d to s ati s fy the re qu i rements of the i ntende d T he de s ign i s i n fluence d b y the i n s tr u ment with wh ich they a re u s e d 4.1.2 Probe types T he prob e i s de s c rib e d b y the fol lowi ng: — typ e o f materia l to b e e xam i ne d , i e ferromagne tic, non- ferromagne tic with h igh or low conduc tivity; — the ge ome tr y o f the e xam i ne d z one; — whe ther it i s formable or no t; — fa m i ly, — the re ceiver typ e; — the nu mb er o f elements (tra n s m itters a nd/or re ceivers) ; — s hap e a nd as s embly o f elements and s p aci ng; — pu rp o s e o f the exam i nation, e g dete c tion o f d i s conti nuitie s , s or ti ng or th ickne s s me a s urement, e tc ; — s p e ci fic — the e g co a xi a l prob e, s u r face prob e; fe atu re s , e g fo c u s e d, sh ielde d, e tc ; func tion o f the elements (tran s m i s s ion or re cep tion) a s wel l a s the typ e o f me a s u rement (ab s olute or d i fferenti a l) may co e xi s t i n the s a me array prob e dep end i ng on the p attern s , the s e quenci ng and the instrument software 4.1.3 Interconnecting elements T hey may i nclude the fol lowi ng: — ac tive device s , e g mu ltiplexer ( bu i lt-i n or ex terna l) , ampl i fier; — c able s a nd/or ex ten s ion s; — conne c tors; — s l ip ri ngs; — ro tati ng he ad s; — polarizers 4.1.4 Physical characteristics The following are to be stated among others: — e xterna l s i z e a nd sh ap e; — weight; — i n formation for me ch an ic a l mounti ng; © ISO 2017 – All rights reserved ISO 20339:2017(E) — mo del numb er a nd s eria l nu mb er; — materia l o f prob e hou s i ng; — comp o s ition a nd th ickne s s o f — pre s ence and pu rp o s e o f core or sh ield; — typ e o f i ntercon ne c ti ng elements (s e e — at le a s t one p o s ition mark (ele c tric a l centre; s e e 4.1.5 fac i ng materi a l; 4.1.3 ); 8.5) Safety T he prob e a nd its i nterconne c ti ng elements s l l me e t the appl ic able s a fe ty re gu l ation s re ga rd i ng electrical hazard, surface temperature, or explosion Normal use of the probe should not create a hazard 4.1.6 Environmental conditions T he temp erature and hu m id ity for norma l u s e, s torage and tran s p or t s hou ld b e s p e c i fie d for the prob e and its interconnecting elements The tolerance of the probe and its interconnecting elements to the effects of interference noise and ele c tromagne tic rad iation sha l l form to ele c tromagne tic comp atibi l ity (E M C ) regu lation s Materials used in the manufacture of the probe should be resistant to contaminants 4.2 Electrical characteristics T he ele c tric a l cha rac teri s tic s o f a prob e ne c te d to a s p e c i fie d leng th a nd typ e o f c able a re the following: — re com mende d nge o f e xc itation voltage for s a fe op eration; — recommended range of excitation frequencies T he ele c tric a l charac teri s tic s o f any e xten s ion c able are the fol lowi ng: — resistance and capacitive reactance per length unit 4.3 Functional characteristics T he fu nc tiona l charac teri s tics o f a n array prob e s l l b e de term i ne d for a defi ne d s ys tem The measurement of the functional characteristics of a probe requires the use of reference blocks The materi a l u s e d for the re ference blo ck i s de term i ne d b y the appl ic ation The functional characteristics of a probe are the following: — a ngu l ar s en s iti vity; — re s p on s e to elementa r y d i s conti nu itie s or va riation s ( hole, s lo t, dep o s it, e tc ) ; — leng th a nd width o f coverage — a re a o f coverage — m i n i mum d i men s ion s o f d i s conti nu itie s — p ene tration charac teri s tics; for for a gi ven p attern; a given p attern; © ISO 2017 – All rights reserved for s tant re s p on s e; ISO 20339:2017(E) — geometric e ffects; — cross-talk; — number of dead elements These characteristics cannot be used alone to establish the performance (e.g resolution, largest undetectable discontinuity, etc.) o f the probe in a given test system for a given application When relevant, the functional characteristics shall be measured on the probe with the interconnecting elements required by the application 5.1 Verification Level o f verifications Two levels o f verification may be required: a) basic level: addresses detection per formance; b) advanced level: addresses characterization performance: — verification o f a motion system where there is a need for mechanization o f some measurements (movement o f the probe); — digitization and scanning speed: number of measurement points per millimetre The qualification o f a process which may imply an agreement between manu facturer and customer is not considered in this document 5.2 Characteristics to be verified The characteristics to be verified are listed in Table Table — Array probe characteristics Characteristic Outer dimensions Con formability