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  Measurement, Test and Calibration
  Measurement Uncertainty

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Author Topic:   Measurement Uncertainty
David Drue Stauffer
Forum Contributor

Posts: 25
From:St. Louis, MO63132United States
Registered: Feb 2000

posted 12 September 2000 09:32 AM     Click Here to See the Profile for David Drue Stauffer   Click Here to Email David Drue Stauffer     Edit/Delete Message   Reply w/Quote
Does anyone have an easily understandable step by step method for calculating measurement uncertainty for gage calibration items, i.e. micrometers, calipers, etc.? I have an example of one conducted on a thread plug gage that says WHAT was done, but not HOW it was done. NIST info is like reading an ancient elvin tongue. It gives me a headache. I'm an analytical learner and as such, I need a step by step to grasp the concept and find out the why's. Pleases Help. Dave.

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mbruner
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Posts: 11
From:Greenwood,IN,USA
Registered: Feb 2000

posted 15 September 2000 03:58 PM     Click Here to See the Profile for mbruner   Click Here to Email mbruner     Edit/Delete Message   Reply w/Quote
I don't know if the explanation is simpler, but there is some step by step detail at HP's website www.metrologyforum.tm.agilent.com

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Edited html to make active link.

[This message has been edited by Marc Smith (edited 15 September 2000).]

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Marc Smith
Cheech Wizard

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From:West Chester, OH, USA
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posted 15 September 2000 04:43 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
i have read a lot about measurement uncertainty and have quite a few posts and such posted about measurement uncertainty. See the uncertainty directory in Elsmar.com/pdf_files/

I learn like you do. All I can say is I have not fould one 'simple' article. I think I can explain it, but I don't have to do the calculations and such so I have no hands-on experience in determining uncertainty per se. However - you do have to look at what uncertainty is - for example, in an R&R, what is uncertainty? In Gage R&R it's the confidence limits. You buy a thermometer and the instructions say it's accurate to +/-2 degrees - your uncertainty is 4 degrees (as I understand it). When you get to an uncertainty budget, it's the combination of all uncertainties of the entire system.

Comments from others?? I'd like to hear a good simple explaination as well.

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Graeme C. Payne
unregistered
posted 29 September 2000 08:50 AM           Edit/Delete Message   Reply w/Quote
As another reply says, measurement uncertainty is not an easy subject. Even when calibrating the same type of instrument, YOUR uncertainty will be different from anyone else's because you are in a different facility and using different standards. However, a working understanding of measurement uncertainty is necessary for a calibration lab. And, of course, it is required by ANSI/NCSL Z540-1, ISO 17025, and other standards.

Here are a few publications I have found useful. I have tried to list them in order of increasing difficulty.
"An Introduction to Error Analysis" by John R. Taylor (second edition, University Science Books, Susalito CA: 1997. ISBN 0-935702-75-X) This is an excellent book that starts off easy and gradually works into more difficult areas.
"Calibration: Philosophy in Practice" by Fluke Corporation (second edition, Fluke Corporation, Everett WA: 1994. ISBN 0-9638650-0-5) Although geared to electrical/electronic measurements, the principles are usable in every measurement area. Chapter 22 is about uncertainty statements, but first you will need to read either chapters 20 & 21, or the book by Taylor.
"Determining and Reporting Measurement Uncertainties", National Conference of Standards Laboratories Recommended Practice # RP-12. (NCSL, Boulder, CO: 1995) Somewhat easier to understand than the ISO standard (next), but still very technical. This includes a few practical examples writtem by metrology managers.
ANSI/NCSL Z540-2, "American National Standard for Expressing Uncertainty -- U.S. Guide to the Expression of Uncertainty in Measurement". (NCSL, Boulder, CO: 1997) This is the official US adoption of the ISO guide: very technical, but the authoritative standard.

The NCSL publications are available from the organization (www.ncsl-hq.org). The Fluke book is available from your Fluke sales representative. The Taylor book can be ordered through any major online or traditional book retailer.

Please feel free to contact me directly for additional information.

Graeme C. Payne
ASQ Certified Quality Engineer
Graeme@asqnet.org

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Sam
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Posts: 244
From:
Registered: Sep 1999

posted 29 September 2000 10:00 AM     Click Here to See the Profile for Sam   Click Here to Email Sam     Edit/Delete Message   Reply w/Quote
Try this site,
http://gunsmoke.ecn.purdue.edu/CE597N/1997F/students/dominic.j.nocera.1/project/

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