Abstract:
|
The Centro Nacional de Metrología from Mexico (CENAM) proposed in 2003 a comparison in the ac-dc voltage transfer field. CENAM volunteered to act as the pilot laboratory and as a provider of the travelling standard. The proposed SIM comparison of ac-dc voltage transfer difference were to include most of the measurements points evaluated during previously conducted CCEM key comparisons and published in the MRA Appendix B database. However, only one technical protocol and one travelling standard were used, to economize on time and resources. The comparison was conducted following the recommendations and guidelines for CIPM key comparison. The pilot laboratory issued the technical protocol, stating the measured points, the schedule of the comparison to be followed by the participating laboratories, the transportation procedure, as well as the proposed procedure of evaluating the reference values and the link with the corresponding CCEM key comparisons. The technical protocol was reviewed by the participants. After review, the measurement periods as well as the measurement points were modified. The points were selected to evaluate ac-dc voltage transfer difference measurements at 3 V as well as step-up and step-down techniques. It was proposed to evaluate the comparison reference value as the weighted mean of the reported values from laboratories in SIM who took part in the CCEM key comparisons. Finally three comparisons and a supplementary comparison were registered, using one technical protocol and a commercial ac-dc transfer standard Fluke 792A as the travelling standard. The comparison was carried out with little delay during the year 2004. It was stated in the technical protocol that the pilot laboratory would analyze the results from the participants and issue the Draft A of the report. Due to unforeseen situations at CENAM the Draft A was not issued for revision until the end of 2005. In general, the results show good agreement between the participants. At the moment the comments of the participants are awaited, to permit a rigorous analysis of the results, difficult, because most of the reference values of the participants' are correlated due to their common traceability to a third national laboratory.
|