For different temperature measurement range, the user should choose different structure of temperature switch. In the temperature range of 0 ℃ ~ 100 ℃, the solid expansion type temperature switch is usually used. In the temperature range of 100 ℃ ~ 250 ℃, the gas expansion type temperature switch is mostly used. For the temperature range above 250 ℃, only thermocouple or thermal resistance thermometer can be used, which is converted by measurement transmitter, It is analog electric signal, and then the electric signal is converted into switch signal.