Thermocouple comparator choose
I have lm339, lm324. Can this comparator catch 1-2 mv?

Nope, because the offset error is ±1mV.
You should use an instrumentation amplifier to amplify the thermocouple's output voltage, and then feed it to a comparator. That's the safer way.



simulate this circuit &ndash; Schematic created using CircuitLab