17th World Conference on Nondestructive Testing, 25-28 Oct 2008, Shanghai, China
ULTRASONIC TRANSDUCERS CALIBRATION SYSTEM WITH 3D PROCESSING AUGUR 5.4 Andrey E. BAZULIN, Evgeny G. BAZULIN, Dmitry S. TIKHONOV, Аlexey Kh. VOPILKIN SPC “ECHO+”, Moscow, Russia E-mail:
[email protected],
[email protected],
[email protected],
[email protected] Web: http://www.echoplus.ru/eng
Abstract This paper describes ultrasonic transducers calibration system AUGUR 5.4 developed in Scientific and Production Center ECHO+. AUGUR 5.4 is a new generation of calibration systems developed since 1991. The system allows measuring or calculating most part of contact and immersion probes parameters which described in European Standard EN 12688-2. Main system feature is based on use of scanning device with two axes and single hemispherical test block (for contact probes) and small ball-type reflectors (for immersion probes). Single measurement on hemispherical block with pulse-echo technique allows calculating of all pulse parameters (pulse shape, pulse spectrum, sensitivity), probe index, beam axis offset, beam and squint angle, angles of divergence. The principle of full 3D directivity pattern calculation (therefore beam and divergence angles in any plane) based on calculation of multiple-frequency holograms of “omnidirectional source” (FT-SAFT framework). Distance-amplitude curves could be calculated numerically with discrete model of probe’s crystal and set of flat bottom reflectors. Keywords: probe verification, probe calibration, FT-SAFT, ultrasonic transducer, ultrasonic testing, probe parameters Introduction The task of ultrasonic probes verification is a necessary stage of probes manufacturing process and ultrasonic non-destructive examination routine. The procedure of probes verification given for example in Russian Standard GOST 23702-90 [1] and European Standard EN 12668-2 [2]. The comparison of both Standards could be was made by Igor N. Ermolov with consultations from H. Wüstenberg [private communications]. Quantity of probes parameters is 69 for GOST and 23 for EN. Else one Standard is the DNV [3] and this one contains demands to some additional probe parameters verification. The probes calibration systems AUGUR 2.2 [4] and AUGUR 4.4 [5] were developed in SPC “ECHO+” in 1992 and 1996 respectively. The principle of probes parameters measurement based on acquisition of single B-scan from side-drilled hole in rectangular reference block SO-2 with scanning along one axis. This single measurement allows verification of pulse and spectrum parameters, sensitivity, directivity pattern in single plane. For probe index verification additional reference block SO-3 (semi-cylinder block) used. The distance-amplitude curves were calculated numerically taking into account the real probe parameters [6]. The AUGUR 4.4 system used at various Russian enterprises (Steel Works, Russian Railways etc) The modern probes calibration system AUGUR 5.4 was developed in ECHO+ Center in 2007. Its description is given in next part of paper. Brief system description The AUGUR 5.4 system has main parts: system unit with electronic equipment, scanning device with two axes, set of test-blocks and probe holders. See Fig. 1 for details.
System unit is a single channel flaw detector with pulse generator, gain amplifier, ACD and stepper motor controls. System unit plugs to any PC with USB 2.0 cable. Scanning device has two axes with stepper motors. System software (running on the PC) has following main functions: • data acquisition with preset and adjustable configurations; • data processing and probe parameters calculation with accordance to selected probe type and verification methodology; • ultrasonic data and datasheets visualization. Main system technical characteristics: Pulse generator: shock and bipolar with varying length Pulse length adjusting: 0.1…1 ms Pulse amplitude: 50, 100, 150, 200 V Gain range: -20+56 dB with step 1 dB Maximal input signal amplitude: 10±0.1 V Bandwidth (-3 dB cutoff): 0.5-15 MHz TVG range: at least 40 dB Damping resistance: from 25 to 500 Ohms Equivalent noise per root bandwidth: 20×10-9 V / Hz Minimal scanning step size 0.01 mm
The main difference from the previous generation systems is: • second axis of scanning device allows to acquire 2D ultrasonic data and hence calculate probe index and directivity pattern in any plane; • the list of measured or calculated parameters is generally in agreement with EN and DNV. • the hemispherical of semi-cylinder test block could be used as single test block for contact probes verification; • immersion and focusing probes were added in range of probes types available for verification; • adjustable damping resistances, generator pulse amplitude, increased gain diapason and bandwidth, allows to simulate the particular type of ultrasonic equipment and expand the range of probes types available for verification. • system could be plugged to any PC with USB 2.0 connector. System passed trials as measuring instrument in Russian Federation [7]. The system verification routine is mostly according with European Standard EN 12668-1 [8]. The next part contains brief description of probes verification methodology.
