Effect of Oxide Finish on Nickel Alloy Thermocouple Wires

Oxide finish on new long life nickel alloy type K thermocouple wires causes an immediate and permanent calibration shift in swaged assemblies, where mineral oxide insulation is compacted around wires. This permanent shift may be avoided by using wires with bright finish. Micro examination of etched sections gives no clue as to cause of emf deviation. Comparison is made with conventional type K wires (Chromel and Alumel) where this effect is not present.