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Technical Discussions
chintan rana
Engineering,
ELECON EPC PROJECTS LTD., India, Joined Oct 2015, 2

chintan rana

Engineering,
ELECON EPC PROJECTS LTD.,
India,
Joined Oct 2015
2
17:37 Nov-19-2015
help for DGS

hello,
I need help about how to draw DGS curve and also explain acceptance and Rejection norms for ut standard Din 22261
plz guys help me

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
18:07 Nov-19-2015
Re: help for DGS
In Reply to chintan rana at 17:37 Nov-19-2015 (Opening).

DGS stands for Distance Gain Size and the size is based on equivalent flat-bottomed hole (FBH) size. So unless you have a set of a set of blocks wither with the same diameter FBHs at differing stand offs or different diameter FBHs at identical stand off, you cannot construct a DAC. Some probe manufacturers may produce generic diagrams based on near field distances as a probes response in the far field is predictable.

a Google search reveals a wealth of information

 
 Reply 
 
jon wallis
NDT Inspector, -
Netherlands, Joined Feb 2010, 626

jon wallis

NDT Inspector, -
Netherlands,
Joined Feb 2010
626
08:13 Nov-20-2015
Re: help for DGS
In Reply to chintan rana at 17:37 Nov-19-2015 (Opening).

The norm you mentioned is related to machinery in lignite open cast mines - welding connections. I don't have a copy of this very speciic norm so I can't help you with the acc/rej levels.
As it is a German standard it may allow you to use data sheets for your DAC curve, if so, you will need probes with data sheets and preferably equipment where the curves are pre-programmed. If you don't have such equipment, you can draw the dac on the screen in the old fashioned way.

 
 Reply 
 
Victor
Victor
21:28 Nov-15-2017
Re: help for DGS
In Reply to Nigel Armstrong at 18:07 Nov-19-2015 .

I believe it is possible to draw a DGS curve (such as a DAC) using the DGS-specific probe diagram or even a standard DGS diagram.
In modern instruments it has the function of get the curve. In analog instruments there are overlay DGS scales.
Basically, to draw on an instrument is necessary:
1 - choose the appropriate scale for the inspection.
2 - Place a transparent film on the screen (overlay)
3 - Draw a reference point at, eg, 80% corresponding to the near field
N = D² x f / (4V) for round elements
4 - Choose other paths to plot more points
5 - In the DRS diagram determine the gain difference (dB) from the first point to the others paths.
6 - Convert the amplitude differences (DV) found in the diagram by the formula:
Hn = H1 x 10 ^ (- DVn / 20), if H1 = 80 then Hn = 80 x 10 ^ (- DVn / 20)
7 - Interconnect the points to get the DGS curve
8 - The reference gain shall be determined by the backwall gain echo and the difference between the line BW and the reference reflector curve in the DGS diagram.
Several corrections should be applied later, material attenuation, loss transfer, and other losses.

 
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