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A
Scanning device Immersion tank
PC
Test-blocks Probe holders
System unit B
C
D
Fig. 1 AUGUR 5.4 system. A. Common system view. B. System with hemispherical test block. C. System with immersion tank. D. Example of transducer datasheet.
Probes verification methodology Main feature of system is based on use of scanning device with two scanning axes and single hemispherical test block (110 millimeters in diameter) for contact probes and small balltype reflectors for immersion probes. Single measurement on hemispherical block with pulseecho technique allows calculating of all pulse parameters (pulse shape, pulse spectrum, sensitivity), probe index, beam axis offset, beam and squint angle, angles of divergence. The principle of full 3D directivity pattern calculation (therefore beam and divergence angles in any plane) based on calculation of multiple-frequency holograms of “omnidirectional source” measurements where “omnidirectional source” is an inner spherical surface of test block or small ball-type reflector (FT-SAFT framework). The directivity pattern calculation algorithm is as follows: 1. With use of Fourier transform in time domain multiple-frequency holograms calculation. 2. With use of 2D Fourier transform in spatial domain holograms spatial spectrum calculation. 2πf at each frequency f spatial spectrum to 3. With use of wave number k = c directivity pattern conversion. 4. The impulse directivity pattern calculation as a sum of directivity patterns at frequencies f ∈ ( f min , f max ) , where ( f min , f max ) is a probe bandwidth. See Fig. 3 for example of directivity pattern calculation. 3
All probe parameters which are able to be verified by AUGUR 5.4 are enumerated in Table 1.
Parameter (EN terminology)
Table 1. List of probe parameters Measurement or calculation methodology
Pulse spectrum Bandwidth, relative bandwidth
Recording the echo pulse with maximal amplitude from bottom surface of semi-cylinder or hemispherical test-block (contact probes) or flat plexiglas target (immersion probes) Calculation with -20 dB drop (any other drop level is available certainly) Calculation the DFT of pulse Calculation the fl and fu for a -6 dB drop
Center frequency
Calculation as f 0 =
Pulse shape Pulse duration
fl × fu
Focal length
Calculation as ratio of echo pulse amplitude from bottom surface to transmitter pulse amplitude Direct measurement of echo pulse from top and bottom surfaces of test-block Calculation the set of curves with applying probe and flat reflectors discrete model taking into account real probe parameters. Direct measurement also could be applied using additional test blocks Recording the pulse from the probe when probe is clean from coupling liquid Calculation from transducer coordinates relative to center of semi-cylinder or hemispherical test-block when the echo pulse has a maximum amplitude Calculation from spectrum of holograms measured from bottom surface of semi-cylinder or hemispherical test-block (contact probes) or ball-type reflector (immersion probes) Single frequency or impulse directivity pattern could be calculated Calculation by equations from [2] or [9] Calculation by distance-amplitude curve Calculation by probe 3D acoustic field reconstruction by angular spectrum method [10], see Fig. 4 Calculation by DAC as -6 dB drop
Amplitude uniformity along the wide plate*
The acoustic field from point-source is equivalent to data measured by pulse-echo at the previous stages of verification
Plate angle, plate center coordinates**
Calculation of this additional parameters is useful for further coherent treatment of data acquired within this probe
Time of flight in prism**
Calculation is useful for measurement of wear plate thickness (or prism material velocity)
Pulse-echo sensitivity Cross-talk damping of dual crystal probe Distance-amplitude curve (DAC)
Noise curve Probe index, beam axis offset Directivity pattern (beam angle and angles of divergence) in two orthogonal planes. Effective plate size Focal distance, nearfield Focal width
* According to DNV-2000 ** GOST 23702-90
The impedance measurement could be completed with special electronic equipment. The time for common parameters set verification (impulse parameters, sensitivity, probe index and directivity pattern in plane of incidence, noise curve, DAC) could be competed for two 4
or three minutes including probe set up, measurements, calculation and datasheet printing. Verification of full parameters set with 2D scanning and manual analysis of some characteristics could be completed for about twenty or thirty minutes.
