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Technical Discussions
Shane Wilson
Shane Wilson
05:55 Oct-22-2003
Horizontal and Vertical Linearity

I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.



    
 
 
David Harvey
Engineering
ATI - Wah Chang, USA, Joined Nov 2002, 42

David Harvey

Engineering
ATI - Wah Chang,
USA,
Joined Nov 2002
42
06:19 Oct-22-2003
Re: Horizontal and Vertical Linearity
----------- Start Original Message -----------
: I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.
------------ End Original Message ------------

We are using fully digital, pc-based instrumentation, where the horizontal linearity in particular makes no sense. However, we have not been able to get relaxation from the MIL-STD/AMS crowd, and still have to go through the motions of that check.


    
 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
08:03 Oct-22-2003
Re: Horizontal and Vertical Linearity
This question is commonly asked these days. Many people think that because the manufacturers say new technology does not wander no need to do it.

Wrong if the code you are inspecting too requires it then you must perform and document as required by the applicable code. If you do not your inspection does not conform.

Remember the code is based on an all encompassing approach to verification of the technique regardless of individual instrument manufacturers claims.



    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1218

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1218
02:48 Oct-23-2003
Re: Horizontal and Vertical Linearity
This is an interesting question and it has been raised as a discussion item at the ASTM Ultrasonic subcommittee. The purpose of vertical and horizontal linearity verification goes back to the concerns for analogue instruments that used "deflector plates" in the Cathode Ray Tube to deflect an electron beam! It truly is out of place to make people "verify" these linearities for digital units using analgue tchniques. But it is like pulling teeth to get such ingrained habits to change. That said, however, there is no real option in the Codes to replace it. We are looking for options/recommendations to address the unique differences between these particular linearity verification functions. Verification against a "calibrated" sweep generator to check the instrument clock might be an option for the horizontal checks...but then some sort of access is needed to the instrument clock output. In making a workable recommendations it will also require that the manufacturers make a "calibration friendly" instrument is industry wants a realistic option to replace the analogue requirements with a digital option.

Any suggestions?

Ed

----------- Start Original Message -----------
: : I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.
: We are using fully digital, pc-based instrumentation, where the horizontal linearity in particular makes no sense. However, we have not been able to get relaxation from the MIL-STD/AMS crowd, and still have to go through the motions of that check.
------------ End Original Message ------------




    
 
 
Nick Welland
Nick Welland
02:46 Oct-23-2003
Re: Horizontal and Vertical Linearity
----------- Start Original Message -----------
: I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.
------------ End Original Message ------------
Shane,
There has been significant discussion of this point around the industry. To be required to check digital instrumentation against techniques developed for analogue instruments is, on the face of it, illogical. However, when working to a Code which requires such checks, they must be done for comformance purposes. As long as there is a possibility that someone will test using equipment of an earlier generation, Code writers will need to require checks sufficient to give proper assurance of the quality of the testing performed.
Regards
Nick



    
 
 
Randy Plis
Sales, Consultant
AMDATA NDE Technology LLC, USA, Joined Oct 1999, 23

Randy Plis

Sales, Consultant
AMDATA NDE Technology LLC,
USA,
Joined Oct 1999
23
09:16 Oct-23-2003
Re: Horizontal and Vertical Linearity
As long as there is a requirement to do such checks regardless of the generation of equipment, the best solution is to do them as accurately and efficiently as possible. A small handheld device (a little larger than the size of a pack of cigarettes) was developed a few years ago to do such testing. The product, called a CALin, takes on the order of a minute to do the horizontal and verticle checks. A product information bulletin (PIB) about the CALin can be found under Miscellaneous Products in the Literature section of our home page that is available via the NDT.net Exhibition.

----------- Start Original Message -----------
: This is an interesting question and it has been raised as a discussion item at the ASTM Ultrasonic subcommittee. The purpose of vertical and horizontal linearity verification goes back to the concerns for analogue instruments that used "deflector plates" in the Cathode Ray Tube to deflect an electron beam! It truly is out of place to make people "verify" these linearities for digital units using analgue tchniques. But it is like pulling teeth to get such ingrained habits to change. That said, however, there is no real option in the Codes to replace it. We are looking for options/recommendations to address the unique differences between these particular linearity verification functions. Verification against a "calibrated" sweep generator to check the instrument clock might be an option for the horizontal checks...but then some sort of access is needed to the instrument clock output. In making a workable recommendations it will also require that the manufacturers make a "calibration friendly" instrument is industry wants a realistic option to replace the analogue requirements with a digital option.
: Any suggestions?
: Ed
:
: : : I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.
: : We are using fully digital, pc-based instrumentation, where the horizontal linearity in particular makes no sense. However, we have not been able to get relaxation from the MIL-STD/AMS crowd, and still have to go through the motions of that check.
------------ End Original Message ------------




