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- since 1996 -
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Technical Discussions
DAC
DAC
18:40 Dec-29-2009
Material Attenution while using DGS

I have been a member to this forum for several months now and this is my first post. I enjoy reading and absorbing the intelligence that is out there.

I have been using a USN58L for about 3 years and have the DGS option. I have used the DGS option for several techniques and would like to know how to properly use the Material Attenuation function since I work with many exotic grades, primarily consisiting of Monel, Inconel, Copper, and Duplex, but not limited to common grades like 4340, 8630, all forms of stainless steel. I want to make sure that this function is set up properly to get a consistent test and proper test.

Also,

On another note. This option has several transducers programmed into with specific curves for these transducers. When not using one of these transducers what is the proper way to set-up for the transducer being used,...ie GE RHP 1" 2.25mhz standard contact transducer commonly used.

Thanks for all your help,

DAC

    
 
 Reply 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
17:20 Dec-30-2009
Re: Material Attenution while using DGS
In Reply to DAC at 18:40 Dec-29-2009 (Opening).

DGS is basically "DAC Curves from the Factory". It is a pre-calibrated attenuation [& beam spread] curve for that exact model instrument, using that exact transducer, on one specific calibration material. DGS eliminates the need to have calibration blocks, and allows you to use a calibration performed by an experienced factory tech, under ideal conditions.

To use DGS on an exotic material, the factory has to have programed in a curve for that material. To use DGS on any material, not only does a curve have to have been pre-programed into your instrument, but you have to use the exact transducer that the programming tells you to use. And the 'ducer has to be in 'as-new' condition. "DAC Curves for Dummies".

DGS seems to be common in Europe. Typically in the USA, a set of calibration blocks are used to create a DAC curve for the material to be inspected, using your existing transducer, in whatever condition that 'ducer is in. Thus wear or roughness of the 'ducer face and/or the delay tip are part of the calibration you will use to inspect your parts. Personally, I won't certify my DGS results unless the 'ducer is in pristine condition, and the material listed in the factory calibration is an acoustic match to the material being tested. Yes, it is possible to get fairly close results with a worn DGS 'ducer, but how accurate is 'fairly close'?

    
 
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