Resistance standards with values in the Tohm 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 high resistance values differ quite substantially from the calibration techniques applied in the lower resistance ranges. For this reason, the key comparisons carried out so far in the field of dc resistance do not cover the high end of the scale in the Tohm range. The EURAMET technical committee for electricity and magnetism, thus, decided in 2008 to organise a supplementary comparison of resistance at 1 Tohm and 100 Tohm based on well characterized travelling standards.
Final Report 2013-11-12
The comparison has been completed and the results are published in the KCDB.
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 there similar measurement systems were used. The results of the comparison allow the participants to critically review their measurement procedures and uncertainty models.