by David F. Martson
The development and use of intrinsic standards, e.g., Josephson Voltage Standard or JVS, has brought the primary level of uncertainty achievable for DC voltage down to a few nV/V (ppb), while at the test bench, precision digital multimeters (DMM) routinely provide direct reading accuracy to a few µV/V (ppm). Although the references typically employed for traceability (i.e., those used to perform DMM calibrations in primary or secondary laboratories) have remained virtually unchanged, the ancillary equipment required to support their use is obsolete, in this case, the analog DC null detector. This paper discusses alternative approaches to effectively bridge the gap created by that obsolescence, while maintaining DC voltage traceability at levels of uncertainty satisfactory to support the calibration of high accuracy DMMs and associated infrastructure.
