Many thermometers today are electronic. Let’s see how different types of electronic thermometers are made and what are their working principles.
1 ) Most contain a tiny bead of a semiconducting material whose resistance varies with temperature. The bead is called a thermistor, or thermal resistor.
2 ) Others contain a tiny semiconducting diode. The voltage across this diode varies with temperature.
3 ) To measure very high temperatures, a wire made of the metal platinum is used because its resistance also varies with temperature, and platinum is not affected by high temperatures.
4 ) Another electronic thermometer uses two wires made of different materials that are welded together. Typically the wires are made of copper and a nickel-containing alloy. This kind of thermometer is called a thermocouple and is often used in gas furnaces or water heaters to make sure that the pilot flame is burning when the gas to the main burners is turned on.