To compare measured and Civa simulated amplitudes, the user has to assign a reference amplitude which is the output echo signal obtained from a calibration flaw, as it is the case in real inspection procedures. Indeed, for the Defect Response module, it is needed to make a calibration measurement on a reference flaw in order to take into account the electro-acoustic transduction which is not modeled in CIVA. This calibration is used to give a physical sense to the CIVA simulated echo amplitudes. The absolute amplitude of the CIVA simulated echo does not represent the amplitude of the received echo since the electro-acoustic transduction is not modelled. That’s why, the amplitudes simulated with the CIVA Defect Response module have to be considered relatively to that of the calibration flaw: the user has to consider for a given inspected flaw a “relative amplitude” which is the ratio of the current flaw echo amplitude to the amplitude of the reference flaw echo.
This relative amplitude physically corresponds to the ratio of the received electrical signals for the current and calibration defects. The value of this ratio is consequently experimentally measurable and can lead to comparisons between simulation and experiment. In that goal, the user has to evaluate and compare the relative amplitude obtained for a given flaw both in simulation and in measurement.
The use of this amplitude normalization by a calibration technique allows to overcome the complex modelling of the electro-acoustic transduction (not modelled in CIVA), phenomenon already occurred in the echo on the calibration flaw. Ask the support team (supportciva[at]extende.com) for more information about the calibration.
Practical information about Reference Amplitude
In the Defect response module, CIVA offers 3 ways for defining the 0 dB reference amplitude in the “Calibration” tab from the “Computation parameters” panel:
- None: the default reference is the strongest echo of the simulation. Then, the calibration flaw can be directly defined in the simulation configuration to give a reference and allow direct comparison. But the 0dB value may not be assigned to this echo but a stronger one.
- Manual: CIVA asks for a value in points, the CIVA arbitrary unit of echoes absolute amplitude. In this case, it is advised to previously run a simulation with the reference flaw, to note the value in points of the corresponding simulated amplitude (from an Ascan or from the “information” menu) and then to put this value in the calibration tab to be used as the 0dB reference for the others simulation.
- Simulation: CIVA offers the possibility to run a pre-simulation to compute the amplitude of the echo from the chosen flaw in the chosen calibration block and then automatically uses this as the 0dB reference. In Civa 10, this option is only available for mono-element probes.
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