o f the probe Area of coverage Number of elements Arrangement Excitation frequencies Nature of elements Element dimensions Distances between elements Assembly External or built-in multiplexer Length and type o f supplied cable Basic level I I I I M M I I I I I I Advanced level M M M M M M I I I I I I I: measured by the manu facturer or design data, reported on the technical specification M: measured by the manu facturer and/or the user The manu facturer should add what type and orientation o f discontinuity the probe is designed for Where more in formation on the elements is needed by the user (e.g for simulation), then it may be part o f a specific agreement © ISO 2017 – All rights reserved ISO 20339:2017(E) Adapt the scanning to the type o f pattern (separate transmit receive or not, combined transmit receive in absolute measurement) In the case where the probe is explicitly designed for scanning slots non-perpendicular to the probe motion (e.g parallel), an alternative procedure shall be described in the application document Settings 1) The instrument shall be set so that the amplitude of the slot signal obtained is maximized without saturation The amplitude of the background noise (static measurement) should then be 6dB less than the amplitude o f the signal corresponding to the sensitivity threshold as per definition 3.4 The absence o f any saturation signal shall be checked in all subsequent measurements 2) Perform normalization in order to obtain the same amplitude and phase for the reference slot on all the channels; this amplitude shall range between 25 % and 80 % o f the dynamic range o f the instrument This setting shall be kept for all the measurements Results The reference signal Sref is the maximum value of the signal of all the channels during the scan This value shall be recorded As an example, the phase o f the signal obtained when scanning the filled groove (or the non-conductive over layers) may be taken as the origin o f phases for subsequent measurements In the following subclauses, all results shall be expressed relatively to Sref Figure — Probe motion to obtain the reference signal 7.4 Edge effect (measurable in the case of simple geometry, e.g metal sheets, disks) Reference block: Block A1 shall be used for this measurement Probe motion perpendicular directions With the probe mid-way between the slot and the adjacent edge o f the block, the probe is moved from the former balance position on a scanning line to the closest edge of the reference block: 1) along its pre ferred orientation (perpendicular to the slot orientation); 2) perpendicular to its preferred orientation 10 © ISO 2017 – All rights reserved ISO 20339:2017(E) Results 1) S ca n n i ng i n the pre ferre d orientation: T he e dge e ffe c t i s cha rac teri ze d b y the d i s ta nce from the prob e ma rke d ex trem ity o f the ac tive p ar t clo s e s t to the e dge concerne d b y the me a s urement to the edge of the block at which the signal S is such that: S / Sref = A , e.g absolute value of S Sref / Sref = 0,5 (A is a value mentioned in the application document.) 2) Scanning perpendicular to the preferred orientation: Take into account the relative position of the transmitting element The effect is stronger in one direction than in the opposite direction S / Sref = A (A is a value mentioned in the application document.) − 7.5 Response to a slot Reference block: Block A1 shall be used for this measurement Probe motion a) Non-directional probes S c a n the b lo ck with the leng th o f the a rray p er p end ic u lar or p ara l lel to the s lo t (s e e A or T) Figure 4, scan b) Directional probes Scan the block with the expected preferential orientation of the probe perpendicular to the slot (see Figure 4, scan T) Key scan A scan T reference slot NOTE Arrow on probe indicates probe preferred orientation eddy current array p ro b e Figure — Probe motion for the measurement of the response to a slot Results The maximum value Smax/Sref of the signal over the whole scan is taken © ISO 2017 – All rights reserved 11 ISO 20339:2017(E) For each scanning path, the points corresponding to the signal which is 6dB less than Smax/Sref shall be plotted to form a map of the probe response to the slot The scanning path shall be related to the mapping by the representation o f the slot and the probe position mark for the first recorded point (e.g bottom le ft) A more complete representation can be achieved through the use o f more level lines or any equivalent representation (3D mapping, coloured map, etc.) 7.6 Response to a hole Reference block: Block A2 shall be used for this measurement Probe motion Per form successive scans using only one pattern from one side o f the single hole to the other The step between scanning paths shall be equal to 1/5 of the pitch between patterns Results For each scan, record the maximum signal