Investigation of resistance-ratio bridges using the automated resistance bridge calibrator

The following paper analyses the methods applied in calibration of resistance bridges used in primary thermometry. The dominating contribution to uncertainties of resistance bridges comes from their non-linearity. Several methods for assessing resistance bridge non-linearity were reviewed. From these the resistance bridge calibrator (RBC) was identified to have the best applicational properties.With the intent to reduce the well known uncertainty of the RBC due to temperature dependence and to determine the repeatability and reproducibility of this technique, the RBC was automated and placed in a thermally stable enclosure. The automated RBC was completely computer controlled enabling a sequence of measurements to be carried out with no operator present. These measurements provided new information on temperature dependence, time stability of the RBC and repeatability and reproducibility of the calibration technique as such.Conclusions drawn from the measurements show the improvement of calibration technique due to improved temperature stability as expected and the ability to assess the repeatability and reproducibility as a result of automation. Results were reproducible to several parts in 108.