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  Measurement Uncertainty

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Author Topic:   Measurement Uncertainty
LM
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posted 07 July 1999 06:21 AM           Edit/Delete Message   Reply w/Quote
So far, we have been doing internal calibration and just defining the acceptance criteria. Due to the recent ISO 9000 Quality System audit by the local certification body,they say that we have to state the measurement uncertainty each time we perform calibration based on the clause 4.11. I am trying to seek the correct and simplest method of calculating the uncertainty.I would appreciate if somebody could help me.
In addition to that, how do we know that the measurement uncertainty is acceptable or not.
Thanks

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Lassitude
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posted 07 July 1999 03:37 PM     Click Here to See the Profile for Lassitude   Click Here to Email Lassitude     Edit/Delete Message   Reply w/Quote
I'll see what I can dig up on uncertainty, but I hope some others will have some knowledge to share about measurement uncertainty. This could use some good discussion.

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Dawn
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posted 07 July 1999 09:36 PM     Click Here to See the Profile for Dawn   Click Here to Email Dawn     Edit/Delete Message   Reply w/Quote
I have been told by statistical experts to do a gage r & r but I don't know what to do from there. What does that tell me?

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Don Winton
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posted 07 July 1999 09:52 PM     Click Here to See the Profile for Don Winton   Click Here to Email Don Winton     Edit/Delete Message   Reply w/Quote
A search of this forum found this, in no particular order:

https://elsmar.com/ubb/Forum1/HTML/000089.html

https://elsmar.com/ubb/Forum1/HTML/000144.html

https://elsmar.com/ubb/Forum4/HTML/000036.html

https://elsmar.com/ubb/Forum4/HTML/000047.html

https://elsmar.com/ubb/Forum4/HTML/000073.html

Regards,
Don

[This message has been edited by Marc Smith (edited 03 April 2000).]

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Marc Smith
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posted 08 July 1999 11:06 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
A Gage R&R (or Gage R where automated) tells you how much variation is in your measurement system as a per cent of tolerance used.

There is:

Equipment (Gage) Variation (EV), and
Appraiser Variation (AV)

Let's say your EV is 10% and your AV is 15%. You have 25% of your tolerance taken up in variation.

You also have to consider Measurement Uncertainty - kinda a black art right now.

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LM
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posted 15 July 1999 04:50 PM           Edit/Delete Message   Reply w/Quote
Thanks for the search forum and all the input gave. I would appreciate if anyone has additional information.

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BRoyal
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posted 17 July 1999 06:07 PM     Click Here to See the Profile for BRoyal   Click Here to Email BRoyal     Edit/Delete Message   Reply w/Quote
NIST Technical Note 1297, "Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results," can be downloaded off their site. It addresses such subjects as the classification of uncertainty components, combined standard uncertainty and expanded uncertainty. Appendix E is particularly helpful.

Ben Royal

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Marc Smith
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posted 17 July 1999 07:17 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
NIST is at: www.nist.gov/

Also at NIST, check out: www.physics.nist.gov/cuu/Uncertainty/index.html

[This message has been edited by Marc Smith (edited 17 July 1999).]

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Dawn
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posted 17 July 1999 07:47 PM     Click Here to See the Profile for Dawn   Click Here to Email Dawn     Edit/Delete Message   Reply w/Quote
I have been through all these websites and I still am unsure how I am going to express this to a QS Auditor in 3 days for Assessment Registration. Maybe because I'm blonde, but I need down to earth language so I can explain how we are doing it down to earth-I am sure to take a hit for this. Thanks for the help!

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Carlos Mora
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posted 17 July 1999 10:27 PM     Click Here to See the Profile for Carlos Mora   Click Here to Email Carlos Mora     Edit/Delete Message   Reply w/Quote
NIST covers uncertainty in a technical note. Check http://www.physics.nist.gov/Pubs/guidelines/preface.html

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Marc Smith
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posted 28 February 2000 07:20 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Also see:
https://elsmar.com/ubb/Forum4/HTML/000036.html
and https://elsmar.com/ubb/Forum4/HTML/000047.html
and https://elsmar.com/ubb/Forum4/HTML/000072.html

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David Drue Stauffer
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posted 09 March 2000 02:54 PM     Click Here to See the Profile for David Drue Stauffer   Click Here to Email David Drue Stauffer     Edit/Delete Message   Reply w/Quote
This may help you some:


Uncertainty Budget for Thread Pitch Diameter Calibration

Reproducibility: The reproducibility was calculated from thirty readings (10 each from three technicians) utilizing gage blocks, thread wires, super-micrometer and a 1-14 UNS-2A thread set plug. The standard deviation for the reproducibility was calculated at 11.6 micro-inches (.0000116).

Should add the uncertainty of the S-mic when recd - Resolution: The resolution of the super-micrometer providing the value for measurement over wires is 10 micro-inches. We assume a rectangular distribution, that is, the error is equally likely to be any value between 0 & 10u. The guide to measurement uncertainty instructs to divide by the square root of three to convert a rectangular distribution to one standard deviation of 5.77 micro-inches.

