posted 15 January 1999 08:16 AM               

And I found the below at the ISO site:

Guide to the expression of uncertainty in measurement

When reporting the result of a measurement of a physical quantity, some quantitative indication of the result has to be given to assess its reliability and to allow comparisons to be made. The Guide to the expression of uncertainty in measurement establishes general rules for evaluating and expressing uncertainty in measurement that can be followed at many levels of accuracy and in many fields.

1995, 110 p., price group L, CHF 88,50, ISBN 92-67-10188-9

Can some of you help by citing other publications which address the issue?

Also - any 'Practical' comments on MU?

posted 15 January 1999 07:20 PM               

http://www.savtech.demon.co.uk/measurem.htm

http://gunsmoke.ecn.purdue.edu/~nocera/project/tutorial

http://www-uktm.external.hp.com/mikehut/ieepaper/iee2.html

http://www-uktm.external.hp.com/mikehut/one_meas/unc.html

Hope this helps.

posted 30 January 1999 09:57 AM               

Is "Determining and Reporting Measurement Uncertainties", Recommended Practice RP-12, April 1995 from the National Conference of Standards Laboratories." you mentioned above available on the web. I would like to see a copy for some research I am doing.

posted 19 July 1999 06:33 AM               

----------snippo-------

Measurement Error and Uncertainty

The difference between the measured value and the true value of an object of measurement is known as the error. The actual value of an error can never be known exactly, only estimated. An uncertainty statement provides an estimate of the possible error in a measurement. The term "error" is almost obsolete in the measurement arena due to it's ambiquity. It has become fashionable in the scientific community to provide uncertainty statements with all measurements due to the useful information it provides. Those still in the habit of providing error statements as opposed to uncertainty statements are looked upon with scorn and ridicule by scientists, engineers, and other technically intellectual types in the scientific community. By utilizing this tutorial, the user shall avoid subjecating himself or herself to terms such as neandrethral-like, doltish, or flat incompetent by the aforementioned persons.

As an example, let's say you designed an experiment to measure the output voltage of a given circuit. The theoretical output of the circuit is 5 volts. You measure 5.02 volts and publish a paper in which you claim the actual value is 5.02 volts with an error of 0.02 volts. You have now opened yourself to flood of spoken and unspoken questions and criticism pertaining to your own personal value and competence in the technologically advanced world.

However, had you published the same paper and claimed that the measured value is 5.02 volts, +/-0.03 volts at a 95% confidence level, and proceeded to list the involved uncertainty factors with estimates of contributions from each as well as thoroughly describing your method for obtaining and combining these factors, you would certainly be praised and hailed as intellectually advanced, equipped with a desirable skill set, and en vogue with all the current trends in the world of measurement science.

posted 19 July 1999 09:14 AM               

Subject: Re: Q: Certificate of Calibration/Guerra/Naish
Date: Mon, 26 Oct 1998 10:50:29 -0600
From: ISO Standards Discussion

From: [email protected]
Subject: Re: Q: Certificate of Calibration/Guerra/Naish

I am surprised that you would get a non conformance when it comes from the manufacturer. I have worked with a number of companies and at least 9 registrars who have not given any of the 75 companies we have worked with a non conformance for this.

As far as an accredited lab versus a manufacturer being better, there are good and bad in both. But some manufacturers such as Starrett are accredited by Navlab here in the USA.

When approaching the amount of information that is required, if you get a copy of guide 25 it is easy to understand and helps with knowing what is needed for calibration. However, another approach is to obtain a copy of the ISO certificate from the manufacturer as well as any other certification they have. If you have an internal supplier qualification form have them complete it as well. The using the supplier qualification process and history from previous performance (as demonstrated the first time you sent the equipment out for calibration or the hard data sent by them) you can place them on a dock to stock plan with their certificate of conformance along with their catalogue or data sheet as meeting the requirement until you send it out the first time for calibration.