amplitude and plot the corresponding curve (bell shape) Knowing the pitch between patterns, it is then easy to extrapolate the result and measure the amplitude decrease between two adjacent patterns 7.7 Length of coverage The length of coverage is derived from the map of the probe response to the slot, made in 7.5 , by taking the maximum width of the envelope in the scanning direction (see Figure 5) In case there are several di fferent types o f sequencing (impedance mode, separate transmit receive) patterns, the measurement shall be repeated for each of them Key dB line Figure — Example of determination of the length of coverage (L cov) 7.8 Variation in sensitivity between patterns Purpose of the measurement This measurement enables an evaluation o f sensitivity homogeneity from one pattern to another It is the manu facturer’s responsibility and results shall be provided to users Normalization shall always be first carried out as described in 7.3 Reference block: Block A1 shall be used for this measurement Probe motion A linear scan is performed over the surface of the reference block with the centre of the probe passing over the middle of the slot 12 © ISO 2017 – All rights reserved ISO 20339:2017(E) Results In the impedance plane, observe the signal obtained on each channel a) Rigid probes b) — T he pha s e angle o f the s igna l s sh a l l no t var y b y more than ± ° — T he ampl itude o f the s igna l s sh a l l no t var y b y more than ±10 % Conformable probes — T he pha s e angle o f the s igna l s sh a l l no t var y b y more than ± ° — T he ampl itude o f the s igna l s sh a l l no t var y b y more than ±10 % When repro duc ibi l ity c an no t b e en s u re d, th i s wi l l a ffe c t the va ri ation o f the pha s e a ngle o f s igna l s; i n such case: — the pha s e angle o f the s igna l s sh a l l no t var y b y more tha n ± ° When variations exceed the above values, the probe does not conform to this document 7.9 Minimum slot length for constant probe response T h i s veri fic ation i s l i m ite d to the p attern S e e I S O 5 -2 7.10 Lift-off effect Reference block: Block A1 shall be used for this measurement Probe motion T he prob e is lo c ate d over the b a lance are a o f the blo ck and i s move d ver tic a l ly i n defi ne d s tep s B a l ance the prob e when i n contac t with the re ference blo ck, i e z = L i ft- o ff may b e ob tai ne d us i ng non-conductive shims or an appropriate device delivering a measurable mechanical lift-off (probe on a scanner) Results: Plot S(z)/Sref f or height z va r yi ng b y defi ne d s tep s T he e ffe c t o f l i ft- o ff i s cha rac teri z e d b y the c ur ve S(z) against z 7.11 Effect of probe clearance on slot response Reference block: Block A1 shall be used for this measurement Probe motion A linear scan is performed over the middle of the slot: the orientation of the probe with respect to the slo t dep end s on the typ e o f ch an nel s generate d b y the p attern (tra n s vers e or a xi a l) T he prob e cle arance varie s from z ero to a va lue repre s entative o f the e xit from the z one o f i n fluence, s p e ci fie d i n the appl ic ation c u ment The probe is balanced for each value of probe clearance on the balance area of the block Results For each value of the probe clearance z, repeat the measurements described in 7.4 ff f f Smax (z)/Sref against z T he e ect o prob e cle arance on a de e c t s igna l i s cha rac teri z e d b y plo tti ng © ISO 2017 – All rights reserved 13 ISO 20339:2017(E) 7.12 Effective depth of detection of a sub-surface slot T h i s veri fic ation i s l i m ite d to the p attern S e e I S O 5 -2 7.13 Resolution B y defi n ition, re s olution i s the s hor te s t d i s tance b e twe en two de fe c ts enabl i ng the prob e to del iver two distinct signals This functional characteristic depends on the application for which the probe is designed Reference block: Reference Block A2 shall be used Two measurements are proposed 1) T he fi rs t prop o s e d me a s urement le ad s to a n approxi mation o f the re s olution: — the orientation o f the prob e with re s p e c t to the hole mo d i fie s the s i gna l generate d b y the p attern (a xi a l or tran s vers e) For th i s me a s urement, on ly the a xi a l s c an i s relevant; — s c an the re ference de fe c t u s i ng one p attern; — plo t the re s p on s e c u r ve; — s e t the th re shold at − d B with re s p e c t to the ma xi mu m M e as u re the width; — the measured width corresponds to a conservative value of the pattern resolution (see Annex A) 2) T he s e cond me as u rement i s a veri fic ation o f the re s olution o f the comple te a rray: — s c an hole s a nd with an a xia l mo tion (array p ara l lel to the hole s) ; — a response curve comparable to the curve in Annex A probe resolution is at best the same as that of the pattern (s i mu lation ) enable s to veri fy that the 7.14 Defective element or pattern Manufacturer: no defective element or pattern is acceptable Us er: the accep tance c riteri a sh a l l b e s p e ci fie d i n the app l ic ation c ument Coaxial array probes 8.1 General conditions Un le s s o ther wi s e s p e ci fie d: — the me a s u rements apply to i n ner or enc i rcl i ng co a xi a l prob e s with c yl i nd ric a l ge ome tr y and ci rc u l ar s e c tion, a nd they sh a l l b e conduc te d with s tant prob e cle a rance, wh ich wi l l b e s p e c i fie d i n the appl ic ation c u ment; — the results will concern the amplitude and the phase of the signal T he c as e o f co a xi a l prob e s with non- c i rc u lar s e c tion s s l l b e e xam i ne d on a ca s e by c a s e b as i s i n the application document 8.2 Reference blocks Reference blocks (B1 to B3, C1 to C3) are described in general terms 14 © ISO 2017 – All rights reserved ISO 20339:2017(E) They consist o f tubes or bars — The length L of the tube (bar) shall be greater than four times the end effect dimension of the probe as defined by the manu facturer When this feature is not known, it shall be replaced by the active dimension of the probe in the scanning direction — The distance between artificial discontinuities shall be at least three times the active dimension o f the probe — The thickness o f the tube wall (or the diameter o f the bar) is defined in the application document The wall thickness (or the diameter) shall remain constant on the whole length of the tube (or the bar) In the case o f tubes, i f this is industrially achievable, any influence from wall thickness variation is sa fely reduced i f the thickness o f the re ference block is at least three times the standard depth o f penetration for the lowest frequency nominated in the probe specification The detailed requirements of each block shall be given in a procedure The only probe motion considered for characterization is a translation parallel to the reference block axis Block B1 for tubes (C1 for bars) EDM axial slots and EDM transverse slots The length of the slots is at least three times the pattern length The depth o f the slots is 20 %, 40 %, 60 %, respectively OD circum ferential groove, 30 % deep and mm wide (see Figure 6) Figure — Block B1 Block B2 (or C2) A tube (or a bar) with a helical groove 30 % deep over 400° The width is not critical (0,5 mm wide to mm); see Figure Pitch o f the helix: twice the required period o f spatial sampling multiplied by the number o f elements (example: where the sampling frequency is two points per millimetre, the period is 0,5; for a 32 element probe, the recommended pitch will therefore be 0,5 × × 32 = 32 mm) © ISO 2017 – All rights reserved 15 ISO 20339:2017(E) Figure — Block B2 Block B3 (or C3) A tube (or a bar) with four circum ferential grooves, 0,2 mm wide Their depth is 10 %, 30 %, 50 %, 70 %, respectively, see Figure Figure — Block B3 8.3 Reference signal Reference block: B1 (or C1) shall be used for this measurement Measurements Ensure the probe is centred Results Balance the probe on a discontinuity- free portion o f the tube (or the bar) Move the probe over the circumferential groove 16 © ISO 2017 – All rights reserved ISO 20339:2017(E) The instrument is adjusted so that the maximum signal corresponds to a given value o f the instrument dynamic range (e.g 25 %) It shall be verified that no signal saturation occurs in the subsequent measurements The reference signal Sref is the maximum value of the signal during the scan The phase of the reference signal is taken as the origin of phases for subsequent measurements If more convenient, another re ference may be chosen, provided that it is reported In the following subclauses, all results shall be expressed relatively to Sref 8.4 Absence of defective elements Reference block: Block B2 (or C2) shall be used for this measurement Measurement Balance the probe on a defect-free portion of the tube (or the bar) Scan the helical groove by pulling the probe out o f the tube (or the bar) The presence o f de fective elements shall be observed on the display Acceptance criterion Manufacturer: no defective element is acceptable User: the acceptance criterion shall be specified in the application document 8.5 Position mark of the probe (mainly for positioning) The probe position mark placed on the probe body unambiguously defines the electrical centre o f the probe according to the measurement method given below A position mark can be applied where the size and shape o f the probe body or the probe response permits Where this is not possible, it shall be defined by means o f a sketch, or the distance o f the position mark rom a fixed point o f the probe can be recorded f Reference block: Block B1 (or C1) shall be used for this measurement Measurement mode and results — With the probe mechanically set