Difference between uncertainty and expanded uncertainty of measurement

[Dongzkie]

Hello,

please need your brief explanation about this two calibration laboratories with their calibration scope capabilities first one is "expanded uncertainty of measurement(+/-) while the other is "best measurementcapability expressed as an uncertainty(+/-)" whats the difference?

thank you

 

[dwperron]

If you are reading this in the lab scopes of accreditation they may mean the same thing, but you need some more information to be sure.

When a lab lists its Best Measurement Capability (BMC) they should also have a definition of what they are presenting, such as:
"BMCs represent expanded uncertainties expressed at approximately the 95 % level of confidence, usually using a coverage factor of k = 2. "

The "Expanded uncertainty of measurement" statement would be unusual to see on a scope of accreditation, I would expect to see that on their calibration certificates. This also should have language defining what they mean by their statement, such as:

"Uncertainty of Measurement
The uncertainty evaluation has been performed in accordance with ISO/IEC Guide 98-3:2008 (GUM). The reported expanded uncertainty of measurement is stated as the standard uncertainty of measurement multiplied by the coverage factor k such that the coverage probability corresponds to approximately 95%. This probability corresponds to a coverage factor of k=2 for a normal distribution."

Often the BMC is the same as the expanded uncertainty of measurement, but not always (a lab may not need to use their "best" capabilities to provide an adequate result). You need to dig a bit deeper to determine what each lab is stating, and if there is not language in their documents defining these terms you will need to contact the labs to be sure.