    
 
 
Rich Klaassen
Rich Klaassen
00:17 Oct-27-2003
Re: Horizontal and Vertical Linearity
The need for linearity checks has certainly changed over the years, as vacuum tube amplifiers, CRT's and strip chart recorders have become less commonly used. However, there is still a need to validate the performance of a system. In particular, horizontal and vertical linearity directly affect whether a component is accepted or rejected, which in turn can have significant safety and financial repercussions.

Examples of how digital instruments have violated such linearity checks include:
1. When amplifiers are switched in or out of a circuit to achieve the requested gain level, I've seen a 2 dB discontinuity in vertical linearity.
2. When a gate was selected to capture targets at a specified depth, and was shown on the monitor to include a known target at that depth, the target was not shown on the corresponding C-scan. This was a matter of displaying the gate properly; not necessarily a true linearity issue, but a horizontal calibration issue nonetheless.

Digital instruments are particularlysusceptable to false readings because they are so complex, and because there are many potential interactions in the software which are not intuitive to the typical user. Great care should be taken as new guidelines are created for evaulating such instruments.

----------- Start Original Message -----------
: As long as there is a requirement to do such checks regardless of the generation of equipment, the best solution is to do them as accurately and efficiently as possible. A small handheld device (a little larger than the size of a pack of cigarettes) was developed a few years ago to do such testing. The product, called a CALin, takes on the order of a minute to do the horizontal and verticle checks. A product information bulletin (PIB) about the CALin can be found under Miscellaneous Products in the Literature section of our home page that is available via the NDT.net Exhibition.
: : This is an interesting question and it has been raised as a discussion item at the ASTM Ultrasonic subcommittee.The purpose of vertical and horizontal linearity verification goes back to the concerns for analogue instruments that used "deflector plates" in the Cathode Ray Tube to deflect an electron beam! It truly is out of place to make people "verify" these linearities for digital units using analgue tchniques. But it is like pulling teeth to get such ingrained habits to change. That said, however, there is no real option in the Codes to replace it. We are looking for options/recommendations to address the unique differences between these particular linearity verification functions. Verification against a "calibrated" sweep generator to check the instrument clock might be an option for the horizontal checks...but then some sort of access is needed to the instrument clock output. In making a workable recommendations it will also require that the manufacturers make a "calibration friendly" instrument is industry wants a realistic option to replace the analogue requirements with a digital option.
: : Any suggestions?
: : Ed
: :
: : : : I would like to know if horizontal and vertical linearity checks are required on modern digital UT (A-Scan) units eg. Epoch 4.
: : : We are using fully digital, pc-based instrumentation, where the horizontal linearity in particular makes no sense. However, we have not been able to get relaxation from the MIL-STD/AMS crowd, and still have to go through the motions of that check.
------------ End Original Message ------------




    
 
 
David Harvey
Engineering
ATI - Wah Chang, USA, Joined Nov 2002, 42

David Harvey

Engineering
ATI - Wah Chang,
USA,
Joined Nov 2002
42
06:40 Oct-31-2003
Re: Horizontal and Vertical Linearity
We are using a modified functional check based upon ASTM E317. Since there is _some_ flexibility in E317, we have put together a check for the horizontal linearity and for the vertical using the same premise as E317. Our system is being nice to us with gain changes, as we don't have the "jumps" as different attenuator stages kick in, but have to clarify that the a-scan display is only for information - the digital value displayed in the gate window is the correct value.
As to proper display, our calibration standards are designed with holes pretty much through the entire test thickness range, so with each scan of the standard we verify gate performance thru the test range.
But all in all, we do have a challenge before us - the Epoch 3 and the Krautkramer VIS and the Panametrics 9100 (and so on) all have their own nuances, with some fundamental differences much greater than differences we see in the older CRT instruments.
I guess we need to see this addressed at the ASTM Winter meeting. My fear there is that the one who brings it up is also considered the "volunteer".....seeing how fast the change to MIL-STD-2154 has gone, this could be a long-term career move.


    
 
 

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