Weston cell

The Weston- normal element is a special galvanic cell. It was in 1911, used for calibration of the electrical voltage which is measured in volts.

This electrochemical cell was invented in 1893 by Edward Weston ( 1850-1936 ).

It consists of two different electrodes in a saturated cadmium sulfate ( CdSO4 ), whose saturation is maintained by beige passed cadmium sulfate crystals. Consists of the two electrodes and the other a mercury cadmium amalgam, a metallic alloy of cadmium and mercury. The cadmium content in the amalgam electrode is 12 to 13%. With passage of current cadmium ions migrate to the positive electrode mercury. Thus there is not alloyed, and thereby both of the electrodes are more or less the same, situated above the mercury electrode, a mixture of mercury (I ) sulfate ( Hg2SO4 ) and cadmium sulfate crystals. In current passage formed from the cadmium ions and the mercury (I ) sulfate Cadmium sulfate and metallic mercury:

Between the two electrodes is formed at a temperature of 20 ° C, a reference voltage of

Which can be picked at the terminals. The temperature dependence of the voltage is relatively small in this element.

Since 1990, the reference of the electric voltage for the practical measurement is no longer formed by electrochemical standard cells. It is determined by the quantum mechanical Josephson effect, of which the magnitude of the electric voltage can be derived by a much more accurate frequency measurement.