Environmental and transport effects on transfer standards

Advances in measurement techniques and instrumentation over the last 10 years have led to reduced measurement uncertainties in the field of electrical calibrations. At the National Physical Laboratory, the introduction of the quantized Hall effect as the primary standard of resistance, together with the use of cryogenic current comparator bridges has enabled a reduction of the uncertainty on resistance calibrations to 0.05 ppm at the 100 Ω level. This means that the effect of transport on resistance standards can be a dominant uncertainty component in the traceability chain