Advanced Method for Ultrasonic Probe Characterization

Ultrasonic Probe Characterization
It is commonly known that each ultrasonic test requires specific ultrasonic probes chosen for their intrinsic parameters such as frequency, refracted angle, beam width, focal depth, etc. As an advanced NDT procedure developer and as a probe manufacturer among others, Vinçotte has to handle this problematic from the probe desig
n to the final application.

Ultrasonic beams generated either by a conventionalor by a phased array (PA) probe areusually modeled as a simple line segment which is entirely defined using three essential parameters: the refracted angle, the exit point and the probe delay. These are necessary to locate and to size the detected indications in the required examination volume.

These parameters are calculated during the so-called probe characterization process that isachieved using fully or semi-mechanized acquisition system on specific calibration blocks. Given that the inspection performances are based on 100% required volume coverage, on good detection performances and on accurate localization and sizing of the indications, it is crucial to find the best method to calculate these parameters. Thus, in order to automate the entire probe characterization process and to compare the efficiency of several calculation methods, Vinçotte has developed a specific software called APC (Automated Probe Characterization). The first part of this document introduces this process and this new software. The second part presents a comparison between some results given by conventional calculation methods and some results given by the new advanced method.

In ultrasonic testing, according to our quality system, several forms of characterization orcalibration must be achieved:
  • The electronic devices must be annually characterized to ensure that the system performs as designed, this will not be discussed inthis paper;
  • At each inspection, generally before and after, the entire system has to be calibrated in order to guarantee that the required accuracy is achieved. This step is more a verification than a real determination of specific parameters. This will neither be discussed further.
  • At the probe manufacturing and then annually, the probe can be fully characterized ideally using the same equipments (cables and electronic devices) than for further use. For every ultrasonic probe, either conventional or phased array, this process results in some intrinsic parameters and curves: the refracted angle (RA), the exit point (EP) and the probe delay (PD), as well as the sensitivity curve, the beam width curve and the spectral analysis (FFT). This will be treated in this paper;

Since innovations and developments are at the heart of our philosophy, and with the constant evolution of ultrasonic acquisition software, a new approach had to be considered to this basic process. In a first time, in order to improve the representativeness of the main scanning configurations (pipes and planes from the outer side), Vinçotte has developed and manufactured several blocks, each containing specifics reflectors: a half-moon (HM) and a set of side drilled holes (SDH) perpendicular to the scan direction at different depths. An encoded acquisition on such a block will provide the required data to characterize the probe.

In a second time, in order to automate the entire probe characterization process and to optimize the calculation method, the APC software was developed. This processes raw ultrasonic data to calculate the probe parameters. It also computes the average distance between real reflectors positions and relocated ones using the parameters previously calculated. This allowed us to compare the different implemented computation methods and to develop a new advanced method based on results optimization.

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