A product of the research on electrical standards at the BIPM is the use of ac techniques to measure the quantized Hall resistance and relate it to the impedance of standard capacitors. Research into possible metrological applications of high-Tc superconductors is also in hand.
The BIPM has developed a chain linking the impedances of 10 pF and 100 pF capacitance standards, measured at kilohertz frequencies, to the quantized Hall resistance measured at dc or 1 Hz. The use of gate voltages can result in significant decreases in the voltage coefficient (more usually described as the current coefficient) and in the frequency coefficient of the QHR measured at ac.
In voltage metrology, applied research has enabled us to identify, measure and characterize the effects of pressure and temperature on Zener-diode electronic voltage standards. The results are being put to use to improve the reproducibility of Zeners used as travelling standards in international comparisons.
Another area of BIPM research in electrical metrology that is producing interesting results is the application of low-frequency spectral analysis to "dc" measurements. This technique is complemented by the use of the Allan variance, a technique used for about 35 years in time and frequency metrology. Some practical results are the identification and characterization of 1/f noise as the phenomenon limiting the reproducibility of voltage measurements of Zener electronic voltage standards to a 1/f noise floor having a relative value ranging from 2 parts in 109 to 8 parts in 109. These same techniques are being applied to study the limits of sensitive nanovoltmeters.