Robert A LaBudde wrote:
> It's disingenuous to say it's not the junction that produces the EMF.

A common misconception of how thermocouples work is that the junction of
dissimilar metals produces the EMF when one side is at a different
temperature than the other.  In fact, the EMF is generated due to a
temperature gradient in each wire.  Different materials produce different
EMF for the same temperature gradient.  The resulting thermocouple voltage
is the difference in EMF generated by the two materials to the same
temperature drop.  The EMF is generated in the wires themselves.  The
junction is merely a connection point.

> Thermocouples have the failure mode of including extraneous junctions
> due to wire stress or breaks at intermediate points.

It is not due to new junctions, but increasing imperfections in the crystal
structure of the materials as they are subjected to mechanical stresses.
This alters the EMF generated for the same temperature.  Roughly speaking,
the EMF is caused by electron diffusion, and lattice irregularities impede
this diffusion.


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