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- since 1996 -

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Technical Discussions
Mike Jones
Mike Jones
11:58 Mar-23-2010
prove up

This is just for personal info. Is there going to be a difference in inspection if u set up on a 10'' screen on the DSC block then cal. on 1/16'' CDH on a 6" screen using Epoch LTC handheld a-scan unit. vs setting up on a 6" screen on the DSC block then cal. on same 6'' screen on 1/16'' CDH.

 
 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
21:41 Mar-23-2010
Re: prove up
In Reply to Mike Jones at 11:58 Mar-23-2010 (Opening).

No, it won't matter. The Epoch LTC is a digital instrument. Unlike analog machines, digitals measure the time between peaks in clock cycles. The box doesn't care how wide or narrow the screen is. It just measures the 'ticks' from the time it fires the pulser until the receiver receives a signal. What is shown on the screen is just a representation of what the box is 'counting', it isn't the count itself. This is why a digital instrument can be calibrated in metric and can be switched to inches to examine an item [or vice-versa]. The box works in 'ticks' and displays the 'ticks' on an analog display, so we humans can easily interpret the results.

Suggestion: If you are wanting to use the potential accuracy of your digital machine, switch to an IIW Type-1 block to calibrate. It gives a wider span between peaks, thus your Probe Delay, and the Material Velocity will be more accurately measured. Then check your wedge angle to the nearest 1/2-degree. This will then make the digital depth measurement [from the trig function in the box] actually accurate. It really improves your creditability with the welders and the weld engineer when you can state that the flaw bottoms out at 0.458" down, and that is what they find.l

 
 Reply 
 
emil shavakis
University of Massachusetts, USA, Joined Mar 2010, 7

emil shavakis

University of Massachusetts,
USA,
Joined Mar 2010
7
23:36 Mar-23-2010
Re: prove up
In Reply to Roger Duwe at 21:41 Mar-23-2010 .

Roger - Really? .458" Do you believe in UT to the third decimal place (of an inch)? I don't. I think that if you look at the space between "ticks" it is not .001". Lets not confuse accuracy and precision. You can't be more accurate than your instrument's precision. Digital instruments are another realm that we have yet to address or control.

Ed - where are you on this one??

Emil

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
13:53 Mar-24-2010
Re: prove up
In Reply to emil shavakis at 23:36 Mar-23-2010 .

Emil...the original question related to the sensitivity calibration options. However, I concur with your concern for accuracy implied by the number of decimal places. I am not comfortable working in the old imperial units so 3 decimal place "accuracy" seems odd to me. For most practical weld inspections with manual techniques 1 to 2mm seems to be adequate accuracy for locating a flaw for repair.
The "ticks" Roger refers to are more commonly given in units of time (micro-seconds) and since the smallest interval of time used by the instrument is based on its digitisation rate this is a limiting factor indicating the precision of the reading.
I think that one of the issues your concern raises is the failure of UT training to keep up with technology. Coverage of the principles of digitisation as used in UT should be a mandatory topic in basic UT training.
Perhaps you can better explain how the precision of the instrument does not equate to the accuracy of the measurement.

 
 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
14:04 Mar-24-2010
Re: prove up
In Reply to Mike Jones at 11:58 Mar-23-2010 (Opening).

No, it won't matter. The Epoch LTC is a digital instrument. Unlike analog machines, digitals measure the time between peaks in clock cycles. The box doesn't care how wide or narrow the screen is. It just measures the 'ticks' from the time it fires the pulser until the receiver receives a signal. What is shown on the screen is just a representation of what the box is 'counting', it isn't the count itself. This is why a digital instrument can be calibrated in metric and can be switched to inches to examine an item [or vice-versa]. The box works in 'ticks' and displays the 'ticks' on an analog display, so we humans can easily interpret the results.

Suggestion: If you are wanting to use the potential accuracy of your digital machine, switch to an IIW Type-1 block to calibrate. It gives a wider span between peaks, thus your Probe Delay, and the Material Velocity will be more accurately measured. Then check your wedge angle to the nearest 1/2-degree. This will then make the digital depth measurement [from the trig function in the box] actually accurate. It really improves your creditability with the welders and the weld engineer when you can state that the flaw bottoms out at 0.458" down, and that is what they find.l

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 893

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
893
01:27 Mar-25-2010
Re: prove up
In Reply to Roger Duwe at 14:04 Mar-24-2010 .

Roger,

I can appreciate what you are saying, but again I think most welders are easily impressed. On the other hand, when it comes to weld repair, to be precise to the thousnad of an inch doesn't really matter because when they start to arc gouge, they can't control their stick to thousand of inch increament.

 
 Reply 
 

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