Ich meine es muss vererchnet werden:
For a K-type thermocouple, the voltage changes by about 41μV/°C, which approximates the thermocouple characteristic with the following linear equation:VOUT = (41.276μV/°C) x (TR - TAMB)where VOUT is the thermocouple output voltage (μV), TRis the temperature of the remote thermocouple junction (°C), and TAMB is the temperature of the device (°C).

Also vom Messwert des PT100 den Messwert des internen Temperatursesors abziehen und dann verrechnen.