Ultrasonic Flaw Detection Tutorial. Be aware that there are other standards available and that specially designed standards may be required for many applications. The material of the reference standard should be the same as the material being inspected and the artificially induced flaw should closely resemble that of the actual flaw. The use of DAC allows signals reflected from similar discontinuities to be evaluated where signal attenuation as a function of depth may be correlated. A-scan echoes are displayed at their non-electronically compensated height and the peak amplitude of each signal is marked on the flaw detector screen or, preferably, on a transparent plastic sheet attached to the screen. Rather than plotting the entire curve set, instruments will typically display one curve based on a selected reflector size registration level that can be adjusted by the user. Using a suitable reference standard, calibrate the sweep for a distance appropriate for the material to be inspected, ie..
A-scan echoes are displayed at their non-electronically compensated height and the peak amplitude of each signal is marked on the flaw detector screen or, preferably, on a transparent plastic sheet attached to the screen. The transducer was chosen so that the signal in the shortest pulse-echo path is in the far-field Sec. When the echo signals are plotted together, the DAC curve shown in figure 15b results. This model further predicts transducer radiation patterns using the Gauss-Hermite model, which has been used extensively for simulation of immersion mode inspections. After determining the amplitudes for various path lengths 4 , press "Draw DAC" and then press the green "Test now! This technique consists of generating a DAC curve that essentially indicates that a smaller echo at a greater distance may have similar properties to a larger echo at a lesser distance.
Distance Amplitude Correction
Note that one could double the number of points on the DAC curve by using a second equivalent side-drilled hole at a different depth. DAC may be employed in both longitudinal and shear modes of operation as well as either contact or immersion inspection techniques. Click here for the Curvature Correction Table. Disk-shaped reflectors, side drilled holes and hemispherical bottom holes are used as equivalent reflectors when using contact probes.
Description: Most often DAC will allow for loss in amplitude over material depth time , graphically on the A-scan display but can also be done electronically by certain instruments. Disk-shaped reflectors, side drilled holes and hemispherical bottom holes are used as equivalent reflectors when using contact probes. The following applet shows a test block with a side drilled hole. Reference standards which incorporate side drilled holes SDH , flat bottom holes FBH , or notches whereby the reflectors are located at varying depths are commonly used. Examples include inspections of large diameter forgings, such as those used in electrical power generation equipment and in railroad rail.