Everything about The Weston Cell totally explained
The
Weston cell, invented by
Edward Weston in
1893, is a
wet-chemical cell that produces a highly stable
voltage suitable as a laboratory standard for
calibration of
voltmeters. It was adopted as the International Standard for
EMF in
1911.
Chemistry
The
anode is an
amalgam of
cadmium with
mercury, the
cathode is of pure mercury, the
electrolyte is a
solution of
cadmium sulfate and the
depolarizer is a paste of
mercurous sulfate.
As shown in the illustration, the cell is set up in an H-shaped glass vessel with the cadmium amalgam in one leg and the pure mercury in the other. Electrical connections to the cadmium amalgam and the mercury are made by
platinum wires fused through the lower ends of the legs.
Characteristics
The original design was a saturated cadmium cell producing a convenient 1.0183
Volt reference and had the advantage of having a lower
temperature coefficient than the previously used
Clark cell. (Reference cells must be applied in such a way that no current is drawn from them.)
The temperature coefficient can be reduced by shifting to an unsaturated design, the predominant type today. However, an unsaturated cell's output decreases by some 80 microvolts per year, which is compensated by periodical calibration against a saturated cell.
Patent
Further Information
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