The performance of Zener-diode-based electronic voltage standards as transfer devices

The Irish National Metrology Laboratory (NML) maintains its reference voltage standard by means of an ensemble standard comprising a group of electronic voltage standards (EVSs). The maintenance of this standard comprises two parts: the establishment of the traceability to the SI unit of the value assigned to the reference standard which is accomplished by regular bilateral comparison with a higher echelon laboratory, and the surveillance of the NML standard between such comparisons which is accomplished by internal intercomparison. One or more EVSs, of identical construction to those used for the maintenance of the local standard, are used as travelling standards for the bilateral comparison.