Uncertainty Information, Links and a Local Directory Listing

[Marc]

For those of you with uncertainty dancing in your dreams, here are some thread segments. If you read thru them, it's an education in uncertainty. These are culled from the listserve.

See Uncertainty Directory Listing

It's sorta a nice collection of thoughts. They don't have extensions and should load in your browser (depends upon your preferences) - and if you 'download' one (or more) file, you can open it (them) in your favourite text editor. Plain, vanilla ascii (.txt if you will) files.

[Marc]

Date: Mon, 11 Oct 1999 10:24:16 -0700
From: "Dr. Howard Castrup"
To: 'Greg Gogates'
Subject: RE: Uncertainty book help

Amanda,

There are two basic procedures that I know of that are available on-line. One is found at our web site at http://www.isgmax.com - Link was: /unc_broc.htm and the other can be found at the Quametec site at http://www.quametec.com - Link was: /uncproc.htm

There is also commercially available software that may help you out. The packages that I hear mentioned most frequently are

1. GUM Workbench from the Danish Technological Institute http://www.gum.dk - Link was: /e-wb-home/gw_home.html

2. UncertaintyCalculator from Compaq http://www.callabmag.com - Link was: /Freeware.html

3. UncertaintyAnalyzer from ISG http://www.isgmax.com - Link was: /unc_broc.htm

Howard Castrup
President, Integrated Sciences Group

[Marc]

Date: Sat, 9 Oct 1999 15:25:13 +0200
From: Sven Nytoft Rasmussen
Subject: SV: Uncertainty book help

Books on measurement uncertainty, here are two rather new ones, not included in the bibliography which Ralph Veale made available:

The book by Coleman and Steele is quite helpful. The authors do not adhere to the internationally agreed terms, however. Examples are mostly from thermodynamics, fluid flow etc. Hugh W. Coleman and W. Glenn Steele: "Experimentation and Uncertainty Analysis for Engineeers". 2nd. ed. John Wiley & Sons, 1999, ISBN 0-471-12146-0

The book by Adunka strictly follows the GUM method by ISO. It is, as far as I know, available in German only. Adunka's examples are mostly from metering in respect of legal metrology like e.g. heat meters for district heating, calibration of household gas meter etc. Franz Adunka: "Messunsicherheiten, Theorie und Praxis, 1st ed. Vulkan Verlag, 1998, ISBN 3-8027-2186-1.

Sincerely yours

Sven Nytoft Rasmussen, Ph.D.
Manager of center
Center for Metrology and Quality Assurance
Danish Technological Institute
P. O. Box 141
DK-2630 Taastrup, Denmark

Tlf. +45 43 50 44 40
Fax +45 43 50 72 73
Web: WWW.teknologisk.DK

You are welcome to check http://www.gum.dk for furhter information.

[Marc]

Subject: Re: Calibration Issues for Small Firms /Scalies/Hellmann
Date: Wed, 3 Nov 1999 17:37:06 -0600
From: Moderator
From: JJH2000

Charley,

MEASUREMENT UNCERTAINTY is a rather obscure concept because it is precisely what we strive to and assume is eliminated whenever a measurement is taken of a unknown process variable. No one wants to hear that the temperature of water boiling in a pot is sorta 100 degrees Celcius, "give-or-take" 1 degree, or maybe 2 degrees, or 3 degress....and so on. There are many variables that would determine and effect the temperature measurement such as, the elevation above sea leavel, the ambient air pressure around the pot, the degree of accuracy of the temperature measuring device, its degree of precision giving the same indication every time given the same conditions, and so on. It's this "give-or-take" that is the uncertainty of the measurement. To make an anology, a proficient archer can consistently hit a smaller area of the larger target. But even Robin Hood didn't split his arrow with every other arrow shot. But he was good at hitting the bulls eye everytime, or so the legend goes. The bulls eye, itself, is not a point in space, but rather a very small area of the whole target.

To consistenly hit a 1 inch diameter circle at 30 yards, would be the standard for the proficient archer. If Robin utilized his archery skills in hunting, for example, the results would be consistent. The deer would fall every time, and venison would be turning on the spit back at camp every evening. We can quantify and define the MEASUREMENT UNCERTAINTY of Robin's skill by the documenting the size of the bulls eye.

Now the issue becomes how does one quantify and define MEASUREMENT UNCERTAINTY, to make it "known". That is something you must decide. What is the acceptable % error accuracy of your instrumentation? It is determined by the needs of the process being measured.

What is an acceptable percent of the total range for error? I maintain a 0.25% of total range for acceptable accuracy. In other words, the instrument I am calibrating must indicate the same value as the instruments of standard (certified by NIST) within 0.25% of the range being measured. For a 0 to 100 degree Celcius ranged instrument, it must be within 0.25 degrees of the reading of the standarized instrument, or else it fails. This standard has validity in the pharmaceutical, petrochemical and chemical process control environments where I work. But it might not be appropriate for you. Why, for example, should you spend hundreds, thousands, of dollars for a 0.25% accuracy temperature instrumentation device to cook your Thanksgiving turkey when a $3 thermometer from the drug store would be perfectly adequate?

The knowing of the MEASUREMENT UNCERTAINTY is the quantified and documented size of the bulls eye that works for you.

John

[Marc]

Also see: http://Elsmar.com/ubb/Forum4/HTML/000036.html
and http://Elsmar.com/ubb/Forum4/HTML/000047.html