«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. ...»
According to paragraph 6 of the CIPM MRA:
6 Participation in key and supplementary comparisons
Committees should take proper account of regional representation. The number of laboratories participating in CIPM key comparisons may be restricted for technical reasons.
6.2 Participation in key comparisons organized by an RMO is open to all RMO members and to other institutes that meet the rules of the regional organization (including institutes invited from outside the region) and that have technical competence appropriate to the particular comparison.
6.3 Participation in RMO supplementary comparisons is open to those institutes meeting the requirements specified in paragraph 6.2.
At its 2005 meeting, the CIPM decided on the following policy concerning the participation of laboratories in Associates of the CGPM6.
paragraph 1.5 of the CIPM MRA should be interpreted with greater flexibility than before. Any participation of NMIs and designated institutes from Associates in CC comparisons or other activities should be carefully considered by the relevant committee or working group on a case by case basis. Specifically and in exceptional cases Associates may be invited to take part in CC comparisons, studies, pilots and
other formal activities where:
that reports of CC comparisons in which NMIs and other designated institutes from Associates take part may be included in the KCDB although these reports should make clear those results which come from Associates. Their results should not normally contribute to a key comparison reference value in comparisons which are CIPM 2005-05, paragraph 2.4. In the text, CC refers to Consultative Committees and KC refers to key comparisons.
arranged by the Consultative Committee unless it may be shown to be of significant scientific value to other participants;
Associates who are invited to take part in a KC organized by a Consultative Committee may be invited to attend working group meetings at which the results from that comparison are discussed;
that representatives of NMIs or DIs from Associates may be invited, on a one-off, case by case basis, to attend CCs or working groups as guests; and Associates may be asked to pay, as provided for under Article 15 (1921) of the Convention of the Metre, for any extra costs incurred by the BIPM of their participation in comparisons, particularly those which are piloted by the BIPM.
It is important to note that a national metrology institute (NMI) or designated institute (DI) that has never participated in a comparison may wish to acquire a benchmark of its performance before participating in a key comparison. This can be achieved by running pilot studies in parallel to a key or supplementary comparison or by participating in a key or supplementary comparison in “pilot study” mode. The results of the NMIs or DIs participating in the pilot study are not to be used to compute reference values, and the name of the institute will not be published in the KCDB. Participation in “pilot studies” run in parallel to comparisons must be agreed before the comparison measurements starts. Results from pilot studies are not considered sufficient support of CMCs.
4.2. Initiating a CIPM key comparison CIPM key comparisons are initiated at a Consultative Committee meeting.
The Consultative Committee at each of its meetings examines the need for comparisons and decides which ones from a list of key comparisons should be initiated at that meeting, taking into account, among other things, the views of regional metrology organizations. For each comparison, a pilot institute is identified to take the main responsibility for running the CIPM key comparison.
In drawing up the provisional list of participants and an approximate timetable, the Consultative Committee ensures that an adequate number of participants from each of the
main RMOs take part so that corresponding regional comparisons can be properly linked to the CIPM comparison.
In some CIPM key comparisons the number of participants may be limited for technical reasons.
The Consultative Committee may form a coordinating group, nominating two or three institutes from the provisional list to help the pilot institute in drawing up the technical protocol and timetable for the comparison.
The timetable of this and any other comparisons decided by the Consultative Committee should be discussed to ensure that the workload of the whole set is not too great for the participating and pilot institutes, and that the results will be available for the next meeting, normally in three (or occasionally two) years’ time. For this the total circulation time of the standards must be fixed and should not exceed eighteen months unless there are exceptional circumstances.
4.3. Organization of a CIPM key comparison The organization of a CIPM key comparison is the responsibility of the pilot institute which may be helped by the coordinating group. The first task of this group is to draw up the detailed technical protocol for the comparison (see Section 4.4) and its dispatch, inviting participation as defined by the Consultative Committee (see paragraph 6 of the CIPM MRA).
In those committees having permanent working groups or sections responsible for specific areas of activity, the draft protocol must be sent to the chair of the relevant working group or section. The invitation to participate is sent directly to the delegates of member institutes present at the previous meeting of the Consultative Committee, plus absent members. Copies of the invitation and draft protocol are also sent to the BIPM executive secretary of the Consultative Committee7.
