"220V Cooling Fan" temperature sensor is the first development, the most widely used class of sensors. Two conductors of different materials, such as connecting with each other at some point, the connection point of heating in their unheated parts of the potential difference occurs. The potential difference of the value of the temperature unheated parts of the measuring point is related to the two conductors and related materials. This "220V Cooling Fan" phenomenon can be used over a wide temperature range appears, if accurate measurement of the potential difference, and then measuring the unheated parts of the ambient temperature, it is possible to accurately know the temperature of the heat spots. Because it must have two conductors of different materials, so called "thermocouple." Thermocouples made of different materials used in different temperature ranges, "220V Cooling Fan" sensitivity also varies. Thermocouple sensitivity refers add hot spot temperature changes 1 ℃, the output potential difference of the amount of change. For most metallic materials in terms of support of the thermocouple, this value is between about 5 to 40 microvolts / ℃.