Evaluation of an Ultra Stable Zener Based Voltage Reference

This paper describes the behavior of a Zener based voltage standard, during the last decades. This is based on a bank of 140 individual commercial Zeners. This source has been observed with a continuous automatic measuring system for 20 years. A statistical analysis is shown, that comprises the evaluation of Allan deviation on different sectors of Zeners of the source, to decide on the health of them, comparing their behavior over the years. This technique allows checking the stability of this standard source between external calibrations, extending their calibration time.