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- since 1996 -
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Technical Discussions
Selvi
Selvi
13:42 Oct-03-2012
ToFD & PA

Can we change the Gain during scanning after calibration of ToFD & PA?
Is it affect the test result?

 
 Reply 
 
Oliviero
NDT Inspector,
Quality Control srl, Italy, Joined Oct 2008, 414

Oliviero

NDT Inspector,
Quality Control srl,
Italy,
Joined Oct 2008
414
21:47 Oct-03-2012
Re: ToFD & PA
In Reply to Selvi at 13:42 Oct-03-2012 (Opening).

During the concert of your preferred singer, can you raise or decrease the music volume without affecting the listening?
Probabily only in a determinate range and under defined conditions

 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
15:39 Oct-04-2012
Re: ToFD & PA
In Reply to Selvi at 13:42 Oct-03-2012 (Opening).

OMG! How can you open a discussion about changing sensitivity during inspection making no difference between a non amplitude based technique and an amplitude based technique (at least more frequently assumed to be such)?
As far as I know, no code allows to change the sensitivity parameters during scanning.

 
 Reply 
 
James E. Scalf
NDT Inspector,
Global Integrity, Canada, Joined Oct 2012, 274

James E. Scalf

NDT Inspector,
Global Integrity,
Canada,
Joined Oct 2012
274
12:51 Oct-05-2012
Re: ToFD & PA
In Reply to massimo carminati at 15:39 Oct-04-2012 .

Massimo,
I know of many applications where you set your sensitivity level for a given inspection and then add a fixed amount of db (usually 6.0 db in the case of aircraft inspections) to create a scanning level. Doing this has a few advantages: One being that it allows for faster scanning speeds as you are running the test system hot, another is that the likelihood that you will miss smaller relavent discontinuities decreases substantially as adding 6 db double your sensitivity.
There is a small danger though, especially in inexperienced technicians, that someone will forget, while they are scanning, that they are running hot and that they need to remove the added scanning db (return to reference db) from the system prior to sizing or analyzing the indications found.
I know this is done with purely conventional UT as I personally have done this successfully on many occasions and I know it works for PA as well.
I am not sure if it would work for ToFD as I have never worked with that application. I don't think it would as ToFD is "Time of Flight Diffraction" isn't it? That would be an evaluation method not purely a seeking method therefore increased sensitivity would decrease the reliability of the findings.

 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
20:18 Oct-05-2012
Re: ToFD & PA
In Reply to James E. Scalf at 12:51 Oct-05-2012 .

james,
I might have misunderstood the original post, but selvi wrote: "change the gain during scanning". To me, this means after having set the scanning sensitivity.

 
 Reply 
 
Selvi
Selvi
14:02 Oct-09-2012
Re: ToFD & PA
In Reply to massimo carminati at 15:39 Oct-04-2012 .

if acceptance are fracture mechanic based (non amplitude method). then acceptance are based on length and height of defect.
then why can't change?

 
 Reply 
 
Csaba Hollo
,
Retired, Canada, Joined Feb 2010, 301

Csaba Hollo

,
Retired,
Canada,
Joined Feb 2010
301
18:32 Oct-09-2012
Re: ToFD & PA
In Reply to Selvi at 14:02 Oct-09-2012 .

Then I would think if you are looking for a definitive answer to a question, it would be prudent to supply all the facts surrounding the case.

Asking a vague question, then following up with an additional parameter after several comments will only confuse the issue.

 
 Reply 
 
Michele Tonin
NDT Inspector,
UT ONE SL, Spain, Joined Jan 2012, 16

Michele Tonin

NDT Inspector,
UT ONE SL,
Spain,
Joined Jan 2012
16
22:32 Oct-09-2012
Re: ToFD & PA
In Reply to Selvi at 14:02 Oct-09-2012 .

How you can determine the height of defect in PA Sectorial Scan? Not positioning cursors,I guess...

 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
22:33 Oct-09-2012
Re: ToFD & PA
In Reply to Selvi at 14:02 Oct-09-2012 .

you wrote: Can we change the Gain during scanning after calibration of ToFD & PA?
Is it affect the test result?

The answer is: no codes allows this and in addition it can definetely affect the result (what if you decrease 20 dB). Your question is poorly asked.

 
 Reply 
 
Michele Tonin
NDT Inspector,
UT ONE SL, Spain, Joined Jan 2012, 16

Michele Tonin

NDT Inspector,
UT ONE SL,
Spain,
Joined Jan 2012
16
22:41 Oct-09-2012
Re: ToFD & PA
In Reply to Selvi at 14:02 Oct-09-2012 .

How can you determine the height of defect in PA Sectorial Scan? Not positioning cursors,I guess...

 
 Reply 
 
mehdi
Engineering, Advanced NDT
Iran, Joined Feb 2012, 25

mehdi

Engineering, Advanced NDT
Iran,
Joined Feb 2012
25
13:11 Oct-13-2012
Re: ToFD & PA
In Reply to Selvi at 13:42 Oct-03-2012 (Opening).

hi
as you know tofd is a non amplitude base method.it means detecting defects is not related to gain given to instrument.although before start scanning you make a calibration to set up lateral to about 50% of fsh, but obviously when you go to start work on tank or reactor you should change the db. and also during scanning changing db ( not too much) to see better of indications or reduce noise is not harmful because tofd duty is to detect defects and measuring height and length of them.

but for phased array that is an amp base method you are not allowed to change gain even after calibration, because you have calibrated system according calibration block references and drawn tcg and the db saved for calibration is very important.

 
 Reply 
 

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