In the previous post, I talked about measurement uncertainty and gave a few weblinks to, what I think are informative sites.
In case you didn’t have time to look at the EuroChem one on Measurement Uncertainty, here’s both a link and a quick listing of the various sections of their online Guide to the subject. It is very detailed and, I think, informative.
If nothing else, just the list of chapters in the Guide gives a more complete idea of the process involved in quantifying and reporting Measurement Uncertainty. It is not a difficult or very complex subject. It just has more than one step. Yet, each step is clearly identified and covered in this Guide.
Can’t beat the price either!
Note, too, that each chapter is also a seperate weblink. (Also note the extra information here, too, such as a unique, interactive Glossary
After all, the process of making a measurement is always fraught with errors. The key to understanding them is statistics; make more than one measurement under prevailing conditions and learn what the dispersion of results are. It really is that simple.
Just because a manufacturer’s literature doesn’t explain these “little” details, or somehow indicate them in their product literature, doesn’t mean their devices are immune from them. Uncertainty is the biggest trip-wire for any measurement device, both in calibration (traceable only) and use.
Lots of equipment and measurement device manufacturers know these facts; some don’t or act as if they don’t. They do this with skimpy and sometimes meaningless specifications for their products.
The Sales & Marketing people get to write the literature and the specifications for the company products and often want to “Dumb Down” the technical or scientific terms in them, for whatever reasons they have. Some companies don’t or can’t do it due of standards, regulations or a high level of professional ethics.
(I suspect that it’s a combination of not wanting to appear lacking compared to competition, or wanting to forestall any liability, or, just possibly, because they will have to sell harder, or, even more remotely, because they don’t understand them either. More likely it’s some combination of these) Whatever the reasoning, measurement devices can often have poorly written, incomplete technical specifications.
So, in much unregulated commerical literature, the poor, uninformed user is told about measurement accuracies. Then they are left to their own understanding and educational background to interpret these “Dumbed Down” specifications mean.
It really is a joy to read technically complete and well written instruments and measuring device specification. It saves time and makes equipment and vendor choices a heck of a lot easier for me, at least.
Companies that produce complete specification, especially with all the uncertainties and residual temperature coefficients are the kind of vendor that I want to buy things from.
Others may have unique wrinkles or features that I need and, if I need a device from them, I have to ask for more details to fully understand what I am likely to get when we open the box and turn the device on dfor the first time.
Let me finish this rant by quoting from my article last month.
Definitions
“Start by understanding that measurement uncertainty is quantitative while accuracy is qualitative. Now take the next step and flesh out a definition. The Eurachem’s Qualifying Measurement Uncertainty in Analytical Measurement Web site defines the term as the “parameter associated with the result of a measurement that characterizes the dispersion of the values that could reasonably be attributed to the measurand.” It goes on to add that “the parameter may be, for example, a standard deviation (or a given multiple of it), or the width of a confidence interval.” And then states that “uncertainty of measurement comprises, in general, many components.
Some of these components may be evaluated from the statistical distribution of the results of a series of measurements and can be characterized by experimental standard deviations. The other components, which can also be characterized by standard deviations, are evaluated from assumed probability distributions based on experience or other information. It is understood that the result of the measurement is the best estimate of the value of the measurand and that all components of uncertainty, including those arising from systematic effects, such as components associated with corrections and reference standards, contribute to the dispersion.”
This definition may be hazy to some. If you’re still unclear about measurement uncertainty, check out the National Institute of Science and Technology’s (NIST’s) Essentials of Expressing Measurement Uncertainty Web site or the agency’s guidelines.
What do you do when faced with a device that’s not a typical dimension gage? Say, what about the case of Infrared or IR Radiation Thermometers; can you do a Gage R&R evaluation with them?
Been there. Done that.
But it wasn’t simply aiming an instrument into a blackbody furnace N times, or setting one up, aligned to a furnace and turning it on and off X times. Those are foolish exercises, a waste of time in my book, and nothing like a true measure of R&R.
Such a testing method wouldn’t pass a common sense question, like: What did you learn that helps you understand the measurement variability of the device in the hands of a trained or experienced user?
If there is sufficient interest in this subject, I will consider going further and sharing my experience in more depth. However, I need to have a good reason.
Email me: at RandR at temperatures.com if interested. (clearly this email address needs a common modification to work properly- this address format minimizes spam input from email spambots)
If there’s enough interest, say over the next few months-it’s now June 2007, I’ll keep the offer open until the end of the summer-September 20th. If at any point I hear from more than a few dozen interestd parties, I will add the “Rest of The Infrared R&R Story”.
If there’s less than that number by then, I’ll share my info by direct email (bcc to keep the email addresses anonymous) to those who send in their return email address, rather than clogging blog space.
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