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94 Iustina Elena Rotman et al
This measurement error is due to amplification (61 dB) that distorts the back
wall echo base and to the transducer which is positioned near the edge of the
sample.
3.2. Second case. It may be noted that in this case the effect of divergence
and misinterpretation can be eliminated by positioning the transducer on the
axial direction of the sample. In this manner, the repetition rate of the flaw
(PRF) does not influence the accuracy of the signal and the interpretation is
objective. Bottom echo is very clear. (See fig. 5).
Fig. 5 – Ultrasonic testing display. Fig. 6 – The ultrasonic beam shape .
3.3. Third case. Analyzing the measurements made on both samples we can
conclude that the divergence effect can be eliminated by reducing the repetition
rate of the flaw.
a) b)
Fig. 7 –Ultrasonic testing display:
a) – The parasite echo; b) – The additional echo disappears
As we can see in Fig. 7a), parasites echoes are present and at a PRF9 (See
Fig.7b)) these additional effects disappear. In this kind of situations it is
recommended to get more measurements at a minimum level of PRF.