Image Processing Reference
In-Depth Information
For measurements, an experimental prototype, with eight ultrasonic transceivers, has been
arranged for the validation and comparative assessment of the three flaw localization
techniques by 2D traces combination in a real NDE context. It includes as emitter-receiver
probes two 4 MHz piezoelectric linear arrays of 4 elements each one (as it is shown in figure
6), which are controlled by a Krautkramer NDE system model USPC-2100, disposed in the
pulse-echo mode. The main characteristics of this NDE system in the signal receiving stage
are the following: a dynamic range of 110 dB; a maximum effective sampling of 200 MHz in
the digitalizing section. A signal gain of 44 dB and a sampling rate of 128 MHz were selected
in reception for all the signal acquisitions performed in this work. Other general
characteristics of this system are: pulse repetition rate of up to 10 KHz per channel, and 15
MHz of effective bandwidth in emission-reception. The high-voltage pulser sections of this
commercial system were programmed in order to work with the highest electric excitation
disposable for the driven transducers, which is about 400 Volts (measured across a nominal
load of 100 Ohm). A relatively low value for the E/R damping resistance of 75 Ohm was
selected looking for the assurance of a favourable SNR and a good bandwidth in the
received echoes. Finally, the maximum value offered by this equipment for the energy level,
contained into the driving spike, was selected.
It must be noted that in the experimental ultrasonic evaluations performed with the two
arrays, their elemental transducers were operated with the restriction of that only one
transducer was emitting and receiving at the same time. So, the two transducers located in
front of the flaw (in this case: transducers H3 & V2) were operated separately as receivers
in order to obtain useful information from the artificially created flaw (by drilling the
plastic piece), which is clearly smaller than transducer apertures. Thus, only ultrasonic
beams of H3 & V2 transducers (which remain collimated into a 6 mm width due to the
imposed near-field conditions) attain the hole, whereas the other six elemental
transducers radiate theirs beams far away of that hole, and therefore, in any case, they are
not covering the artificial flaw and are not receiving echoes reflected from this flaw
during their acquisition turns.
5. Simulated and experimental flaw detection results for the three
combination techniques. Discussion of their performance
Three sets of experiments are shown in this section. First, the results related to the final SNR
calculated for seven type-I simulated experiments using different combination options will
be presented in the first section part. Second, 2D displays about the location of an isolated
reflector, calculated for a particular combination case and a small SNR ini are also shown.
Third, as results illustrating the type-II experiments, 3 pairs of representations of a real flaw
obtained by means of the 3 different combination techniques of section 3 will be shown and
commented, analyzing the respective performances of the three techniques. The initial data
for these type-II experiments were a set of measured ultrasonic traces acquired with the
ultrasonic set-up of section 4.
The first tasks in type-I experiments (with simulated traces) were performed to confirm
the accuracy of expressions (3), (5) and (8). In these experiments, 11 SNR ini were selected
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). 10.000 sets of measures were generated using a real 4 MHz
echo response sampled at 128 MHz and synthetic noise, composed in this case by 66.66%
of white Gaussian noise (accounting by the “thermic” noise induced by the usual
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