Final report on supplementary comparison EURAMET.EM-S32: Comparison of resistance standards at 1 TΩ and 100 TΩ

Resistance standards with values in the TΩ range play an important role in electrical instrumentation. The calibration of such standards is, thus, a service offered by many metrology institutes. The techniques used to measure very high resistance values differ quite substantially from the calibration techniques applied in the lower resistance ranges. For this reason, the EURAMET technical committee for electricity and magnetism decided in 2008 to organise for the first time a supplementary comparison of resistance at 1 TΩ and 100 TΩ based on well characterized travelling standards. Eighteen European National Metrology Institutes participated in the comparison. With some exceptions, the results supplied by the participants agree reasonably well with the comparison reference value within the expanded uncertainty. As observed in other resistance comparisons, the characteristics of the standards used as transport artefacts ultimately limit the accuracy of comparisons in this field. The transport behaviour is difficult to model and introduces an undesired bias in the laboratory results. The transport uncertainties are at the level of the uncertainties claimed by some of the participants and, thus, limit the meaningfulness of the comparison results. Another remarkable observation is the big difference in the uncertainty statements made by the participants, even in cases where similar measurement systems were used. The results of the comparison allow the participants to critically review their measurement procedures and uncertainty models.