On 8/25/2014 11:02 AM, Don@True-Cal wrote:
Silver or Gold plating on the terminal or wire will introduce the
undesirable dissimilar metal properties, both at the plating
junction and at the plating metal to DUT terminal.
Why?
Any Seebeck effect is immediately offset in the opposite direction,
since both junctions are (under normal conditions) at essentially the
same temperature (e.g. there's a copper-gold thermocouple, the minimal
thermal resistance of a micron of gold on the contact(s), then a
gold-copper thermocouple). It seems to me that the improved consistency
of the contact outweighs any loss from the thermocouples.
A more typical contact would be copper-nickel plate-gold plate, but the
concept is the same. Unless there is heat flowing through the entire
assembly so one thermocouple is warmer than the offsetting one (e.g.
shortly after plugging in a banana plug warmed by body heat), they
simply cancel.
Even if connecting gold plated to nickel plated contacts, it works out
the same - a copper-nickel-gold-nickel-copper connection is completely
offset. It's when the offsetting thermocouples occur across a
temperature gradient that you have problems.
--
Mike
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