The main points to be decided by the group headed by the pilot institute are the
• List of participants with full details of mailing and electronic addresses.
• Travelling standard or standards to be used in the comparison.
• Whether or not a pilot comparison or any other preliminary work needs to be carried out among a restricted number of participants to verify the performance of the travelling standard.
• Pattern of the full-scale comparison, which ranges from the simple circulation of a single travelling standard around all the participants to the sending of an individual travelling standard directly to each participant from the pilot institute, or from each participant to the pilot institute or some combination of these.
• Starting date, detailed timetable, means of transport and itinerary to be followed by each travelling standard. This starting date is subsequently referred to as the starting date for the comparison.
• Procedure in the case of failure of a travelling standard.
• Procedure in the case of unexpected delay at a participating institute.
• Customs documents to accompany the travelling standards, either ATA carnet or other for those participants not qualifying for the ATA scheme.
4.4. Technical protocol for a key comparison The coordinating group8 draws up the detailed technical protocol. This technical protocol is an important part of the comparison and specifies in detail the procedure to be followed. It is important to remember, however, that the purpose of a key comparison is to compare the standards as realized in the participating institutes, not to require each participant to adopt precisely the same conditions of realization. The protocol should, therefore, specify the procedures necessary for the comparison, but not the procedures used for the realization of the standards being compared.
The points treated in the protocol should include the following:
For those cases where there is no coordinating group, the responsibility relies on the pilot institute.
• Detailed description of the devices: make, type, serial number, size, weight, packaging, etc., and technical data needed for their operation.
• Advice on handling the travelling standards, including unpacking and subsequent packing and shipping to the next participant. This should include a complete list of the content of the package including handbooks, etc., and the weight and size of the whole package.
• Action to be taken on receipt of the standards in a participating institute.
• Any tests to be carried out before measurement.
• Conditions of use of travelling standards during measurement.
• Instructions for reporting the results.
• Proposal for the method of determination of the key comparison reference value.
• List of the principal components of the uncertainty budget to be evaluated by each participant, and any necessary advice on how uncertainties are estimated (this is based on the principles laid out in the ISO Guide to the Expression of Uncertainty in Measurement). In addition to the principal components of the uncertainty, common to all participants, individual institutes may add any others that they consider appropriate. Uncertainties are evaluated at a level of one standard uncertainty and information must be given on the number of effective degrees of freedom required for a proper estimation of the level of confidence.
• Timetable for communicating the results to the pilot institute. Early communication helps to reveal problems with the travelling standard during the comparison.
• Financial aspects of the comparison, noting that in general each participating institute is responsible for its own costs for the measurements, transport and any customs charges as well as any damage that may occur within its country. Overall costs of the organization of the comparison, including the supply of the transfer devices, are normally borne by the pilot institute.
• Insurance of transfer devices is decided by agreement among the participants taking account of the responsibility of each participant for any damage within its country.
4.5. Circulation of transfer standards and customs formalities The pilot institute is responsible for organizing the circulation and transport of the standards and ensuring that the participants make proper arrangements for local customs formalities.
The equipment must be handled with care, i.e. only by qualified metrology personnel.
It is desirable and in some cases essential that the transfer instruments be hand-carried. If this is not deemed essential, certain precautions must nevertheless be taken. As goods are usually delivered to a shipping department in an institute a warning note should be attached to the package indicating that the package should be opened only by laboratory personnel. The participating institutes are responsible for transport to the next institute according to the circulation scheme. The method of transport as defined in the instructions should be respected.
Before dispatching the package, each participant must inform the next participant and the pilot institute, giving transport details.
If an ATA carnet is used, it must be used properly. Upon each movement of the package the person organizing the transit must ensure that the carnet is presented to customs on leaving the country, and upon arrival in the country of destination. When the package is sent unaccompanied, the carnet must be included with the other forwarding documents so that the handling agent can obtain customs clearance. In no case should the carnet be packed with the device in the package. In some cases it is possible to attach the carnet to the package.
After arrival of the package, the participating institute should inform the pilot institute of this by completing and returning a form that is included in the package. Immediately after receipt, the participating institute should check for any damage of the standards, in particular scratches and rust, and report this to the pilot institute.
If a delay occurs the pilot institute should inform the participants and if necessary revise the time schedule or the order of circulation between countries.