«CIPM MRA-D-05 Version 1.6 Measurement comparisons in the context of the CIPM MRA CIPM MRA-D-05 Contents 1. Background 1.1. On the CIPM MRA 2. ...»
are completed. The measurement results, together with the associated uncertainties and any additional information required, should be reported in the format given in the instructions as part of the protocol, usually by completing the standard forms annexed to the instructions.
A result from a participant is not considered complete without an associated uncertainty, and is not included in the draft report unless it is accompanied by an uncertainty supported by a complete uncertainty budget. Uncertainties are drawn up following the guidance given in the technical protocol.
If, on examination of the complete set of results, the pilot institute finds results that appear to be anomalous, the corresponding institutes are invited to check their results for numerical errors but without being informed as to the magnitude or sign of the apparent anomaly. If no numerical error is found, the result stands, and the complete set is sent to all participants.
4.7. Report of a CIPM key comparison The pilot institute is responsible for writing the report of the key comparison. The report passes through a number of stages before publication, and these are referred to here as Draft A, Draft B and Final Report.
The first draft, Draft A, is prepared as soon as all the results have been received from the participants. It includes the results transmitted by the participants, identified by name, and a first calculation of the key comparison reference value. However the results are not communicated if there are any outliers, until the participants concerned have been contacted to ensure that there are no arithmetic, typographical or transcription errors involved.
the agreement of all participants and on the basis of a clear failure of the travelling standard or some other phenomenon that renders the comparison or part of it invalid.
As the results may be changed due the reason explained above, Draft A (in all its versions) must be considered confidential and distributed among the participants only. As results may change, Draft A reports cannot be used as support for claiming CMCs.
Until all the participants have agreed on the report, it should be considered to be in Draft A stage, it being possible to have successive versions (Draft A1, A2,…etc).
In calculating the key comparison reference value, the pilot institute will use the method considered most appropriate for the particular comparison (normally that proposed in the protocol), subject to confirmation by the participants and, in due course, the key comparison working group and the Consultative Committee. After deciding the key comparison reference value and its uncertainty, the deviation from the reference value and the expanded uncertainty at a 95% level of confidence (k = 2 for infinite number of degrees of freedom) of the deviation are deduced for each of the individual results (degrees of equivalence). At this stage the participants may review the initial decision to include or not bilateral degrees of equivalence, subject to approval of the corresponding CC.
Once the final version of Draft A, which includes the proposed key comparison reference value and degrees of equivalence, is approved by the participants, the report is considered as Draft B. It must then be submitted for approval by the corresponding Consultative Committee. At this stage, the results are not considered confidential and can be used to support CMCs and can be used for presentations and publications, except for the key comparison reference value and the degrees of equivalence which must be considered confidential until they are approved by the Consultative Committee and published in the KCDB.
The working group on key comparisons is normally charged with examining Draft B prior to its distribution to all members of the Consultative Committee, to ensure that it meets all the requirements set by the committee. In the case of those Consultative Committees having permanent working groups dealing with specific areas of activity, the Consultative Committee may ask these working groups to undertake the functions of the key comparison working group.
Entry of the results, including the degrees of equivalence, into the KCDB must wait until Draft B has been approved by the Consultative Committee, at which point the Draft becomes the Final Report. At that stage, the mention “Draft B” in the title or contents should be replaced by the mention “Final Report”. Approval by the Consultative Committee may be given by correspondence on the recommendation of the working group on key comparisons.
Each Consultative Committee will set its own procedures for approving the results of key comparisons in the most efficient and timely way possible.
In the event of disagreement concerning the results or the interpretation of the results of a key comparison, which cannot be resolved by the participants, by the key comparison working group or by the Consultative Committee, the matter is referred to the CIPM for a decision.
An institute that considers its result unrepresentative of its standards may request a subsequent separate bilateral comparison with the pilot institute or one of the participants.
This should take place as soon as possible after the completion of the comparison in progress.
The subsequent bilateral comparison is considered as a new and distinct comparison.
5. RMO key comparisons To allow the participation in key comparisons of all the NMIs and DIs of an RMO, the RMOs may organize their own key comparisons.
5.1. Participation in RMO key comparisons Participation in RMO key comparisons is decided by the corresponding committees of the RMO, but only the results corresponding to NMIs or DIs from Member States of the BIPM or Associate States and Economies of the CGPM that have signed the CIPM MRA will appear in the tables of numbers (including the degrees of equivalence) and in the graphs (including the graphs of equivalence) published in the KCDB. The policy for reporting comparisons that involve participants who are non-signatories to the CIPM MRA is stated in paragraph 8.
