Thermocouples are based on the seebeck effect. When joining two different materials, a small potential difference appears that depends on the nature of the materials and is variable with temperature. Knowing this we can measure that small tension and thus know the temperature. This voltage is very weak, so it must be amplified.
In addition, when connecting the sensor to the plate, another thermocouple appears due to the fact that they are different materials. This thermocouple is what we call a cold junction and we must compensate it to know the real temperature in the thermocouple that interests us.
This module from the plug-and-play series (Grove) uses a thermistor to detect the ambient temperature and thereby compensate the junction cold.
The detector used is a type K thermocouple and allows us to measure temperatures from -50 to 600ºC with a precision of ± (2.0% + 2ºC)
In related products you can see the related shields for Arduino Uno and/or Mega
Temperature range: -50 ..600ºC
Accuracy: ± (2.0% + 2ºC)