An Ultra Stable Zener Voltage Standard - Fifteen Years of Surveillance

The maintenance of the National dc Voltage Standard of Uruguay is carried out by means of electronic sources based on Zeners. As they are not primary standards, it is necessary to send them to National Metrology Institutes abroad. As these trips are a problem, a very stable source was developed to extend the calibration period. This paper describes the evolution of a 10-V dc Zener standard, developed in 2005, and continuously observed up to now. An automatic system compares the outputs of this standard with other similar one and conventional commercial Zener standards. During all this period, five comparisons were done against Josephson standards, the last one in 2019. Exceptionally stability has been observed, as it is shown in this work.