on an adapted fixture, move Re ference Block B1 (or C1) in order to scan the OD circumferential groove Find and keep the position of the block corresponding to the maximum signal Place a mark on the probe cable (or on the test bench) then record the length corresponding to the distance from the groove to the block end from which the scanning was initiated on the probe body — Engrave a mark on the probe body 8.6 End effect This verification is limited to the pattern See ISO 15548-2 8.7 Length of coverage Block B1: reference defect: a circumferential groove Repeat the measurements described in 7.5 © ISO 2017 – All rights reserved 17 ISO 20339:2017(E) On the curve obtained, mark the two extreme points at –6dB The distance between the two points is the length of coverage of the probe 8.8 Homogeneity of axial response Reference defect: a through-wall hole with an area less than 1/10th of the area of coverage of the p attern (re ference blo ck to b e defi ne d) Results D efi ne an a ngu la r origi n on the blo cks Move the probe on the whole length of the block Report the maximum amplitude Smax Rotate the block (or the probe) with an angle α in relation with the pitch between elements (e.g 1/5th of the pitch) Rep e at the s c an n i ng i n order to cover ° (che ck that there i s a n overlap o f e xam i ne d z one s) Plot Smax (α) / Sref against α The curve obtained is known as the radar curve (see Figure 9) Interpretation: — the d i fference i n a mp l itude b e twe en two ma xi mu m a mpl itude p oi nts corre s p ond s to the homo geneity o f a xia l re s p ons e; — the difference between vertical coordinates of the highest maximum and the lowest minimum ampl itude (cro s s i ng p oi nt) corre s p ond s to the vari ation i n s en s itivity Key Y X measured amplitude (a.u.) minimum distance between the hole and the probe (a.u.) function measure Figure — Theoretical curve 18 © ISO 2017 – All rights reserved ISO 20339:2017(E) Alternative measurement mode Scan the hole with an element centred on the defect Report the maximum amplitude Smax Rotate the probe with an angle corresponding to half the distance between two elements Scan the defect Report the amplitude Smin Ro tate the prob e with the s ame angle a s previou s ly i n order to bri ng the adj acent element i n front of the defect When scanning the defect with this element, it is expected to obtain the value Smax obtained after the previous measurement D evi ation from a xia l s ym me tr y i s defi ne d a s [Max(Smax Smax)]/Max(Smax) × 10 = d % ) − m i n( 8.9 Eccentricity effect T h i s veri fic ation i s l i m ite d to the p attern S e e I S O 5 -2 8.10 Fill effect This characteristic is not an essential functional feature of a probe as it is rather application related M ore over, th i s veri fic ation i s l i m ite d to the p attern S e e I S O 5 -2 8.11 Effective depth of penetration T h i s veri fic ation i s l i m ite d to the p attern B lo ck B (or C ) Balance the probe on a defect-free portion of the block S0 is the maximum signal obtained over the deepest defect S(d) is the maximum signal over the groove of depth d S(d) is plotted against d The effective depth of penetration Peff is the smallest value of d for which: [S0 S(d)] / S0 − ≤ 10 % 8.12 Effective depth of detection under ligament T h i s cha rac teri s tic sh a l l b e veri fie d on ly for i nterna l co a xi a l prob e s T h i s veri fic ation i s l i m ite d to the p attern S e e I S O 5 -2 Influence o f interconnecting elements B o th ele c tric a l elements a nd fu nc tiona l charac teri s tics ca n be a ffe c te d by the add ition T h i s i n fluence s l l b e eva luate d b y rep e ati ng the me a s u rements de s crib e d i n O f s p e c i fic i mp or tance a re the — o f i ntercon ne c ti ng 6.1 and 6.2 fol lowi ng: a mpl itude re s p on s e; — phase response © ISO 2017 – All rights reserved 19 ISO 20339:2017(E) Annex A (informative) Simulation of surface probe resolution A.1 Simulation I n the fol lowi ng s i mu lation, the d i s conti nu ity i s a hole, ,1 m m d iame ter and , m m de ep The pattern features two coils, mm diameter The distance between coils is 1,2 mm The size of the pattern is mm × 2,2 mm The pattern operates in separate transmit receive mode Axial scan of the hole: 20 © ISO 2017 – All rights reserved ISO 20339:2017(E) −3 dB width = , m m − d B width = , m m A.2 Simulation C on s ider a blo ck with d i s conti nu itie s; the d i s tance b e twe en them i s , m m (−3 d B width) © ISO 2017 – All rights reserved 21 ISO 20339:2017(E) The discontinuities are not resolved A.3 Simulation I n the th i rd s i mu late d ca s e, the d i s tance b e twe en d i s conti nu itie s i s , m m (− d B width) The probe starts to resolve the two discontinuities 22 © ISO 2017 – All rights reserved ISO 20339:2017(E) ICS 19.100 Price based on 2 pages © ISO 2017 – All rights reserved