PT 100 is a temperature sensor and a resistance thermometer. Its principle is to measure the temperature according to the change of resistance. The resistance value of PT 100 sensor changes with the change of temperature, and its changing rule is that the resistance value increases with the increase of temperature and decreases with the decrease of temperature. The resistance value of PT 100 sensor varies from -200℃ to +850℃, and the changing rule is that the resistance value will increase by 0.385 Ω with the increase of temperature 1℃.