FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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Since the velocity measured is actually a value taken over the whole region of
insonification, we looked at the effect of changing the acoustic beam
diameter. Our observations using transducers of increasingly larger diameters
(from 0.2 cm for à focused beam up to 4 cm) show that the scatter diminishes.
Increasing the diameter amounts to measuring a value that is averaged over a
wider area. In order to appraise the scatter, we have measured the velocity
at different locations on the same plaques. The results are illustrated in
Fig. 3 for a 1.25 cm (i in) diameter transducer. The standard deviation is
found to be (Sv/v)expe. = _+ 0.0018. However, if we repeat the measurement
several times at the same location on the plaque, the standard deviation is
(6v/v)repeat = _+ 0.0010. This tends to show that the scatter partly has its
origin in non homogeneities found across the plaque.
In turn, we can estimate the theoretical experimental uncertainty by
considering the relation from which the velocity is calculated and the various
instrumental errors. We obtain a value of (ôv/v)theo. = i 0.0012, which is
to be compared with (