Probe index
Impulse shape
Fig. 2 Common view of B-scan from hemispherical block. Диаграмма нап равленности в основной плоскости (ма ксимальная) на частоте 1.7969 МГц 45 40
Растровое изображение спектра двумерной голограммы на частоте 1.7969 МГц
Directivity pattern in plane of incidence
35
-10 60
30
-8 25
-6
50
20
kу, рад/мм
-4
15
40
-2
10
0
5
30
2 4
0 -100 -8 0 -60 -40 -20 0 20 40 60 80 1 00 Диаграмма направленности в дополнительной плоскости (максимальная) на частоте 1.7969 МГц угол, град 45
20
40
6 10
8
Directivity pattern in perpendicular plane
35 30
10 -10
-5
0 kx, рад/мм
5
10
25 20 15 10 5 0 -140
-120
-100
-80
-60
-40 -20 угол, град
0
20
40
60
Fig. 3 Example of 3D directivity pattern calculation from 2D angular spectrum of multifrequency holograms (left side). At the right side two slices of directivity pattern shown.
B
A X
X
Focal distance width and length
Y Amplitude uniformity along the plate
Z
Fig. 4 Example of acoustical field measurement and calculation. A – measurement of field of pitchand-catch probe with plate length 30 mm, the reflector is bottom of hemispherical test block. B – calculation of immerse probe field from single measurement in the near field. One can see the near field zone and far field zone structure, focal distance.
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Summary and discussion The simple and compact system for probes verification was developed. The list of probe parameters which available for verification is in agreement with EN 12688-2. One of the systems is working on Vyksa Steel Works to complete standards of probes calibration routine in international project NordStream. References [1] GOST 23702-90 (Russian Federation standard). Ultrasonic transducers. Testing methodology. 1990. [2] EUROPEAN STANDARD. EN 12668-2:2001. Non-destructive testing. Characterization and verification of ultrasonic examination equipment – Part 2: Probes. [3] Offshore standard DNV-OS-F101, Det Norske Veritas, 2000. [4] Badalyan V.G., Bazulin E.G., Bychkov I.V, Vopilkin A.Kh., Kaplun S.M., Lomakin A.V., Pentjuk M.V., Ruben E.A., Tikhonov D.S., Stern A.M. – A computerized system for testing and certifying AUGUR 2.2 ultrasonic nondestructive test transducers, Russ. j. nondestruct. test., 1993, vol. 29, no2, pp116-122. [5] Probe calibration system AUGUR 4.4, The Federal Agency of the Russian Federation on Technical Regulating and Metrology certificate RU.C.34.003.A №14077. [6] Antipin V.E., Gusarov V.R., Perlatov V.G. Role of distributed transfer functions for electroacoustic transducers in the metrological security of an ultrasonic inspection. Sov. J. Nondestr. Test. (Engl. Transl.) ; Vol/Issue: 24:8; Translated from Defektoskopiya; 24: No. 8, 4449 (Aug 1988) [7] Probe calibration system AUGUR 5.4, The Federal Agency of the Russian Federation on Technical Regulating and Metrology certificate RU.C.27.003.A №30200. [8] EUROPEAN STANDARD. EN 12668-1:2001. Non-destructive testing. Characterization and verification of ultrasonic examination equipment – Part 1: Instruments. [9] Nondestructive testing hand-book in 7 volumes. Chief editor V.V. Kluev. Vol. 3. Ultrasonic testing, I.N. Ermolov, Ju.V. Lange, Mashinostroenie, 2004. – p864 (in Russian). [10] Ermert, H, Karg, R. Multifrequency acoustical holography. IEEE Transactions on Sonics and Ultrasonics. 1979, Vol. 26, Issue 4, pp. 279-285.
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