ILAC p14:12/2010 - Accredited Calibration Certificate Uncertainty

[merrick65]

I have a question in regards to ILAC P14:12/2010. I would like feedback/thoughts on the following sections :

4.1 Accreditation bodies that are full members of or are applicants to the ILAC Mutual Recognition Arrangement (the ILAC MRA) shall require their accredited calibration laboratories to estimate uncertainties of measurement for all calibrations and measurements covered by the scope of accreditation.

6.1 ISO/IEC 17025 requires calibration laboratories to report, in the calibration
certificate, the uncertainty of measurement and/or a statement of compliance with an
identified metrological specification or clauses thereof.

Accredited calibration laboratories shall report the uncertainty of measurement, in
compliance with the requirements in 6.2 – 6.5 of this section.

6.2 The measurement result shall normally include the measured quantity value y and the associated expanded uncertainty U. In calibration certificates the measurement result should be reported as y ± U associated with the units of y and U………

6.4 Contributions to the uncertainty stated on the calibration certificate shall include relevant short-term contributions during calibration and contributions that can reasonably be attributed to the customer’s device. Where applicable the uncertainty
shall cover the same contributions to uncertainty that were included in evaluation of the CMC uncertainty component, except that uncertainty components evaluated for the best existing device shall be replaced with those of the customer’s device.
Therefore, reported uncertainties tend to be larger than the uncertainty covered by the CMC. Random contributions that cannot be known by the laboratory, such as transport uncertainties, should normally be excluded in the uncertainty statement. If,
however, a laboratory anticipates that such contributions will have significant impact on the uncertainties attributed by the laboratory, the customer should be notified according to the general clauses regarding tenders and reviews of contracts in
ISO/IEC 17025.

6.5 As the definition of CMC implies, accredited calibration laboratories shall not report
a smaller uncertainty of measurement than the uncertainty of the CMC for which the
laboratory is accredited.

I take it to mean that all accredited calibration certificates will be required to have uncertainties calculated for each reading and displayed on the certificate. This does not include a general statement that lists the CMC. I would also think that each reading shall have at least 5 readings to deal with repeatabilty. I’m not sure how labs doing small dollar items calipers, micrometers, indicators will be able to calculate uncertainties for each individual calibration and still make money. I would like input from any assessors that are on here also.

I basically would like to know how the US accreditating bodies that are full members to the ILAC MRA are going to implement P14.

According to ILAC this policy shall be enforced as of Nov 2011.
ILAC P14 can be downloaded from ILAC. http://www.ilac.org/ilac_p14_12_2010.html

I hope this makes sense.

[dgriffith]

In Reply to Parent Post by merrick65

....6.2 The measurement result shall normally include the measured quantity value y and the associated expanded uncertainty U. In calibration certificates the measurement result should be reported as y ± U associated with the units of y and U………


I take it to mean that all accredited calibration certificates will be required to have uncertainties calculated for each reading and displayed on the certificate. This does not include a general statement that lists the CMC. I would also think that each reading shall have at least 5 readings to deal with repeatabilty.

Each test point should have the associated uncertainty. The noise in the sample is part of the lab's budget and becomes part of the expanded uncertainty for that point. Best practices would dictate whether they use the std dev of the sample, or std dev of the mean.

[Hershal]

Merrick65, you are essentially correct regarding the uncertainty on accredited certs. However, ILAC has backed away from P14 just a bit and taken the position that the higher level Standard (ISO/IEC 17025:2005) is to be used until at least April 2012 when the P14 will supposedly be fixed one way or another. ISO/IEC 17025:2005 allows use of an accepted metrological specification which in the US means the Test Uncertainty Ratio (TUR) Rule, while P14 currently does not.

The US based ABs (all six) have all been requiring accredited certs to have uncertainty anyway. However, P14 requires uncertainty for each reading as you have pointed out.

My best guess is that this will lead to a dramatic increase in the non-logo certs (non-accredited), and likely also lead to higher charges for accredited cals here in the US. In a country where all labs must be accredited then P14 will likely have very little effect beyond the current situation.

Still, cross your fingers.