As participation in CIPM key comparisons may be limited in number for technical reasons, it is recommended that if possible, RMO key comparisons be open to participation of NMIs of other regions.
The RMO key comparisons must be linked to the corresponding CIPM key comparisons by means of joint participants. This is mandatory to demonstrate global equivalence. To achieve this, it is recommended that at least two of the participants in the preceding CIPM key comparison participate also in the RMO key comparison.
5.2. Organization of RMO key comparisons
The RMO key comparisons must follow the same protocol as a preceding CIPM key comparison and must be approved in advance as “key” by the corresponding Consultative Committee. Instead of the method to determine a reference value, the RMO key comparison protocol must include the way in which the results will be linked to the corresponding CIPM key comparison reference value.
The mechanism for approval depends on the particular Consultative Committee’s practice.
5.3. Reports of RMO key comparisons The procedure for reporting an RMO key comparison is basically the same as that described in Section 4.7. Only key comparisons carried out by a Consultative Committee or the BIPM (CIPM key comparisons) lead to a key comparison reference value. For a key comparison carried out by an RMO, the link to the CIPM key comparison reference value is obtained by reference to the results from those institutes that have also taken part in the CIPM key comparison.
The complete results of the linked RMO key comparison are shown in exactly the same form in the pages of the original CIPM key comparison in the KCDB. However, the link for “participants” in the page for the RMO comparison lists only the laboratories that participated in this exercise.
6. Subsequent bilateral key comparisons Subsequent bilateral key comparisons are normally carried out for one of the following
After completing a key comparison, an institute that considers its result unrepresentative of its standards may request a subsequent bilateral comparison with one of the other participants.
An institute that was not ready to participate at the time a key comparison was conducted may request a subsequent bilateral comparison with one of the participants.
The results of subsequent key comparisons may be added to the data for the previous key comparison in the KCDB, with a note specifying that these results correspond to the subsequent comparison. Except for BIPM ongoing comparisons, when a Consultative Committee chooses to include new participants, no key comparison reference value is computed for these new results and they are not normally used to modify the key comparison reference value obtained from the results of the original participants. The results are linked to the original key comparison through the joint participation and the linking laboratories original results remain valid. In such cases, degrees of equivalence are computed for the participants in the subsequent comparison with respect to all other participants and to the previous key comparison reference value.
The results of subsequent key comparisons may be assigned a separate identifier at the request of a Consultative Committee. This identifier will usually be the name of the previous comparison plus a suffix.9 As with the results of RMO key comparisons, the complete results of the linked subsequent comparisons are shown in exactly the same form in the pages of the original CIPM key comparison and that of the subsequent comparison. However, the link for “participants” in the page for the subsequent comparison lists only the laboratories that participated in this exercise.
Bilateral comparisons are no longer assigned the special identifier “BK” for registration in the KCDB.
This allows potential additional participants to join in the comparison without the need to modify the identifier.
Bilateral comparisons of standards with long-term stability carried out by the BIPM may be conducted according to special arrangements not necessarily covered by this document.
7. Supplementary comparisons Supplementary comparisons are normally organized by the RMOs to cover areas or techniques not covered by key comparisons. These are complementary to key comparisons and are not intended as second-level comparisons. Their final reports are published in the KCDB, but degrees of equivalence are not necessarily computed.
The rules for the participation in CIPM and RMO key comparisons also apply to CIPM and RMO supplementary comparisons (paragraphs 4.1 and 5.1).
Bilateral supplementary comparisons should follow the same procedure as multilateral supplementary comparisons.
7.1. Participation in supplementary comparisons Participation in supplementary comparisons is decided by the organizing body, usually the RMO. As with RMO key comparisons, it is recommended that participation is open to NMIs and DIs from other RMOs. The policy for reporting comparisons that involve participants who are non-signatories to the CIPM MRA is stated in paragraph 8.
7.2. Reports of supplementary comparisons
Preparation of the reports of supplementary comparisons should follow the same threestage process: Draft A, Draft B, Final Report. The differences are:
– approval is given by the corresponding RMO committee;
– degrees of equivalence relative to a supplementary comparison reference value may be computed, but this is not mandatory.
- Reports approved by the RMO must be forwarded to the CC Executive Secretary and the Chair of the relevant working group (e.g. Key Comparison or CMC Working Group) of the CC to allow for a six-week period of comment and editorial control. If at the end of the period, no objections have been raised within the working group of the CC, the final report,