Combination type standard cells with low-temperature coefficient using composite amalgam electrode cells

In order to take full advantage of recent progress in Josephson voltage standards, improvements of the standard cells maintaining the unit of voltage is of major concern. In particular, the systematic error due to temperature fluctuations, which is an important factor limiting the measurement accuracy, would be significantly reduced if cells were available with smaller temperature coefficients. Our previously reported research on Cd-Pb composite amalgam electrode cells has now been extended to include cells with Cd (10 wt percent)-Sn(5) and Cd(10)-Sn(5)-Pb(5) composite amalgam electrodes. These new cells were found to exhibit the same general characteristics and stability with time as the Cd and Cd-Pb cells reported earlier, except that the temperature coefficients of the Cd-Sn cells were found to be −15 μV/K, slightly smaller than had been observed for the Cd-Pb cells, and the temperature coefficients of Cd-Sn-Pb cells were found to be +23 μV/K. Combination type standard cells, consisting of various series combinations of these four kinds of cells, have been constructed, in which the overall temperature coefficients of the assemblies have been made very small by proper selection of the kinds of cells used and their relative polarity. Voltage standards at the 1-V level having temperature coefficients smaller than 1 μV/K at 20,25, and 30°C have been produced in this way.