ASTM E2554 for Estimating and Monitoring the Uncertainty of Test Results
ASTM E2554 Standard Practice for Estimating and Monitoring the Uncertainty of Test Results of a Test Method in a Single Laboratory Using a Control Sample Program
4. Summary of Practice
4.1 A standard material or control sample is measured repeatedly over time. The presumption of this practice is that the variation experienced on this material will be indicative of the laboratory total expected variation. Incorporation of specific known or potential sources of variation in the testing program is encouraged.
4.2 A control chart is prepared and the results are evaluated to identify short-term variation and longer-term variation. These data can then be used to determine an estimate of uncertainty standard deviation.
4.3 Laboratories already having control chart procedures in place may use existing data.
4.4 Ongoing monitoring of the test method is conducted using an uncertainty control chart.
5. Significance and Use
5.1 Laboratories accredited under ISO 17025 are required to present uncertainty estimates for their test results. This practice provides procedures that use test results to develop uncertainty estimates for an individual laboratory.
5.2 Generally, these test results will be from a single sample of stable and homogeneous material known as a control or check sample.
5.3 The true value of the characteristic(s) of the control sample being measured will ordinarily be unknown. However, this methodology may also be used if the control sample is a reference material, in which case the test method bias may also be estimated and incorporated into the uncertainty estimate. Many test methods do not have true reference materials available to provide traceable chains of uncertainty estimation.
5.4 This practice also allows for ongoing monitoring of the laboratory uncertainty. As estimates of the level of uncertainty change, possibly as contributions to uncertainty are identified and minimized, revision to the laboratory uncertainty will be possible.