The uncertainty of the instrument is based upon the catalogue or data sheet which will tell you it is within a tolerance. As long as that tolerance provides you with the accuracy you need, and they have provided a certificate of assurance that they have met it and that it meets international standards you should be able to pass your audit. If you ask for them you can sometimes get a copy of the procedures used by the manufacturer so as to show your registrar the method the manufacturer is using.

I can also send you a sheet with the information that you should be seeing on the certificate after you send it out. You can email me direct if you would like a copy.

posted 19 July 1999 12:42 PM               

quote:

---

Mrc,
Is "Determining and Reporting Measurement Uncertainties", Recommended Practice RP-12, April 1995 from the National Conference of Standards Laboratories." you mentioned above available on the web. I would like to see a copy for some research I am doing.

Regards,
Don

---

Don:

posted 20 October 1999 12:07 AM               

-------snippo--------

From: Charley Scalies
Subject: Q: Calibration Issues for Small Firms /Scalies

Measurement Uncertainty
How do/can very small firms, with no in-house technical expertise in metrology, comply with the ISO90001, 4.11.1 requirement to be sure inspection, test and measuring equipment is "..used in a manner which ensures that the measurement uncertaintly is known..." Alternatively, how would you describe "measurement uncertainty" to a lay person?

Accuracy vs. Precision
How would you describe the difference to a lay person?

posted 20 October 1999 09:00 AM               

Uses a very good example comparing accuracy,precision and reliability to a target.
Example; you fire 5 shots at a target:

1- Accuracy - did you hit the target?
2- Precision - How close are the five shots grouped together?
3- Reliability - Can you do this consistently.

Note also that there can be varying combinations of accuracy,precision and reliability.

Measurement uncertainty Maximum error that may be added (algebraically) to a reading.
i.e., systematic errors, random errors, human errors . . . .

posted 23 October 1999 01:33 AM               

Subject: RE: Calibration Issues for Small Firms /Scalies/Everson/Kozenko
From: [email protected]

> Shooting arrows at the target and getting them close the
> bullseye is the accuracy.
>
> Precision is if I am able to have the arrows hit the same small area
> everytime, but they made still be away from the
> bullseye....I was precise, but not accurate..

Mine's similar, but I believe the explanation called for is "degree of precision."

Picture a car tire swinging laterally on a rope, over a 30 foot arc, ten

yards in front of you.

Accuracy would be throwing a football at the swinging tire and at least hitting the darn thing. Anything is accurate if it hits the target. Remember the expression: "Close doesn't count, except in horse shoes and hand grenades."

Diagonally from tire rim to tire rim it's usually about 15 inches (... and my contract with NASA expired so I won't convert that to cm's ). The girth of a spirally-thrown football is about, oh, eight inches, so the degree of precision of a throw that goes through the moving tire could be expressed as the required degree of precision of plus or minus one girth. (In other words, in order for the football to clear the center of the tire, it needs to be precisely on center, or no more than one girth-thickness in any direction away from center, along the same plane created by the tire.)

Degree of precision is usually expressed as a set value with a plus-or-minus dimension, but there are cases when it may be expressed as Plus 0 minus X, or Plus X minus 0, or variants in between.

For example, when reaching for a description of the degree of precision in throwing a water balloon, one would rather have a tolerance of Plus 0 so that the splash still would hit the target, which usually happens even at Plus 0 minus 5 feet. Hitting the "20" on a dart board, however, would call for a vertical Plus 9 inches Minus 0 if the bulls eye were considered the "anchor" for the measurement. This one's a complicated example too, because the "20" on a dart board is pie shaped, so the horizontal (side to side) tolerance of the shot increases as the vertical goes from 0 to 9 inches.

Clear as mud?

David Kozenko

-------snippo--------

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
and https://elsmar.com/ubb/Forum4/HTML/000076.html
and https://elsmar.com/ubb/Forum4/HTML/000120.html

posted 28 February 2000 06:20 AM            

Let say a thickness displacement meter used to measure 0.80+/-0.0125mm.
(Measurement uncertainty for the IMTE is +/-0.0004mm)

Question:
Is it correct if I set the acceptance criteria (Acceptable uncertainty) for the IMTE as 30% of 0.0125mm?