The use of within-group comparison of an ensemble standard to investigate the humidity dependence of electronic voltage standards

Abstract

A group of stable artifacts, each with the same nominal value, may be used as a local reference standard. We describe how a within-group comparison technique may be used to track the variations of the individual members of the group with respect to the group mean. This technique has been applied to a group of 13 commercially available Zener diode-based electronic voltage standards that is used to maintain a representation of the voltage unit at the 10 V level. The results form a time series of values which may be used to detect deviations of the output of an individual standard from its predicted behaviour. One of the standards was found to exhibit a distinct regular annual cycle that was strongly correlated with the ambient relative humidity. By representing the humidity variation as a series of steps it was possible to model the behaviour of this standard as a superposition of the standard’s response to all preceding humidity steps. The best estimate of the model parameters indicate that the response of this standard to a step change of humidity has a longer time constant and higher sensitivity than those found for other types of electronic voltage standards.