Long-term drift analysis of Zener voltage standards and proposal of an initial calibration interval using calibration records accumulated for 15 years

Abstract

In electrical metrology, voltage is a key quantity together with resistance for realising all electric standards in the low-frequency range. Zener voltage standards are accepted as the most stable to disseminate voltage references traceable to the Josephson standard devices. We study the long-term drift of the Zener devices to propose their initial calibration interval (CI), statistically analysing the calibration records accumulated for 15 years at the Korea Research Institute of Standards and Science (KRISS). First, we apply the direct method where the measurement reliability is obtained by integrating the probability density functions acquired from kernel density estimation (KDE). Markov chain Monte Carlo (MCMC) has been successfully demonstrated to determine the parameters of the Weibull reliability model. A numerical experiment was performed to confirm that the MCMC method works properly and is able to replace the S3 method of NCSLI. The direct method agrees with the MCMC within the highest posterior density (HPD) obtained by the MCMC method. The KDEs of the parameters acquired by the MCMC method enable the uncertainty of the parameters to be expressed in probability distributions rather than in confidence intervals. The final result proposes an initial CI of the 10 V output taps in the Zener devices without any calibration record of 8.8 months with a 0.91-month standard deviation for 90% of the measurement reliability target (MRT) and a 16 μV tolerance limit.