Sparkybg shared his controller for soldering irons using Hakko T12 type tipe in the project log forum:
T12 have thermocouple in series with the heater with a voltage of around 9mV at 450 degrees celsius, so the voltage to the heater must be turned off to measure the voltage of the thermocouple. Don’t measure the resistance of T12. It is pointless to use it when a thermocouple is already available, and is far more precise than resistance.
Via the forum.