1. Gas thermometers: hydrogen or helium gas is used as temperature measuring material, because hydrogen and helium gas liquefaction temperature is very low, close to absolute zero, so it has a wide temperature measuring range. This kind of thermometer is very accurate and is often used for precise measurements.
2. Resistance thermometers: divided into metal resistance thermometers and semiconductor resistance thermometers, are based on the resistance value changes with temperature this characteristic made. Metal thermometers are mainly used in platinum, gold, copper, nickel and other pure metal and rhodium iron, phosphorus bronze alloy; Semiconductor thermometers mainly use carbon, germanium, etc. Resistance thermometers have been widely used for their convenience and reliability. Its measurement range is around -260℃ to 600℃.
3. Thermocouple thermometer: it is a temperature measuring instrument widely used in industry. Made of thermoelectric phenomenon. Two different wires are welded together to form the working end and the other ends are connected to the measuring instrument to form a circuit. The working end is placed at the measured temperature, the working end and the free end temperature is not the same, there will be electromotive force, so there is a current through the loop. By measuring electrical quantities, the temperature at one known place can be determined at another. It is suitable for high temperature and low turbidity measurement between two substances with large temperature difference. Some thermocouples can measure high temperatures up to 3000℃, while others can measure low temperatures close to absolute zero.