Industrial Ultrasonic test.

Perhaps the first three paragraphs of this article (quoted below) will help you decide:

New Way for Utilizing DGS Technology

The echo amplitude is main criteria for rejecting defected parts since the first practical use of ultrasonic echo technique.The DGS (AVG) diagrams announced by J.Krautkramer in were the first ones that used a disk-shaped reflector as a clear sensitivity and sizing reference, which was adopted immediately worldwide. Since then:

• experimentally measured variations of amplitude with distance from flat bottom holes are known as DAC
• the standard universal attachment scales supplied with different kinds of Krautkramer high repeatable probes are known as DGS scales.

The major advantage of DGS scales is that they allow the calibration of sensitivity and the sizing of defects using one easy detectable reflector only (inner surface of the cylinder in the very reproducible reference standard). However, the disadvantage of known DGS is the relative complexity of the "spider's web" of universal attachment scale. The "one curve only" shape of experimental DAC makes it a preferred solution in many cases, in spite of the need to use numerous reference standards and blocks for each kind of probe, material and inspection task.

Both methods are equally effective if used appropriately.

DGS has slightly better provided correct probes and correct DGS diagrams are used and correct attenuation analysis is done.

DAC is also effective but require correct calibration test piece

At the end of the day the qualification and experience of the testing personnel is of paramount importance.

I agree with the previous comments. Both methods are similar. DGS is cheaper as it doesn't involve the manufacturing of calibration test pieces.

Just two points:

If you have to comply with some codes or standards, you should follow the required specific method.

Both methods give a comparison of the echo produced by real flaws against echoes produced by artificial flaws. (In some cases "real-like" defects are induced in the test piece, but this advantage in the determination of flaw size bears an increment in the cost of test pieces manufacturing)

Kind regards

Dear all

I've read your discussion and I have another question which is related to the topic:

There is a peak in DGS or DAC diaqrams, I mean reasonably we must have just a decreasing diagram when a defect goes in a deeper position,so what is that peak?

Best regards

Rastegar

Hi,

The response signal (ultrasonic pressure) decrease with distance for "small reflectors" (smaller than effective beam cross area) inversely proportional to the square of distance but only in the far field region. If you are in the near field region, the response is a different thing, with some maximum and minimum.

kind regards