MeasurementBlog

In The August 24th Industrial Automation Newsletter at SensorMag.com I wrote a brief article about Uncertainty and how it is properly used in understanding and reporting measurements.

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.

TEMPERATURES.COM, INC. publishes information about measurement devices and measurement on its websites. The sites have articles, directories and news to foster competent measurements & analysis in industry & science. Sites are free. Submissions by visitors are encouraged and reviewed. Sites as of August 2007 are: lehos tecHeadlines, measureNEWS, About Temperature Sensors, TempSensor Directories, TempSensorNEWS, Measurement Databases, (MeasurementBlog.com)MeasurementMedia.com and MeasurementDevices.com