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Technical Discussions
Chanappa D Dhotre
Engineering, Paut
IXAR, India, Joined Jun 2019, 1

Chanappa D Dhotre

Engineering, Paut
Joined Jun 2019
19:42 Oct-07-2019
Distance amplitude curve

I have a doubt about Dac curve
If we have 20 mm block SDH at 5mm, 10mm , 15 mm and I have 14mm job thickness than how to draw dac for half skip distance Dac and full skip distance Dac

Please anybody can give me full information about it would be helpfull..

Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 848

Michel Couture

NDT Inspector,
Joined Sep 2006
16:24 Oct-08-2019
Re: Distance amplitude curve
In Reply to Chanappa D Dhotre at 19:42 Oct-07-2019 (Opening).

Depending of the code to which you are working to, the specification for the fabrication of a calibration block to establish a DAC will be given somewhere. One good example is the ASME code. Generally, to fabricate a block, one should have a SDH at 1/4T, 1/2T and 3/4T. If you are using flat stock, you can use the back side of the flat stock for the 3/4T SDH.

When drawing your DAC, find out which SDH will give you the highest amplitude, bring the amplitude to 80% FSH and his will be your Reference dB. With the three SDH, you will be able to have a DAC with 1/4T, 1/2T, 3/4T, 5/4T, 6/4T, 7/4T and 9/4T.

The test block to use should also be within 25% thickness of the piece that is to be inspected. In your situation with a 14mm plate your test block should have a thickness between 11 and 17mm.


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