Meeting the ISO/IEC Requirements for Traceability and Measurement Uncertainty. APLAC Approaches. Dr Bernard King NARL, Australia

Transcription

1 Meeting the ISO/IEC Requirements for Traceability and Measurement Uncertainty APLAC Approaches Dr Bernard King NARL, Australia

2 Interpretation of ISO/IEC Requirements Extensive consultation leading to common interpretation and new Guides APLAC held 3 day Workshop in May 01 to develop a common interpretation, across five fields. Draft guide produced Final guide expected by end of 2002 Will supplement an ILAC guide

3 Some of the Difficulties Anxiety in labs and accreditation bodies Need for training of lab staff and assessors Time / cost of additional work Lack of customer demand Some countries / fields are moving faster than others Need to interpret requirements in a pragmatic, progressive and common sense way ILAC MRA will help ensure level playing field

4 Interrelated Requirements in ISO/IEC Specification of measurement requirement Method validation Traceability Measurement Uncertainty

5 ISO/IEC Method Validation Requirements Specifically required for in-house methods Implicitely required for all methods Long standing requirement, but often inadequately addressed Needs to be subject to closer scrutiny If method validation data is available, then evaluating MU is not difficult

6 ISO/IEC Traceability Requirements Measurements must be traceable to SI, where feasible Where above is not feasible, traceability to other measurement standards must be established This can be achieved by use of transfer standards, that are themselves traceable to higher level standards

7 Example 1- Cd in soil Measurand &Units - Total Cd in soil, measured in mg/kg Equation C = I. dc. V mg/kg di m. R I. dc is traceable to SI through PSRM di R is traceable to SI through matrix RM or... m and V are traceable to SI through calibrated standards If the model is valid then C is also traceable to SI

8 Reference CRM RM Commercial Chemicals Traceability of RMs Comments / Traceability Can be accepted Can be accepted after assessment Lab are responsible, however: Often best available Often entirely adequate For physical measurements there are accreditation requirements for calibration, but for chemical measurements there is little yet in place!

9 ISO/IEC MU Requirements An uncertainty evaluation is required for all measurements Labs shall at least attempt to: identify all significant components make a reasonable estimation of U ensure that reported results do not give a false impression of U.

10 Reproducibility Based MU Combine other significant effects with reproducibility Reproducibility Sampling Effects MU Bias Effects

11 Summary of International MU Policy Target implementation date - Dec 2002 ISO GUM and Eurachem / CITAC strategies are recommended but not compulsory Strategies based on reproducibility need to also consider other significant effects MU estimates can be based on available or readily obtainable data, including professional judgement The degree of rigour required in evaluating uncertainty depends on the end use of the measurement

12 cont... The evaluation of uncertainties associated with qualitative tests is not required, but the probability of false identification does need to be considered. Any limitations associated with traceability and MU claims need to be reported with results It is expected that reporting MU, where relevant and necessary, will become the norm with time

13 Conclusions Measurements need to facilitate sound decisions Effort required depends on the level of acceptable MU A matter for professional judgment Not as difficult as it first seems Eg- If validation data available MU takes 0.5 to 2 days Reasonable progress is being made in implementing the new requirements in a pragmatic and harmonized way.

14 Sources of Help Literature - policy papers, guides, journals, web Training courses, seminars, workshops, eg. On RMs, MU and validation Web- based training on MU at