|
2.
Measurement Process Characterization
2.3. Calibration 2.3.3. What are calibration designs? 2.3.3.3. Uncertainties of calibrated values
|
|||
| Type B uncertainty associated with the restraint |
The reference standard is assumed to have known value, R*, for
the purpose of solving the calibration design. For the purpose of
computing a standard uncertainty, it has a
type B uncertainty that contributes
to the uncertainty of the test item.
The value of R* comes from a higher-level calibration laboratory or process, and its value is usually reported along with its uncertainty, U. If the laboratory also reports the k factor for computing U, then the standard deviation of the restraint is $$ {\large s}_{R^*} = \frac{U}{k} \, .$$ If k is not reported, then a conservative way of proceeding is to assume k = 2. |
||
| Situation where the test is different in size from the reference | Usually, a reference standard and test item are of the same nominal size and the calibration relies on measuring the small difference between the two; for example, the intercomparison of a reference kilogram compared with a test kilogram. The calibration may also consist of an intercomparison of the reference with a summation of artifacts where the summation is of the same nominal size as the reference; for example, a reference kilogram compared with 500 g + 300 g + 200 g test weights. | ||
| Type B uncertainty for the test artifact | The type B uncertainty that accrues to the test artifact from the uncertainty of the reference standard is proportional to their nominal sizes; i.e., $$ {\large s}_B = \frac{Nominal \,\, Test}{Nominal \,\, Restraint} {\large s}_{R^*} \, .$$ | ||