Gage blocks: The blocks used in the calibration of plug gage diameters are grade one. In the calibration of a 1 thread plug gage we need only the 1 gage blocks. We will assume that the block value can be anywhere within the +/- 2u tolerance of the block. We will also allow this tolerance to expand by the 1.3u (1/2 of the k=2 value) uncertainty reported on the gage block certification. Therefore the gage block tolerance plus the uncertainty was divided by the square root of three to get to one standard deviation of 1.91 micro-inch.
2 gage block at 2.94 micro-inch (from1.1 & 4)
3 gage block at 3.64 micro-inch (from 1.3 & 5)
4 gage block at 5.25 micro-inch (from 3.1 & 6)
5 gage block at 11.7 micro-inch (from 1.1 & 4, 1.3 & 5)
6 gage block at 14.2 micro-inch (from 1.4 & 4, 3.1 & 6)
7 gage block at 15.4 micro-inch (from 1.3 & 5, 3.1 & 6)
8 gage block at 18.7 micro-inch (from 1.3 & 2, 1.3 & 5, 3.1 & 6)
9 gage block at 20.5 micro-inch (from 1.1 & 4, 1.3 & 5, 3.1 & 6)
10 gage block at 24.1 micro-inch (from 1.3 & 2, 1.1 & 4, 1.3 & 5, 3.1 & 6)

Thread wires: Wires used were supplied at size with an uncertainty value of 12 micro-inches. As this value is reported at two standard deviations will bring to one standard deviation for the completion of this budget.

Force applied: A reproducibility study was conducted on the effect of force in relation to the digital values displayed on the super-micrometer. The study consisted of three operators with ten readings each. This test produced a standard deviation of 5 micro-inches.

Anvil parallelism: The super-micrometers anvils have a parallelism requirement of 20 micro-inches of which is routinely verified through calibration. Assuming the worst condition and a rectangular distribution, we can arrive at one standard deviation of 11.55 micro-inches.

Temperature: The gage blocks used are made of chromium carbide which carries a coefficient of expansion that is approximately 4.7 x 10-6. The majority of thread plug gages cycling through our metrology lab are made primarily of steel which carries a coefficient of expansion that is approximately 6.4 x 10-6. For the purpose of this study we will use the 1 block size. We will assume that all components have been stabilized to the room environment of 68o +/- 1o F. As the temperature sensing device has its own uncertainty of 05 o, we will use 1.05o temperature error. In this scenario we receive an error of 4.9 micro-inches on the block and 6.7 micro-inches on the thread plug gage. Using the difference of we can provide a rectangular distribution and arrive at one standard deviation of 1.04 micro-inches.
2, 1.05 o change = 3.5 with one std. dev. of 2.0 micro-inch
3, 1.05 o change = 5.4 with one std. dev. of 3.1 micro-inch
4, 1.05 o change = 7.2 with one std. dev. of 4.2 micro-inch
5, 1.05 o change = 8.9 with one std. dev. of 5.1 micro-inch
6, 1.05 o change = 10.7 with one std. dev. of 6.2 micro-inch
7, 1.05 o change = 12.5 with one std. dev. of 7.2 micro-inch
8, 1.05 o change = 14.3 with one std. dev. of 8.3 micro-inch
9, 1.05 o change = 16.1 with one std. dev. of 9.3 micro-inch
10, 1.05 o change = 17.8 with one std. dev. of 10.3 micro-inch

Uncertainty Budget for Thread Pitch Diameter Calibration

All Values expressed in micro-inches

Source ofUncertainty Standard Deviation Limits Uncertaintyu u2
Reproducibility (A) 11.6 134.56
Gage blocks 1.3 2 1.91 3.648
Thread wires 12 6 36
Resolution 10 5.77 33.293
Force (A) 5 25
Anvil parallelism 20 11.55 132.25
Temperature 1.8 1.04 1.082

Sum = 365.833
Combined uncertainty, uc = 19.127
Expanded uncertainty, U = 38.3
2 pitch diameter Expanded uncertainty, U = 38.7
3 pitch diameter Expanded uncertainty, U = 39.2
4 pitch diameter Expanded uncertainty, U = 40.3
5 pitch diameter Expanded uncertainty, U = 45.8
6 pitch diameter Expanded uncertainty, U = 49.0
7 pitch diameter Expanded uncertainty, U = 51.0
8 pitch diameter Expanded uncertainty, U = 55.8
9 pitch diameter Expanded uncertainty, U = 58.9
10 pitch diameter Expanded uncertainty, U = 64.7


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Marc Smith
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posted 09 March 2000 03:02 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Ah! A wizard! The detail is appreciated! I hope you stop by often!

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Dawn
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posted 01 April 2000 11:01 PM     Click Here to See the Profile for Dawn   Click Here to Email Dawn     Edit/Delete Message   Reply w/Quote
Is there some way to determine the uncertinty right off the Gage R & R calculations?
And how would you suggest we state it in every work instruction? Thanks!!!!!

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Marc Smith
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posted 07 May 2000 02:09 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Dawn:
Is there some way to determine the uncertinty right off the Gage R & R calculations?
And how would you suggest we state it in every work instruction? Thanks!!!!!

I would love an answer from an expertas well!

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Ryan Wilde
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posted 19 May 2000 09:11 PM           Edit/Delete Message   Reply w/Quote
Measurement uncertainty, as it applies to calibration, is a bit more than a gage r&r. I see that a few posts have already pointed you to the method, but I also saw the word "easy" in there somewhere.

To this end, there is a FREEWARE uncertainty calculator program available. It was developed at Compaq Metrology, and conforms to ANSI/NCSL Z540-2 and the GUM. The program is in two parts, to ease installation from floppy disks.

Go to http://www.proficiency.org and click the "Software Download" page. The program is "Uncertainty Calculator 2.5".

The program will not teach you the ins and outs of uncertainty budgets, such as proper distribution for contributors or effective degrees of freedom, but it does make the calculation process very simple once you do have the knowledge.

I hope this helps.

Ryan Wilde

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