http://www.omega.com/temperature/Z/pdf/z021-032.pdf

I don't think this is the PPT that Inge found. However, this PDF covers the
material questions of our thread. The science is sound. Just remember, the
authors sell thermal couples. 

I once worked on a study of thermal couples for use in reflow ovens. We were
hired by an OEM interested in the effects of time, temperature, and flux gas
on thermal couples performing real time measurement in reflow soldering
environment. We monitored change in voltage across the junction and change
in wire resistance.

I don't have the data, as I have moved to a new company. I recall the change
in performance of the thermal couples, over a 18 month testing period, was
negligible in terms of the precision provided by the monitoring system
provided in the oven, and that required to maintain control of the a reflow
process, plus or minus 3°C. 

While Murphy was an optimist, I maintain that the auditor expecting Steve to
change thermal couples after five excursions is misinformed.

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