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Technical Discussions
Martyn
Martyn
02:08 Jul-28-2006
Re: Calibration rule for digital UT instruments
----------- Start Original Message -----------
: : : : : Current ASME (and other) rules for UT scope calibration - e.g. linearity, cal. check frequency, duration etc. are out of date and (I judge) inadequate for current digital instruments with cal storage capabilites. The rules do not address the real issues - verification of cal when switching between, real need to fully re-cal etc.
: : : : : Also I feel today's instruments stability is far greater than when the Codes were written, so . . . has anyone written or found a good set of practical "rules" that fit today's need. Are there any efforts to codify these rules?
: : : : That's a very good question. One that the ASME V Code Committee should probably address. I wonder if anyone has submitted a Technical Inquiry.
: : : ------------ End Original Message ----------
: : : I think not. I sat w/ SecV last month. I'm writing my own. Does anyone care to co-author and submit as a Code Case?
: : ASTM E07-06 committee has already formed a working group on this and made some revisions to E-317. Similar tests can be run on analogue and digital units but old terminology often gets in the way. e.g. a CRT (cathode ray tube) is now rarely used and the A-scan display is usually on a computer-like monitor.
: : Larry's comments on stability of instruments is another matter and very valid! Most Codes have "required" calibration intervals that are quite short. For most digital units these could be longer.
: : Ed
: -T----------- End Original Message ------------
: There is one major factor I see often with the use of digital calibrations,mainly with thickness measurements,People take for granted that the computer goes to "0" digitally but Hardware used cannot resolve the rejectable measurement due to nearfield of the transducer.
------------ End Original Message ------------

I believe the current code does indeed address the need to verify the calibration when switching from one probe to another, as would be the case when changing cals via the digital scope. One should be very weary of assuming that a stored calibration is still valid, without a reverification. Items such as wear face deterioration, temperature, probe/wedge coupling etc. can all lead to a small, yet significant, variation in calibration. better to just perform the quick and dirty verification as called out in the code, in my opinion.



    
 
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