Characterisation of the effects of time and pressure on a group of electronic voltage standards

Although primary metrology laboratories use standards based on the Josephson effect to maintain a local reference standard for dc voltage, artefact standards are still the standard of choice in many secondary laboratories. The National Metrology Laboratory, Dublin maintains a local reference standard for dc voltage by means of an ensemble of Zener-diode based electronic voltage standard units. Electronic voltage standards have a number of shortcomings over Josephson standards for use as a local reference standard. In particular their output voltages are influenced by several external factors. In order to make optimum use of the NML reference standard it is important that the output voltage of individual units be characterised for the effects of these influence factors so that appropriate corrections can be applied. This thesis describes techniques and procedures used to characterise the effects of time and pressure on electronic voltage standards and reports the results obtained for the devices used at NML. The methods of analysis, which can be applied to the results of interlaboratory comparisons in order to quantify the temporal characteristics of electronic voltage standards, are discussed. The temporal regression parameters and associated uncertainties, which were estimated for all the NML units, are presented and the use of within-group comparisons as a means of surveying the behaviour of individual units is illustrated. An experimental set-up suitable for the measurement of the pressure coefficients of electronic voltage standards is described. The design and development of important aspects of this set-up, including the test chamber, they systems used to control and monitor temperature and pressure, and the data acquisition and analysis program are described. The results of the measurements of the pressure coefficients of five types of commercially available electronic voltage standards are presented.