How should I place a thermocouple?
Rules for thermocouple placement for an induction heating process
If a thermocouple is used to measure the temperature of the surface of a metal part, the thermocouple should be well-anchored to that surface, either by welding it to the surface or attaching with high temperature glue. Smaller wire diameter should be used for the thermocouple to reduce the coupling to the magnetic field. Also the wire should be placed so that there is minimal interaction with the magnetic field.